A Guide to Good Occlusal Practice: A Guide to Good Practice (BDJ Clinician’s Guides) [2nd ed. 2022] 3030792242, 9783030792244

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BDJ Clinician’s Guides

Stephen Davies

A Guide to Good Occlusal Practice Second Edtiton

BDJ Clinician’s Guides

This series enables clinicians at all stages of their careers to remain well informed and up to date on key topics across all fields of clinical dentistry. Each volume is superbly illustrated and provides concise, highly practical guidance and solutions. The authors are recognised experts in the subjects that they address. The BDJ Clinician's Guides are trusted companions, designed to meet the needs of a wide readership. Like the British Dental Journal itself, they offer support for undergraduates and newly qualified, while serving as refreshers for more experienced clinicians. In addition they are valued as excellent learning aids for postgraduate students. The BDJ Clinicians’ Guides are produced in collaboration with the British Dental Association, the UK’s trade union and professional association for dentists. More information about this series at http://www.springer.com/series/15753

Stephen Davies

A Guide to Good Occlusal Practice Second Edition

Stephen Davies Specialist in Restorative Dentistry Lecturer in Occlusal and Temporomandibular Studies Division of Dentistry, Faculty of Biology, Medicine and Health University of Manchester A Lead Clinician, Temporomandibular Disorder Clinic University Dental Hospital of Manchester Manchester UK

Originally published by BDJ Books, London, 2002 1st edition: © BDJ Books 2002 ISSN 2523-3327     ISSN 2523-3335 (electronic) BDJ Clinician’s Guides ISBN 978-3-030-79224-4    ISBN 978-3-030-79225-1 (eBook) https://doi.org/10.1007/978-3-030-79225-1 © Springer Nature Switzerland AG 2002, 2022 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

There is a very long list of contributors to this work. Without their expertise this multi-disciplinary work on the provision of Good Occlusal Practice would not have been possible. I am very fortunate to have had the expertise, support and energy of such a loyal and kind group of professional friends. Special thanks go to Indika Weerapperuma who, in addition to having contributed to two chapters, has been my sounding board for ideas and has proofread the book. Each chapter has evolved from an initial discussion with the specialist(s), from which a first draft was created. Throughout the development, Occlusion has been kept as the central theme. After a lifetime of teaching the Occlusion, it is my experience that both undergraduate and postgraduate students approach the subject with the mistaken belief that it is somewhere between difficult and incomprehensible. It has been a privilege to experience a colleague’s joyous realisation that the subject is not as difficult as they thought. It is my sincere hope that the reader’s reaction will be the same. At Springer/Nature: I would firstly like to thank James Sleigh for the invitation to rewrite the 2002 BDJ book A Clinical Guide to Occlusion; my special thanks go to Alison Wolf who has consistently supported and guided me through the publication stage of this work. I would like to thank Mrs Mandy Lynam, who as my dental nurse would not let me dismiss a patient with a poorly occluding restoration even if I had wanted. Gordon Lucas, my technician partner, has been the talented and reliable provider of all my indirect restorations for more than 40 years. Finally, I would like to acknowledge the clinical companionship and academic encouragement that the Manchester Dental School and Hospital provides; I am blessed to be part of that community. Finally, and above all others, I want to thank my wife for her patience and understanding. When I qualified and we married in 1971, we both thought that Dentistry would just be my job. 2022, Manchester, UK

Stephen Davies

v

Contents

1

What Is Occlusion?������������������������������������������������������������������������������������   1

2

 The Examination and Recording of the Occlusion: Why and How ��������������������������������������������������������������������������������������������  23

3

Good Occlusal Practice in Simple Restorative Dentistry ����������������������  43

4

Good Occlusal Practice in Advanced Restorative Dentistry������������������  79

5

Good Occlusal Practice in Removable Prosthodontics�������������������������� 119

6

Occlusion and Orthodontics��������������������������������������������������������������������� 141

7

Occlusal Considerations in Periodontics������������������������������������������������� 165

8

Good Occlusal Practice in Children’s Dentistry ������������������������������������ 191

9

Bruxism������������������������������������������������������������������������������������������������������ 207

10 Occlusion  and Non-carious Tooth Surface Loss�������������������������������������� 219 Section 10.1: General Considerations on the Management of Non-carious Tooth Surface Loss������������������������������������������������������������  220 Section 10.2: Creating the Space for the Restoration of the Worn Teeth���� 239 Section 10.3: Case Histories to Illustrate Restorative Strategies ��������������  247 11 Good  Occlusal Practice in the Provision of Implant-Borne Prostheses ������������������������������������������������������������������������ 279

vii

Contributors

Chapter 3

Phillip Smith Senior Lecturer/Hon Consultant Restorative Dentistry, School of Dental Studies, The University of Liverpool, Liverpool, UK

Chapter 4

Phillip Smith Senior Lecturer/Hon Consultant Restorative Dentistry, School of Dental Studies, The University of Liverpool, Liverpool, UK

Chapter 5

J. Fraser McCord Consultant in Restorative Dentistry, Manchester, UK

Chapter 6

Ovais Malik Consultant in Orthodontic, University Dental Hospital of Manchester, Manchester, UK David Waring Consultant in Orthodontic, University Dental Hospital of Manchester, Manchester, UK

Chapter 7

Ian Dunn Specialist Periodontologist, Clinic 334, Wilmslow, UK Kevin Seymour Professor of Periodontology, Division of Dentistry, University of Manchester, Manchester, UK

Chapter 8

Vidya Srinivasan Consultant in Paediatric Dentistry, University Dental Hospital of Manchester, Manchester, UK Catherine Watts Speciality Dentist in Paediatric Dentistry, Manchester, UK

Chapter 9

Hannah Beddis Consultant in Restorative Dentistry, Leeds Dental Institute, Leeds, UK

ix

Contributors

x

Chapter 10   Section 10.1 Hannah Beddis Consultant in Restorative Dentistry, Leeds Dental Institute, Leeds, UK   Section 10.2 Amin Aminian Specialist in Prosthodontics, Clinic 334, Wilmslow, UK   Section 10.3 Hannah Beddis Consultant in Restorative Dentistry, Leeds Dental Institute, Leeds, UK Philip Dawson Red Rose Dental Practice, Wigan, Greater Manchester, UK Johanna Leven Consultant in Restorative Dentistry, University Dental Hospital of Manchester, Manchester, UK Alicia Patel Manchester, UK Appoline House, Grantham, UK Indika Weerapperuma Hon Lecturer, University of Manchester, Manchester, UK Kinross Dental Care, Colombo, Sri Lanka Chapter 11

Amin Aminian Specialist in Prosthodontics, Clinic 334, Wilmslow, UK Peter Young Specialist in Oral Surgery, Dentist@29, Northwich, UK

Readers’ Voices

Tara Bharadia  5th Yr Dental Student Dr. Davies has always said that occlusion is easy, and this book is the proof! In the run up to finals, a once mystical and daunting topic now seems tame and manageable. All the terms are properly explained right at the start and there are chapters to refer to when you have specific questions further on in your career. You will come away being confident with the theory as well as comfortable with the practical elements of examination and treatment considerations. I would recommend this book to anyone who is confused by Occlusion! Don Jayawardena  Dental Core Trainee This book has easy to understand explanations regarding terminology and in taking occlusal records. Most important to me as a DCT it gives clear guidance on when to reorganise or to conform—a question I am often asked! The author suggests planning the occlusion using the EDEC principle, and he highlights useful techniques for taking pre-treatment records; these are useful in my current restorative DCT post. Chris Needham  Experienced GDP, Pre PG qualification Despite being an experienced GDP, Occlusion was a subject that I thought I might never fully comprehend. This book really does simplify Occlusion, explaining the common pitfalls and how to avoid them. I have picked up many techniques that I now use daily. This is essential reading for all General Dental Practitioners, because it will give them confidence to carry out Good Occlusal Practice in all of their treatments. I feel much more confident to pursue PG education in Advanced Restorative Dentistry. Amy  Burns  Post Graduate Student A refreshing common-sense approach to dealing with clinical scenarios from simple cases up to more advanced dentistry. I have previously found the subject of occlusion daunting; however the step-by-­ step approach in this book has broken it down into easy to grasp concepts. I feel confident applying this to my clinical work, and it has given me a robust understanding which has been invaluable for studying for my MSc. April Scholey  GDP with PG qualification A brilliant summary of how occlusion affects our everyday dentistry. Postgraduate education has taught me that occlusion is that missing link that ties together all aspects of dentistry. It can be the cause of restoration failure and needs to be considered at the planning stage, not as an xi

xii

Readers’ Voices

afterthought. This book is an excellent, evidence-based summary that encompasses a long career of research and clinical practice from an inspiring practitioner—all condensed in one place! James Darcey  Consultant in Restorative Dentistry This book seeks to demystify Occlusion. It is logical in progression from basic to advanced aspects of Good Occlusal Practice in Restorative Dentistry. It outlines the key information and reinforces the most important messages, not least the EDEC principle. This update also discusses newer thinking on more flexible approaches to rehabilitation which introduces pragmatism into case planning and delivery of treatment. I would recommend all practitioners read and keep a copy of it on their shelves for reference. Nick  Grey  Professor of Dental Education, University of Manchester and National Teaching Fellow This book is a ‘must read’. It covers the management of clinical issues that confront the profession and does so in a reader-friendly way.

1

What Is Occlusion?

Objective The aim of this book is to explore the role of Occlusion in Dental Practice. There is an enormous range of opinion within the dental profession regarding the significance of Occlusion [1]. It is very important that the profession in general and practising dentists in particular have a balanced view of Occlusion. To be controversial from the start, having a broad consensus within the profession on the importance of Occlusion is more important than every patient having a balanced occlusion. The fact that the study of occlusion is characterised by extremes of opinion makes it confusing and difficult for individual dentists to subscribe to a philosophy which is in line with contemporary good practice supported by evidence from practice-­based research. I hope that this book will make it easier for individual dentists to find a philosophy that helps them in their everyday practising life; and that some of the ideas expressed in this book will find favour with the profession. Above all, I hope that the reader will detect a ‘common-sense approach’, whilst still finding it supported by evidence. There is some evidence that ‘Occlusion’ could be covered in undergraduate curriculums with a more ‘coordinated teaching strategy’. I will be pleased if this book can make a contribution to that aim [2]. Patients need a balanced occlusion

Dentists need a balanced view on occlusion

© Springer Nature Switzerland AG 2022 S. Davies, A Guide to Good Occlusal Practice, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-79225-1_1

1

2

1  What Is Occlusion?

In this chapter, we will discuss: 1. What is ‘Occlusion’. 2. Why Occlusion is important. 3. The significance of Ideal Occlusion.

Range of Opinion At one end of the spectrum there are dentists who believe that they can go through their working lives with scant regard for their patients’ occlusion. They seem to believe that they can conduct their practice ignoring the occlusal consequences of the treatments that they perform daily. Whereas all dentists know of the importance of the good marginal adaptation of their restoration to the health of the adjoining dental and periodontal tissues, some dentists do not appreciate the potential consequences of poor occlusal contact to the opposing teeth and their supporting structures. This is bizarre given the fact that very few dental treatments do not involve the occlusal surfaces of teeth. Conversely there is a body of opinion that considers Occlusion to be of such systemic import to the well-being of our patients, that ‘Occlusion’ takes on an almost mystic importance and attracts a cult-like devotion (Table 1.1). This can lead some dentists to advocate occlusion as being the key to resolving or preventing a range of disorders far removed from the Masticatory System, for example prolapsed lumbar discs. Often such enthusiastic fervour is associated with a didactic prescription of ‘occlusal rules’, to which there must be slavish adherence in the treatment of every patient! It may be harsh to describe the devoted adherence to a particular Occlusal Philosophy as a ‘cult’, but sometimes characteristics like gurus and followers and an intolerance of any other belief can justify this perception. There are several dangers in these extremes: Both may lead to inappropriate levels of care for our patients. • The ‘Occlusion doesn’t matter’ group may undertreat patients or provide treatments that can lead to iatrogenic damage. • Whereas the ‘Correct Occlusion is the key to a whole body musculo-skeletal harmony’ group may overtreat patients by providing irreversible treatments without a solid evidence base.

Table 1.1  It has been claimed without evidence that occlusion causes Temporomandibular disorders Excessive ear wax Prolapse of lumbar disc Reduced strength in deltoid and rectus femoris muscles

Poor posture Speech defects Negative influence on the craniosacral mechanism Lack of beauty

Guidelines of Good Occlusal Practice

3

The Confusion and Controversy that is generated by this wide range of opinion on the importance of Occlusion causes an anxiety in the minds of undergraduate and postgraduate students. It makes many of them feel that Occlusion must be very difficult. It is not surprising that these two extreme views co-exist so easily within a thinking profession because the one appears to provide the justification for the other. The ‘occlusion doesn’t matter’ group probably justify their reluctance to become ‘involved in occlusion’ on what they perceive to be the exaggerated and unsubstantiated claims of the group who believe occlusion to be the central pillar of holistic care. This congregation of opinion in turn may be so frustrated by the apparent disregard of the study of occlusion that they are led to ‘gild the lily’ by overstating the importance of occlusion and then in the absence of what they perceive to be an inability ‘to see the obvious’ they go on to lay down rules, which they encourage all dentists to follow for every patient. ‘Occlusion’ There is no escape Dentists cannot: · · ·

Repair ü ï Move ý teeth Remove ïþ without being involved in occlusion

It is the objective of this book to explore the role of occlusion in dental practice in a manner based on reason, common sense and evidence. There is good and bad practice in occlusion as in other aspects of clinical dentistry. I hope, therefore, to establish the concept of Good Occlusal Practice, in all of the dental disciplines.

Guidelines of Good Occlusal Practice These Must Be Guidelines Not Rules All patients are different, reacting to similar stimuli in different ways. This is an accepted truth in medicine, so I do not see why it should not apply to Occlusion in dentistry. As a consequence, I believe that a patient’s individual needs can and should be left to the individual clinician. It is my hope that the Guidelines of Good Occlusal Practice in this book will appeal to my colleagues. And that, upon reflection, the reader will agree that some are obvious, and hardly needed stating. The fog of confusion and controversy must be cleared, because no practising dentist can care well for their patients without having regard for Good Occlusal Practice.

4

1  What Is Occlusion?

Fig. 1.1  The Masticatory System

Enamel

Dentine

Pulp Teeth

Masticatory system Periodontium

Articulatory system TMJ

Gingivae

Bone

Periodontal membrane

Muscles

Occlusion

The Importance of Occlusion in Dental Practice Occlusion can be very simply defined: it means the contacts between teeth. Before describing the significance of the different ways in which occlusal contacts are made Occlusion needs to be put into context. The Masticatory (or stomatognathic) System (Fig. 1.1) is generally considered to be made up of three parts: • Tooth Tissues. • Periodontal Tissues. • Articulatory System. Many dentists feel that they qualified from their dental school with a very good knowledge of the first two parts of the Masticatory System, namely the Teeth and the Periodontal Structures, but they can feel vulnerable in their knowledge of the third part: the Articulatory System. It appears that some dentists feel that their time at university did not prepare them adequately in this area. Possibly Occlusion may be undertaught in the undergraduate curriculum. ‘Occlusion’ = Contacts between teeth In my view, we should not be too hard on our Schools as the undergraduate dental education must, by necessity, concentrate initially on the first two parts of the Articulatory System. Dental Schools must produce newly qualified dentists who are

Is the Articulatory System a True System?

5

able to treat patients. Only once the dental undergraduate has an understanding of the diseases that affect the dental and periodontal tissues (parts 1 and 2 of the Masticatory System) can the schools start to allow the student to treat patients. There is consequently justification for the study of the Articulatory System being considered to be chronologically the third area of study. But because of the inescapable fact that almost all dental treatment has an occlusal consequence, it is wrong to consider the study of the Articulatory System to be less important than the first two parts of the Masticatory System. The Articulatory System is the biomechanical environment in which dentists provide most of their treatments. Given the increasing quantity of knowledge to be amassed in the modern undergraduate course, it may be that those responsible for setting the dental undergraduate curriculum will not be able to cover the Articulatory System as they would wish. Now that there is a universal acceptance of the need for continuing education, it may be more realistic to consider a comprehensive study of the Articulatory System as the first mandatory element of a postgraduate dental education. Although it may be, by necessity, the last to be learnt it is not less important than the other parts of the Masticatory System.

Is the Articulatory System a True System? A system is defined as: ‘A set or assemblage of things connected, associated, or interdependent, so as to form a complex unity’ [3]. The Articulatory System meets these criteria, so the answer to this question is: Yes. In this system one can imagine the temporomandibular joints as the hinges, the masticatory muscles as the motors and the dental occlusion as the contacts (Fig. 1.2b). When viewed in these mechanical terms (Fig. 1.2b), it is clear that the elements of the Articulatory System are inescapably connected. Furthermore, it can be argued that they are obviously interdependent because a change in any part will clearly affect the other two parts (Fig. 1.3a). But it should be remembered that this effect will not necessarily be an adverse one. In fact, one must suppose that the system as a whole can, in the vast majority of cases, compensate for change. This phenomenon can be described as Adaptive Capability and is a feature of living systems. In contrast, a machine has been described as a ‘System that is not the result of a fertilized egg’, i.e. it is not capable of adaptation [4]. This is an important reassurance to clinicians, as it means that an intervention to or alteration of one element of a system, such as the dental occlusion, will not always have an adverse effect on another part of the system, for example, the masticatory muscles. Any dentist who believes that a change in the occlusion will always have an adverse effect on the muscles or the TMJs is treating the patient mechanically, which given the definition of a machine is a damning commentary of their clinical nous. This concept of adaptive capability is important when considering Ideal Occlusion, as will be discussed later.

6 Fig. 1.2  The Articulatory System

1  What Is Occlusion? Temporomandibular Joints

a

Muscles

Occlusion Hinges

b

Motors

Fig. 1.3 (a) Interconnections of the articulatory system. (b) Interconnections of the masticatory system

Contacts

a Change in

Change in

TMJ

leads to

Occlusion Masticatory muscles

Muscles

leads to

Occlusion TMJ

Occlusion

leads to

TMJ Masticatory muscles

Articulatory System

b Change in

Change in

Teeth

leads to

Periodontia Articulatory muscles

Periodontia

leads to

Teeth Articulatory system

Articulatory System

leads to

Teeth Periodontia

Masticatory System

Static Occlusion

7

This realisation that the Articulatory System has the potential to adapt does not, however, abrogate the clinician from responsibility. In fact, the possibility as opposed to the certainty of an adverse reaction (lack of adaptation) makes the challenge of preventing iatrogenic injury greater.

Do No Harm The most important elements of ‘doing no harm’ during our treatments is firstly the ability to carry out thorough examination and monitoring protocols, and secondly to provide treatment that will not change the occlusion or change it in a way that is most likely to be within the adaptive capabilities of the rest of the system. These will be presented later in the text. The same sort of analysis of the interconnection within the Masticatory System can be made (Fig. 1.3b). The importance of ‘occlusion’ in dental practice is based primarily upon the relationships that it has within these interconnected biomechanical systems. When one considers how almost all forms of dental treatment have a potential for causing occlusal change, the need to establish what constitutes good occlusal practice is overwhelming and obvious.

Analysis of Occlusion Having stated that occlusion simply means the contact between teeth, the concept can be further simplified by defining those contacts between the teeth • when the mandible is closed and stationary as the Static Occlusion, • and those contacts between teeth, when the mandible is moving relative to the maxilla as the Dynamic Occlusion.

Static Occlusion The first essential question when considering a patient’s static occlusion is: ‘Does Centric Occlusion occur in Centric Relation?’ This question will be clarified after defining terminology. Terminology has been a ‘red herring’ and has been the cause of enormous and sometimes acrimonious debate. I have preferred terms, but do not feel that they are important; it is the concept behind the terms that matter. Centric Occlusion (CO) can be described as the occlusion the patient makes when they fit their teeth together in maximum intercuspation. Common synonyms for this are Intercuspation Position (ICP), Bite of Convenience or Habitual Bite. It is the occlusion that the patient nearly always makes when asked to close their teeth together, and it is the ‘bite’ that is most easily recorded. It is, also, how unarticulated

8

1  What Is Occlusion?

models fit together. Finally, it should be remembered that it is the occlusion to which the patient is accustomed. It is interesting, but not essential, for us to analyse how this position of the mandible to the maxilla [jaw relationship], in which the teeth fit together, is achieved. The shape of the occlusal surfaces of the teeth determines this jaw relationship, and there is a centrally influenced neuromuscular control that guides the mandible into the relationship with the maxilla. Anything, therefore, that changes either the occlusal surfaces of the teeth or the ability of the muscles to guide the mandible to the habitual position can change this jaw relationship. • A restoration to a single tooth can change the overall occlusion, and so the jaw relationship. • Anaesthetising and/or fatiguing the masticatory muscles may prevent them articulating the mandible to the maxilla into the habitual position. This sums up the challenge in Restorative Dentistry. Of course, as already stated the Masticatory System will usually adapt, but not always. And the consequences can be grave. The reason why this book will not give Rules is that Occlusal Change does not lead inevitably to adverse consequences. But we will give Guidelines, because when adverse reactions do occur, they can be severe; a situation that all dentists and patients wish to avoid. Centric Relation (CR) [synonyms: Retruded Contact Position, Terminal Hinge Axis Position] is not an Occlusion. CR has nothing to do with teeth because it is the only ‘centric’ that is reproducible with or without teeth present [5]. Centric Relation is a jaw relationship: it describes a conceptual relationship between the maxilla and mandible. All attempts to lay down rigid definitions of centric relation are plagued by the fundamental difficulty that there is no sure or easy way of seeing where it is. Centric Relation has been described in three different ways: anatomically, conceptionally and geometrically.

Anatomical Centric Relation can be described as the position of the mandible to the maxilla, with the intra-articular disc in place, when the head of the condyle is against the most superior part of the distal facing incline of the glenoid fossa. This can be paraphrased as uppermost and foremost (Fig. 1.4). This is subject to debate. Some clinicians prefer the idea that Centric Relation occurs in an ‘uppermost and midmost’ position within the glenoid fossa whereas others support the idea that it is in an ‘uppermost and rearmost’ position; the so-called ligamentous position.

Static Occlusion

9

Fig. 1.4 Functional anatomy of the temporomandibular joint PB el.att. IZ AB BLZ SPt IPt

fib.att. fib.att. = fibrous attachment to posterior neck of condyle el.att. = elastic attachment to fossa BLZ = bilarminar zone PB = posterior band of meniscus IZ = intermediate zone of meniscus AB = anterior band of meniscus SPt = attachment to the superior pterygoid (superior head of lateral pterygoid) IPt = attachment to the inferior pterygoid (inferior head of lateral pterygoid)

The problem with the goal of placing the head of the condyle in the uppermost and midmost position is that the radiograph that commonly used to determine this position is not a reliable test [6]. Whereas the uppermost and rearmost [ligamentous position] offers the possibility of consistency because of the anatomical limitations of the glenoid fossa, many practitioners, including the author, find that asking patients to curl their tongue back and pushing on the mandible does not deliver a consistent position. This is probably due to the reaction of the lateral pterygoid to the pressure. There is support for the uppermost and foremost hypothesis from a study of anatomy: the bone and fibrous articulatory surfaces are thickest in the anterior aspect of the head of the condyle and the most superior aspect of the articular eminence of the glenoid fossa. In any event, determining where exactly the head of the condyle is in the glenoid fossa is a futile exercise, with no clinical significance. This is because there is no reliable means of determining that relationship. To make any head of condyle/glenoid/fossa relationship a specific treatment goal is for this reason flawed.

10

1  What Is Occlusion?

Geometrical Centric Relation can be described ‘as the position of the mandible relative to the maxilla, with the intra-articular disc in place, when the head of the condyle is in ‘Terminal Hinge Axis’. In order to understand what this frequently used term means, it is easier to initially think about only one side of the mandible, and to remind ourselves the movements of the head of the condyle when we open our mouths. The mandible opens by firstly a rotation of the condyle and then a downwards, forwards and medial translation occurs. Therefore, when the mandible starts to open and when it finishes its closure, the movement of the head of the condyle is purely rotational. If we look at Posselt’s Envelope of Motion [7], we can see that an imaginary point on the chin will describe a near perfect arch during the beginning of the opening cycle and the end of the closing cycles. Geometrical

CR

Pe rfe

ct

arc

Hinge movement terminal opening arc

Mandible is in terminal hinge axis

This provides the ‘terminal hinge point’ (of rotation) of one side of the mandible. Because the mandible is one bone with two connected sides, these two terminal hinge points are connected by an imaginary line: the terminal hinge axis. When the mandible rotates about this axis, it is in Centric Relation; simply because it is the start of opening or the end of closure. Another way of saying that it is in the rotational phase of mandibular movement.

Significance of Centric Relation

11

It is the fact that the mandible is describing this simple arc, when the heads of condyle are in the terminal hinge axis that has an important clinical significance. This will be discussed later, when the techniques for finding Centric Relation are presented.

Conceptual Centric Relation can be described as that position of the mandible relative to the maxilla, with the articular disc in place, when the muscles that support the mandible are at their most relaxed and least strained position. This description is pertinent to an understanding of ‘Ideal Occlusion’, a concept that is discussed later. This definition of Centric Relation suggests that there could be a jaw relationship that is ‘qualitatively better than others’ for another element of the Articulatory System, namely the muscles.

Significance of Centric Relation Although there may be arguments about the exact definition of Centric Relation or how it is best found clinically, thankfully there is broad agreement between dentists that a reproducible position of the mandible relative to the maxilla exists. Dentists agree that this reproducibility is not provided by the occlusal surfaces of the teeth: patients with no teeth still have a Centric Relation. Furthermore, there is inter- and intra-operator reliability in finding it.

‘Freedom in Centric’ Another aspect of the static occlusion is the presence or absence of ‘Freedom in Centric’, this is also known as ‘Long Centric’. The word ‘centric’ is adjective and so strictly it should never be used without a noun. Consequently, this long-established term would better read: Freedom in Centric Occlusion or Long Centric Occlusion. I hope that the reader will forgive this mild pedantry. Freedom in Centric Occlusion is present when the mandible is able to move slightly anteriorly in the same horizontal and sagittal plane while maintaining tooth contact (Fig. 1.5b). Alternatively, there will be no Freedom in Centric Occlusion if either the front teeth or the posterior occlusion does not allow this horizontal movement (Fig. 1.5a). An easier way of imagining Freedom in Centric Occlusion is to consider whether the front teeth occlude harder or sooner than the back teeth. If they do hit together harder or sooner then there is no Freedom in that Centric Occlusion. Two common examples of occlusions that may not have this freedom are firstly those Angles Cl II div (ii) incisor relationship and when anterior crowns have been provided with palatal surfaces that are too thick.

12

1  What Is Occlusion?

Fig. 1.5 (a) No freedom in centric occlusion. (b) Freedom in centric occlusion

a

b

In Fig. 1.5a, there is no Freedom in Centric Occlusion. Another way of thinking about this phenomenon is to consider that the occlusal contacts have ‘locked in’ the mandible to the maxilla. In contrast Fig. 1.5b demonstrates a situation where the mandible can move anteriorly, for a short distance, in the same sagittal and horizontal planes. Other aspects of the Static Occlusion that can be described are • the extent of the posterior support, • the Angle’s classification of the incisor relationship together with measurement of the overbite and overjet, • the existence of any crossbites. The answer to the question ‘Does Centric Occlusion occur in Centric Relation?’ is a useful one, because it describes the relationship of the mandible to the maxilla when the teeth fit together. In some ways the answer to the question ‘what is the Jaw Relationship when the teeth fit together’ would be more useful. But given that there is no way of reliably imaging the position of the head of the condyle in the glenoid fossa [6], this is a question to which there is no answer. The word ‘Centric’ is an adjective. It should only be used to qualify a noun. Centric what?

Dynamic Occlusion

13

Dynamic Occlusion The dynamic occlusion refers to the occlusal contacts that are made whilst the mandible is moving relative to the maxilla. The mandible is moved by neuromuscular influences. But the pathways along which it moves are determined not only by the muscles controlled by CNS, via the nerves, but also by two guidance systems. The posterior guidance system [synonym: posterior determinate of mandibular movement] of the mandible is the temporomandibular joints. As the head of the condyle moves downwards, medially and forwards the mandible is moving along a guidance pathway which is determined by the intra-articular disc and the articulatory surfaces of the glenoid fossa, all of which is enclosed in the joint capsule. When teeth are touching during a protrusive or lateral movement of the mandible then those touching teeth are also providing guidance to mandibular movement. This is the anterior guidance [anterior determinate of mandibular movement]. Based upon this analysis, it is the author’s belief that whichever teeth touch during eccentric movements of the mandible, that those teeth provide the Anterior Guidance. Because no matter how far back these guiding teeth are, they are anterior to the Temporomandibular Joints [the Posterior Guidance of the Mandible]. This means that a patient with a severe anterior open bite would still have Anterior Guidance of their mandible; it could, for instance, be on the second molars. The guidance might be on back teeth but because those teeth are still in front of the TMJs, they are the teeth that provide the Anterior Guidance of the mandible. Therefore, despite the ambiguity of the word ‘anterior’ in the term anterior guidance, it does not mean that the anterior guidance of the mandible is always on the front teeth. So logically, because all teeth are in front of the posterior guidance system of the mandible, whichever teeth touch during an excursive movement of the mandible are providing the anterior guidance. This definition differs from that given in some restorative textbooks, when the term anterior guidance is used to describe only the guidance, which involves the front teeth. I think this definition does not stand up to critical analysis, and I think those who subscribe to it are describing what they consider to be ideal dynamic occlusion [see below]. There are other terms that are used to describe a patient’s Dynamic Occlusion: • ‘Canine Guidance’ refers to a dynamic occlusion that occurs between the canines during a lateral excursion of the mandible. A canine-protected occlusion refers to the fact that the canine guidance is the only dynamic occlusal contact during this excursive movement. • Group Function. In this type of anterior guidance, the contacts are shared between several teeth on the working side during a lateral excursion. To qualify for the term ‘group function’, the contacts within the group that are towards the front of the mouth should be the earliest and/or hardest contacts. • This contrasts with the term ‘Working Side Interference’, which infers a heavy or early occlusal contact towards the back of the mouth during an excursive movement.

1  What Is Occlusion?

14

• A ‘Non-Working Side Interference’ is an anterior guidance on the back teeth on the non-working side during lateral excursion. During a Lateral Excursion Non-Working Side: The side on which the head of the condyle does translate downwards, forwards and medially. Working Side: The side on which the head of the condyle does not translate downwards, forwards and medially

Note The Working Side [WS] is the side of the mandible towards which the mandible is moving during a lateral excursion. The Non-Working Side [NWS] is the side of the mandible away from which the mandible is moving. These terms can be confusing when considering the temporomandibular joints, because it is the TMJ on the Non-Working Side which is moving the most.

Ideal Occlusion One reason why some restorative textbooks define anterior guidance as being solely the dynamic occlusal contacts between the front teeth is that it is generally considered to be more ideal if the anterior guidance is on those front teeth. Furthermore, the fact that the pejorative word ‘interference’ is used to describe an occlusal contact between back teeth infers that anterior guidance on back teeth is less than ideal. This introduces the concept of ‘ideal occlusion’ and this raises three important considerations: 1. Which jaw relationship might be considered the most ideal for the muscles of mastication? 2. If a dynamic occlusal contact that is between back teeth is deemed ‘a posterior interference’, with what is it interfering? 3. If some occlusions are ideal, for what or for whom are they ideal?

Ideal Occlusion Q. Who or what is it ideal for? Posterior Interference Q. Who or what is it interfering with?

Ideal Occlusion

15

Let us examine this concept of Ideal Occlusion by firstly answering the questions posed above. Then we can determine whether the concept of Ideal Occlusion has a useful function in routine clinical dentistry.

Answer to Q.1 It is potentially more ideal if the teeth fit together (Centric Occlusion), in a ‘position of the mandible to the maxilla, with the disc in place, where the muscles supporting the mandible are at their most relaxed and least strained’ (the conceptual description of Centric Relation given above). This establishes the concept that in the realm of the Static Occlusion the occlusion might be considered ideal or not ideal for another part of the Articulatory System, namely the muscles of mastication (Fig. 1.6b).

Answer to Q.2 If two molars on the side from which the mandible is moving during an excursive movement can be described as a Non-Working Side Interference, then with what are they interfering? The posterior guidance of the mandible is provided by the temporomandibular joints. As the head of the condyle translates down the articular eminence on the Non-Working Side (which, paradoxically, is the side that is moving the furthest), then the mandible is being guided by this joint. If, as this is happening, two posterior teeth hit against each other on the same [NW] side, then for the simple reason that these two posterior teeth are close to the joint, there is potential for that contact to influence or ‘interfere’ with the movement of the condyle within that joint. Contrast this with the situation, where the anterior guidance is provided not by those posterior teeth [which are close to the joint] but by front teeth which are further away. Then the likelihood of ‘interference’ of condylar movement within the non-working side temporomandibular joint is less. Anterior guidance, therefore, on back teeth [whilst still providing anterior guidance to the mandible] is described as a Posterior Interference because it may interfere with the posterior guidance system of the mandible, namely the temporomandibular joints. Posterior interferences are, therefore, considered to be a less ideal type of dynamic occlusion. The term ‘ideal’ relates to whether or not it is ideal for another part of the Articulatory System: the temporomandibular joints (Fig. 1.6a).

Answer to Q.3 An occlusion may be qualified by the terms ideal or less than ideal by the effect it potentially can have on the other parts of the Articulatory System.

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1  What Is Occlusion?

Fig. 1.6  Occlusion is ideal for another part of the articulatory system

Temporomandibular Joints

a

Ideal occlusion

Muscles Temporomandibular Joints

b

Muscles

Ideal occlusion

Definition of Ideal Occlusion This is given in established texts [8] as: • The coincidence of Centric Occlusion in Centric Relation (CO = CR). • When there is freedom for the mandible to move slightly forwards from that occlusion, in the same sagittal and horizontal plane (Freedom in Centric Occlusion). • When the mandible moves there is immediate and lasting posterior disocclusion (or anterior guidance is on the front teeth). There is no such thing as an intrinsically bad occlusal contact, only an intolerable number of times for that patient at that time in their life to function or parafunction on it. This historical definition of Ideal Occlusion is presented only after having considered for what or whom this type of occlusion is ideal and gives the justification of why a particular type of occlusion could be considered as being potentially ideal for other parts of the Articulatory System. It is of paramount importance to appreciate that the term ‘ideal occlusion’ means something quite different from the term ‘correct occlusion’.

The Importance of Ideal Occlusion as a Concept

17

To state that an occlusion is correct or wrong betrays a mechanistic approach to the subject. Patients are not machines and an occlusion can only be judged on the reaction that it produces in the tissues of the system in which it inter-reacts. That reaction will be infinitely variable between individuals and will in some contexts vary within an individual with time. That is why the more recent definition of Ideal Occlusion in a later edition of the same textbook [9] moved away from this mechanistic description [‘A machine is a System that is not the result of a fertilized egg’ [4]] to a physiological description. This essentially states that an occlusion is ideal • for that patient, • at that time in their life, • if there are no adverse reactions to it. This is a major change in the way that dentists are asked to consider Occlusion. It essentially suggests: • Dentists should examine the Occlusion before starting treatment, • to determine whether there are any adverse reactions to that Occlusion. • If there are none, there is no need to change anything, because that patient has an Ideal Occlusion—for them—at that time. By virtue of the frequently observed fact that most patients seem to adjust to some strange looking occlusions without any adverse reaction most dentists will welcome this approach. ‘If it is not broken don’t fix it’ is a longstanding piece of excellent advice. It is the definition of broken that has changed in the field of dental occlusion. By broken we now mean that there are no adverse reactions; it does not mean that the occlusion does not conform to the mechanical definition as given above. This is also why the term ‘Malocclusion’ can be challenged [10], and is certainly not as descriptive as the term ‘MalAdaptive Occlusion’ [11]. We will return to these considerations, when discussing Good Occlusal Practice in Simple Restorative Dentistry.

The Importance of Ideal Occlusion as a Concept 1. Pre-treatment Examination and Records The first and most important reason for defining ideal occlusion is that it gives a benchmark against which patients’ occlusion can be measured. This needs to be done before, during and after dental treatment. This is of paramount importance to the health of our patients, especially in the increasingly litigious environment in

18

1  What Is Occlusion?

which we work. It cannot be overstated how important it is for a dentist to be able to demonstrate that their treatments did not result in a change in Occlusion, Jaw Relationship and/or Muscle Health and Function. This is especially true if it is being claimed the changes were beyond the patient’s adaptive capability and so resulted in harm. The key to this is the ability to examine all parts of the Stomatognathic or Masticatory System. If the reader takes only one message from this book, the author hopes that it will be this one. It is of paramount importance that dentists examine and record the pre-existing occlusion before providing any treatment which might involve a change to the occlusion. Mounted study models are a good way of examining and recording a pre-­ treatment occlusion. This is not needed or practicable for the vast majority of dentists, treating the vast majority of their cases. Alternatively, and infinitely easier, notes can be made, which describe the patient’s occlusion. These notes use the criteria of Ideal Occlusion as a benchmark. To record an occlusion using only the criteria of Angle’s classification is of limited value, whereas to use the benchmark of ideal occlusion is considerably more informative (see Fig. 1.7). This concept of a pre-treatment occlusal analysis will be discussed in much greater detail in the chapter on Simple Restorative Dentistry. 2. Management of Myofascial Pain The second reason why ideal occlusion is an important concept is found in the longheld view that an important factor in the development of Myofascial Pain [MP] is ‘the individual patient’s lack of adaptation to a less than ideal occlusion’ [5]. This statement does not attribute an exclusively causal relationship between a less than ideal occlusion and MP. Different patients will have different thresholds of tolerances to occlusion; furthermore the same patient can have a different tolerance to their occlusion at different times. For these patients the provision of an ideal occlusion is, therefore, one but by no means the only way of treating the condition. When an ideal occlusion is provided this should always be initially in a temporary and reversible way: that is a Stabilisation Splint [12]. 3. Provision of Treatments That Affects the Occlusion [and Jaw Relationship]: Conformative Versus Re-Organised Approaches [These concepts and the techniques needed to follow them will be covered in much greater detail in the chapters on Restorative Dentistry.] In providing treatment with an occlusal element, one of the first questions to be decided in the treatment planning stage is whether the aim is to maintain the same occlusion during treatment. If the pre-treatment occlusion is to be preserved, then it is described as ‘Conformative Approach’ [13, 14]. Before deciding to conform to the pre-existing occlusion, not only does that occlusion need to be examined but, in addition, any signs of existing adverse reactions to that occlusion must be noted. If there are signs, then there may be a

The Importance of Ideal Occlusion as a Concept Fig. 1.7  Example of a record of a patient’s occlusion, using ideal occlusion as the benchmark

Date 19/3/19

19

Occlusal record for Robert Black 1 New St Old Town

Skeletal 1 Angles 1

Static occlusion Does CO occur in CR? No If not.. prem contact in CR? Roughly: Left molar Exactly: Disto buccal cusp of lower left 8 against mesial marginal ridge of upper 7 and distal of upper left 6 Direction of slide from CR to CO: 3 mm Anterior slightly vertical and slightly to the left Freedom in Centric Occlusion? No Dynamic occlusion

Non-working side interferences Working side interferences Crossover position Canine guidance Group function

NWS Int WS Int

RHS

LHS

17 (FGC) v 48

No

No

No

17 v 48 No

No No

Yes (bridge 13)

No

No

No

Notes No tongue scalloping or cheek ridging Tooth surface loss (anteriors ) and history of cuspal fracture at tooth 17

case for occlusal adjustment; otherwise ‘trauma from occlusion’ may be replicated. Some dental treatment, such as most major restorative, will, however, inevitably change the patient’s occlusion and usually it will, as a consequence, change the relationship between the upper and lower jaws. In the past, this has been known solely as the ‘Re-Organised Approach’. It will be described in some detail later in this book. For now, let us define the ‘Re-Organised Approach’ as a different Occlusion (and Jaw Relationship) from the ones that the patient had before treatment. Because it is ideal, as defined mechanically [see below †], it is considered to potentially be better tolerated by the patient’s Articulatory System, than a random change in occlusion and jaw relationship would be. The starting point of designing an Occlusal Prescription in the Re-Organised Approach is to find and record Centric Relation.

20

1  What Is Occlusion?

Implicit in the concept of the ‘Re-Organised Approach’ is the requirement to • plan, • design, • prescribe the Occlusion before embarking on the treatment. It should not be the result of happenstance, which somewhat cruelly could be parodied as the ‘un-organised, and I hope we get lucky and the patient can adapt’ Approach. The problem with the binary choice between the Conformative and Re-Organised approaches is that it does not explain the success of treatments such as the Dahl Technique, Orthodontics or developing new occlusions and jaw relationships by the careful application of composite restorations in worn dentition cases* [Orthodontics and the restoration of the worn dentition are subjects of chapters in this book]. *Note: Some dentists in restoring the worn dentition by composite ‘build ups’ will have done a design phase and so have a very clear occlusal prescription to which they are going to restore the case; this then will still fall within the definition of the Re-Organised Approach. Some dentists will, however, not design the end point of their restoration in this way, but they will still provide an occlusion to which the patient will be able to successfully adapt. It is for these cases that there is a need for some Guidelines of Good Occlusal Practice. The author, therefore, in consultation with colleagues, who have contributed to this book, suggests a third option: • It is not the Conformative Approach, because the Occlusion and the Jaw Relationship are changed. • It is not the Re-Organised Approach, because it does not follow the prescription of a careful pre-treatment design phase. It is a: • slow, • careful, • adjustable, –– development of a new Occlusion, • that is subject to continual monitoring for signs of adverse reactions. –– in the tooth, –– periodontal, –– Articulatory, –– Systems. This could be called ‘Monitored Developmental Approach’ [15]. The features of this approach are: 1. All of the elements of the Masticatory System are examined for any signs of mal-adaptative reactions to changes that the treatment is creating; before, during and after treatment.

The Importance of Ideal Occlusion as a Concept

21

2. There is no pre-treatment design wax up, or any other technique that envisages the end point of treatment. 3. The new occlusion/jaw relationship is provided over a period of time. 4. There is a degree of reversibility to the treatment modality. The reasons for these suggestions are: 1. It is essential that the patient does not have mal-adaptative reactions that develop during or after* treatment or are exacerbations of a pre-existing condition. 2. The Occlusion and Jaw Relationship are not being prescribed to a specific model, and so there is no need to design this on mounted models first. 3. By evolving the Occlusion over a period of time, the adaptive capability of the patient is supported. 4. If the constant monitoring shows some adverse reaction, it is important that the occlusal treatment can be easily adjusted. *If things start to go wrong post-operatively, the temporary and removable provision of an Ideal Occlusion, as defined mechanically/anatomically†, can be quickly provided. This can be considered instead of reversing the treatment. It means that the dentist should be able to make, fit and adjust a Stabilisation Splint. † • Centric Occlusion in Centric Relation. • No Posterior Interferences. • Freedom in Centric Occlusion.

Risk Management The purpose of Guidelines of Good Occlusal Practice is to increase the chances of healthy function, by reducing the risk of damage to the inter-related tissues of the Masticatory System. Providing dentists these Guidelines of Good Occlusal practice and the rationales that have helped to develop them are the two main aims of this book.

Guidelines of Good Occlusal Practice

1. The examination of the patient involves the Teeth, Periodontal Tissues and Articulatory System. 2. There is no such thing as an intrinsically bad Occlusal Contact, only an intolerable number of times to [para]function on it. 3. The patient’s occlusion should be recorded, before any treatment is started.             to be continued ………………

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1  What Is Occlusion?

References 1. Smith BGN. Occlusion: 1. General considerations. Dent Update. 1991;18:141–5. 2. O’Carroll EO, Leung A, Fine PD, Boniface D, Louca C. The teaching of occlusion in undergraduate dental schools in the UK and Ireland. Brit Dent J. 2019;227:512–7. 3. Oxford University Press. Shorter Oxford English dictionary. Oxford: Oxford University Press; 1973. 4. Greenfield S, editor. The private life of the brain: emotions, consciousness, and the secret of self. London: Penguin Books. ISBN-13 978-0-141-00720-5. 5. Ash MM, Ramfjord SP. Occlusion. 4th ed. Philadelphia: Saunders; 1995. p. 76. 6. Horner GQ. The effects of positioning variations in transcranial radiographs of the temporomandibular joint: a laboratory study. Br J Oralmaxillofac Surg. 1991;29:241–2. 7. Posselt UOA. Studies in the mobility of the human mandible. Acta Odontol Scand. 1952;10:19. 8. Ramfjord SP, Ash MM. Occlusion. 2nd ed. Philadelphia: Saunders; 1971. p. 178. 9. Ash MM, Ramfjord SP. Occlusion. 4th ed. Philadelphia: Saunders; 1995. p. 84–5. 10. Davies SJ. Malocclusion—a term in need of dropping or redefinition? Br Dent J. 2007;202:12. 11. Gremillion HA.  Relationship between TMD and occlusion. J Evid Base Dent Pract. 2006;6:43–7. 12. Moufti MA, Lilico JT, Wassell R. How to make a well-fitting stabilization splint. Dent Update. 2007;34:398–408. 13. Wise M.  Occlusion and restorative dentistry for the general dental practitioner. Br Dent J. 1982;152:319–20. 14. Davies SJ. Occlusion in restorative dentistry: conformative, re-organised or unorganised. Dent Update. 2004;31:334. 15. Davies SJ, et al. Occlusion: is there a third way? A discussion paper. Br Dent J. 2021;321:160–2.

2

The Examination and Recording of the Occlusion: Why and How

Before presenting ‘how’ to examine and record of the Occlusion, some attempt should be made to justify ‘why’ it is necessary. A study of the influences of mandibular movements may appear to be a strange way of justifying the need to examine a patient’s occlusion, but hopefully the reader will agree with me that it will be helpful to have an understanding of the control mechanisms that enable us to occlude our teeth together.

In this chapter, we will discuss: • What makes up the mandibular locomotive system. • Why an understanding of it is important in the study of Occlusion. • How the occlusion can be simply and quickly examined and recorded.

The mandible moves, relative to the maxilla, by virtue of two influences. Firstly, locomotor forces are provided by the muscles under the control of the nervous system: neuromuscular control. Secondly, there are two hard tissue guidance systems: these are the temporomandibular joints and the occlusal surfaces of the teeth.

Mandibular movement • Controlled by the Neuromuscular system • Influenced by two hard guidance systems: Temporomandibular joints, and Occlusal surfaces of teeth

© Springer Nature Switzerland AG 2022 S. Davies, A Guide to Good Occlusal Practice, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-79225-1_2

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2  The Examination and Recording of the Occlusion: Why and How

Neuromuscular Control The Muscles Mandibular Muscles (The term mandibular muscles is preferable to masticatory muscles in the same way that ‘leg muscles’ is a more embracing term than ‘walking muscles’.) Within the articulatory system, the muscles have been simply expressed as the ‘motors’. Whereas it is the ‘hard’ occlusal surfaces of the teeth and articulatory surfaces of the bones which provide the guidance of mandibular movement, it is muscles which provide the locomotive force to move the mandible during function and parafunction. The muscles which are joined to the mandible and are therefore responsible for its movement are singularly and collectively immensely complicated motive entities. It may be because anatomy was the first medical science that the function of a muscle has historically been described purely by an analysis of its origin and insertion. This is dangerously simplistic and has sometimes resulted in a mandibular muscle having been labelled as simply as an ‘opening’ or ‘closing’ muscle. It takes no account of the complex antagonistic and synergistic interrelations of muscle function, which are responsible for supplying the motive power of mandibular movement. Electromyographic recording when linked to either simple observation or sophisticated jaw tracking systems offers an enhanced understanding of the functions of the mandibular muscles. The lateral pterygoid muscle offers a good example of how the understanding of its function was enhanced by electromyography, beyond the simple anatomical assumptions previously held [1].

Individual Mandibular Muscles The Masseter Muscle Anatomy: The masseter originates from the zygomatic arch, inserts into the outer surface of the angle of the mandible and comprises superficial, intermediate and deep parts. Function: Its principal action is to elevate the mandible, so closing the jaws; it is also an accessory muscle in mandibular protrusion. Parafunction: It is active in tooth clenching and is the most frequently affected muscle by this parafunctional habit.

The Temporalis Muscle Anatomy: This is a large, fan-shaped muscle arising from the lateral aspect of the skull in the temporal fossa and converges to a tendinous insertion, which, running

Individual Mandibular Muscles

25

below the zygomatic arch, inserts into both the coronoid process and anterior border of the ascending ramus of the mandible. It is significant that the orientation of the muscle fibres varies greatly: • The posterior fibres run almost horizontally forwards. • The anterior fibres run vertically. • The intermediate fibres have varying degrees of orientation. Function: The action of this muscle depends upon which fibres are contracting: • The anterior fibres raise the mandible when the mouth is closing. • The horizontal posterior fibres retract the mandible. The horizontal fibres of the temporalis muscle are the only muscle fibres that retract the mandible; no other muscle performs this function. Parafunction: The temporalis muscle is frequently a tender muscle in bruxists.

Lateral Pterygoid Muscle Anatomy: This is a muscle which has two heads and, it is now thought, two insertions. The smaller superior head arises predominantly from the infra-temporal surface of the greater wing of the sphenoid and inserts into the anterior part of the intra-articular disc and capsule, while the larger, inferior head arises from the lateral surface of the lateral pterygoid plate and inserts into the neck of the mandible just below the condyle. Function: While it is accepted that there is some overlap of activity of the two heads, the superior pterygoid is predominantly active during clenching and is thought to stabilise the condyle disc assembly. In function, it is not active during opening. Being as it is attached into the disc it might be supposed that it is responsible for the forward movement of the disc during opening, whereas the disc moves because it is attached to the head of the condyle. It is active during closing, when it is the antagonist to the elastin fibres of the bilaminar zone . The inferior pterygoid is active during mouth opening and draws the condyle forwards, medially and down the slope of the articular eminence. Therefore, when both right and left pterygoid muscles act together, mouth opening and mandibular protrusion occur, but when only one muscle contracts the condyle on that side is drawn forwards and the mandible pivots around the opposing condyle. So the chin moves towards the opposite side. Parafunction: This active/passive cycle is altered, however, in parafunction, when it has been demonstrated that there is an overall disruption of the pattern with both heads (or ‘muscles’; if superior and inferior bellies are considered to be separate muscles) showing a marked and simultaneous increase in activity. This can cause pain in the pre-auricular region. In addition, it may possibly lead to disc displacement, and the patient may develop TMJ clicking and locking.

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2  The Examination and Recording of the Occlusion: Why and How

Medial Pterygoid Muscle Anatomy: The bulk of this muscle originates from the area between the two pterygoid plates; there is, however, a small, more superficial head arising from the maxillary tuberosity. These two heads fuse and the muscle passes posteriorly and laterally downwards to insert into the inner aspect of the angle of the mandible. The orientation of the fibres parallels that of the anterior fibres of the masseter muscle. Function: The action of the medial pterygoid muscle is to elevate the mandible and it is also active during protrusion and lateral mandibular movement. Parafunction: It is not a muscle that can reliably be palpated for tenderness, nor tested by resisted movement, and so its involvement in parafunction can only be surmised. It may become hypertonic in patients who parafunction in extreme mandibular movement.

Digastric Muscle Anatomy: This muscle has two parts: the anterior and posterior bellies. They are connected by a tendon which passes through a fibrous loop on the upper border of the hyoid bone. The posterior belly arises from the mastoid notch and the anterior belly is inserted into the mandible near the symphysis. This insertion into the mandible qualifies it for inclusion as a ‘mandibular muscle’. Function: When the hyoid bone is fixed (by the infrahyoid muscles) the action of this muscle is to assist the lateral pterygoid muscle in opening the mouth. Its action is therefore to depress mandible. In the action of swallowing, the hyoid bone is raised by both right and left digastric muscles contracting together. Parafunction: Tenderness in this muscle is frequently encountered in patients who brux or clench on their anterior teeth and manifests as pain behind the ascending ramus or under the body of the mandible.

Mylohyoid Muscle Anatomy: This thin sheet of muscle arises from the whole length of the mylohyoid line on the inner aspect of the mandible. The fibres meet in the median raphe, which inserts into the body of the hyoid bone. This muscle separates the submandibular and sublingual regions. Posteriorly the muscle has a free border. Function: The action of this muscle is to raise the hyoid bone and the tongue during swallowing.

Suprahyoid, Infrahyoid and Cervical Muscles Function and parafunction: The reason why a brief consideration of the function and parafunction of these muscles should be discussed as part of the subject of

How Does the Mandible Move?

27

occlusion is that claims are made that occlusion can have an effect on the wider musculo-skeletal system. This supposition is based upon a consideration of head posture. The hyoid bone is attached to the mandible by the suprahyoid muscles. The infrahyoid and suprahyoid muscles by stabilising the hyoid bone enable the suprahyoid muscles to be tangentially involved in mandibular movement. Head posture is also affected by the action of these muscles, as shown by the fact that the head moves slightly back as the mandible opens. Conversely, head posture could potentially affect the function and health of these muscles. This may provide an explanation for an association between forward head posture and myalgia of the head and neck muscles. Similarly, the cervical muscles are largely responsible for head posture, and there may be an overlap between some TMD and symptoms from the cervical spine.

How Does the Mandible Move? Before answering this question, I would like us to consider that the movement of the mandible relative to the maxilla is one of the many Locomotor Systems in the body. The primary functions of the Locomotor systems are supporting and moving the body. The principal components of these locomotive systems are the joints, muscles and bones. In addition, there is cartilage, tendons and ligaments. So, the Mandibular Locomotor System is the system that performs the many functions of the mouth. It can exhibit both parafunction and dysfunctions.

Neural Pathways The mandible is controlled not only as a result of voluntary movement, but also by reflexes, most notably a jaw closing reflex and jaw opening reflex. The jaw closing reflex protects the mandible and associated structures during violent whole body movement; it can result in damage to the teeth, especially if the occlusal contacts are not flat and in line with the long axis of the root. The jaw opening reflex is to protect the teeth during sudden and unexpected mastication of a hard object or to protect the lips, cheeks and tongue during mastication. These voluntary and involuntary movements are controlled by the central and autonomic nervous systems, via sensory and motor nerves. There is input to these systems from both peripheral receptors and the higher centres. These peripheral receptors or proprioceptors are situated not only in joints, muscles and the epithelium as in all other human locomotor systems, but also in the periodontal membranes. It is the presence of these periodontal proprioceptors that makes the Articulatory System unique amongst human locomotor systems. Consequently, if the movements within this locomotor system result in teeth touching (either in function or parafunction), then these proprioceptors are stimulated. This means that any change in a patient’s occlusion, as a result of dental treatment,

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2  The Examination and Recording of the Occlusion: Why and How

can ‘be sensed’ by the patient’s central nervous system. It is because of this consideration that dentists cannot ignore the effect of changing the occlusion when providing routine care.

Neuromuscular Guidance and Motor Engrams A motor or motion engram can be considered a permanent fragment of memory. Movement or Motor Engrams are learned, that is to say a product of plasticity within the Central Nervous System. They are defined as: ‘Memorized motor patterns used to perform a movement or a skill that are stored in the motor area of the brain’[2]. They organise and control muscle synergies and so are responsible for all of the movements that we can make. Some are basic movement such as walking, and some advanced ones represent special skill such as sporting activities or playing a musical instrument. There is a motor engram that determines the relationship between the Mandible and Maxilla when we close our teeth together into the position of maximum intercuspation [or Centric Occlusion]. This motion engram controls the mandibular muscles to establish the Jaw Relationship of our normal bite. Although engrams are permanent fragments of memory, they can be permanently corrupted, for example, as a result of brain injury; or more commonly temporarily corrupted, for example, the effect of alcohol on the ability to walk in a straight line. Similarly, the muscles’ ability to respond accurately to a motion engram can be compromised by fatigue, for example, the difficulty an athlete may have in walking after completing a marathon race.

This Is an Important Consideration in Restorative Dentistry The significance of the influences that control the relationship of the mandible to the maxilla is apparent when we consider how dental procedures can affect the patient’s ability to close in the jaw relationship of their normal bite. Firstly, motion engram or the mandibular muscles’ ability to follow it can be corrupted: • Local anaesthetic can affect motor nerves. • Fatigue in masticatory muscles after a prolonged dental visit can affect the muscles’ ability to follow the motion engram. Secondly, even if the motion engram and the muscles’ ability to follow it are intact, but the dental treatment has significantly altered the occlusal surfaces of teeth, then the motor engram will be redundant because the teeth will no longer fit together in the jaw relationship that the motor engram will determine. This is something of which the patient will be aware once the anaesthesia has worn off, because the periodontal proprioceptors will sense it.

The Hard Guidance Systems

29

A significant aim of this book is to provide guidance on how to avoid this treatment outcome.

The Hard Guidance Systems There are two systems that provide hard guidance during mandibular movements. These are classified as the posterior and the anterior guidance systems; they are sometimes called the posterior and anterior determinants. These guidance systems are interrelated and are parts of one overarching system: the Articulatory System. An understanding of these guidance systems is important to dentists, because the occlusion provides the Anterior Guidance. Very few restorative treatments do not involve the occlusal surfaces of teeth.

Posterior Guidance The principal elements of the temporomandibular joint [TMJ] are: • the head of the condyle, • the intra-articular disc, • the glenoid fossa. The TMJ provides the posterior guidance system of the mandible. This is obvious, because the head of the condyle is the most posterior part of the mandible. When we open our mouths, the heads of both condyles firstly rotate and then they translate downwards, forwards and medially. These movements can be quantified: • The angle of downward movement is known as the ‘Condylar angle’. • The angle of medial movement is known as the ‘Bennett angle’. • The amount of forward and downward movement is not measured in the joint, but can be extrapolated by measuring how wide the mouth opens.

Lateral Excursion During a lateral excursion of the mandible, one condyle translate downwards, forwards and medially in much the same way that it does during a straight opening. The direction of travel of the mandible is away from the side in which the condyle is moving. Whereas the head of the condyle is moving very little in the TMJ on the side to which the mandible is moving. Somewhat confusingly the side on which the TMJ is essentially opening [downward, forward and medial translation] is called the Non-­ Working Side (NWS) and the side on which there is no significant translation is known as the Working Side (WS). These counterintuitive terms have their origin in the consideration of mastication.

2  The Examination and Recording of the Occlusion: Why and How

30

Although there is no significant translation within the Working Side TMJ, there can be a movement of the condyle. This is sometimes called ‘Bennett Movement’. A better term is ‘immediate side shift’, because the movement is: • Immediate [It occurs at the very beginning of the Lateral Excursion.] • Non-progressive [It finishes almost as soon as it has started.] • Lateral [obviously if the mandible is moving medially on the NWS.] • • • •

This movement is variable from patient to patient. is the consequence of the WS condyle being joined to the NWS condyle. is difficult to observe, measure and reproduce on an articulator. can be significant to the comfort of a posterior restoration.

Figure 2.1 provides an illustration on mandibular movement during a right lateral excursion. Bill is controlling the Working Side, and Ben is in charge of the Non-Working Side.

Condylar angle

Bennet angle

H Horizontal plane

Vertical plane

Ben Bill H

FDM FDM

Fig. 2.1  Illustration of the direction of mandibular movement

The Hard Guidance Systems

31

Anterior Guidance The anterior guidance system of the mandible is provided by whichever teeth touch during the excursive movements of the mandible, whilst teeth are in contact. These contacts are known as the Dynamic Occlusion. This definition of Anterior Guidance or the Anterior Determinates of the Occlusion may be challenged by some, who will define Anterior Guidance as the guidance that is exclusively on anterior teeth. Whereas some will agree with the concept that if the Posterior Guidance [or determinate] is provided by the TMJs then whichever teeth touch during an excursive movement of the mandible must provide the Anterior Guidance, because all teeth, even the molars, are in front of the joints. However, it is generally considered to be more ideal if these Anterior Guidance contacts occur at the front of the mouth, because then they are as far away as possible from the posterior guidance system. This reduces the possibility of the two guidance systems interfering with each other. So Anterior Guidance on front teeth can be considered ‘ideal anterior guidance’. The concept of Ideal Occlusion is described elsewhere in this work.

Relevance of a Study of Guidance Systems to Occlusion The reason why dentists need to concern themselves with mandibular movements and the influences that control them is that most dental treatment involves the occlusal surfaces of teeth: that is to say that dentists inevitably are changing one of the guidance systems of mandibular movement. There is little evidence to suggest that a change in occlusion will precipitate morphological changes within the joint. It would appear, therefore, that the most likely adaptation in the ‘system’ occurs in the teeth and their supporting structures. These ‘adaptations’ are • wear, • movement, • fracture.

Articulatory System: Occlusal Harmony? How to determine what is an occlusion that complements to the TMJ may appear to be an impossible question to answer; in reality the solution is very simple. The key is to carry out a competent examination of the whole of the Articulatory System. This will include the TMJs and the supporting muscles, which will determine whether there is a Temporomandibular Disorder. If there is, then the first clinical decision to take, with the patient’s involvement, is whether or not to treat it before providing any other treatment.

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2  The Examination and Recording of the Occlusion: Why and How

Secondly, the patient’s pre-treatment occlusion is examined and recorded, as part of this Articulatory System Examination. This will answer the question: ‘can treatment be provided without changing the patient’s pre-existing occlusion? If it can, then the Conformative Approach is adopted. If it cannot, then it will be safer if the new occlusion is going to be more ideal rather than less ideal. This is known as the ‘Re-Organised Approach’. Both of these approaches constitute Good Occlusal Practice. It would not be Good Occlusal Practice to change the Occlusion, and the Jaw Relationship to one that was not only different but also less ideal to other elements of the Masticatory to System: an Occlusion to which it might be more difficult for the patient to adapt. This introduction has brought us to the conclusion that an examination of the patient’s pre-treatment occlusion is essential.

Examination of the Occlusion (Fig. 2.8) Occlusal examination • Against the benchmark of ideal occlusion • Three essential questions

Introduction The Occlusal Assessment is the third part of an Examination of the Articulatory System. For this exercise, the concept of Ideal Occlusion is to provide a benchmark against which the patient’s occlusion is compared. Using Ideal Occlusion in this way does not infer that the provision of an Ideal Occlusion is the treatment objective; it is simply a ‘zero’ against which to evaluate the patient’s pre-treatment occlusion.

The Three Question Examination Question 1. Does Centric Occlusion Occur in Centric Relation [Retruded Contact Position]? Centric Relation describes a relationship between the two jaws. It has nothing to do with teeth and so is not an occlusion. Patients with no teeth still have Centric Relation; in fact it is the jaw relationship that a dentist making a new set of Complete Dentures is trying to find, because it is a consistent and reproducible position (Fig. 2.2). When the head of the condyle is moving purely in the rotational phase of its movement, then the mandible is in a terminal hinge axis. This concept provides one of the three pillars of the definition of Centric Relation that is given in the previous section. If the head of the condyle is the stationary centre about which the mandible is rotating, then the mandible will describe an arc, during this phase of TMJ

Examination of the Occlusion

33

Static occlusion Does CO occur in CR? If not.. prem contact in CR? Roughly: Exactly: Direction of slide from CR to CO:

Fig. 2.2  Occlusal examination—question 1

Fig. 2.3  Illustration of the relationship between the condyles moving when the mandible is in a terminal hinge axis and a ‘perfect’ arc is experienced during gentle bimanual manipulation

movement. Whereas if the mandible is not in terminal hinge axis, then the head of the condyle will not be purely rotating, because there will be an element of translation. As a consequence, the mandible will not describe a pure arc (Fig. 2.3).

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2  The Examination and Recording of the Occlusion: Why and How

Manipulation of patient to find the Centric Relation. It is feeling that the patient’s mandible is describing a perfect arc during manipulation that gives the experienced operator the confidence that the Terminal Hinge Axis of the mandible has been found. There is one important test that provides the operator with the confidence that Centric Relation has been found. This test is based upon the fact that the Centric Relation is a jaw relationship not guided by teeth nor by the patient’s muscles. Rather it is discovered by the operator arcing the mandible in Terminal Hinge Axis towards the maxilla. If done correctly the end point of this arc will be consistent, i.e. the same parts of the same teeth will touch each time the exercise is repeated. There will be excellent inter- and intra-operator reliability. The point at which the first teeth touch can be described as the Premature Contact [in the Centric Relation]. This is why Centric Relation is the only ‘centric’ that is consistent, with or without teeth present. The end point of the closing arc in Terminal Hinge Axis (Centric Relation) may not be a single contact but an even set of contacts between all of the teeth. The even set of Occlusal Contacts is known as Centric Occlusion [or Intercuspation Position]. In this case the Centric Relation and Centric Occlusion coincide. The positional difference between Centric Relation and Centric Occlusion can further be examined by noting the direction and length of slide of the mandible from the Premature Contact in Centric Relation to their Centric Occlusion. This slide can be observed by asking the patient to squeeze their teeth together after they have been gently guided to their consistent Premature Contact. If Centric Relation (CR) and Centric Occlusion (CO) do not coincide, in many ways it would make more sense to describe the jaw relationship when the teeth are in Centric Occlusion, and not the other way round; but that is impossible to do because there are no landmarks on the jaws that can be examined whilst the patient is holding his or her teeth in Centric Occlusion. So the question has to be: ‘Does CO occur in CR?’ (Fig. 2.2) Question 2. Does the Patient Have Freedom in Centric Occlusion? This investigation will answer the question: ‘Is the patient’s Centric Occlusion locked in?’ This means when the patient is biting together normally on the back teeth, do their incisor teeth hit so hard as to prevent the mandible from moving slightly forward. It the incisor contacts do prevent this forward motion in the same sagittal and horizontal planes, then there is No Freedom in Centric [Occlusion], and the mandible is potentially locked in.It can be examined in one of three ways: 1. Marking the occlusal contacts and seeing if the anterior contacts are heavier than the posterior ones. 2. Asking the patient to close together slowly and reporting which teeth hit first. 3. Feeling for tremors [fremitus] on the upper incisor teeth with our fingernail whilst the patient repeatedly taps up into Centric Occlusion. Despite testing this with a gloved fingernail it is an easy and reliable test (Fig. 2.4). The way in which the static occlusion is examined is illustrated in Fig. 2.5.

Examination of the Occlusion

35

Static occlusion Freedom in Centric Occlusion?

Fig. 2.4  Occlusal examination—question 2 • Operator seated comfortably • Patient is supine, at elbow height • Patient’s neck extended slightly • Use both hands • Thumbs over mental symphasis • Fingers on the lower border of mandible, not sublingually • Ask the patient to relax their jaw and let you open their mouth

• Slowly and gently arc mandible up and down with minimum force • Only the patient’s mandible should be moving • Slowly increase the upward component of each arc, until premature contact is reached • Ask the patient to put a finger in the air when they feel first contact • Repeat at least three times • Ask patient: It is the same each time? • Ask patient to use raised finger to point where they feel first contact • Ask patient to squeeze teeth together from premature contact, so as to note the direction of slide • With chairside assistance use articulating paper or foil to mark premature contact

Fig. 2.5  How to find the Centric Relation

36

2  The Examination and Recording of the Occlusion: Why and How

Dynamic occlusion RHS

LHS

Non-working side interferences Working side interferences Crossover position

NWS Int WS Int

Canine guidance Group function

Fig. 2.6  Occlusal examination—question 3

Question 3. Where Is the patient’s Anterior Guidance? (Fig. 2.6) It has already been discussed that, in the opinion of the author, the term ‘anterior guidance’ should not be taken to mean only guidance that is on the front teeth. It is the mandible that is being guided, by both the temporomandibular joints (the posterior guidance) and whichever teeth touch during excursive movements (the anterior guidance) (Fig. 2.7). However, the benchmark against which the patient’s dynamic occlusion is measured is, again, the Ideal Occlusion. In an Ideal Dynamic Occlusion the anterior guidance will be on the front teeth, either Canine Guidance or Group Function. This is confirmed by the conventional wisdom that if the back teeth provide the Anterior Guidance, we call them Posterior Interferences; either on the Non-Working Side or on the Working Side.

Examination of the Occlusion Fig. 2.7  How to examine anterior guidance

37 • Finding whether there are Non working side interferences, by trying ‘a pull out’

• During this right lateral excursion, there is a NWS interference between UL6 (26) and LL7 (37)

• Examining for the existence of working side interferences by marking the contact between the teeth during a slide to the working side (as illustrated) • Next mark the centric occlusion stops in a different colour (not illustrated) • Example of canine guidance

• Example of a group function

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2  The Examination and Recording of the Occlusion: Why and How

Why do we use the pejorative term: interference? Because they have the potential to interfer with the Temporomandibular Joints [the Posterior Guidance]. Because Posterior Interferences are closer to the joints that the more ideal Canine Guidance or Group Function would be. Finally, the extent and or position of the Posterior Interferences can be recorded by seeing whether they extend up to or beyond the Crossover Position. This is the position during a lateral excursion when, in a Class I occlusion, the lower canine has crossed buccal to the upper canine (Fig. 2.8).

Date

Occlusal record for Skeletal Angles

Static occlusion Does CO occur in CR? If not.. prem contact in CR? Roughly: Exactly: Direction of slide from CR to CO:

Freedom in Centric Occlusion? Dynamic occlusion RHS

LHS

Non-working side interferences Working side interferences Crossover position

NWS Int WS Int

Canine guidance Group function Notes

Fig. 2.8  Example of a record of a patient’s occlusion, using ideal occlusion as the benchmark

Recording of the Centric Occlusion

39

Because the paper is thin it is much easier to use it if it is supported by a rigid holder

Fig. 2.9  Paper tissue (for drying occlusal surfaces of teeth) and two colours of thin (40 μ) articulating paper (for making occlusal contacts) held by Miller forceps

Recording of the Centric Occlusion It is essential to have a good record of the patient’s occlusion before any treatment is provided that has the potential for occlusal change. There is a need to establish easy and universally reproducible ways of recording the patient’s occlusion. In addition, records are essential for medico-legal reasons. These records can not only be the familiar three-dimensional ones but can aslo be a two dimensional record of the marks left by articulating paper (Fig. 2.9).

Two-Dimensional Records of the patient’s Centric Occlusion In the main, these rely on firstly marking the static and dynamic occlusal contacts between the teeth using paper or silk that is impregnated with ink. Counterintuitively a very thin layer of petroleum jelly smeared onto the articulation paper improves the deposit of the marking ink from the paper to the tooth surface, especially if the surface is polished composite or porcelain. Different coloured inks can be used to mark the Static and Dynamic Occlusions. In the opinion of the author, the paper should not be thicker than 40 μm. In addition to this use of articulating paper or silk to mark the contacts, shimstock foil can be used to determine whether there is a contact by seeing whether it will pull through an occlusal contact. Shimstock is only 8 microns (μm) thick. After creating the occlusal marks on the teeth, a way of recoding them is needed. This can be by • written description writing, [for example: the contact anterior to the prepared tooth is between the palatal facing incline of the buccal cusp of UR5 and the buccal facing incline of the buccal cusp of LR5] • diagram [see use of Occlusal Sketch [3–5] in subsequent chapters], • photograph, • digital scans.

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2  The Examination and Recording of the Occlusion: Why and How

With the exception of the scan all these two-dimensional techniques have the advantage that they are means of determining the actual occlusal contacts between the teeth. They have the disadvantage that is inherent in a two-dimensional record of a three-dimensional entity.

Three-Dimensional Record of the patient’s Occlusion This, of course, means study models. They have the advantage of being a permanent copy of the patient’s occlusion, but the production of this copy of the patient’s anatomy immediately introduces a host of potential errors. • The impressions have to be accurate, • the models from those impressions must be perfectly cast, • and accurately related to each other in a static and dynamic occlusion. This exercise depends not only upon face bows and articulators, but also on the correct use of a range of impression, registration and casting materials.

Discussion Mounted study models must be accurate; otherwise they are pointless. In order to confirm that they are accurate they must be verified. This verification must be done against either patient’s occlusion, which would require a check visit; or against a second record which could be a simple two-dimensional record of the patient’s occlusion. This was the reason for the development of the Occlusal Sketch technique. The advantage of a two-dimensional occlusal is it enables the models to be mounted without the inherent difficulties of most bite registration materials [6].

Articulators Articulators are not essential. Their use is not a guarantee of success or of an easy life. Articulators are useful tools, if the dentist wishes to replicate the way in which the patient’s jaws move one against another [7]. This is valuable information as it assists in the accurate recording of the dynamic occlusion. The nearer that a particular articulator can reproduce the patient’s movements, the closer it will be possible to construct occlusal schemes that predictably conform to the dentist’s objectives, whatever they may be. In deciding which articulator to use, it is important to ask the question: ‘What movements of the mandible do I wish to reproduce, for this patient at this time?’ The key point about this approach is that it determines the level of predictability at which the dentist and technician wish to operate. If, as often is the case, a dentist and technician are not going to operate with very sophisticated articulators, it does not mean that success is denied to them. It simply means that when checking the occlusion of the restoration it is more likely that adjustment will be necessary. Similarly, if a dentist and technician are operating with sophisticated articulation, it

References

41

does not remove the dentist from the responsibility of checking the occlusion of the restoration at the fit appointment.

Facebows A facebow is a device that enables the maxillary arch to be spatially related to various anatomical landmarks on the patient’s face. This assists in mounting the maxillary cast within the articulator. The most important consequence of this is that the maxillary cast will have a similar relationship to the hinges of the articulator as the patient’s maxilla to their TMJs. This matters if the articulator is going to be used for anything other than the static occlusion in Centric Occlusion. It can appear surprising that the facebow helps mount the upper model to the hinges of the articulator, when it is the mandible that moves in the patient, until we remember that it is the upper member of the articulator that moves relative to the static lower member. Guidelines of Good Occlusal Practice

1. The examination of the patient involves the Teeth, Periodontal Tissues and Articulatory System. 2. There is no such thing as an intrinsically bad Occlusal Contact, only an intolerable number of times to [para]function on it. 3. The patient’s occlusion should be recorded, before any treatment is started. 4. Compare the patient’s occlusion against the benchmark of Ideal Occlusion. 5. A simple, two-dimensional record of the patient’s occlusion taken before, during and after treatment is an aid to Good Occlusal Practice.

References 1. Juniper RP.  Temporomandibular joint dysfunction; a theory based upon electromyographic studies of the lateral pterygoid muscle. Br J Oral Maxillofac Surg. 1984;22:1–8. 2. Kent M.  The Oxford dictionary of sports science and medicine. Oxford: Oxford University Press; 2007. ISBN-13: 9780198568506 3. Davies SJ, Gray RJM, Al-Ani MZ, Sloan P, Worthington H. Inter- and intra-operator reliability of the recording of occlusal contacts using the ‘occlusal sketch’ acetate technique. Brit Dent J. 2002;193:397–400. 4. Davies SJ, Al-Ani Z, Richmond R, Worthington HV, Smith PW.  Occlusal sketch: a reliable technique for technicians to check the occlusion of marked models. Eur J Prosthodont Restor Dent. 2005;13(2):65–8. 5. Davies SJ, Al-Ani MZ, Jeremiah H, Winston D, Smith PWS.  Reliability in recording static and dynamic occlusal contact marks using transparent acetate sheet. J Prosthet Dent. 2005;94:458–61. 6. Walls AWG, Wassell RW, Steele JG. A comparison of two methods for locating the intercuspal position (ICP) whilst mounting casts on an articulator. J Oral Rehab. 1991;18:43–8. 7. Cabot L. Using articulators to enhance clinical practice. Br Dent J. 1998;184:272–6. https:// doi.org/10.1038/sj.bdj.4809600.

3

Good Occlusal Practice in Simple Restorative Dentistry

Many theories and philosophies of occlusion have been developed [1–12]. The difficulty in scientifically validating the various approaches to providing an occlusion is that an ‘occlusion’ can only be judged against the reaction it may or may not produce in a tissue system (Dental, Periodontal or Articulatory). Because of this, the various theories and philosophies are essentially untested and so lack the scientific validity necessary to make them ‘rules’. Often authors will present their own firmly held opinions as ‘rules’. This does not mean that these approaches are to be ignored; they are, after all, the distillation of the clinical experience of many different operators over many years. But they are empirical. In developing these guidelines this book has unashamedly drawn on this body of perceived wisdom. But the aim is also to involve and challenge the reader by asking some basic questions, and by applying a common-sense approach to a subject that can be submerged under a sea of dictate and dogma.

In this chapter, we will discuss: • The ‘conformative approach’ to restorative dentistry. • Some techniques for achieving this goal. • Can and should the occlusion be improved within the conformative approach?

Discussion Does Occlusion Matter in Simple Restorative Dentistry? It is easy to justify a chapter on restorative dentistry in a book on occlusion. Dentists are constantly involved in the management of their patients’ occlusion during routine restorative dental procedures, because the occlusal surfaces of the teeth are

© Springer Nature Switzerland AG 2022 S. Davies, A Guide to Good Occlusal Practice, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-79225-1_3

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3  Good Occlusal Practice in Simple Restorative Dentistry

44

usually involved in the provision of restorations. The significance of this obvious statement lies both in the relationship that the occlusion has within the Articulatory System and the effect that trauma from the occlusion may have on the tooth, and its periodontal support. All dentists wish to avoid these problems: dentists want predictable success for their patients and themselves. Successful occlusal management leads to: • predictable fitting of restorations and prostheses, • longevity and absence of iatrogenic problems, • patient comfort and occlusal stability. ‘Fingers crossed’ dentistry equals stress.

The Starting Point: Examination It is a general principle in medicine that before treatment is provided a careful clinical examination is carried out. Dentistry generally holds to this principle, but with perhaps one exemption. Some dentists were not taught at dental school to examine and record the pre-existing occlusion before providing a restoration. Instead it has become customary to provide the restoration and then to ‘check’ the occlusion afterwards. If this is our habit, we should ask ourselves the question against what are we checking the occlusion of our restoration? It cannot be the pre-existing occlusion if we did not examine it first. In restorative dentistry the principle of providing a new restoration that does not alter the patient’s occlusion, or the jaw relationship of that Occlusion is described as the ‘Conformative Approach’, and the vast majority of restorations are provided following this principle.

The Conformative Approach Explanation The Conformative Approach is defined as the provision of restorations ‘in harmony with the existing jaw relationships’ [13]. In practice this means that the occlusion of the new restoration is provided in such a way that the occlusal contacts of the other teeth remain unaltered [14]. If the occlusal contacts of all the other teeth are the same, then it follows that relationship of the mandible to the maxilla remains unaltered. Of course, if this is not the case, then the new occlusion will require a new motor engram* to guide the muscles to create a change in the condyle/fossa relationship i.e. a different jaw relationship. *see Chap. 2.

The Conformative Approach

45

Justification The answer as to why dentists should wish to adopt the Conformative Approach is often given as being ‘because it is the easiest’. In fact, this is not the case; the easiest approach is undoubtedly not to consider whether the new restoration changes the patient’s occlusion, maybe hoping not to change it too much. The reason why the Conformative Approach is favoured is not because it is the easiest but because it is the safest. Assuming that there are no pre-existing adverse effects on any of the tissue systems, the obvious approach is to follow the ‘if it isn’t broken, don’t fix it’ maxim. A clinician is less likely to introduce problems for the tooth, the periodontium, the muscles, and the temporomandibular joints, if the occlusion of a new restoration or restorations does not change the occlusion or the jaw relationship. Conversely, introducing change requires the patient to adapt in some way. This is why the Conformative Approach is the safest way of providing a restoration. No matter how far the pre-existing occlusion is from a mechanical description of an Ideal Occlusion (see Chap. 1), the advice in the Conformative Approach is not to change the Occlusion or the Jaw Relationship.

Two Requirements if you Wish to Adopt the Conformative Approach 1. The Examination Protocol is sufficiently robust to determine whether there are any pre-existing adverse reactions to the pre-treatment Occlusion. 2. The clinician examines the Occlusion before providing treatment and potentially changing it.

When to Use the Conformative Approach? Q: When do you use the conformative approach? A: Whenever you can. The Conformative Approach is desirable and appropriate for the vast majority of our restorative cases. It is possible to provide a restoration to the conformative approach when: 1. The patient has an Ideal Occlusion, i.e. Centric Occlusion (CO) is in Centric Relation (CR) with Anterior Guidance free from Posterior Interferences. This is unusual, it is much more likely that:

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3  Good Occlusal Practice in Simple Restorative Dentistry

2. The patient does not have an Ideal Occlusion, and that the removal of the existing occluding surface of the tooth to be restored will not result in an inevitable change in the Centric Occlusion or Anterior Guidance. Examples of an occasion where this will not be possible is either if the tooth that is to be restored is a deflecting contact; i.e. it provides the principal guiding contact from CR to CO, or if the tooth is providing a heavy posterior interference. In the case shown in Figs. 3.1 and 3.2, it is attractive to think that the dentist when restoring either of the lower third molars [LL8 is the premature contact in CR, and LR8 is a non-working side posterior interference] only has to provide restorations that do not ‘interfere’. The danger in this approach is that the new occlusion may still not be an ideal one, because of the existence of other potential interferences. This new ‘less than ideal’ occlusion may be one to which the patient could have greater difficulty to adapt to than the previous less than Ideal Occlusion. This may lead to iatrogenic problems [‘My problems only arose after you did that filling’]. This is fingers crossed dentistry. 3. Finally there should not be an existing Temporomandibular Disorder (TMD). If there is, the decision must be taken whether or not to treat it first, since it is possible that the treatment of the TMD will result in a change of the patient’s occlusion. a

b

Fig. 3.1 (a) Teeth touching in CO. (b) Premature contact in CR

a

b

Fig. 3.2 (a) Left lateral excursion. (b) Non-working side interference during left lateral excursion

The Conformative Approach

47

Although the principle of not changing the patient’s occlusion is paramount within the Conformative Approach, this, of course, refers to the occlusal contacts that the patient has between their teeth that are not being presently restored. It does not mean that the new restoration should slavishly reproduce the exact occlusion of the tooth in need of restoration. One of the purposes of restoring a tooth would probably be lost if that was the case. How the occlusion may be improved is best considered within the principles of ‘ideal occlusion’. On the tooth level, ideal occlusion is described as an occlusal contact that is: ‘in line with the long axis of the tooth and simultaneous with all other occlusal contacts in the mouth’. This means the elimination of incline contacts. Incline contacts are considered to be potentially harmful, because of the lateral force that they may generate. A lateral force on a tooth may have harmful sequelae, which are illustrated in Fig. 3.3: Fig. 3.3 Possible consequences of an incline contact

Tooth fracture

Tooth jiggling

Mandibular deflection

So as long as the jaw relationship is the same, it is still the Conformative Approach. So, within the Conformative Approach it is not only possible, but advisable to improve the occlusion of the restored tooth by the elimination of incline contacts either by careful design of the occlusal platform of the new restoration or by judicious alteration of the opposing tooth. The acid test is whether or not the occlusal contacts of the other teeth (those which are not involved in the restoration) are changed. If the occlusal relationships of these other teeth are changed then the approach is not the Conformative but the Re-Organised Approach. This is not wrong, but requires a different approach and is described later in respect of both simple and complex restorative dentistry. Figure 3.4a, b shows a restoration that needs to be replaced. The existing amalgam was provided ‘low’ [15]. It has no contact against the distal marginal ridge of opposing premolar. Figure  3.4c, d shows the new restoration, which occludes against the lower premolar, but does not change the occlusion between any other teeth.

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3  Good Occlusal Practice in Simple Restorative Dentistry

a

c

b

d

Fig. 3.4  Improving the occulusion within the conformative approach. (a) “Low” restoration to replaced. (b) absence of occlusal contact has probably allowed over-eruption of lower premolar. (c) new restoration with contact against lower premolar. (d) new restoration

Technique for Following the Conformative Approach Introducing the E.D.E.C. Principle When considering the provision of simple restorative dentistry, no matter what type of occlusal restoration is being provided the sequence is always the same. The ‘E.D.E.C. principle’ that is presented here (Fig. 3.5) is a system that has been devised to give a logical progression through the sequence of providing a restoration, to the Conformative Approach. It can be adapted to other aspects of clinical practice, as will be seen later in this book, and is useful in both direct and indirect restorations. It can be summed up in one sentence: ‘Examine before you Check’. Fig. 3.5  E.D.E.C. protocol

E = Examine D = Design E = Execute C = Check

E.D.E.C. Protocol for Direct Restorations  tage 1 : E. Examine S Firstly, examine the occlusion before picking up a handpiece. The examination is in two parts: the static and the dynamic occlusions. The examination of the static

Technique for Following the Conformative Approach

a

b

c

49

d

Fig. 3.6  E.D.E.C. protocol. (a) Pre-existing Occlusion. (b) Rubber Dam Ready to remove old restoration. (c) Initial check Is this the same? Not quite! (d) But after Minor adjustment it Conforms to 6a

occlusion in Centric Occlusion (not in Centric Relation) is done by asking the patient to tap onto thin articulating paper or foil; this is done before any rubber dam is placed (Fig. 3.6a, b). When the restoration is completed, the Static Occlusion is checked against the pre-treatment record (Fig. 3.6c). And if necessary small adjustments can be made to ensure that there are no changes in the pre-treatment contacts of adjacent teeth (Fig. 3.6d). It is self-evident that in order to be sure that a new restoration allows the other teeth to occlude exactly as they did, you need to see how they occlude before you start. Fig. 3.7 shows that prior to the restoration of LR5 the existing occlusion has been marked up. This enables the dentist to ensure that the occlusion of the other teeth is not changed [Conformative Approach] when replacing the MOD amalgam and the fractured lingual cusp. Marking up the occlusion of the adjacent teeth at the start of the procedure will make the occlusal adjustment of the new restoration much easier and more reliable. Even the thinnest articulation paper/foil is thicker than Shimstock, which has a thickness of only 8 μ. So many clinicians prefer to use this; by checking whether it will pull out from between an occlusal contact. When the Shimstock cannot be removed with the teeth in occlusal contact, this is called ‘a holding contact’. Figure 3.8 shows the use of Shimstock to check that an occlusal holding contact binds.

 tage 2: D. Design S Before starting, dentists visualise the design of the cavity preparation. Every practising dentist has an image in their mind’s eye of what the cavity will look like before preparing a tooth for restoration. Of course, during.  tage 3: E. Execution S There may need to be alterations to this design because of the extent of the caries or areas of unsupported enamel. Visualise the end before starting the beginning.

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3  Good Occlusal Practice in Simple Restorative Dentistry

Fig. 3.7  Prior to the restoration of LR5 (old MOD amalgam and temporary repair of lingual cusp) the Occlusion is marked to facilitate the Conformative Approach. [Courtesy of Dr. Chris Needham]

Fig. 3.8  Does occlusal contact hold shimstock?

 tage 4: C. Check S Often it will be found that any previous restoration is in infra-occlusion, as in Fig. 3.4b. This is because dentists are often anxious to avoid the dreaded ‘high restoration’. But the avoidance of a supra-occluding restoration by deliberately providing infra-­ occluding restorations is not Good Occlusal Practice. It may avoid some of the

Technique for Following the Conformative Approach

51

immediate problems of a ‘high’ restoration, but as a tooth, with a non-occluding restoration, erupts into an occlusion there may be consequences such as an ‘incline contacts’ (see Fig. 3.3). Finally, we check the new restoration does not prevent all the other teeth from occluding in exactly the same way as they did before the placing of the new restoration. This is either done by referring to some diagrammatic record made or by reversing the colour of the paper or foils used pre-operatively, or from memory. The only difference in the pre-treatment visualisation under the E.D.E.C. protocol is the suggestion is that this visualisation is better done after a simple occlusal examination (Fig. 3.6a, b). The existing occlusal marks will either be preserved by being avoided in the preparation or will be involved in the design of the new restoration. Under the E.D.E.C. protocol, the pre-existing occlusion is included as a factor to consider when designing the restoration. They do not have to be exactly duplicated as it may be possible to improve them (from being ‘incline contacts’ to being ‘cusp tip to fossa/marginal ridge’ relationships), or it may be possible to add an occlusal contact especially if the restoration being replaced was in infra-occlusion, or there is a need for greater occlusal stability. In the illustrated case (Fig. 3.6), it can be seen that the occlusal contact against the mesial marginal ridge of the restored UL4 (24) is slightly too heavy (Fig. 3.6c); this has prevented the palatal cusp of this tooth from occluding and has changed the occlusion of the canine. After minimal adjustment, this has been rectified (Fig. 3.6d). For simplicity of illustration, the dynamic occlusion has not been shown in the series. [Footnote on series 3.6a–d: It is not suggested that if the restoration had been left as illustrated in Fig. 3.6c, that there would have been significant consequences for the patient. The most likely consequence is that the patient would have been marginally aware of a small change in their bite, then after a few days it will have seemed to have ‘bedded in’. The point of showing this series of photographs is that unless the pre-treatment occlusion is marked, one cannot be confident that one has conformed. Without the pre-treatment examination, every dentist would have assumed that the occlusion in Fig. 3.6c was the pre-treatment occlusion.] Checking that nothing changed, without knowing what it was before we started, makes no sense.

E.D.E.C. Protocol for Indirect Restorations E.D.E.C. protocol can still be followed for indirect restorations (Fig.  3.9). The essential difference between a direct and an indirect restoration is that a second Fig. 3.9  E.D.E.C. protocol for indirect restoration

E D E C

= = = =

Examine and record the pre-existing occlusion Design the restoration Execute the restoration Check the occlusion at the fit appointment

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3  Good Occlusal Practice in Simple Restorative Dentistry

operator is involved, namely the laboratory technician. A more useful representation of the working relationship between the clinic and the laboratory is to consider the technician to be a second operator rather than an assistant. The technician has expectations from and responsibilities to the dentist. Figure 3.10a, b, c shows the E.D.E.C. protocol being applied to the replacement of an upper lateral incisor by an adhesive bridge. [Notes: 1. The incisor being replaced was restored by a post crown and suffered a catastrophic vertical root fracture. [Maybe a history that is suggestive of Occlusal Trauma?] 2. This restoration was placed over 30 years ago, when it was considered to be best practice to use two abutments, and a fixed-fixed design. Figure 3.10a shows the pre-treatment Examination of the Dynamic Occlusion, before the preparation. Figure 3.10b shows that the Operator decided to avoid the risk of changing the Dynamic Occlusion by adopting a Design of the bridge preparation that did not

Conformative Approach: Example

Conformative Approach: Example

Examine Design Execute Check

Examine Design Execute Check

a

b

Good Occlusal Practice in the

Conformative Approach Examine Design Execute Check

c Fig. 3.10 (a) Pre-treatment dynamic occlusion. (b) design of preparation to preserve pre-treatment. (c) dynamic occlusion conformation of conformative approach (use of pre-operative photograph)

Technique for Following the Conformative Approach

53

interfere with the pre-treatment Occlusal Contacts. Executing that design has proved to be successful as the bridge has never debonded. Finally, as Fig. 3.10c shows it was possible to Check [in this instance by a photograph] that the Dynamic Occlusion had not been changed.

 ecause Indirect Restorations Need Two Operators, there Are B some Consequences to the Treatment Sequence These involve the • taking, • transfer, of records (Fig. 3.11). • checking  Fig. 3.11  The sequence of events in a two operator situation (indirect restorations)

Dentist examines Patient’s pre-treatment occlusion Dentist record pretreatment Occlusion

Dentist checks Occlusion at fit appointment Dentist maintains Occlusion by good temporary restorations Technician makes restoration on accurately mounted models

In the Clinic The dentist not only has to examine the occlusion but the results of that examination have to be accurately recorded; and then that record has to be transferred to the technician. This is the clinician’s responsibility. Also, because of the delay in treatment to allow for the technician to make the restoration, the clinician has the responsibility to maintain the patient in the same occlusion during that interval. Consequently, it is imperative that the patient is dismissed from the preparation appointment with a temporary restoration that has been checked to be in occlusion [not in supra- or infra-occlusion].

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3  Good Occlusal Practice in Simple Restorative Dentistry

In the Laboratory The technician has the responsibility to ensure that the pre-existing occlusion is not changed, by constantly referring to that accurate record, during the laboratory phase of treatment.

Stage 1 of the E.D.E.C. Protocol: E. Examine –– Stage 1a: by the Dentist. –– Stage 1b: by the Technician.

Stage 1a: Examination by the Dentist The examination of the patient’s pre-existing occlusion is carried out in exactly the same way as described for the direct restoration. But for the provision of an indirect restoration there is a need for anatomical information to be transferred accurately to the second operator: the laboratory technician. A record must be made. The provision of an indirect restoration always involves the transfer of anatomical information from the clinic to the laboratory: 1. the impressions leading to a model of the patient’s dental arch on the laboratory bench. In the past these records have been in the form of three-dimensional physical records; in the future it will be done digitally. Irrespective of the medium, the need for accuracy will remain. 2. the occlusal relationship of teeth (the ‘Bite’) is equally an important record as the shape of the teeth (the ‘impressions’), because the technician cannot carry out her or his responsibilities without knowing how the upper and lower models relate to one another. • There is no point in the technician designing the occlusion of the restoration on models that do not accurately conform to the patient’s occlusion. • The inter-arch record [the bite] must be accurate, in order to give the technician a chance of mounting the models accurately.

Inter-Arch Occlusal Records, or ‘Bites’ There are three ways in which this anatomical information can be physically transferred: 1. Two-dimensional bite records that will require accurate interpretation. 2. Three-dimensional bite records that will require accurate handling. 3. A combination of both, where one record can be used to verify the other.

Stage 1 of the E.D.E.C. Protocol: E. Examine

55

Fig. 3.12  Photograph of pre-existing occlusion

Patient:

Job: crown on tooth LR5 (45)

There are occlusal stops as follows: Tip of LR3 (43) Paiatal cusp of UR4 (14) Paiatal cusp of UR6 (16) Mesio buccal cusp of LR6 (46)

against cingulum of UR3 (13) against distal marginal ridge of LR4 (44) against central fossa of LR6 (46) against mesial marginal ridge of UR6 (16)

There is canine guidance on the right and left sides

Fig. 3.13  Example of written record of patient pre-existing occlusion

Two-Dimensional Bite Records 1. Photographs: As digital intra-oral photography becomes more available, the clinician will be able to send the technician a photograph of the patient’s pre-­ existing occlusion (Fig. 3.12). 2. Written record: It is quick, simple and effective in some situations for the clinician to simply tell the technician what the occlusion should be when the restoration is finished (Fig. 3.13). 3. Occlusal Sketch [16–18] ‘Occlusal sketching’ is a technique of recording, onto an acetate sheet, a record of the static and dynamic occlusal marks in the patient’s mouth that have been made by using articulating paper or foil. The acetate strip is designed to be viewed in two different perspectives. One is appropriate to the clinician treating a supine patient and the other is convenient for the technician to use on the bench in conjunction with the articulated models. The

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3  Good Occlusal Practice in Simple Restorative Dentistry

a

b

c

d

Fig 3.14 (a) A sketch is made of the patient’s occlusion (before preparation of a bridge) by the dentist at the chairside. (b) This sketch is reconfigured at the laboratory as an aid to the technician to confirm the correct mounting of the models (c) The bridge is constructed in the laboratory to ‘conform’ with the occlusion (d) At the fit stage, the dentist uses the sketch as an aid to check conformity between the pre- and post-operative occlusions

occlusal sketch is an easy way for the clinician and the technician to check that the occlusion of the restoration conforms to the pre-existing occlusion (Fig. 3.14a–d).

 ite Registration Materials B Taking an accurate bite record is difficult [19]. There are many different materials and they all have their pros and cons [20]. It is easy to be misled into believing that when one material fails to produce a good result that a different material would have succeeded. No particular bite registration material guarantees success; it is the technique that matters. In reality it is nearly always a misunderstanding of the objective of the exercise that has resulted in an inaccurate record. The objective is to record, in the ‘bite’ material, only the correct spatial relationship of the prepared tooth to its antagonists. Other teeth should contact as before, that is to say that there should be no material between the other teeth. The inadequacies of models as anatomical records of the teeth and mucosal surfaces give rise to most of the problems. Impressions often do produce models that are not completely accurate [21]. An incomplete impression of an occlusal fissure or

Stage 1 of the E.D.E.C. Protocol: E. Examine

a

57

b

Fig. 3.15  Oral soft tissue is replicated by hard model material: potential source of error

of an interdental embrasure could very likely result in a significant difference between the occlusion of the patient’s teeth and the models. As a consequence, the opposing model will not have a true relationship with the working model; it will keep the ‘other teeth’ apart. Even if the models are completely accurate and allow the bite registration material to adapt in exactly the same relationship to the models as they had to the teeth, then there is still the problem that in the mouth the mucosal surfaces are soft and compressible, whereas on the models the mucosal surfaces are replicated by hard incompressible gypsum. So, any contact between the bite registration material and the mucosa of the models will probably hold the bite registration material away from its true relationship with the models of the teeth (Fig. 3.15a, b). So, the opposing model will not have a true relationship with the working model: it will keep the ‘other teeth’ apart.

 ifferent Bite Registration Materials D Before considering what material to use, dentists must acknowledge that some dental technicians prefer to use: 1. Nothing They believe that the most accurate way to occlude models in Centric Occlusion [Intercuspation Position] is to fit them together with no material between them. Those [most technicians] who believe this are probably right [20]. Away from their clients, many technicians will admit to throwing the bite record in the bin.

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2a. Soft Pink Wax This commonly used material (Fig.  3.16a) has the major disadvantage that it distorts even at room temperature (Fig. 3.16b). It cannot, therefore, be an accurate means of transferring a bite record. a

b

Fig. 3.16  Distortable soft pink wax

2b. Hard [Beauty] Wax This material (Fig. 3.17) has the advantage that it is more brittle at room temperature, so any inaccuracies when checking in the mouth or using it in the laboratory are likely to cause a revealing fracture of the material. Used correctly it is time-consuming, but can produce a rigid, brittle ‘bite’ record.

Fig. 3.17  Use of hard beauty wax

Stage 1 of the E.D.E.C. Protocol: E. Examine

59

2c. Preparation Only Bites The advantage of this technique (Fig. 3.18a, b, c) is that no material (see 2.1 above) is placed between the occlusal surfaces of all other teeth. The bite registration is restricted to only the tooth that is being prepared and its antagonist. a

b

c

Fig. 3.18  Use of pattern resin to make a ‘Prep. Only Bite’

It is possible to use this for multiple restorations, but it is prudent to do one at a time, always checking with Shimstock that the original occlusal contacts are preserved, i.e. the bite has not been opened up.

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3  Good Occlusal Practice in Simple Restorative Dentistry

This is known as the ‘Alternate Prep Technique’ (Fig. 3.19a, b, c, d, e). a

Alternate Prep Technique

b

c

d

e

Fig. 3.19 (a–c) A hypothetical case to illustrate [the alternate preparation technique].  (d) If there is no posterior support, don’t prepare all the teeth. Instead prepare every other tooth (e) Firstly the crowns are made on the alternative preparations; using the untouched teeth as the occlusal guide. Then the remaining crowns can be made; using the first 3 crowns as the guide. Clinical Sequence: 1. Prepare 3 teeth [Alternative ones] 2. Take a Bite and an Impression 3. Prepare the remaining 3 teeth, and take an Impression

3. Combination of Three-Dimensional and Two-Dimensional Bite Records By using a two-dimensional record the accuracy of the use of a three-­dimensional bite can be checked. This is a means by which the mounting of some models can be verified.

 tage 1b: E…Examination by the Technician S The provision of an Indirect Restoration to the Conformative Approach is dependent upon teamwork between the Dentist and the Dental Technician. Communication is the essential requirement for any good team performance. Once the laboratory has models of the patient’s dentition and the relationship [Occlusion] between them, she or he can start their examination of the case. But maybe before they examine the case, they need to be sure that the occlusion of the models is accurate. Hence….

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61

Model Verification It can be useful for the technician to have some easily transferable second record of the occlusion, because it will mean that the occlusion of the models can be checked in the laboratory to see that it is the same as the dentist saw in the mouth. This process is known as ‘Model Verification’ and is an essential first step of the fabrication of the Indirect Restoration. Let us remember that the objective is the accurate transfer of the patient’s anatomical information from the clinic where it is recorded to the laboratory where it is duplicated. This is the aim of taking impressions and bites and the subsequent casting and mounting of the models. It follows, therefore, that there should be a stage when the laboratory technician is able to check the accuracy of her or his mounted models. This process is called ‘Model Verification’. If the mounting of the models is inaccurate, it is likely that Occlusion of the Restoration will be wrong. Figure 3.20 shows how a technician or dentist can compare the occlusion of the models against a clinical record of the patient’s occlusion. In this case the accuracy was not there. Figure 3.21a, b and c shows how the Occlusal Sketch can be used by the technician and the dentist to ensure that at all stages of the restorative process the occlusion can be checked to see that it has not changed. Fig. 3.20  An Occlusal Sketch enables the Technician to see that the mounting of the models is wrong

Mark on model

No mark in mouth

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3  Good Occlusal Practice in Simple Restorative Dentistry

a

b

c

Fig. 3.21 (a) Occlusal Sketch configured for the technician to check the occlusion of the mounted models against the record of the patient’s occlusion. (b) Close up of the record of the patient’s occlusion [Occlusal Sketch] and the mounted model. Note the same occlusal contacts. Technician’s check. (c) Close up of the record of the patient’s occlusion [Occlusal Sketch] that was taken at the preparation appointment, now used to confirm that the fitting of the inlay has not changed the occlusion. Clinician’s check

Figure 3.22 illustrates how the Occlusal Sketch can be used in the clinic to record the patient’s Occlusion before treatment.

I f at this Verification an Error Is Detected then the clinician has three choices: 1. Do all or part of the process again, 2. Engage in model grooming [see below for explanation]. 3. Proceed with fabrication of the restoration having decided to ignore the error, and so with the expectation that some adjustment will need to be made in the mouth at the fit or try in stage. If this is anticipated, it may be prudent to advise the patient before starting to grind on the restoration [Difference between a Reason and an Excuse].

Stage 1 of the E.D.E.C. Protocol: E. Examine

63

Fig. 3.22  Using occlusal sketch to record the occlusion

Which option is chosen should depend on the case including the size of the error. The first and last have definite drawbacks. If the error is gross, model grooming will not help and repeating the process is the best option. Option 3 may be the only option; it will be less than ideal for the technician, clinician and patient. However, it will take less time than having to remake the restoration. To deliberately ignore the inaccuracy is not a sin; it is simply an admission that the restoration delivered from the laboratory is not going to be as accurate as it could be. Some of the predictability, therefore, has gone, so the expectation of adjustment at the fit stage has increased. In the ‘real world’, clinicians have to make compromises constantly; in fact, the skill of a clinician might be judged by their ability to choose and manage compromise. The clinician who decides to ignore an error at the verification stage has made a conscious decision to reduce the level of predictable success and is committed to making the adjustments to the occlusal surface of the restoration at the fit stage whereas the clinician who is ignorant of an error is in uncharted waters and may not be able to navigate the patient safely into port. There is a world of difference between deciding to ignore something and being ignorant of it. If the error is small, then model grooming is a good option.

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1 Impression making

laboratory fabrication of restoration

2 Model casting

5 grooming (if necessary)

3 Model mounting

4 Check the Occlusion of the models against Occlusal Sketch, or other record

Fig. 3.23  The stages before starting laboratory fabrication of the restoration

Model Grooming Model grooming is the description given to the process of adjusting the models so that they more accurately reproduce the occlusal contacts of the patient’s dentition. Implicit in the use of the word ‘grooming’ is understanding that these are small not gross adjustments to the occlusal surfaces of the plaster models. Some authorities state, quite rightly, that as soon as the technician or dentist scratches those models, they are not a completely accurate representation of patient’s teeth. Consequently, they object to the concept of model grooming on the grounds that …... ….it should not be necessary. Of course, this is self-evidently true. If the impression, casting and mounted processes have been performed entirely without any error, then the models will exactly duplicate the patient’s teeth and the occlusal contacts between those teeth. Whereas everybody involved in this process of anatomical information transfer should strive for this perfect replication, it is almost certainly the case that nobody achieves this high goal every time. So, it follows that whereas model grooming should not be necessary, model checking is always necessary (Stage 4, Fig. 3.23). It is emphasised that this model verification stage requires providing the technician with a second occlusal record; this can be a two-dimensional record (e.g. occlusal sketch, or written record or photograph). If the models are not accurate, the process of grooming is designed not necessarily to make them completely accurate, but to reduce the inaccuracy. Figure 3.24a–h illustrates the process of grooming some models; it shows how a very small amount of adjustments to the models can restore accuracy. The difference between an Excuse and a Reason is Timing.

Stage 1 of the E.D.E.C. Protocol: E. Examine

65

b

a Occlusion markedon upper teeth

Occlusion on lower teeth, viewed from above

c

d

1

1

e

g

f

h

Fig. 3.24  Case illustrating model grooming (a–h) (c) Occlusion of Mounted Models compared with Occlusal Sketch. (d) Occlusion of upper Mounted Model compared with Occlusal Sketch and photograph of upper dentition (e) Model Grooming in Progress (f) Model Grooming Continues: First sign of improving accuracy [UR4] (g) Model Grooming Completed: Lower model now has same occlusion as in the mouth. (h) Model Grooming Completed: Upper model has same occlusion as in the mouth

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3  Good Occlusal Practice in Simple Restorative Dentistry

Fig. 3.25  Trimming a silicone bite record so that it fits onto the models

Bite registration pastes often need trimming

Summary of the Examination Phases  hree Important Guidelines Emerge T 1. If possible, the bite registration material should only be used between the prepared tooth and its antagonists rather than used to take a full arch record. 2. If a bite registration does record the relationship of other teeth, it must be carved back (Fig. 3.25) so that no part of it touches the models of the mucosal surfaces or of the embrasures. 3. The technician should check the accuracy of occlusion of her or his mounted models before constructing the indirect restoration. It is imperative, therefore, that the mounting of the models should be verified against a second record of the patient’s occlusion, which the dentist should provide. The ‘second record’ may be: (a) a second bite registration in a different material. For example, if an ‘easy’ material like an elastomer has been used, it may be wise to use a harder material (in both senses) such as acrylic resin or hard wax. (b) a two-dimensional one, such as a written record of holding tooth contacts (see Fig. 3.13) or an Occlusal Sketch (see Fig. 3.14a, b). 4. If the models are not accurately occluded, then the mounting must be repeated, or small modifications made to the models [Model Grooming]. Figure 3.26a, b, c, d, e Illustrates the Sequence to Record the Occlusion when Providing an Indirect Restoration. It illustrates the use of: 1. the Preparation Only Bite, using Pattern Resin, 2. Shimstock to check the other teeth are still touching.

Stage 1 of the E.D.E.C. Protocol: E. Examine

a

c

67

b

d

e

Fig. 3.26 (a–e) The use of occlusal sketch, shimstock and preparation only bite record in the conformative approach to PROVIDE AN INDIRECT RESTORATION AT LR6. (a) STEP 1 Mark the occlusion, using 40  μ articulating paper. STEP 2 Record the existing Occlusion using the Occlusal Sketch. (b) STEP 3 Find the contacts that hold the Shimstock [Shim Check contacts]. STEP 4 Record these on the Occlusal Sketch (c) Step 5 Make the ‘Prep Only Bite’ (d) Dental Nurse’s Job. Step 6 Ensure that the ‘Prep Only Bite’ has not separated any of the ‘Shim Check Contacts’ (e) Finally using the same holding contacts, the Dental Nurse can check the Occlusion of the Temporary Crown

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3  Good Occlusal Practice in Simple Restorative Dentistry

Stage 2 of the E.D.E.C. Protocol D. Design –– Stage 2a: by the Dentist. –– Stage 2b: by the Technician.

Stage 2a: D. Design by the Dentist Indirect Restorations: Design of Preparation by the Dentist but with the ‘Second Operator’ in Mind From an occlusal point of view, the tooth preparation is designed in exactly the same way as for a direct restoration. The fundamental differences are that firstly the technician is going to make the restoration and secondly that, dependent on the material to be used, there will be certain requirements with regard to sufficient clearance between the top of the preparation and the opposing teeth (Fig. 3.27). Fig. 3.27  Use of flexible bite gauge

If, because of clinical considerations (e.g. nearness of the pulp), the clinician suspects that the technician may not have sufficient room, for say an adequate thickness of porcelain in a metal ceramic crown, then it is much better to give the technician permission to reduce the height of the opposing tooth than to risk a high crown. It is essential in this situation to advise the patient at the preparation appointment that adjustment to the opposing tooth may be necessary next time, giving the reason. Patients will accept a dentist adjusting an opposing tooth is the explanation is given before the crown is fitted; after the crown is fitted the adjustment and its justification likely to be interpreted as an excuse for poor workmanship.

69

Stage 2 of the E.D.E.C. Protocol D. Design

The difference between an Excuse and a Reason is Timing.

Alternatively, once the models have been cast in the laboratory, and after discussions between dentist and technician, it may be decided that the best course of action would be to further reduce the height of the preparation. In this circumstance this can be done simply by the use of a coloured separator medium on the die, or very accurately by the use of a transfer coping with an open top made to fit the adjusted height of the preparation (Fig. 3.28).

Fig. 3.28  Transfer coping to indicate by how much the preparation has been reduced in the laboratory

Stage 2b: D. Design by the Technician When considering the design of an indirect restoration, the Occlusal Prescription that is ideal will vary depending upon the condition and circumstance of that tooth. Figure 3.29a shows an upper canine that had suffered a significant fracture involving the labial subgingival aspect of the root. Clearly to have prescribed an occlusion for the crown after post and core placement, that provided Canine Guidance would have been foolhardy. a

b

Fig. 3.29  Canine Guidance isn’t always “ideal”. There are no rules

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3  Good Occlusal Practice in Simple Restorative Dentistry

This despite the fact that in many situations Canine Guidance is considered the Ideal. Here Canine Guidance would not have been ideal for this tooth.

There Are no Rules in Occlusion! Figure 3.29a shows how the dynamic Occlusion was recorded before the restoration of this tooth. By marking and recording the static and dynamic occlusion of the adjacent teeth at the Design [D of E.D.E.C.] stage, it was possible to Execute [E of E.D.E.C.] this restoration in such a way as not to occlusally overload this tooth. It was possible to Check [C of E.D.E.C.] the Occlusal Prescription of the final crown against the Occlusal Sketch Record of the Dynamic and Static Occlusion before the crown was cemented. The design of Indirect Restoration is often done exclusively by the Technician, although the ultimate responsibility lies with the Dentist. Even if the dentist does leave it entirely to the technician, the dentist must provide the technician with the records that will be needed to design an appropriate [Ideal] Occlusal Prescription. Some of these records are described.

Techniques to Aid the Design of Indirect Restorations The Customised Anterior Guidance Table [C.A.G.T.] This is a technique by which a template is made of the existing or designed guidance of the upper anterior teeth. It is made to fit the Articulator. It enables the technician to provide new restorations to the front teeth that conform to the envelope of movement that the table has recorded. It may sound a complex procedure, but in reality, it is an easy exercise to perform, for a dentist or dental technician. Firstly, it will help to understand what is the aim of a C.A.G.T. Put at its most succinct we are trying to create a ‘static record of a dynamic movement’. This means that we will make a template that will guide the upper member of the articulator [the part of an articulator that moves] to follow the same envelope of movement as the patient exhibited when they move their lower jaw to each side. So, this is a tool to use in the Conformative Approach, but now it is the Dynamic Occlusion that is being copied. What is being copied will depend upon the case: 1. It may be the patient’s pre-existing Occlusion. For instance, if a patient needs some veneers or crowns on some of their upper anterior teeth, and it has been decided to copy, for functional and aesthetic reasons, the existing guidance on the unrestored teeth, the use of a C.A.G.T. can ensure that the technician conformed to and not changes the pre-existing guidance.

Techniques to Aid the Design of Indirect Restorations

a

71

b

Fig. 3.30  Use of Custom Anterior Guidance Table

Figure 3.10a, b shows a case where it was decided to conform by designing the wings of the adhesive bridge that did not remove the existing Dynamic Occlusal contacts. If it had been decided that the wings needed to cover all of the palatal surfaces of the abutment teeth [or nowadays: tooth], then a C.A.G.T. could have been used to ensure that the occlusion of the bridge did not substantially change the guidance. 2. If the restoration of the upper anterior teeth has involved a Provisional Restoration Stage, it is used to test, over an extended period of time, the function and appearance of well-fitting acrylic crowns. After these provisional restorations have proved to be aesthetically and functionally satisfactory, the guidance and shape must be copied. A C.A.G.T. will facilitate this objective. 3. If the Design of the proposed restoration(s) has been determined by a Wax Up, then the C.A.G.T. can facilitate the transfer of the envelope of movement of the wax up to the articulator, before the final restoration is being made. Figure 3.30a, b shows how a C.A.G.T. was constructed from the pre-operative study model (Fig. 3.30a). Then when the upper anterior teeth have been prepared [losing, for ever, the Anterior Guidance to which the patient had accommodated], the C.A.G.T. provides a guide to the technician so that he or she could conform to the pre-treatment Dynamic Occlusion (Fig. 3.30b). Customised Anterior Guidance Tables may be made from many different materials: • Light Cured or Autopolymerising Special Tray Material. • Light Cured Composite Material (preferably out of date material). • TAK Hydroplastic Beads.

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Functionally Generated Pathway The great advantage of this technique is that it produces a hard record of both the opposing static and dynamic occlusions in only three stages, two of which are carried out in the mouth. There is, therefore, much less room for error. The construction of a functionally generated pathway is often considered to be difficult and a ‘special’ procedure in much the same way as the use of a facebow or rubber dam. In reality and in common with these other techniques it becomes, with practice, simple, logical and a time saver. Technique: A soft, plastic material (e.g. tacky wax) is applied to the teeth, and the patient is asked to perform a lateral excursive movement on that side. This carves grooves into the wax that represents the movement, e.g. ‘pathway’ of the lower teeth relative to the upper teeth. This impression is then cast in the mouth using a quick setting plaster applied with a brush. The cast can then be mounted in the laboratory, and used, in conjunction with the ‘normal’ opposing model. Alternatively, and probably easier, the patient is asked not only to bite together in centric occlusion (Fig.  3.31a and b) but also to go into excursive movements (Fig. 3.31c). A pattern acrylic (e.g. Duralay or GC Pattern Resin) [22] can be built up on the prepared tooth, and then, before it sets, the patient carves out a pathway that the opposing tooth has taken relative to the prepared tooth (Fig. 3.31d and e). At the laboratory, this record can be mounted on to the working model on a twin stage articulator [22] (Fig. 3.31f), or two opposing models can be cast on a regular articulator. In this way, casts are made not only of the opposing tooth in Centric Occlusion (Fig. 3.31g), but also of the movements of the opposing teeth (Fig. 3.31h). So a Functionally Generated Pathway indicates not only where the cusp tips of the opposing teeth are in Centric Occlusion [static occlusion], but also where they move relative to the prepared tooth [dynamic occlusion]. Similar to the Customised Anterior Guidance Table, this is a static record of a dynamic movement.

Dynamic Occlusion Bite Registrations These records, which are also known as Lateral Wax Records, enable the condylar angle to be set in the articulator to the value that is comparable with the movement of the patient’s TMJ (Fig. 3.32a). By doing this, it is possible to accurately anticipate the movements of the opposing teeth during mandibular excursive movements. Setting the condylar angles correctly will be a benefit to the technician when designing the cuspal angles of the indirect restorations. If the condylar angle is set wrongly on the articulator, then the model teeth will not fit into the Lateral Wax Record (Fig. 3.32b). These records are difficult. In the clinic it is difficult to record one position during the patient’s lateral excursion. In the laboratory, the inherent difficulties caused

Techniques to Aid the Design of Indirect Restorations

a

b

c

d

e

f

g

h

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Fig. 3.31 (a) Patient in Centric Occlusion. UR4 is being going to be prepared for a DO inlay. (b) Wax record of Centric Occlusion. (c) Patient goes into right lateral excursion. (d) Duralay recording the pathway of the LR5 (45) relative to upper premolars during right lateral excursion (e) Pattern Resin [now set] record of LR5 against upper premolar, including prepared UR4 [DO Inlay Preparation] (f) Twin stage articulator. (g) Centric Occlusion opposing the inlay preparation of UR4 (14). Record of opposing Static Occlusion (h) The Duralay record is used to cast an opposing model. This represents all of the movements that the opposing tooth makes against the UR4 and 5. Record of opposing Dynamic Occlusion

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a

b

Fig. 3.32 (a) Wax record is correctly seated, ...indicating that the condylar angle is 45° (scale FH) Frankfurt Horizontal (KaVo Articulator) (b) Wax record does not fit onto the teeth accurately, ... because the condylar angle is wrong

by the compressibility of even the hardest waxes [e.g. Aluwax, as illustrated] have to be managed. This is why many operators have decided to set the condylar angle to an arbitrary value of 25 degrees. This still allows some cuspal morphology in the restoration. Alternatively it is easy to set the condylar angles using observation of the space or lack of it between the patient’s molars on the non-working side (Fig. 3.33a–c). Both of these techniques will still reduce the likelihood of introducing unwanted occlusal interferences in excursive mandibular movements.

Stage 3 of E.D.E.C. Protocol: E. Execute From an occlusal point of view one of the most significant considerations is the provision of a temporary restoration that duplicates the patient’s occlusion and is going to maintain it for the duration of the laboratory phase. The temporary restoration must not only be a good fit on the preparation and against the adjacent teeth but also be made with an occlusion against the antagonistic teeth; but without changing the occlusion of the other teeth [Conformative Approach]. In this way the temporary crown will maintain the same spatial relationship with adjacent and opposing teeth. By far the easiest way of achieving these aims is to make a custom temporary crown. With a little preparation, custom temporary crowns can be made quite quickly. Figure 3.34a–d shows the preservation of the patient’s pre-existing occlusion through the temporisation, laboratory and cementation phases.

Stage 3 of E.D.E.C. Protocol: E. Execute

a

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b

c

Fig. 3.33 (a) The observed gap between the posterior teeth on the Non-working Side, during a right lateral mandibular excursion (b) Adjust the Condylar Angle of the Articulator until the gap between the model teeth is the same as the observed gap between the posterior teeth in the mouth. (c) If the Condylar Angle is set too high [or low], then the gap between the model teeth will not be the same as the gap between the patient’s teeth

a

b

c

d

Fig. 3.34 (a) Prepared tooth with occlusal marks on adjacent teeth. (b) Temporary crown in place with occlusal marks on adjacent teeth (c) Definitive crown on mounted model (d) Definitive crown in mouth, with occlusion marked

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Stage 4 of the E.D.E.C. Protocol: C. Check Checking the occlusion of the restoration that we have provided in the Conformative Approach involves answering the following questions: 1. Are the Occlusal Contacts of the other teeth exactly as they were before we started? It is impossible to answer this question unless the Pre-treatment Occlusion was examined [and maybe recorded] before starting treatment. 2. Is the Static Occlusal Contact [Occlusal Stop] on the new restoration as ideal as possible? Is there a cusp tip to fossa or marginal ridge contact? If possible, are the contacts in line with the long axes of both teeth? [No Incline Contacts]. 3. (a) Posterior Restoration: Unless we have decided to copy an existing Posterior Interference, have we ensured that there is no Dynamic Occlusal contact during excursive movements of the mandible? (b) Anterior Restoration: Does our new restoration provide the same anterior guidance as the tooth did before restoration?

 an the Occlusion of Other Teeth Be Improved during C the Conformative Approach? Figure 3.4a–d shows how a tooth was restored, within the Conformative Approach, but with a better Occlusal Contact before treatment. It is still with the Conformative Approach because the occlusion between the other teeth was altered. Some restorative authorities advise that teeth that are not directly involved in the restoration (tooth to be restored and its opposing tooth) can be altered to improve the occlusion, within the ‘Conformative Approach’. It is an attractive idea to try to improve the occlusion of the surrounding teeth, by say removing the incline contacts. The difficulty is to be certain that a small change to the occlusion to other teeth is not changing deflecting contacts and so changing the jaw relationship. If modification to these deflecting contact teeth is envisaged, with the implicit risk of a change in Jaw Relationship, there is a need to use the Re-Organised Approach. This is true, no matter how few teeth are being restored. Sometimes the restoration on just a single tooth can result in a change in the jaw relationship and a consequential unbalanced occlusion for the patient. Occlusal adjustment to multiple teeth with a consequential change in the jaw relationship is a complex and careful procedure requiring planning. It is called ‘Equilibration’ and will be described in the next chapter as part of the Re-Organised Approach.

References

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In the Conformative Approach Only modify Occlusal Contacts when you know that they are not Deflecting Contacts [Premature Contacts in Centric Relation].

Guidelines of Good Occlusal Practice

1. The examination of the patient involves the Teeth, Periodontal Tissues and Articulatory System. 2. There is no such thing as an intrinsically bad Occlusal Contact, only an intolerable number of times to [para]function on it. 3. The patient’s occlusion should be recorded, before any treatment is started. 4. Compare the patient’s occlusion against the benchmark of Ideal Occlusion. 5. A simple, two-dimensional record of the patient’s occlusion taken before, during and after treatment is an aid to Good Occlusal Practice. 6. The Conformative Approach is the safest way of ensuring that the occlusion of a restoration does not have potentially harmful consequences. 7. Ensuring that the occlusion conforms to the patient’s pre-treatment state is a product of Examination, Design, Execution and Checking (the E.D.E.C. protocol).

References 1. Beyron H. Optimal occlusion. Dent Clin Amer. 1969;13:537–54. 2. Celenza FV, NasedkinJ N. Occlusion. The state of the art. Chicago: Quintessence Publishing Co.; 1978. 3. Dawson PE.  Evaluation, diagnosis, and treatment of occlusal problems. St Louis: C V Mosby; 1989. 4. Gross MD, Mathews JD.  Occlusion in restorative dentistry. London: Churchill Livingstone; 1982. 5. Howatt AP, Capp NJ, Barrett NVJ.  A colour atlas of occlusion and malocclusion. London: Wolfe Publishing Ltd; 1991. 6. Lucia VO. Modern gnathological concepts. St Louis: C V Mosby Co; 1961. 7. Mann AW, Pankey LD.  Oral rehabilitation. Part 1. Use of the P-M instrument in treatment planning and restoring the lower posterior teeth. J Prosthet Dent. 1960;10:135–42. 8. Pameijet JHN.  Periodontal and occlusal factors in crown sand bridge prosthetics. Dental Centre Postgraduate Courses; 1985. 9. Schluger S, Yuodelis T, Page RC.  Periodontal disease  — basic phenomena. Clinical management and occlusal and restorative interrelationships. Philadelphia: Lea and Febiger; 1977. p. 392–400. 10. Schuyler CH. The function and importance of incisal guidance in oral rehabilitation. J Prosthet Dent. 1963;13:1011–29. 11. Stewart CE. Good occlusion for natural teeth. J Prosthet Dent. 1964;14:716–24.

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12. Stuart CE, Stallard H. Principles involved in restoring occlusion to natural teeth. J Prosthet Dent. 1960;10:304–13. 13. Celenza FV, Litvak H.  Occlusal management in conservative dentistry. J Prosthet Dent. 1976;36:164–70. 14. Foster LV.  Clinical aspects of occlusion:1. Occlusal terminology and the conformative approach. Dent Update. 1992;19:345–8. 15. Applied Occlusion Page 9 Wassell Naru, Steele, Nohl Quintessence ISBN: 9781850970989. 16. Davies SJ, Gray RJM, Al-Ani MZ, Sloan P, Worthington H. Inter- and intra-operator reliability of the recording of occlusal contacts using the ‘occlusal sketch’ acetate technique brit. Dent J. 2002;193:397–400. 17. Davies SJ, Al-Ani MZ, Richmond R, Worthington HV. P S Smith occlusal sketch: a reliable technique for technicians to check the occlusion of marked models Eur. JProsthodontRestDent. 2005;13:65–8. 18. Davies SJ, Al-Ani MZ, Jeremiah H, Winston D, Smith PWS.  Reliability in recording static and dynamic occlusal contact marks using transparent acetate sheet. J Prosthet Dent. 2005;94:458–61. 19. Murray MC, Smith PW, Watts DC, Wilson NFH. Occlusal registration: science or art? IntDent J. 1999;49:41–6. 20. Walls W. Steele a comparison of two methods for locating the intercuspal position (ICP) whilst mounting casts on an articulator. J Oral Rehab. 1991;18:43–8. 21. Wassell RW, Ibbetson RJ. The accuracy of polyvinyl siloxane impressions made with standard and reinforced stock trays. J Prosthet Dent. 1991;65:748–57. 22. Baylis MA, Williams JD. Using the twin-stage occluder with a functionally generated record. Quint Dent Technol. 1986;10:361–5.

4

Good Occlusal Practice in Advanced Restorative Dentistry

In most patients, their Occlusion is functional, comfortable and aesthetic. So, if a tooth or teeth need to be restored, the most appropriate way to provide the restoration(s) is not to change anything: the static and dynamic occlusions or the jaw relationship of their pre-treatment Centric Occlusion, i.e. to adopt a ‘Conformative’ Approach. The patient’s occlusion may not, in fact usually will not, fulfil the old fashioned and redundant definition of an Ideal Occlusion, which is: • ‘Centric Occlusion occurring in Centric Relation • Free of Posterior Interferences. • Freedom in Centric (occlusion)’. This is because the pre-treatment occlusion and jaw relationship is ideal for that patient. We know this because we have examined for adverse reactions to that occlusion and found none. So, following the Conformative Approach is both common sense and a good practice. It is an example of the ‘If it isn’t broken, don’t fix it’ maxim. There will, however, be situations where the Conformative Approach cannot be followed. It is important to be able to recognise these and to have strategies and protocols to be able to successfully restore a mouth to the ‘Re-Organised Approach’. This section aims to describe what is ‘Good Occlusal Practice’ in the ‘Re-Organised Approach’.

© Springer Nature Switzerland AG 2022 S. Davies, A Guide to Good Occlusal Practice, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-79225-1_4

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In this part, we will discuss: • The re-organised approach. • When and how to re-organise an occlusion in restorative dentistry.

The term ‘Re-Organised Approach’ may conjure up the idea of mouth full of crowns and bridges. This may be the case in rare situations, but it is not only the ‘major’ cases that need the extra thought and processes that comprise the Re-Organised Approach’. Equally often with some care in designing the treatment plan, a complex case can be broken down into sequences so that the Conformative Approach can be followed. This will be illustrated in addition to a description of how to ‘re-organise’ an occlusion. • The ‘conformative approach’ is not always possible or appropriate for ‘small cases’. • The ‘re-organised approach’ is not always needed or appropriate for ‘large cases’.

When Is the Conformative Approach Not Appropriate? Answers: 1. When it is not possible. 2. When it is not wanted.

1. When it Is Not Possible This appears to be stating the obvious. But there are some caveats. Firstly: Changing the occlusion may not be inevitable, even in complex cases. It may be that a carefully designed treatment plan will always leave sufficient reference points of the pre-existing occlusion. This will mean that the new restorations can be provided to an occlusion which does maintain the pre-treatment jaw relationship. This is the Conformative Approach and is sensible to adopt it for a patient who has had no adverse reactions to their existing Occlusion, within the Articulatory, Dental or Periodontal Systems.

 lternative Preparation (‘Prep One/Miss One’) Technique A Figure 4.1a–c shows a theoretical case where by preparing alternative teeth, and taking bite registrations after the first two teeth (LL4, LL6) were prepared; the

When Is the Conformative Approach Not Appropriate?

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b

c

Fig. 4.1 (a) Pre-operative view before proposed crown preparation of LL4, 5, 6, 7 (34, 35, 36, 37). (b) LL4 (34) and LL6 (36) are prepared and Duralay ‘bites’ taken on these teeth using occlusal contacts on LL5 (35) and LL7 (37) to ensure the ‘conformative approach. (c) All teeth are now prepared, but bites against LL4 and 6

pre-­existing occlusion and jaw relationship is be preserved by the unprepared teeth (LL5, LL7). The intermediate registrations, as seen in Fig. 4.1b, become the reference point after those teeth (LL5, LL7) are prepared (Fig. 4.1c). All of these preparations could have been done in the same visit; the only ‘extra’ work would have been the intermediate bite registrations on teeth LL4 and 6. Alternatively, if this seems a bit too complicated or risky, the dentist may choose to prepare and fit the crowns of the first phase before starting the second phase, at a different appointment. The important thing to avoid, in this theoretical case, is simultaneous removal of the occlusal surfaces of all four teeth by the sweep on a large diamond bur, only to then wonder how to take an accurate bite record. That action could cruelly be called the Un-organised Approach [1]. Figure 4.2a shows the right side of the posterior occlusion for a patient, who had undergone a full mouth restoration that had been poorly designed. The LHS posterior occlusion was also inadequate. The crowns on the lower anterior teeth needed to be replaced before the posterior occlusion could be restored as they were ill fitting with consequential gingival irritation. The dilemma was, therefore, to replace the lower anterior crowns without changing the Jaw Relationship. This was achieved by the Alternative Preparation Technique (Fig. 4.2b, c).

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a

b

c Preps

Old Crowns

Fig. 4.2  Alternative Prep Technique

The reference points of the pre-existing occlusion may be lost with the first sweeps of the air rotor.

‘Unorganised’: not formed into an orderly whole—Oxford English Dictionary (OED).

‘Organise’: to give a definite and orderly structure.—OED.

• The E.D.E.C. protocol principle when restoring complex cases to the Conformative Approach. • E = Examine the pre-existing occlusion. • D  =  Design an operative procedure which allows the conformative approach. • E = Execute that plan. • C = Check that each stage of the restoration conforms to the occlusion of the previous stage.

When Is the Conformative Approach Not Appropriate?

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a

b

Fig. 4.3 (a, b) Shows a case involving the restoration of most of the teeth

Figure 4.3a illustrates the stages that were needed to ensure that it was possible to design a Conformative treatment plan.

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The stages followed the phases of the E.D.E.C. protocol. E. Firstly in addition to an assessment of the dental and periodontal conditions, an Articulatory System Examination was used to check for any Temporomandibular Disorder and to record the pre-existing occlusion and jaw relationship. D. The new occlusion was designed using a wax up of some models, but in the same jaw relationship. E. This design was carefully executed in a sequential treatment plan. C. With many checks built into the process (Fig. 4.3b). The juxtaposition to a large case that can, with careful planning, be done to the Conformative Approach is the small case in which the clinician needs to be alert that the Conformative Approach will not be easy. This is the situation as presented in Fig. 4.4, where because of an incomplete examination or lack of planning it was not recognised that the provision of a single crown for the patient without changing the existing occlusion and jaw relationship proved very difficult. This was because the dentist intending to restore the tooth to the pre-existing occlusion/jaw relationship destroyed the occlusal surface of the one tooth that determined where that jaw relationship was. It is important to realise that the jaw relationship can change by the loss of one occlusal contact, during the preparation of one tooth. It can be avoided by following the E.D.E.C. principle, and any of the techniques described above.

Fig. 4.4  Contrast the occlusion in the jaw relation of C.O. with C.R.

Figure 4.4 shows the mounted models of a patient who needed a crown on the lower right second molar. The first photograph shows the patient’s habitual bite, or Centric Occlusion (C.O.). The second photograph shows the same models mounted in Retruded Jaw Relation or Centric Relation (C.R); the first contact in C.R. is shown by the arrows.

When Is the Conformative Approach Not Appropriate?

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This premature contact in C.R. could be described as the Deflecting Contact; that is to say that this contact plays a role in deflecting or guiding the jaw relationship away from the Terminal Hinge Axis of C.R. to the Jaw Relationship in which the teeth fit together (C.O.).

Deflecting Contact

Don’t imagine a patient closing onto the first contact in C.R., then sliding into their C.O. It is more accurate to think that this first contact teaches the patient to avoid it when closing. So they close directly into the jaw relationship of their C.O., by means of a learnt motor engram.1 Another example of maintaining the occlusion/jaw relationship that could have been used in this case, where the tooth to be prepared provided an important Centric Stop, is the ‘Preserving the Centric Stop’ technique. Surprisingly this technique, first described in 1983, [2] is not commonly used. It provides a simple and elegant solution to the problem of preserving the same occlusion when there are few occlusal land marks; a situation often seen when restoring the last tooth in the arch. Figure 4.5a–g illustrates this technique.

Preserving the Centric Stop for Bite Record

Surgery 1. Mark the Centric Stop. 2. When doing the Preparation, do not cut down the Centric Stop. 3. Take Imps and Bite. 4. Make temporary crown allowing for preserved Centric Stop (see Fig. 4.5g) or Remove Centric Stop to Fit Temporary. Laboratory 1. Cast Impression. 2. Mounted Models …… using. Preserved Centric Stop and the bite record. Only then 1. Remove Centric Stop on Model. 2. Make Crown or Bridge.

 see Chap. 2 for explanation of (Motor) Engram.

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a

b

d

c e

f

g

Fig. 4.5 (a) Teeth prepared for crown, but with the Centric Stops preserved. (b) Small check impression taken before rubber dam is removed. (c) Mounted Model of full arch impression. (d) Digitised lower model AFTER technician has removed Centric Stops. (e) Crowns on mounted models [the buccal aspects of the teeth anterior to the crowns is not accurate, because the patient was in fixed orthodontic brackets]. (f) Checking that the occlusion of the other teeth is preserved. (g) the temporary crowns placed onto the working model to illustrate where the Centric Stops were

When the Conformative Approach Is Not Adopted, There Are Only Two Possibilities

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Question: When Is the Conformative Approach Not Appropriate? 1. When it is Not Possible So far we hve discussed ways by which an initial analysis that suggested that the Conformative Approach was not possible, would be overcome. There will, of course, be situations that the Conformative Approach is impossible; the techniques employed to adopt the Re-Organited Approach are discussed later. The Second scenatio is when the Conformative Approach is not desirable:

2. When it Is Not Wanted It may be that the treatment objectives, of the dentist and patient, exclude the ‘Conformative Approach’. Examples would be: • An increase in vertical height is wanted or indicated. • A tooth or teeth is/are significantly out of position (i.e. over-erupted, tilted or rotated). • A significant change in appearance is wanted. • There is a history of occlusally related failure or fracture of existing restorations.

 hen the Conformative Approach Is Not Adopted, There Are W Only Two Possibilities First Possibility Plan to provide new restorations to a different occlusion, which is defined before the work is started: ‘visualise the end before starting the beginning’. The Re-Organised Approach. The E.D.E.C. protocol can be used to achieve this.

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The E.D.E.C. Principle in the Re-Organised Approach

E = Examine • the existing occlusion (Centric Occlusion), including jaw relationship in which it occurs. • Determine which teeth occlude in C.O. • Find and Record Centric Relation (Retruded contact position, Terminal Hinge Axis). • Record which teeth touch in CR (Premature Contact). • Observe the direction of the slide for the Premature contact to CO. D = Design and plan the new occlusion. This may involve: • Models mounted in CR. • Equilibration of those models (Mock Equilibration), and equilibration of the patient’s existing dentition. • Design wax up. E = Execute the new occlusal prescription to the Design created above. C = Check that you are conforming to this newly designed occlusion in the definitive restorations.

Second Possibility Change the occlusion, without having planned the new one and the jaw relationship in which it occurs. This occlusion will not be the same (i.e. will not conform) with the previously well-tolerated one. It is an occlusion that has been arrived at by accident, and one has to hope that the patient can adapt to it. This is ‘I hope that I get lucky, and the patient can adapt’ Approach. See section below on: ‘What are the Risks of Changing the Patient’s Occlusion?’

What Is the Treatment Objective of a Re-Organised Occlusion? At its very simplest, it is to provide restorations, which although changing the occlusion are likely to be well tolerated by the patient, at every system level. It is not a guarantee that the patient will be able to tolerate the new Occlusion and Jaw relationship, but by following the perceived wisdom [3] of providing: • A Balanced Occlusion in the Ideal Jaw Relationship (Centric Occlusion in Centric Relation). • No Posterior Interferences in the Dynamic Occlusion (Anterior Guidance at the front of the mouth, i.e. Canine Guidance or Group Function). • Freedom in Centric Occlusion (the mandible is not locked in by the front teeth contacting sooner or harder than the back teeth).

Malocclusion

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In addition to these Guidelines, which relate to the Articulatory System, the Occlusion would be considered ideal on the Tooth Level, if it provides: • Multiple simultaneous contacts. • No cuspal incline contacts. • Occlusal contacts that are in line with the long axes of the restored teeth. • Smooth and, wherever possible, shallow guidance contacts. By following these Guidelines of the Re-Organised Approach, a dentist is minimising the likelihood of an adverse reaction when it is either inevitable or desirable to change the occlusion. An adverse or poorly tolerated reaction to Occlusion may be within any of the systems of the Masticatory or Stomatognathic System. The adverse reactions include the following:

1. Articulatory System Although there is no evidence that ‘poor occlusion’ can cause a Temporomandibular Disorder, many dentists who specialise in the management of Temporomandibular Disorders and/or complex restorative cases have experience of patients not being able to tolerate a change in their occlusion.

2. Periodontal System • Occlusal Trauma to the periodontal tissues can lead a reversible hypermobility. Good Occlusal Practice in Periodontology is the subject of a separate chapter in this book.

3. Dental Tissue System • Fracture of restorations or of the teeth. • Excessive tooth surface loss. • Hypersensitivity, and even Irreversible Pulpitis [4]. Singularly or collectively these represent unwanted outcomes to dental treatment and contravene the first rule of treatment: ‘Do No Harm’. Most dentists who have been actively involved in the provision of extensive restorative treatment plans have some experience of the distress that any or all of these sequalae can create. This is why those dentists who do provide extensive restorative treatments will try to reduce the chances of their patient reacting adversely to the new Occlusion/ Jaw Relation. For this reason, the goal of the Re-Organised Approach is the provision of an occlusion according to the perceived wisdom as listed above.

Malocclusion No occlusion can be said to be ‘intrinsically bad’; an occlusion may only be judged by the patient’s reaction to it. For this reason, many prefer the term: MalAdaptive Occlusion [5]. It puts the patient’s reaction to the occlusion at the centre of the

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diagnostic assessment of an occlusion. Judging an occlusion only by the patient’s reaction to it may mean the pejorative term; ‘Malocclusion’ is meaningless [6]. No matter what terminology and the philosophy behind it is used, it is universally accepted that it is indefensible for a dentist to irreversibly and invasively change a patient’s occlusion because they do not like the look of it, or it does not conform to what they think is a good occlusion (should we call this: “Bonocclusion”?).

How to Re-Organise an Occlusion So That It Is ‘Ideal’? So the starting point of the Re-Organised Approach is the realisation that the Conformative Approach is either not possible or not appropriate to the patient’s needs.

Re-Organised Approach Has Two Stages 1. Design the New Occlusion in Centric Relation 2. Execute that Design So essentially the only difference between the Conformative and the Re-Organised approaches is that the Re-Organised approach is the conformative approach with the extra and pre-treatment phase of designing a new occlusion, and then maybe executing that design in provisional restorations, before providing the definitive or ‘final’ restorations. It is useful, therefore, to consider a major restorative case by dividing the Re-Organised Approach into two distinct parts: 1. careful and detailed design of the new occlusion followed by 2. meticulous adherence to that design. This makes for a slower treatment of the patient but it will produce a successful outcome. Those dentists and patients who opt for a ‘diving in quickly’ approach frequently come to regret at their leisure. In summary, it is impossible to confidently proceed directly to changes in the occlusal scheme. For the most part some form of ‘mock up’ is employed, usually in the form of a wax-up. Planning (Design) and managing (Following that Design) change in occlusal relationships is a challenge. But the changes are ideally made in the provisional restorations, then providing the definitive restorations is a matter of copying that design; i.e. it becomes the ‘Conformative Approach’, where the conformity refers to copying the carefully prepared design.

 HASES of Providing Restorations P to the Re-Organised Approach The E.D.E.C. protocol can be used in the Re-Organised Approach to provide a phased approach.

Step 2 The Examination Phase E.D.E.C.

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It is similar to its use in the Conformative Approach as described in the previous chapter. But it is more complicated. In particular it has a much more important Design Phase. Step by Step Technique of Providing Restorations to the Re-Organised Approach (following the E.D.E.C. principle, see Box “The E.D.E.C. principle in the Re-Organised Approach”).

Step 1 of the Re-Organised Approach is to try to find a way of avoiding it. This has been discussed above.

Step 2 The Examination Phase E.D.E.C. A comprehensive examination of all of the Stomatognathic (or Masticatory) System will need to be conducted. This involves: • Teeth. • Periodontal Tissue. • Articulatory System. Any active pathology in the teeth or periodontia must be identified and stabilised. With the exception of the occlusal analysis, these examinations are outwith the reference of this book. (E = Examine the existing occlusion) Recording Jaw Relationships. The first essential part of the examination is to determine whether the patient’s existing Centric Occlusion occurs in Centric Relation. If CO does occur in CR, then there is no need to employ the Re-Organised Approach as, although proposed restorations may improve the occlusion, they will be provided those restorations in the same Jaw Relationship (so we are using the Conformative Approach). If on the other hand, and as will usually be the case, CO does not occur in CR, and if the dentist has decided that the Conformative Approach is not an option, the process of restoring the mouth to the Re-Organised Approach begins.

Step 2.1 Is to Find Centric Relation and then to Record the Teeth That Touch in the Premature (or First) Contact in Centric Relation This was covered in Chap. 2. There are various ways in which these records can be taken; Fig. 4.6a–c shows a simple technique. A small piece of warm impression compound (Greenstick) is applied to the upper anterior teeth. Whilst it is still soft, the operator gently guides

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a

b

c

d

e

f

Fig. 4.6  Recording centric relation jaw relationship

the patient’s mandible into the compound. The mandible should be following a near perfect arc, indicating that the head of the condyles are in Terminal Hinge Axis (Chap. 1). This is in the rotational phase (as opposed to the translationary phase) of TMJ movement. The rotational phase is the beginning of the opening or the end of the closing cycle. Once the greenstick has cooled and hardened it will act as a template to guide the patient into Centric Relation. Then inter-arch records can be taken to record this jaw relationship. Sometimes this record is taken at the first touch between the teeth that make up the premature contact; at other times, because the operator can sense that as soon as this premature contact is achieved the patient’s mandible tenses, the record is taken just short of the premature contact. Then we must rely on the facebow record to allow the technician to close the last bit on the articulator, without significant deviation from the patient’s closing arc.

Step 2 The Examination Phase E.D.E.C.

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Figure 4.6d–f illustrates the ‘Gothic Arch Trace Technique’ [7]. This uses a small platform of auto-polymerising acrylic on the upper incisors, and shaped so that only the tip of one lower incisor touches against it. The patient then makes excursive movement with articulating paper held between the acrylic and the ‘stylus’ of the lower incisor. This creates the traces, as shown, in Fig. 4.6a, c. This technique may have more certainty about finding Centric Relation, because the point at which the lateral and protrusive traces conjoin can be considered to confirm Centric Relation. But it can be a challenge when using some bite registrations material between the back teeth to ensure that the patient closes onto that point, so allowing for an accurate interarch record.

Step 2.2 Mount and Verify the Accuracy of some Models In order to design the new occlusion, some models will need to be mounted in a semi-adjustable articulator, in Centric Relation. The mounting and models must be accurate. If the mounting of the models does not replicate what is in the mouth, their value is nullified or at least reduced. So, the mounted models should be verified. This can be done against the patient or often more conveniently against records that have been taken of the occlusion. There are various means of checking that the occlusion as marked on the models is the same as was found in the mouth. These include photography and written records, and the Occlusal Sketch technique [1, 8]. Figure 4.7a shows a note to the laboratory technician pointing out the occlusion on his models was different from the record on an Occlusal Sketch which was the record of the patient’s occlusal marks. This means that either the models or the mounting was inaccurate. In this case it was the Centric Occlusion that was being verified. Using Fig. 4.7b, the reader can, if they wish, see if they can spot the four differences between the Occlusion of the models and Occlusal Sketch record of the patient’s CO. By contrast, Fig. 4.7c illustrates how the Occlusal Analysis section of the Articulatory System examination was used to confirm that the mounting of some models gives the same premature contact in CR as was found in the mouth, confirming that the models had been mounted in the patient’s Centric Relation jaw relationship.

Step 2.3. Model Grooming If the Model Verification process shows that the mounting of the models is wildly inaccurate, then probably to ensure any sort of predictability in our proposed restorations it will be necessary to start again. Thankfully, it is unusual that the error is that large. More commonly there will be some minor discrepancies, which can be reduced by a procedure called Model Grooming. This is an anathema to some authorities; they take the view if the mounting of the models is inaccurate then the only option is to take the records and start again. A more pragmatic view is if the accuracy of the models can be improved by models adjustment then they are still useful. Consequently, the concept of Model Grooming can be seen as a means of achieving Verifiably Accurate Mounted Models. See Fig. 4.8a–i.

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a

! !

what are the differences?

b

MOUNTED MODELS MOUTH

Fig. 4.7  Model verification

Step 3 Only now the Design Phase (E.D.E.C.) can begin

c

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Record of Premature contact in CR

Lower Right

Fig. 4.7 (continued)

The Examination Phase (E.D.E.C.) is complete when the dentist has some accurate Study Models, mounted in Centric Relation. • The examination phase of the process is completed when the clinician has a set of articulated models that are an accurate representation of the patient’s occlusion and jaw relationship.

Step 3 Only now the Design Phase (E.D.E.C.) can begin This is essential to the concept of Re-organising the Occlusion: the provision of new occlusion for the patient that is prescribed to be as Ideal as possible. This Design Phase is the essential difference between the Conformative and Re-Organised Approaches. Once the design of the new Occlusion has been developed on the Articulator, then the challenge for the dentist and technician is to copy that design or Conform to that design.

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a

b

Fig. 4.8 (a) The Occlusal Contacts are marked on the upper teeth, and recorded on an Occlusal Sketch. Static Occlusion is in Blue NOTE the Occlusal Contact against the Palatal Surfaces of the Upper Anteriors and on the mesial aspect of the Palatal Cusp of the UR4. (b) Similarly the Occlusal Contact on the lower teeth are viewed from above in the surgery. Then recorded on an Occlusal Sketch. (c) Shows there to be some differences between the mounting of these models, and the record of the patient's occlusion, as recorded on the Occlusal Sketch. (d) Illustrates these discrepancies. (e–h) Shows that after very few minutes of adjusting the heaviest contacts on the models that the discrepancies between the patient's occlusion, recorded by the Occlusal Sketch, and the occlusion on the mounted models are eliminated. (h) Model grooming is completed

Step 3 Only now the Design Phase (E.D.E.C.) can begin

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d

c

No marks on the models

e

f

g

h

Fig. 4.8 (continued)

The Design Phase may include: • Mock Equilibration. • Equilibration of Natural Teeth and Existing Restorations. • Pre-restorative Orthodontics. • 2Diagnostic Wax Up • Provisional Restorations.

Step 3.1 Mock Equilibration This is sometimes indicated and appropriate. The aim of this procedure is to see whether by minor adjustments to the teeth that it will be possible to create a Centric Occlusion in Centric Relation. To discover  Please note that a Wax Up is not a diagnostic procedure or test. From now on the term ‘Design Wax Up’ will be used.

2

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this, two sets of models mounted in Centric Relation will be needed. Then it will be possible for the Clinician, Technician and patient to compare the equilibrated models to the original untouched ones. This procedure is not ‘spot grinding’. Rather it involves careful adjustments to the slopes of the cusps, in order to create a situation where the cusp tips hit against a flat part of the opposing tooth, normally the central fossa or marginal ridges. When sensitively and carefully done, it will improve the morphology of teeth rather than will reduce or destroy morphology as spot grinding can. Figure 4.9a–d illustrates this. Some dentists consider this beyond their abilities; it is unlikely that it was taught at Dental School. But with a bit of practice on some models it becomes an intuitive

a

b

1

1

c 1

2 Fig. 4.9 (a) Ready to Answer the Question: Can this patient’s teeth be equilibrated to create C.O. in C.R.? (b) Starting Point: Premature Contact in Centric Relation. (c) After minor adjustments it can be seen on the lower arch that a more balanced Occlusion is being achieved. (d) Centric Occlusion now occurs in Centric Relation, on the models and so can be achieved in the mouth

Step 3 Only now the Design Phase (E.D.E.C.) can begin

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d 2

3

e

Fig. 4.9 (continued)

process. This is a skill that can be learned on mounted models. After a period of practice on models (mock equilibration), the dentist may feel confident to carry out an equilibration for their patient. If not, then the patient would be referred to a specialist for this phase of the treatment. But remember the specialist learned how to do it on some models. The notes that were taken during the model equilibration will, as long as it was done on accurate models, act as a ‘script’. Adjusting a patient’s occlusion without seeing that a satisfactory end point is achievable, on the accurate unwanted models first, is nerve wracking, dangerous and imprudent. Of course, no adjustment to the models should exceed what the clinician considers to be appropriate in the mouth. MOCK or Model Equilibration

Answers the question: ‘Can this patient’s teeth be equilibrated to provide a balanced Centric Occlusion in Centric Relation?’

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Figure 4.10a–f illustrates another case, where the difference between CO and CR looked like it might be too big to allow for an effective equilibration. But after a relatively short period of time it was possible to achieve CO in CR, without adjusting the teeth to any significant level. It is important to never do anything to the models that you would not be prepared to do to teeth. So, in both these cases, the clinician could proceed with some confidence to Step 3.2.

a

• Duplicated and VERIFIED Mounted Study Models • Le Cron carver • Articulating Paper 40µ • A Lunchtime

b

Models 1

Models 2

Identical and Mountedin C.R.

Fig. 4.10  Model or MOCK Equilibration

Step 3 Only now the Design Phase (E.D.E.C.) can begin

c

101

Models 1 Ready to Go

Models 2 Don’t Touch

d

From This

To This After 10 MINUTES

Fig. 4.10 (continued)

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e

f

Fig. 4.10 (continued)

Step 3 Only now the Design Phase (E.D.E.C.) can begin

103

Step 3.2 Equilibration of the Natural Teeth Because the equilibration will already have been performed on the models, the end point and the adjustments required to reach it will already be known. This is why the ‘mock equilibration’ is essential. Otherwise the clinician might start to wonder whether they can finish what they have started! • The aim of equilibration is to effect changes in the Centric Occlusion to give it, as far as possible, the features of an Ideal Occlusion: • Multiple simultaneous contacts. • No cuspal incline contacts. • Occlusal contacts that are in line with the long axes of the teeth. • Smooth and, where possible, shallow guidance contacts. • Centric Occlusion occurring in Centric Relation. • Freedom in Centric Occlusion. • No posterior interferences. This aim of an equilibration (of the teeth or provisional restorations) is to achieve Ideal Occlusion, before providing definitive restorations. The design that has been envisaged on the models can be copied in order to realise in the mouth. The occlusion that has been developed in the design phase becomes the template for the definitive restorations. The equilibration of the teeth is done over two visits with about 1 week’s interval. Obviously, it is never with local anaesthetic.

Step 3.3 Move or Remove Teeth Sometimes the Mock Equilibration process will show that a tooth or teeth present such an obstacle to the creation of Centric Occlusion in Centric Relation that it will need to either be moved to a position that is compatible with the aim of the treatment plan [9] or, in extreme circumstances, be removed. The duplicate models used in the mock equilibration offer the very best means of demonstrating to the patient what can and cannot be achieved by equilibration.

Step 3.4 Design Wax Up Often a wax up is done to fit into the existing conclusion that has been created by the equilibration process. However sometimes the clinician will wish to provide in an occlusion that is much closer to what would have been present, before the premature loss of some posterior teeth. In this case some means must be used that will design the ideal occlusal planes on the patient’s mounted models. Accurately mounted and now equilibrated casts are modified by the application of wax as a mock-up of the final restorations or prostheses.

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Whether this exercise is done by the clinician or the technician does not alter the fact that the final responsibility of design of the proposed restoration of the mouth rests with the clinician. If, therefore, the technician does the wax up it is of paramount importance that she or he understands that there are clinical limitations to the provision of restorations. It is possible to ‘cheat’ in the laboratory but not in the mouth. To pass the sole responsibility to the dental technician for the design of an occlusion that the dentist is going to have to follow and to which the patient is going to have to adapt is either an act of faith or more likely folly. The Design Wax Up gives positive information on the occlusal scheme that can be generated. It is a valuable guide to the treatment objective for both the clinician and the technician. Both parties should agree on it, before the patient’s teeth are touched. Doing a Design Wax Up has many advantages: • It can also reveal information regarding the need for crown lengthening and orthodontic tooth movement. • It is a useful guide for the optimum crown preparation. • It will provide the template for the temporary restorations. • It gives the patient an opportunity to visualise the treatment and empowers them to grant informed valid consent. • It demonstrates to our technician colleagues that we are ‘going the extra mile’. The greatest difficulty in designing the occlusion in a design wax up is to create the occlusal planes. This can be assisted by the use of a ‘flag’ on the articulator. The techniques used are based upon the concept of the ‘Occlusal Plane Survey Centre’. By the use of this device an approximation of the centre of the curves of Wilson and Spey can be made (Fig. 4.11). Fig. 4.11  Occlusal Plane Survey Centre after Monson O.P.S.C A.S.P. line 4 inches (101 mm)

Condyle

4 inches (101 mm)

4 inches (101 mm)

C.P.S.P.

A.S.P. M.P.S.P. Curve of Spee

Step 3 Only now the Design Phase (E.D.E.C.) can begin

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Although this concept relates to work that Monson did in the 1920s and 1930s, it still has relevance [10, 11]. It is based upon Monson’s observations that: • In an ideal occlusion the occluding surfaces of all of the posterior teeth and the tips of the canines would touched an imaginary sphere. • The head of the condyles lay on the circumference of the sphere. • This sphere would have an average radius of approximately 4 in. (or 10 cm). • The curves of Wilson and Spee, would be arcs on this sphere. More recently another technique [12] has employed the same concept, although translating the arbitrary radius as 10 cm. Although this concept was postulared many decades ago, work done in 1997 using 3-dimensional image analysis substantially confirmed its relevance [13]. Figure 4.12a–f shows the process of using the concept of the O.P.S.C. to create a design wax up that can closely represent the occlusal planes that would have been present if the lower left first molar had not been lost (Fig. 4.12g). a

1

3

2

The Broadrick Flag Technique

4

1-4 on Hanau Articulator

Fig. 4.12  The use of Broadrick Flag to design an ideal Occlusion

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b

acknowledgement: www.authorstream.com

c

5

acknowledgement: www.authorstream.com Fig. 4.12 (continued)

Step 3 Only now the Design Phase (E.D.E.C.) can begin

5

d

7

6

e

Cutting the occulusal planesin the wax Fig. 4.12 (continued)

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8

5-8

108

f

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from flat occlusal ploanes

to carved diagnostic wax up E Design E C

g

before

Fig. 4.12 (continued)

after

Step 3 Only now the Design Phase (E.D.E.C.) can begin

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h

Fig. 4.12 (continued)

The alternative, which could be presented as an option to the patient, has been to restore the missing lower left first molar to an occlusal plane that would have been determined by the crown on the upper left first molar, which had over-erupted into the space below it. In this particular case the patient opted to have the better occlusal planes by having the crown on the upper left first molar replaced, and so this was also waxed up (Fig. 4.12h). Figure 4.13a–f shows an alternative system (Simplified Occlusal Plane Analyzer: Denar S.O.P.A.) using the same principle. It can be seen (Fig. 4.13a–f) that a very minimal adjustment to the distobuccal cusp of the opposing tooth allowed for the lower right sextant to be restored to this prescription.

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a

b

c

d

e

Fig. 4.13  Use of Simplified Occlusal Plane Analyzer S.O.P.A. [Denar] to Design Ideal Occlusion of proposed restoration. [Acknowledgement Mr Gordon Lucas, Dental Technician] (a) S.O.P.A. flag in place. (b) Finding Occlusal Plane Survey Centre [OPSC]. (c) Occlusal plane is carved into the wax, using the OPSC. (d) Design Wax Up completed. (e) But, the over-erupted opposing tooth prevents other teeth from touching. (f) A problem that can be solved by a modest modification of the disto-buccal cusp

Step 3 Only now the Design Phase (E.D.E.C.) can begin Fig. 4.13 (continued)

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f

Fig. 4.14  Wax up of complex restoration using Broadrick Flag Technique

Summary of Flag Techniques Based upon Sphere of Monson It is emphasised that these techniques are an aid to creating a Design Wax Up. It does not suggest that all occlusions should be restored to a sphere that has a radius of 4 in.! That would be ridiculous. Using these techniques gives the clinician, who is planning the restoration of an occlusion, the opportunity to provide smooth and harmonious occlusal planes with a predictable effect upon the existing teeth. It is an opportunity to see the occlusal changes of the proposed restoration, before picking up a handpiece. Figure 4.14 shows some bigger cases where a Flag Technique has been used. • The planning and design phase of the process is completed when the clinician has a set of articulated models and is confident that they are an accurate representation of the end point of the treatment plan.

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Step 3.5 Provisional Restorations Provisional restorations are often useful and sometimes essential in the Re-Organised Approach. All the Design information regarding the occlusal scheme of the final restorations can be programmed into the provisional restorations. It is an opportunity to test the patient’s tolerance to the new Occlusion and Jaw Relationship. Subtle changes may be required and can easily be made to the provisional restorations. Whether you consider it to be part of the Design Phase rather than the Execute Phase will depend on how many adjustments you have to make. Cases when the re-organisation of the occlusion includes an increase in vertical dimension by the provision of crown or bridges are amongst the most difficult, and so are the most essential to plan carefully. The new occlusion, including the change in the vertical dimension, can be tested against the patient’s tolerance by the placing of provisional restorations. Nowadays many patients have their worn dentitions resorted by the application of adhesive composite. There are differences in this sort of adjustable approach and the techniques described, in this chapter, for the restoration of a severely compromised dentition using laboratory made restorations and prostheses to the Re-Organised approach. This third approach has already been described as the ‘Monitored Developmental Approach’ [14] and is discussed in Chap. 10 Section A. Figure 4.15a shows a patient with a reduced Overall Vertical Dimension (OVD) and severely worn teeth (Fig. 4.15b). The treatment involved indirect restorations and some partial dentures. It was carried out to the Re-Organised Approach, and in contrast to some of the techniques above did not involve the adjustment of the premature Contact in Centric Relation. The initial treatment was fit a Stabilisation Splint that also provided some veneers (Fig.  4.15c–f). It was made to both find Centric Relation and help the patient to decide the appearance of the upper anterior crowns. Once Centric Relation had been found it was noted that the restoration of the Occlusion could be done to the vertical height of the Premature Contact, because it would provide the space for the anterior restorations and it restored the OVD (Fig. 4.15g). Then the Provisional Anterior Crowns could be fitted once the posterior occlusion had been restored to a Flag Designed Occlusion (Fig.  4.15h), followed eventually by the Definitive Restorations (Fig.  4.15i–k). The Definitive Crowns were made using a Custom Anterior Guidance Table (see Chap. 3) constructed from the template of the Provisional Crowns.

Step 4 Execute that Design in the Definitive Restorations This involves all of the skills that have been learned in following the Conformative Approach. The clinician’s responsibility is to provide the technician with accurate impressions and bite records. The technician’s responsibility is to verify the mounted models and then to provide restorations that conform to the Occlusal Prescription that has been established.

Step 4 Execute that Design in the Definitive Restorations

a

d

b

c

e

g

i

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f

h

j

k

Fig. 4.15 (a) Patient’s profile, suggesting loss of vertical dimension. (b) Patient’s dentition exhibiting significant tooth surface loss. (c) Upper stabilisation splint with labial veneers to fit over unprepared upper anteriors. (d) Mirror view of upper stabilisation splint. (e) Anterior view of upper stabilisation splint. Note the provision of median diastema, at the patient’s request. He later changed his mind. (f) Provisional restoration of vertical dimension and labial support by the upper stabilisation splint. Compare with Fig. 4.14a. (g) Restoring to the Premature contact in C.R. gave space for the restorations of the upper anteriors and restored the OVD. (h) Provisional Crowns restored to the Premature contact in C.R. (i) Mirror view of upper definitive restoration by partial denture and anterior crowns as developed in the ‘provisional’ phase. (j) Mirror view of upper definitive restoration by partial denture and anterior crowns as developed in the ‘provisional’ phase. (k) Restoration of vertical dimension and labial support

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This involves not only the Static Occlusion but also the Dynamic Occlusion. If, as in the case above, anterior teeth are involved in the restoration of the occlusion, a Custom Anterior Guidance Table is a simple and useful way of duplicating the guide pathways developed in the provisional restorations into the definitive crowns (Fig. 4.16a–f).

a

b

c

d

e

f

Fig. 4.16 (a) The models, including provisional crowns on upper anterior teeth, are used to carve a custom incisal guidance table in a slow setting autopolymerising acrylic. (b) Custom incisal guidance table. The incisal pin of the articulator is resting in a position that is related to the centric occlusion of the models. (c) Custom incisal guidance table is used to guide the upper working model into the same left lateral excursion as was present in the provisional restorations. (This would be a right lateral excursion in the patient). (d) Close up of custom incisal guidance table, guiding upper model into a left lateral excursion. (e) Using this technique it is easy to see exactly what the crown length and palatal contour should be to provide the same canine guidance as was present in the provisionals. (f) Custom incisal guidance table determining the length of right canine definitive crown

Summary

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Summary An advanced restorative treatment plan involving the re-organisation of a patient’s occlusion, using laboratory made restorations and prostheses, presents a major challenge for the restorative team. Successful completion will depend on: • Good communication and the transfer of accurate anatomical information between the clinic and laboratory. • Careful planning by the clinician. • The skills of the clinician and the technician. • The clinician will need to have: –– An accurate record of the patient’s pre-treatment occlusion. –– A clear idea of the occlusion of the definitive restoration, including the jaw relationship at which it is to occur. –– A detailed sequential plan on how the treatment will progress from the patient’s pre-treatment occlusion to the planned restoration. –– Clearly stated objective of every phase of treatment. –– Ensured that the patient understands the need for this careful approach. Although it can appear to be a very long way from the starting point to the declared objective, ‘every long march has to start with a first step’. As long as the objective is defined; and if the successful completion of each clearly defined step is the foundation for the next phase, success will be the outcome. The key is a sequential treatment plan. It is hoped that some of the measures outlined in this chapter will be an aid to dentists wishing to help their patients to these objectives.

The Need for the Restorations Comes First!

• Ideal occlusion is a concept in the treatment of a patient who needs multiple restorations. • It is not a treatment objective in itself. A patient should never be provided with multiple restorations solely to provide an ideal occlusion.

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 hat Are the Risks of Ignoring Good Occlusal Practice W in Advanced Restorative Dentistry? Not everything that can go wrong does go wrong. So if a dentist considers that some or all of the steps outlined in this chapter represent too big a burden for them, or for their patient to tolerate both from a time and financial standpoint, they will probably wonder what are the consequences of ignoring these guidelines. Some dentists will consciously have decided to ignore the advice given in this and similar publications, which is a clinical judgement; others will simply be ignorant of them (there goes that excuse, dear reader!). For whatever reasons these and similar advices are ignored, these dentists will have decided to hope that whatever occlusion and jaw relationship their full mouth restoration provided that are ones to which their patient will be able to adapt. When we consider how many dentists provide major restorations that do not provide as ideal occlusion/jaw relationship as possible, and how few of those cases go seriously wrong, one has to admire that adaptive capability of our patients. So, it could be argued that the dentists who choose the un-organised/I hope the patient can adapt approach may have a point. Although most patients might be able to adapt to change, not all can; and there is no way of predicting which can and which cannot. Risk is a mixture of not only likelihood but also consequence. Most people when assessing risk give consequence or outcome greater weight than likelihood. • People wish to give up smoking not because of the likelihood of developing lung cancer but because of the consequence of that disease. • Nervous airline passengers are anxious not about the likelihood of the airplane crashing, which they rationally know is very small, but because of the consequence of that event. It is the experience of all secondary or specialist referral centres that the consequence of a patient not being able to adapt to a change in occlusion/jaw relationship following extensive restorative treatment is frequently life changing severe. These patients can present with. • severe psychosocial distress, • a history of repeated restoration failure, • significant pain or articulatory system dysfunction. The management of these cases is inevitably much more complex than doing the case more carefully in the first place. Those of us who take as our primary responsibility ‘to do no harm’ will want to follow the protocols outlined above or similar ones.

References

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Guidelines of Good Occlusal Practice

1. The examination of the patient involves the Teeth, Periodontal Tissues and Articulatory System. 2. There is no such thing as an intrinsically bad Occlusal Contact, only an intolerable number of times to (para)function on it. 3. The patient’s occlusion should be recorded, before any treatment is started. 4. Compare the patient’s occlusion against the benchmark of Ideal Occlusion. 5. A simple, two-dimensional record of the patient’s occlusion taken before, during and after treatment is an aid to Good Occlusal Practice. 6. The Conformative Approach is the safest way of ensuring that the occlusion of a restoration does not have potentially harmful consequences. 7. Ensuring that the occlusion conforms to the patient’s pre-treatment state is a product of Examination, Design, Execution and Checking (the E.D.E.C. protocol). 8. The ‘Re-Organised Approach’ involves firstly the establishment of a ‘more ideal’ occlusion in the patient’s pre-treatment dentition or provisional restorations; and then adhering to that design using the techniques of the ‘Conformative Approach’.

References 1. Davies SJ. Occlusion in restorative dentistry: conformative. Re-organ Unorgan Dent Update. 2004;31:334–45. 2. Christensen LC.  Preserving a centric stop for interocclusal records. J Prosthet Dent. 1983;50:558–60. 3. Ramfjord SP, Ash MM.  Occlusion. 3rd ed. Philadelphia: WB Saunders; 1983. ISBN: 0721674399 OCLC:8033676 4. Neelakantan P, Subba Rao CV, Vasudevan C, Indramohan J. Can traumatic occlusion cause endodontic problems? A case report. Gen Dent. 2011;59:e153–5. 5. Gremillion HA. The relationship between occlusion and TMD: an evidence-based discussion. J Evid Base Dent Pract. 2006;6(1):43–7. 6. Davies SJ. Malocclusion: a term in need of dropping or redefinition? Br Dent J. 2007;202: 519–20. 7. Myers M, Dziejma R.  Relation of gothic arch apex to dentist-assisted centric relation. J Prosthet Dent. 1980;44:78–81. 8. Davies SJ, Al-Ani MZ, Jeremiah H, Winston D, Smith PWS.  Reliability in recording static and dynamic occlusal contact marks using transparent acetate sheet. J Prosthet Dent. 2005;94:458–61. 9. Briggs PF, Bishop K, Djemal S.  The clinical evolution of the ‘Dahl principle’. Br Dent J. 1997;183:171–6. 10. Lynch CD, McConnell RJ.  Prosthodontic management of the curve of Spee: use of the Broadrick flag. J Prosthet Dent. 2002;87:593–7.

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11. Gupta R, Luthra RP, Sheth HH. Broadrick’s occlusal plane analyzer: a review. Int J Appl Dent Sci. 2019;5(1):95–8. 12. Kois Dento-­facial analyzer. Panadent Worldwide Patent US6582931B1. 13. Ferrario VF, Sforza C, Miani JR. Statistical evaluation of Monson's sphere in healthy permanent dentitions in man. Archs Oral Biol. 1997;42(5):365–9. 14. Davies SJ et al. Occlusion: is there a third way? A discussion paper Br Dent J 2021;231:160–2. https://doi.org/10.1038/S41415-021-3267-6.

Suggestions for Further Reading Galindo D, Soltys JL, Graser GN. Long-term reinforced fixed provisional restorations. J Prosthet Dent. 1998;79:698–701. Howat AP, Capp NJ, Barrett NVJ. A colour atlas of occlusion and malocclusion. Wolfe Publishing Limited; 1991. p. 447–55. Parker MW. The significance of occlusion in restorative dentistry. Dent Clin N Am. 1993;37:341–51. Ramfjord SP, Ash MM. Reflections on the Michigan occlusal splint. J Oral Rehabil. 1994;21:491–50. Wassell R, Nark A, Steele J, Nohl F. Applied occlusion Quintessence. ISBN-13:9781850970989.

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The loss of teeth may result in patients experiencing problems of a functional, aesthetic and psychological nature. This chapter addresses the very important subject of occlusal considerations for partial and complete dentures. The occlusion is particularly important given the bearing that occlusal factors have, especially on edentulous patients. Historically complete denture prosthodontics has been at the forefront of the

In this chapter, we will discuss: • The features of an ideal occlusion in removable prosthodontics. • Why these features make it ‘ideal’ for denture stability. • Some techniques for achieving these aims.

study of occlusion, and many of the terms used in occlusion have their origin in this subject. The reason that occlusion has always been a consideration in the provision of removable complete prosthetics is because the adoption of good occlusal practice has a significant and immediate impact on the overall success of the treatment, as it affects denture stability. If an inappropriate occlusion is built into a denture, then the patient will be unlikely to be able to accommodate to that denture, and the dentist will be immediately aware that the treatment has been unsuccessful. The reason why the correct distribution of occlusal forces is so important in the design of removable prosthetics is because the prosthetic teeth that provide the occlusion are not directly attached to the patient. Students of occlusion have good reason to be grateful to the science of prosthodontics, and it remains a part of the undergraduate course where clear guidance on ‘good occlusal practice’ will be available.

© Springer Nature Switzerland AG 2022 S. Davies, A Guide to Good Occlusal Practice, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-79225-1_5

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Terminology Terms like ‘non-working side’ or the more accurate term in a prosthetic sense ‘balancing side’ are based on a study of occlusion from the perspective of complete dentures and refer to the side of the dentures which are not being used for chewing during a lateral excursion. This can lead to confusion when considering the temporomandibular joints during that same lateral excursion because the ‘non-working side’ joint is moving much more than the one on the ‘working side’. The terms ‘Centric Relation’ and ‘Centric Occlusion’ will be used instead of their synonyms of ‘Retruded Contact Position and Intercuspation Position’. Additionally, the term ‘Static Occlusion’ will be used to describe occlusal contacts when the mandible is closed and still, and the term ‘Dynamic Occlusion’ will be used to describe occlusal contacts when the mandible is moving. These terms will be used in preference to the ‘prosthetic’ terms of ‘occlusion’ and ‘articulation’. Terminology

Centric Relation (CR) = Retruded Contact Position (RCP). Centric Occlusion (CO) = Intercuspation Position (ICP). Balanced Static Occlusion = Balanced Occlusion. Balanced Dynamic Occlusion = Balanced Articulation.

Classification Prostheses are often considered under the categories of partial or complete dentures, but partial dentures may be supported by teeth, mucosa or a combination of both, and given the fact that the nature of that support dictates the design of the ideal occlusal platform, partial dentures are divided into the following sections: • Tooth-supported dentures • Tooth and mucosa-supported dentures • Mucosa-supported dentures

Tooth-Supported Dentures In a denture supported by teeth: • The occlusion is sensed. • The prostheses are less likely to cause instability, if poorly designed.

The concept of the occlusal prescription being ‘conformative’ or ‘re-organised’ has been discussed previously. The former conforms to the constraints of the patient’s present occlusal scheme while the latter alters or re-organises the current scheme to

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Fig. 5.1 Occlusal diagnostic appliance (stabilisation splint)

Fig. 5.2  Hybrid prosthesis

a more idealised occlusion, sometimes at a raised occlusal vertical dimension. If a partial denture is tooth supported, then the design of the occlusion provided by that prosthesis should be to ‘conform’ with and be complementary to the existing occlusion. The only exceptions to this would be ‘rehabilitative’ prostheses, which are occlusal diagnostic splints (Fig.  5.1) and hybrid prostheses (essentially overdentures) (Fig. 5.2). The difference between the two is that the splint is not intended to be definitive, whereas the hybrid prostheses is. Conventional wisdom indicates that the dentist must determine the patient’s ability to withstand a raised occlusal vertical dimension with a temporary (diagnostic) prosthesis prior to prescribing the definitive denture/prosthesis. If a partial denture is totally tooth-supported, the patient’s occlusion is entirely borne by teeth. This has two important occlusal consequences. Firstly, it means that occlusal load will be ‘sensed’ by the proprioceptors of the periodontal membranes. Secondly, it is less likely that a poorly designed occlusion will be immediately manifested by the denture being unstable than would be the case if the support was in part or totally mucosa supported.

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Examination The most important aspect of the examination of the patient, for whom a toothborne partial denture is to be made, is to confirm that it will indeed be solely supported by the existing teeth, and not in part by the soft tissues. It is advisable, as in all patients for whom a treatment is envisaged, to carry out a comprehensive examination not only of the dental and periodontal tissues but also of the articulatory system.

The EDEC Principle

E = Examine the pre-existing condition. D = Design the prosthesis. E = Execute the prosthesis. C = Check the occlusion at completion.

The EDEC Principle E = Examination. The examination of the patient’s pre-treatment occlusion is the first stage.

Treatment D = Design. The support for the partial denture must be provided by the abutment teeth in such a way as to avoid a change in the occlusal contact of the other teeth, otherwise the treatment would not be within the conformative approach. Ideally, the rests should also be designed to transfer the occlusal load down the abutment teeth along their long axes. E = Execute. The design criteria as expressed above may require modification of the abutment teeth and/or the opposing teeth. If this is the case, a clear rationale for the changes can be presented to the patient and is likely to be much better received than alteration to the dentition after or at the fit of the prosthesis. C = Check. At the delivery stage, a check is made that the prosthesis has added to the patient’s occlusal platform rather than altered its position or dynamic occlusal characteristics. This is easily achieved providing a record of the patient’s pre-treatment static and dynamic occlusal contacts has been recorded. It does not matter whether this is a three-dimensional record such as mounted study models on a semi-adjustable articulator, or a two-dimensional record such as a written record or ‘occlusal sketch’

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of articulating paper marks. It is obviously impossible to confirm that the treatment has been provided within the conformative approach unless this pre-treatment record exists.

Tooth and Mucosa-Supported Dentures/Prostheses The mucosa under a denture is capable of displacement to a degree that is 20 times greater than that of teeth via the periodontal membrane [1]. Furthermore, there is a difference not only in the amount of displacement under load but also in the type of deformation. The periodontal membrane of teeth, under occlusal force, undergoes a simple elastic deformation, whereas mucosa undergoes viscoelastic deformation. This means that the recovery from mucosal deformation is more prolonged than that of a tooth in its socket. These quantitative and qualitative differences between tooth support and mucosa support have an important clinical significance and obviously could cause problems in the construction of a prosthesis in which the occlusal load is going to be shared between what are two very different tissues.

Examination The examination of a patient’s mouth before the provision of a tooth/mucosa-­ supported removable prosthesis is designed to assess the support, retention and stability provided by the teeth, the ridges and the mucosa. A simple chart is suggested as an aid to this objective (Chart 1). For a patient with favourable prospects for support, retention and stability of their tooth/ridge/mucosal tissues, the chart may appear as in Chart 2. Patient expectations can be better managed if a chart similar to this is used as part of the examination phase.

Treatment The principal consequence of occlusal loading onto the more deformable mucosa will be the loss of occlusal contact. This is a particular problem in patients with freeend saddles. It was for this reason that Applegate described a technique of denture construction [2], universally known as the ‘altered cast technique’, which consists of the following stages: 1. Following the recording of the definitive impression, the metal framework is cast and tried in. If satisfactory, the saddle area(s) is(are) covered with light-cured denture base material. 2. The base of the saddle areas is on-laid with light-bodied impression material and an impression recorded of the saddle area with the dentist pressing on the toothborne elements of the framework.

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3. The original master cast is sectioned at the distal abutments and the saddles areas discarded. The new saddle area(s) is(are) prepared by pouring from this new impression. The intention of this technique is to ensure that the occlusal pressure will still be resisted by the ridges after the natural teeth have been minimally displaced into their sockets. An identical clinical procedure may be undertaken for a reline, and this may be sufficient to restore the occlusion in saddle areas (Table 5.1). Table 5.1  An example of a completed examination

Teeth

Ridge

Mucosa

Support

good perio.

square

firm

Retention

good undercuts

favourable

good

favourable

Stability

Mucosa-Supported Dentures 1. Partial Dentures Dentists should be under no illusion that mucosally supported partial dentures will, within a relatively short time, lose occlusal contact with the opposing arch as the underlying bone is resorbed; this type of denture cannot be relied upon to provide a lasting occlusion. In addition, the problem implied in the term ‘gum strippers’ is well known; a typical example is shown in Fig. 5.3, illustrating the iatrogenic effects of selecting a mucosally supported design. Simple relines are only likely to exacerbate the resorption. However, not all such designs are necessarily examples of poor dentistry; for instance, training dentures (Fig. 5.4) are sensible treatment options when the state of total edentulousness is deemed to be unavoidable.

Examination It is because of the shortfalls, occlusal and others, that such dentures must only be used appropriately. It is, therefore, important that a comprehensive examination of the patient enables an accurate assessment of the prognosis of the patient’s dentition.

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Fig. 5.3  Gum stripper

Fig. 5.4  Training denture

Fig. 5.5  Occlusion at insertion

Treatment Figures 5.5 and 5.6 show an entirely mucosa-supported lower partial denture; immediately after having been supplied to the patient (Fig. 5.5), there is an occlusion between the denture and the patient’s maxillary teeth, whereas after 6 months (Fig. 5.6), there is no occlusal contact against the opposing teeth.

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Fig. 5.6  Lack of occlusion after 6 months

2. Complete Dentures It has been said that ‘a patient with no eyes cannot see, a patient with no legs cannot run, yet a patient with no teeth expects to eat and act with dentures as with natural teeth’ [3]. It is unlikely that this can be achieved, but it remains the goal. The design of an occlusion in complete dentures is different from that of the dentate patient. While both are concerned with the final act of intermaxillary closure, the absence of direct attachment between the dentures and the patient’s musculo-skeletal system requires a different set of guidelines of good occlusal practice. For all these reasons, it is important to consider the role of occlusion in complete denture philosophy. The fundamental philosophies governing the biomechanics of complete dentures state that there is a fine inter-relationship between support, retention and stability, and the success of the prosthesis will be dependent in a very large part on these features. Importantly, occlusion is considered a major factor governing stability [4]. The minimal level of occlusion that any practitioner should prescribe in complete dentures is balanced occlusion; this is described by the British Society for the Study of Prosthetic Dentistry [5] as ‘even, harmonious bilateral contact between teeth or tooth analogues in retruded contact position (RCP)’. In our terminology, this means a ‘balanced centric occlusion in centric relation’ (CO = CR). This is a ‘static occlusion’ concept, and this type of an occlusion would ensure that, as a patient elevated the mandible into CR, the dentition would be stable. There would be no tilting/displacing force on the dentures, and so stability would not be compromised. Factors that might compromise this stability are illustrated in Fig. 5.7. They are: • Unilateral prematurities. • Occlusal tables that are too large. • Injudicious placement of teeth.

Mucosa-Supported Dentures a

127 b

c

Fig. 5.7 (a) Unilateral prematurity. (b) Too large an occlusal table. (c) Injudicious placement of teeth Fig. 5.8 Christensen phenomenon

• For many patients, a simple occlusal prescription is all that will be required, i.e. the patient has ‘evolved’ to using essentially vertical mandibular movements with little or no lateral and protrusive mandibular movements. • In this case, no elaborate occlusal scheme is indicated, nor is a semi-­ adjustable articulator, because the dynamic occlusion can be ignored.

For other patients, however, lateral and protrusive movements are part of their normal ‘ruminatory’ mandibular pattern, and for these patients, a balanced dynamic occlusion (balanced articulation) is required. In other words, consideration must be

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b

Fig. 5.9 (a) F/F with compensating curves. (b) F/F with compensating curves

given not only to the static but also to the dynamic occlusal prescription. In this situation, the teeth of the maxillary denture must maintain harmonious sliding contacts with the teeth of the mandibular denture in all excursive movements, otherwise denture stability may be significantly compromised. For example, in a natural dentition, the act of protrusion usually results in a posterior open bite (the Christensen phenomenon, Fig. 5.8). Such a situation would lead to instability in complete dentures; hence, compensating curves (Fig. 5.9a, b) are incorporated into the dentures. The same philosophy holds for lateral excursions. This means that the ‘ideal occlusion’ for a patient with complete dentures differs from the ‘ideal occlusion’ for a dentate patient, for example it is ‘ideal’ for complete denture stability if there is no posterior disclusion during lateral excursions, whereas immediate and lasting posterior disclusion is usually considered to be ideal for the dentate patient. It is because teeth on a denture are not attached to the patient’s neuro-muscular skeletal system, and there is no possibility of neural stimulation via periodontal proprioceptors that the criteria of what makes an ‘ideal occlusion’ have changed. Although there are mechanoreceptors in the denture bearing oral mucosa, they do not continue to send a stream of impulses to the sensory cortex. It, therefore, beholds the dentist to determine the occlusal requirements of complete denture wearers prior to prescribing complete dentures [6]. If balanced articulation is required, there is no valid reason for not: • Using a facebow. • Accurately determining condylar angles. • Harmonising the occlusion to match mandibular movements.

Summary It is a prerequisite for stability in all complete dentures that posterior occlusal contacts occur simultaneously and bilaterally; furthermore, these contacts should occur in centric relation and at the appropriate occlusal vertical

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dimension. In some patients (those with a ruminatory chewing pattern), it will also be necessary to harmonise the dynamic occlusion in order to ensure denture stability.

Examination of the Complete Denture Patient The purpose of the examination is to lead to the correct decisions being taken at each stage, so that a successful treatment strategy can be made.

1. The Examination of the Denture Bearing Surfaces An assessment of the denture bearing surfaces will involve assessment of: • Shape of the ridges: Moses suggested a classification of ridge shape and described the retentive and support characteristics of each (Table 5.2) [7]. The ideal occlusion for the prosthesis will, therefore, relate to the ridge shape. • Nature of denture bearing area: Firm or flabby; and sensitive or comfortable to finger pressure. A sensitive or mobile ridge will require an occlusal prescription that is designed to reduce the transmission of force. • Space: If there is very little space between the ridges (usually at the posterior part of the mouth), then the distal extent of the occlusal platform will be necessarily reduced in length. It is better that the dentist discovers this at the examination stage rather than the technician when mounting the models. Table 5.2  Moses classification of Ridge shapes

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Fig. 5.10 Diagnostic biscuit

2. The Examination of the Existing Dentures Do the existing dentures exhibit? • Inadequate freeway space. • Evidence of excessive wear: loss of vertical dimension, crossbite and anterior posturing. If the answer to any of these questions is ‘yes’, then the new dentures are not going to be made to the ‘conformative approach’, but rather the occlusion will be changed, i.e. the ‘re-organised approach’ will be adopted. The examination of how the patient masticates. The answer to this essential question will in most cases determine whether the patient needs only a balanced static occlusion in centric relation (‘balanced occlusion’), or whether in addition they should have a balanced dynamic occlusion (‘balanced articulation’). In order to determine whether the patient has a chewing pattern that involves essentially only vertical mandibular movements, or also uses lateral and protrusive movements, they must be observed masticating. This seems self-evident, and yet very few patients are treated after determining, by observation, the type of chewing that is used. The appropriate occlusal prescription of the denture cannot be determined without this part of the examination which involves the use of the ‘diagnostic biscuit’ (Fig. 5.10).

Treatment Treatment Strategy This will have evolved during the examination:

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Should the Conformative or Re-Organised Approach Be Used? In the vast majority of patients with a restorative/prosthetic need, the conformative approach is the method of choice. It offers the dentist the relatively simple task of providing treatment which conforms to the occlusion to which the patient has been accustomed. In the edentulous patient, the re-organised approach may be indicated if the patient exhibits: • A temporomandibular disorder. • A grossly overclosed vertical dimension. • A pre-existing inappropriate occlusal pattern that has led to denture instability.

 oes the Patient Need a Balanced Dynamic Occlusion (Balanced D Articulation) or Only a Balanced Static Occlusion (Balanced Occlusion)? This question can only be answered by determining, by observation, the type of mastication that the patient employs. This has major consequences for the treatment of the patient, and an assessment, therefore, of the patient chewing is an essential part of the examination of an edentulous patient.

Stages of Construction 1. The design of the fitting surfaces: ‘impression taking’. It is the dentist’s responsibility to design the denture supporting area on some accurate models, and it is outside the scope of this section to expand on this aspect of full denture construction other than to say that it should not be left to the technician. 2. Determining the interarch relationship: ‘bite registration’. The term ‘bite registration’ is a poor one, as the patient is not asked to bite into anything; in fact, if they do, it is likely that they will make an uncontrolled mandibular movement away from CR. The purpose of this stage is to record the relationship between the upper and lower jaws, in the vertical, horizontal and anterio-posterior planes. Before this stage can be completed, the decision whether to make the dentures to the conformative or re-organised approach must have been taken. In addition, it must have been decided whether only a balanced static occlusion (balanced occlusion) or also a balanced dynamic occlusion (balanced articulation) is needed. If balanced articulation is indicated, a facebow record must be taken so that the occlusal rims can be mounted into a semi-adjustable articulator.

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a

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b

Fig. 5.11 (a) Gothic arc trace apparatus. (b) Gothic arc trace arrowhead

Gothic Arch Trace One means by which a balanced articulation is created on that articulator is the gothic arch trace. This trace is made on a ‘central bearing apparatus’ (Fig. 5.11a). This comprises upper and lower acrylic plates onto which is mounted centrally a stylus and a platform. These will record a ‘map’ of the patient’s range of movements, by asking the patient to go into: • Protrusive. • Right lateral. • Left lateral excursions. The provision of full dentures will involve three stages: Colloquial term Actual function 1. ‘Impression making’ Designing of the fitting surfaces 2. ‘Bite registration’ Determining the interarch relationship 3. ‘Setting up the teeth’ Providing the ideal occlusion

The starting point of these movements as inscribed by this trace is the arrowhead (Fig. 5.11b) and represents centric relation (CR or RCP). If it proves impossible to obtain an arrowhead, this means that the patient does not have a reproducible maxillo-mandibular relationship. This is an important finding and would indicate the need for some further pre-definitive treatment in order to discover a reproducible jaw relationship (i.e. CR). This could be achieved by the use of ‘pivotal appliances’. A polished pivotal appliance (Fig. 5.12) may look unusual, but it is remarkable how well they are tolerated. After fitting, further adjustments are easily made to find the new occlusal vertical dimension (OVD) and to provide occlusal stability. When all adjustments have been made and the patient has been wearing the appliance comfortably for a period,

Treatment

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Fig. 5.12  Registering CR with a pivotal appliance

it is a simple procedure to register centric relation with a registration material placed before and behind the pivots. Pivotal appliances may be made on acrylic bases, or from the patient’s previous dentures. It may be wise to make a copy of the patient’s denture with which to make the pivotal appliance. It will then be possible to return the original denture intact to the patient. 3. Providing the ideal occlusion. ‘Setting up the teeth’. The occlusion of the dentures that will be ‘ideal’ for the patient is the one which will limit the tilting of the dentures and so minimalise disruption to the peripheral seal, risking instability. As stated, this occlusal prescription will take into account the patient’s denture bearing tissues and their chewing pattern. On the basis of occlusal form, there are four types of posterior teeth: [8]. • Anatomic teeth: these ‘duplicate’ the anatomical form of natural teeth and typically have 30–40° cuspal angles. Modified forms have 20° cuspal angles, and these are typically used in complete dentures, on the basis that it is easier to obtain balanced articulation with 20° cuspal angles. • Non-anatomic teeth: these have occlusal surfaces that are not anatomically formed and are designed with mechanical and not anatomical principles in mind. • Zero-degree teeth and • Teeth without cusps: these may be used for patients who have essentially vertical chewing movements as only their static occlusion needs to be balanced (balanced occlusion), i.e. there is no need for a balanced dynamic occlusion (balanced articulation). In those patients who need a balanced dynamic occlusion, a cuspal form is essential. The dentist has to consider what is appropriate for the patient. If large ridges are present, anatomical teeth will probably suffice. Whereas, if the ridges

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are flat or where implant-supported dentures oppose maxillary complete dentures, then teeth with non-anatomical cuspal form may be indicated [8, 9] as large cusps may induce instability via a tripping effect.

• Good occlusal practice is different in the edentulous patient from that in the dentate patient. • The form of an ideal occlusion for a particular edentulous patient will depend on their chewing pattern and ridge form.

The EDEC Principle in Complete Denture Construction (E = Examine, D = Design, E = Execute, C = Check) The construction of complete dentures is a sequential process. The successful completion of one stage is the prerequisite of starting the next. In order to prevent introducing errors into the sequence, it is important to consider what each stage needs to achieve. The EDEC principle is one way of defining the objectives of the process. E = examine. The examination of • The denture bearing surfaces. • The existing dentures. • The masticatory pattern. will be the basis for. D = the design of the occlusion of the prosthesis. The first stage of full denture construction is: E = the execution of that design. This comprises the procedures up to and including the jaw registration. It involves: • Defining the relationship between the denture bearing surfaces in three planes. • The design of the ideal static and dynamic occlusion for that patient. At one end of the spectrum, this design may be a copy of the patient’s previous prosthesis: the ‘Conformative Approach’. Alternatively, there may be need to design changes in

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• The vertical height. • Jaw relationship. • Occlusal prescription: the ‘Re-Organised Approach’. The design will be achieved and recorded in the jaw registration, when this information is passed on to the laboratory technician. From that moment, the emphasis of the dentist, during the try-in and completion stages, moves from designing and executing change. C = checking that there is no deviation from the record supplied to the technician; i.e. from the bite registration to completion, the dentist’s responsibility is to conform to the Design.

Combination Syndrome [10] The final section under the heading of ‘mucosa supported dentures’ considers the type of occlusion that is required when a full denture is opposed by teeth or a fixed prosthesis, a condition referred as the ‘Combination Syndrome’ [10]. There are three scenarios: 1. Complete maxillary denture opposed by dentate/partly dentate mandibular arch. 2. Complete mandibular denture opposed by dentate/partly dentate maxilla. 3. Complete maxillary denture opposed by implant retained lower complete denture (‘New Combination Syndrome’).

1. Complete Maxillary Denture Opposed by Dentate/Partly Dentate Mandibular Arch In this situation, these can be considerably displacing forces on the upper denture resulting from mandibular movements, so the retention of the upper denture must be maximised. Displacing forces can be reduced by co-ordinating the maxillary teeth and maxillary plane of occlusion to mandibular movement. This is achieved by: • Using a facebow to transfer the plane of the upper arch to the condylar axis. • Using a central-bearing screw to create an arrowhead (gothic arch) tracing. • Setting the articulator condylar angles to accord to the border tracings on the arrowhead tracing. • Establishing, carefully, at trial insertion, that CR (RCP) is reproducible. • ‘Milling in’ the occlusion to suit the patient. This will inevitably be necessary, as cuspal inclines of the denture teeth will be unlikely to be equal to those of the patient’s natural mandibular teeth. • Reviewing of the patient after 3 days to refine the cuspal anatomy.

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Special Case T he Maxillary Atrophic Ridge In this scenario, an upper complete denture has been occluding, for a long time, against only the lower anterior natural teeth: that is to say the issue of a lack of posterior occlusion has not been addressed. Usually and maybe surprisingly, the patient has found that, for many years, the upper complete denture has not been unretentive. The consequence of this is that, unless the patient attends for frequent examinations to have their remaining six teeth examined, there are very limited opportunities for the dentist to warn of the danger inherent to this situation. Eventually, the day usually comes when the patient finds that they cannot occlude against the upper denture without a socially embarrassing loss of retention of their upper denture. Unfortunately, they are wrong, if they assume that this situation can be easily remedied by a new conventionally made new upper complete denture. This is because the initial examination reveals that they have a severely atrophic upper premaxillary alveolar ridge [flabby ridge]; see Fig. 5.13a–c. [This case is kindly provided by Mr. Indika Weerapperuma Hon Lecturer, University of Manchester and Kinross Dental Care, Sri Lanka.] This then is an example of a ‘Mal-Adaptive Occlusion’, on the level of the alveolar bone. It represents a significant challenge to the dentist, requiring a Selective Impression Technique, whereby the posterior maxillary impression is taken in a muco-compressive material, and the anterior maxillary impression is taken in a muco-static material. This is to minimise the displacement and distortion of the

a

c

Fig. 5.13  Atrophic ‘flabby’ premaxillary ridge

b

Combination Syndrome

137

uniquely soft tissue of the upper anterior ridge [6], it is not easy and has no guarantee of successful outcome. It is relevant to mention this condition in a book on Good Occlusal Practice because, if given the opportunity, the dentist has an obligation to warn the patient of what may be the consequence of an upper complete denture occluding against only lone standing lower anterior teeth.

2. Complete Mandibular Denture Opposed by Dentate/Partly Dentate Maxilla Success is even more difficult to achieve in this clinical scenario than the former, and although similar techniques are recommended, two major problem areas are often present: • Impaired support potential of the mandibular denture-bearing tissues. • Unfavourable peri-denture anatomical forces, i.e. muscle attachments.

3. Complete Maxillary Denture Opposed by Implant Retained Lower Complete Denture (‘New Combination Syndrome’) This third scenario is now encountered with increasing frequency. This application of implants is rightly considered for the patient who is suffering because of their unretentive and uncontrollable lower complete denture. But dentists should be aware of the possibility of the patients developing a ‘New Combination Syndrome’. At its simplest, this syndrome will clinically present as ineffective mastication, often associated with a very unretentive upper denture. At its most extreme, the patient may exhibit periods when they are unable to exert any control over their mandible or find any position where they can rest it, exhibiting a severe mandibular tremor. The hypothesis on how this syndrome arises is as follows: As the lower denture becomes more retentive: • It is known that there is a significant increase in displacing forces transmitted to the upper denture by virtue of the increased retention afforded to the lower denture by the mandibular implants. This force may be considerably in excess of the retention that has been provided to the upper denture, a retention that was perfectly acceptable when it was opposed only by an unretentive lower denture maybe on an atrophic ridge. • It is thought that there may be a significant change in the patient’s chewing pattern and that this might occur sometime after the implant retained lower prosthesis has been fitted.

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Before implants were used, the patient probably developed a purely vertical chewing pattern in an attempt to accommodate to the extremely unretentive lower denture. Once the lower denture is retained by the implants, however, the patient may revert back to a masticatory pattern that includes lateral and protrusive movements (the ruminatory pattern of mastication). The occlusion of the dentures, which was acceptable whilst the patient was chewing only with vertical movements, could now be ‘tripping’ the upper denture.

Complete denture construction is a sequential process: • Examination denture bearing surface existing dentures masticatory pattern. • Design the appropriate occlusion. • Execute that design (up to and including jaw registration). • Check that there is no deviation from that design (from registration to completion).

As the chewing pattern changes, the features of the ideal occlusal prescription also change.

Solutions Some of the solutions include: • The basic principles of good retention and stability are not only still needed, they are more important. • The occlusion should be designed to reduce the displacing or ‘tripping’ forces, even in a patient who appears at the time of examination to have a vertical masticatory pattern (‘accommodative chomping’). • The possibility that the patient will need some implants on the upper jaw should be raised, ideally before the implant treatment of the lower jaw is finalised.

Treatment Strategies and Summary The principle is to design and provide an occlusion that is ideal—ideal for the important criteria of denture success—stability. An occlusion is needed that will reduce the displacing forces on the denture(s).

Treatment Strategies and Summary

139

The basic equations are:

Force  Retention  Instability Force  Retention  Stability

The occlusal prescription provided is a major factor in determining the size of the force applied to the dentures. The retentive capacity of the denture is defined by the patient’s tissue and masticatory patterns.

Force > Retention = Instability Force 9 mm. • Impacted teeth. • Missing teeth. • Severe crowding >4 mm.

2.  Benefits of Orthodontic Treatment 2.1  Evidence Supporting Benefits of Orthodontic Treatment Orthodontic treatment can be used to improve both skeletal jaw and dental discrepancies. Irregular tooth positions resulting in protruding teeth or teeth in an adverse occlusal relationship can be moved to improve both the aesthetics and the function of the dentition. The correction of tooth position will encourage a more balanced and protective occlusion. In addition, some specific problems such as impacted teeth or congenitally missing teeth can be addressed by orthodontic treatment. There are other well-recognised benefits to undertaking orthodontic treatment. When the authors use terms like ‘correct’ or ‘improve’, the reader is asked to keep in mind that we believe that an occlusion should be qualified not only by its adherence to a set of arbitrary rules but by the effects it may have on the tissue systems. So, for instance, an incisor crossbite that a patient may find aesthetically acceptable, and is not resulting in jiggling, migration, wear, or gingival recession, may need monitoring rather than active correction. There is good evidence that the reduction of a large overjet resulting in protruding teeth can reduce the risk of trauma to those front teeth. Whereas there is only weak evidence to support the use of orthodontic treatment with the aim of improving dental health by making it easier to maintain good oral hygiene and so reduce of caries risk.

2.2  Risks of Orthodontic Treatment As with most interventional treatment, there are risks associated with orthodontic treatment. While most orthodontic treatment is completed with no adverse effects, certain risks are usually accepted as part of the consent process. Most significant risks are staining of teeth if good oral hygiene is not maintained. Other

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6  Occlusion and Orthodontics Benefit

Evidence

Appearance

Dento-facial aesthetics

Evidence – improved satisfaction with dental appearance

Function

Mastication

Evidence – equivocal

Speech

No evidence that orthodontic treatment will correct speech disorders

TMD

Weak link relating some malocclusions to TMD

Tooth impaction

Tooth impaction - risk of dentigerous cyst, roof resorption associated with unerupted canines

Caries and periodontal disease

No evidence that orthodontics reduces caries risk

Trauma

Reduction in OJ has been related to reduction in trauma

Well being/selfesteem

Teasing about teeth caused distress. No evidence that malocclusion causes poor self esteem in long-term

Dental Health

Psychological

Fig. 6.1  The benefits of orthodontic treatment

acknowledged risks include root resorption (estimated to be approximately 1 mm), loss of vitality and relapse (Fig. 6.1).

3.  Examination of the Occlusion and Articulatory System 3.1  Extra-Oral: Orthodontics for the Face Orthodontics was previously concentrated on achieving the ideal occlusion, often focussing on obtaining a Class 1 incisor relationship. This was sometimes done without consideration of the face and facial profile. In contrast, most contemporary orthodontics is undertaken with ‘Orthodontics for the Face’ in mind. This may indicate modification of the occlusion to include functional appliances or orthognathic surgery. An examination of the skeletal pattern in all three planes (horizontal, vertical and transverse) is vital to ensure the correct diagnosis and treatment is reached (Fig. 6.2).

3.  Examination of the Occlusion and Articulatory System The front view will indicate any skeletal asymmetry. The view also provides a smile assessment and dental centre-lines

145

The vertical line (perpendicular to the Frankfurt plane) indicates a class 2 skeletal pattern

Fig. 6.2  The extra-oral assessment

3.2  Intra-Oral: Identifying the Occlusal Pattern While Angle described occlusion according to the molar relationship (Table 6.2), a more meaningful relationship and classification is to assess the incisor occlusion. The assessment of the occlusion is assessed in three planes (horizontal, vertical and transverse) to fully quantify the occlusion (Fig. 6.3). The amount of incisor overjet along with the molar and canine relationship gives an indication of the extent of discrepancy. An assessment of crowding should also be recorded to allow a full diagnosis along with an IOTN score. This can be achieved using an orthodontic diagnosis sheet (Fig. 6.6a–c). A full orthodontic assessment should also generally include radiographs which can be used to aid diagnosis and assist with treatment planning • OPG (Fig. 6.4). • Lateral cephalogram (Fig. 6.5).

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Table 6.2  Angle’s molar classification Class 1—The mesiobuccal cusp of the permanent maxillary first molar occludes IN the groove between the mesial and middle buccal cusps of the permanent mandibular first molar. (“Old Glory”)

Class II—The mesiobuccal cusp of the permanent maxillary first molar occludes ANTERIOR to the groove between the mesial and middle buccal cusps of the permanent mandibular first molar Class III—The mesiobuccal cusp of the permanent maxillary first molar occludes DISTAL to the groove between the mesial and middle buccal cusps of the permanent mandibular first molar

Class 1 molar r/s

Increased overjet indicating a class 2 div 1 incisor r/s

Fig. 6.3  The intra-oral assessment

Increased overbite with upper Class 1 molar r/s incisors occluding in lower 1/3 of lower incisor crowns

3.  Examination of the Occlusion and Articulatory System Fig. 6.4  An OPG radiograph giving an overview of the dentition and supporting tissues

147

The Orthopantomogram is used to detect missing teeth and an assessment of the root morphology.

The lower 2nd pre-molars are congenitally missing with retained deciduous molars The Lateral cephalogram is used to assist in clinical findings. The radiograph can demonstrate measurements of skeletal discrepancies and incisor angulations. The standardised tracing of the radiograph

Fig. 6.5  Lateral cephalogram and measurement tracing

3.3  Mandibular Displacement It is important to record not only the patient’s habitual bite (Centric Occlusion [CO] or InterCuspation Position [ICP]) but also the patient’s ideal jaw relationship (Centric Relation [CR], alternatively referred to as Retruded Contact Position [RCP]) or Terminal Hinge Axis. During the examination, it should be determined if CO occurs in CR. If it is not: • Quantitative and qualitative assessments could be made; i.e. Q. how big and in which direction is the slide from CR to CO? • Which teeth provide the first contact in CR (Premature Contact in CR, or Guidance contact(s) in CO)?

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3.4  Should Treatment Be Undertaken to Create Occlusion in CR? The short answer must be NO, because a significant proportion of the population do not have a CO that occurs in CR; and they suffer no ill effect. However, if orthodontic treatment is indicated anyway in a patient where CO does not occur in CR, then depending on the difference between CO and CR, it may be that to provide a CO in CR is a justified treatment objective. Because of the large percentage of subjects who do not have any adverse reaction to having an occlusion that does not occur in CR, clearly it is not always necessary to undertake orthodontic treatment (or restorative treatment) to create a CO that occurs in CR. If, however, there is a premature contact in CR and it is easy to orthodontically remove it, then especially in a child, it may be a justifiable treatment objective. In adults, however, that have no adverse reactions from the fact that CO does not occur in CR, there can be little justification because they probably will still have a comfortable occlusion and good function. Of course, consideration of whether the aim of orthodontic treatment could include an occlusion in CR, can only be made after a comprehensive examination that includes finding CR.

3.5  Examination of the Articulatory System The occlusal analysis comprises only one part of the Articulatory System examination: the muscles and temporomandibular joints should also be examined. The three elements of an examination of the Articulatory System can be incorporated into an orthodontic examination protocol (Fig.  6.6). This comprehensive examination will record the extra-oral skeletal pattern, the oral soft tissues, signs and symptoms of the TMJs and mandibular muscles and the position of the teeth and their occlusal contacts. It is a rapid and easily followed examination protocol that provides a good assessment for both orthodontic diagnosis and screening for Disease, Dysfunction or Discomfort within the Articulatory System; i.e. a Temporomandibular Disorder. The examination of the patient’s occlusion must not only include assessment of the habitual bite or centric occlusion (CO), but also the occlusion in centric relation (CR). This is because the presence of large discrepancies between CO and CR may be a positive indication for orthodontic treatment. Equally, such discrepancies should not be introduced during orthodontic treatment. In restorative terminology, orthodontic treatment is not provided to the conformative approach. Whether it is to the re-organised approach or the newly suggested ‘Monitored Developmental’ approach will be left to the reader, for fear of being pedantic. But to leave or create a large discrepancy between CO and CR would be to provide the patient with an occlusion to which they may have difficulty in adapting.

3.  Examination of the Occlusion and Articulatory System

149

The conventional wisdom in restorative dentistry is that if the jaw relationship is going to be changed, then it is safer (i.e. less likely to produce an adverse response) if it is changed to centric relation (the re-organised approach) rather to some random jaw relationship (the un-organised approach), when the clinician just hopes that the patient can adapt to the change.

General Record Patient

Date Age Plaque control

Medical history

Gingivitis +

good mod

++

poor

+++

Jaw and Facial Examination Skeletal Pattern 1 II

III

TMJ Tender to palpation?

Noises

mild

Lateralpole

Clicks

Crepitus RightLeft

mod

severe

Intra-auricularly

Right Left or Bilateral Soft or Loud Consistent or Intermittent Opening or closing or both Early Mid Late Painful or Painless Single or Multiple or Bilateral Painful or Painless

Range of Motion (mm) Vertical maximal comfortable Pathway of opening Lateral or deviating lasting straight D I or transient to

Muscle Tenderness Temporalis

Centre Lines

Masseter

Lateral Pterygoid

Lips Comp

midface U

Tongue thrust

L

Incomp

Fig. 6.6  Orthodontic examination including articulatory system exam

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6  Occlusion and Orthodontics Dental and occlusal examination

Erupted teeth

Absent teeth

Unerupted teeth

Lower arch

Upper arch Crowding mild

Crowding

Inclination none

procliped

mild

Inclination none

procliped

mod

spaced

AV

mod

spaced

AV

sev

fraenum

retrocliped

sev

fraenum

retrocliped

Incisor Class

Overjet in CO .............mm

1

If zero Freedom in CO? Yes No Overjet in CR

1/1 11/1 11/11

.............mm

X-Bites

Fig. 6.6 (continued)

Increased Average Reduced Edge to Edge Complete Incomplete

scissors IOTN DHC................. AC.................

displacement no. ......mm

Overbite

R

L

ANT

HT ST

3.  Examination of the Occlusion and Articulatory System

151

Dental and occlusal examination (cont.)

Buccal segments Molars I R

...unit

L

...unit Canines I

R

...unit

L

...unit

II

III

II

III

Static Occlusion Does CO occur in CR? .............. IF NOT prem contact in CR? Roughly or exactly Direction of slide from CR to CO ......................................

Dynamic Occlusion RHS

LHS

Non-Working Side Interferences Working Side Interferences Crossover Position

NWS int WS int

Canine Guidance Group Function

Fig. 6.6 (continued)

That said, orthodontic treatment has the enormous advantage that it changes occlusions and the jaw relationship slowly (Evolution), rather than the rapid changes that is often associated with restorative treatment plans (Revolution). It is the recognition of this fact that has led to the suggestion, made in Chap. 1, of a third classification: ‘The Monitored Developmental’ approach.

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4.  Treatment Options Orthodontic treatment can be divided into three categories, depending on the aims of treatment: • Orthodontic camouflage. • Growth modification. • Orthodontics and orthognathic surgery. To understand this, we should be familiar what an orthodontist considers to be the aetiology of what they consider to be the malocclusion. The aetiology consists of the following: 1. Skeletal factors 2. Dento-alveolar factors 3. Soft tissue factors 4. Habits 1. Skeletal factors should be considered in three planes: anteroposterior, vertical and transverse. Patients can present with discrepancy of the upper and lower jaw in any of these planes. 2. Dento-alveolar factors will generally present as crowding of the teeth as a result of discrepancy between the overall tooth size and arch dimension. 3. Soft tissue factors can alter the teeth position if the muscular forces are imbalanced, as the teeth lie in a position of muscular balance between the lips, cheeks and tongue. 4. Digit sucking is an example of habit, which can have a significant effect, depending on intensity and duration, upon the occlusion. So, as stated, when faced with these discrepancies, the orthodontist has three main choices: 1. Camouflage treatment, whilst accepting the skeletal pattern. 2. Attempt growth modification with functional appliances. 3. Orthognathic surgery, when patient has ceased growth.

4.1  Camouflage Treatment If the treatment is directed at camouflage, either the orthodontist may choose to accept the interarch relationship, attempting to camouflage the problem by only aligning the teeth, or space can be created in the dental arches by several means: • Extractions. • Arch expansion. • Distalisation of the upper buccal segments. • Incisor advancement or interproximal enamel reduction.

4.  Treatment Options

153

Once space has been created, other teeth can be moved into it in order to achieve the treatment goals. Whereas dental appearance can be anticipated reliably, facial appearance is less predictable. So although a good occlusal outcome can be anticipated when planning camouflage treatment, it might be done at the expense of facial aesthetics. From a facial aesthetic perspective, it is more difficult to a good result by camouflage alone (Fig. 6.7).

a

b

c

d

Fig. 6.7 (a–d) Patient with 2 division 1 incisor relationship on a severe skeletal 2 base with increased overjet and overbite and incompetent lips. (e–h) Patient after two phase functional/fixed appliance treatment showing good occlusion but disappointing facial appearance

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6  Occlusion and Orthodontics

e

f

g

h

Fig. 6.7 (continued)

This is an important point when considering occlusion and orthodontics:

I mprovement in the Occlusion Alone May Not Satisfy the Patient’s Aesthetic Aspirations

This is the reason why there a debate in orthodontics around the detrimental effect of camouflage treatment on facial profile. It is the reason why growth modification treatment is favoured by many orthodontists for children with a skeletal malocclusion.

4.  Treatment Options

155

The reason why growth modification and orthognathic surgery are discussed in a book on occlusion is that orthodontic success cannot be judged by occlusal outcome alone.

4.2  Growth Modification Growth modification comprises an attempt to modify the underlying hard or soft tissues to bring about skeletal and dentoalveolar change. In a growing child, a functional appliance is most common treatment choice for a developing Class II skeletal problem. It has the aim of enhancing mandibular growth and restrain maxillary growth (Fig. 6.8). a

b

c

d

Fig. 6.8 (a–d) Pre-treatment photographs of a Class 2 patient before functional appliance treatment. (e–h) Post-treatment photographs showing good dental and facial appearance

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6  Occlusion and Orthodontics

e

f

g

h

Fig. 6.8 (continued)

 . How Do Functional Appliances Work? Q • Do functional appliances modify growth? • OR Do functional appliances work principally by dento-alveolar change? Current evidence shows functional appliances cause an initial small but meaningful increase in mandibular growth in young patients. But when these patients are monitored to the completion of orthodontic treatment, no significant skeletal differences is found between the treatments started in childhood and those started in adolescence. The only difference is lower incidence of dento-alveloar trauma in the patient who started treatment in childhood [4]. It can be concluded, therefore, that the long-term gain in mandibular growth is very small with functional appliances [5].

4.  Treatment Options

157

a

c

b

d

Fig. 6.9 (a, b) Pre-treatment photographs of a patient before orthognathic surgery. (c, d) End of treatment photographs after orthodontic/orthognathic treatment showing good dental and facial appearance

4.3  Orthognathic Treatment Orthognathic treatment is considered to be the gold standard for comprehensive correction of severe dentofacial discrepancy. It involves a combination of orthodontics and orthognathic surgery (Fig. 6.9). It is undertaken by a multidisciplinary team of clinicians involving, orthodontist and oromaxillofacial surgeon. This treatment is undertaken at the end of growth to improve post-treatment stability. This treatment should only be carried out for patients who have major concern with their oral function, facial and dental appearance and the quality of life [6].

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6  Occlusion and Orthodontics

5.  The ‘Extraction vs Non-Extraction’ Debate The extraction versus non-extraction debate is almost as old as the advent of orthodontic practice, and up to now, this debate remains. Again, the orthodontist must look beyond the occlusal result. Lip support is dependent on the presence of teeth. One theory is that unsuitable extractions will reduce lip support because of the retroclination of the upper incisors; whereas non-extraction treatment might result in lip fullness. Therefore, facial profile, not just occlusion, is a factor for the orthodontist when considering extraction or non-extraction treatment (Fig. 6.10). a

b

c

d

Fig. 6.10 (a–d) Shows 2 division 1 malocclusion patient before treatment with extractions. (a) Demonstrating bi-maxillary proclination. (b) Lateral view. (c) Occlusal view with upper and lower arch crowding. (d) Buccal view illustrating proclination of upper and lower teeth. (e–h) Post-­ treatment photos after extraction treatment showing good dental and facial appearance

6.  Orthodontics and Temporomandibular Disorders (TMD)

e

g

f

h

159

Fig. 6.10 (continued)

It is a difficult area to research as most studies are retrospective and consequently subject to significant bias. Current evidence indicates that correctly planned and performed orthodontic treatment including that involving premolar extractions does not have a detrimental effect on facial profile [7].

6.  Orthodontics and Temporomandibular Disorders (TMD) This is not a book on temporomandibular disorders, but a brief examination of this question is valid.

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160

6.1  Does Orthodontic Treatment Cause TMD? Based on clinical experience and the currently available evidence, it does not support any aetiological relationship. At present, there is no strong evidence to support the theory of orthodontic extractions and treatment causing TMD.  High-quality randomised clinical trials, with no bias, are needed to support the claims between malocclusion and TMD. More information with regard to aetiology, diagnosis and assessment of TMD is still required. The association between TMD and orthodontics remains contentious, but there is no evidence to support an increase in the prevalence of TMD in patients with malocclusion [8]. It is debated that certain form of orthodontic treatment can lead to TMD. One theory is that premolar extraction in orthodontic treatment can cause posterior condylar position (presumably because over retraction of the maxillary incisors can happen during space closure forcing the mandible posteriorly) [9]. An alternative theory is that first premolar extractions allow the buccal segment teeth to move forward resulting in a decrease in the vertical dimension of occlusion, which results in TMD [10].

6.2  Can Orthodontic Treatment Be Part of TMD Management? There is no evidence that occlusion is a significant aetiological factor in the development of TMD. Some TMD patients, however, return to being symptomatic after the withdrawal of successful splint therapy. For these patients, there may be justification to make some carefully prescribed changes to their occlusion. Ideally these changes will be designed on sets of articulated study models. So, very rarely the long-term management of a TMD patient will include, after certain important criteria have been met, an element of: • • • •

Tooth modification Tooth restoration Tooth movement Tooth replacement

Equilibration Restorative dentistry Orthodontics Prosthodontics

So, it can be seen that because orthodontics is one means of changing the occlusion, orthodontics will, occasionally, be one element of a treatment plan. Consequently, it is within this broad context, and only in the few cases where there is a demonstrable need for a dentist, who is competent in the management of TMD, to consult with a specialist orthodontist. As a result of this collaboration, treatment beyond the usual non-invasive and conservative TMD management may be indicated. Other text will need to be consulted for more detail on the management of TMD.

Conclusions

161

6.3  Summary • The association between orthodontics and occlusion is significant. –– Providing an improved occlusion is not the only success outcome measure by which to judge orthodontic treatment; facial appearance is important. • Satisfactory orthodontic treatment outcome (including a good occlusion) can be attained by camouflage, growth modification or orthognathic treatment. –– Extraction of teeth is required as a part of many courses of orthodontic treatment. There is no evidence that orthodontic treatment with extractions damaging facial appearance. –– Orthodontic treatment with extractions has often been blamed for causing TMD, but no statistical correlation has been found between orthodontic treatment and TMD. • The goals of orthodontic management can be multi-variable. –– On the one hand, an argument can be made for providing an optimal occlusion. –– But there is little evidence in the literature to suggest that this is always necessary. –– Lots of people do not have an optimal occlusion and do not suffer any ill effects. –– Some features of optimal occlusion do, however, provide pleasing aesthetics. • In line with the first rule of medical intervention: ‘Do No Harm’, it is wise for an orthodontist to assess, in their initial examination, whether their patient is suffering from any adverse effects to their pre-treatment occlusion. This is to avoid exacerbation of any pre-existing problems. • There is lack of evidence to support the theory that orthodontic treatment can reduce the sign and symptoms of TMD. • The aim of orthodontic treatment is to provide the patient with an appearance that. –– Is acceptable to the patient’s wishes, –– Within society’s aesthetic norms. –– Is within the adaptive capability of the patient’s tissue systems.

Conclusions There is no good reason for not doing a comprehensive examination of the patient’s articulatory system as part of the initial assessment before orthodontic treatment. Figure 6.6 provides a protocol for doing this.

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Guidelines of Good Occlusal Practice

1. The examination of the patient involves the Teeth, Periodontal Tissues and Articulatory System. 2. There is no such thing as an intrinsically bad Occlusal Contact, only an intolerable number of times to (para)function on it. 3. The patient’s occlusion should be recorded, before any treatment is started. 4. Compare the patient’s occlusion against the benchmark of Ideal Occlusion. 5. A simple, two-dimensional record of the patient’s occlusion taken before, during and after treatment is an aid to Good Occlusal Practice. 6. The Conformative Approach is the safest way of ensuring that the occlusion of a restoration does not have potentially harmful consequences. 7. Ensuring that the occlusion conforms to the patient’s pre-treatment state is a product of Examination, Design, Execution and Checking (the E.D.E.C. protocol). 8. The ‘Re-Organised Approach’ involves firstly the establishment of a ‘more ideal’ occlusion in the patient’s pre-treatment dentition or provisional restorations; and then adhering to that design using the techniques of the ‘Conformative Approach’. 9. An ideal occlusion in Removable Prosthodontics is one which reduced de-stabilising forces to a level that is within the denture’s retentive capacity. 10. The occlusal objective of orthodontic treatment is not clear, but a large discrepancy between centric occlusion and centric relation should not be an outcome of treatment. 11. An ‘orthodontic’ examination of the occlusion should include: the Dynamic Occlusion; and the Jaw Relationship in which the patient has their Centric Occlusion.

References 1. Benson PE, Da'as T, Johal A, Mandall NA, Williams AC, Baker SR, Marshman Z. Relationships between dental appearance, self-esteem, socio-economic status, and oral health-related quality of life in UK schoolchildren: a 3-year cohort study. Eur J Orthod. 2015;37(5):481–90. https:// doi.org/10.1093/ejo/cju076. 2. Johal A, Alyaqoobi I, Patel R, Cox S. The impact of orthodontic treatment on quality of life and self-esteem in adult patients. Eur J Orthod. 2015;37(3):233–7. https://doi.org/10.1093/ ejo/cju047. 3. Shaw WC, Richmond S, O'Brien KD, Brook P, Stephens CD. Quality control in orthodontics: indices of treatment need and treatment standards. Br Dent J. 1991;170(3):107–12. 4. Thiruvenkatachari B, Harrison J, Worthington H, O’Brien KD. Early orthodontic treatment for class II malocclusion reduces the chance of incisal trauma: results of a Cochrane systematic review. Am J Orthod Dentofac Orthop. 2015;148:47–59.

References

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5. Tulloch JFC, Philips C, Koch G, Proffit WR. The effect of early intervervention on skeletal pattern in class II malocclusion; a randomised contrlled trial. Am J Orthod Dentofac Orthop. 1997;111:391–400. 6. Malik OH, Waring DT, Llyod R, Misra S, Paice E. An overview of the surgical correction of dentofacial deformity. Dent Update. 2016;43:550–62. 7. Leonardi R, Annunziata A, Licciardello V, Barbato E. Soft tissue changes following the extraction of premolars in nongrowing patients with bimaxillary protrusion: a systematic review. Angle Orthod. 2010;80:211–6. 8. Luther F. Orthodontics and the temporomandibular joint: where are we now? Part 2. Functional occlusion, malocclusion, and TMD. Angle Orthod. 1998;68:305–18. 9. Gianelly AA.  Orthodontics, condylar position and temporomandibular joint status. Am J Orthod Dentofac Orthop. 1989;95:521–3. 10. Luecke PE, Johnston LE. The effect of maxillary first premolar extraction and incisor retraction on mandibular: testing the central dogma of “functional orthodontics”. Am J Orthod Dentofac Orthop. 1992;101:4–12.

7

Occlusal Considerations in Periodontics

In this chapter, we will discuss: • Whether occlusal trauma is significant in the aetiology of periodontal disease. • Whether occlusal treatment is indicated for patients suffering from periodontal disease. • Making a diagnosis of trauma from occlusion. • Tooth mobility. • Occlusal equilibration and the splinting of teeth. Periodontal disease does not directly affect the occluding surfaces of teeth, consequently some may find a section on periodontics a surprising inclusion. Trauma from the occlusion, however, has been linked with periodontal disease for many years. Karolyi published his pioneering paper, in 1901 ‘Beobachtungen uber Pyorrhoea alveolaris’ (occlusal stress and ‘alveolar pyorrhoea’) [1]. However, despite extensive research over many decades, the role of occlusion in the aetiology and pathogenesis of inflammatory periodontitis is still not completely understood [2–4].

© Springer Nature Switzerland AG 2022 S. Davies, A Guide to Good Occlusal Practice, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-79225-1_7

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7  Occlusal Considerations in Periodontics

 hy Should Trauma from Occlusion Be Considered to Have W a Role in the Aetiology of Periodontal Disease? Occlusal trauma Injury to the periodontium resulting from occlusal forces which exceed the reparative capacity of the attachment

Periodontitis The result of an interaction between a susceptible host and bacterial factors in dental plaque, which exceeds the protective mechanisms of the host.

Inflammatory Periodontal Disease: ‘Periodontitis is the result of an interaction between a susceptible host and bacterial factors in dental plaque, which exceeds the inherent protective mechanisms of the host’. Compare this definition with the one for: Occlusal Trauma (a Pathology) has been defined as ‘injury to the periodontium resulting from occlusal forces which exceed the reparative capacity of the attachment apparatus’: i.e. the tissue injury occurs because the periodontium is unable to cope with the increased stresses it experiences. Both the processes result in injury to the attachment apparatus because the periodontium is unable to cope with the pathological or physical insult, which it is enduring. It is natural, therefore, that dentists ask themselves two questions: 1. Does occlusal trauma have a role in the aetiology of periodontal disease? 2. Should occlusal treatment be considered for the patient with compromised periodontal attachment? Before attempting to answer these two questions, the different types of trauma from occlusion need to be defined, and how to diagnose occlusal trauma needs to be examined. The Aim of This Chapter Is to Answer Two Questions

Question 1. Does occlusal trauma have a role in the aetiology of periodontal disease? Question 2. Should occlusal treatment be considered for the patient with a compromised periodontal attachment?

How to Classify ‘Trauma from Occlusion’ (a Force) Historically, trauma from occlusion has been classified as either primary or secondary.

Occlusal Trauma and Periodontitis

167

Primary occlusal trauma results from excessive occlusal force applied to a tooth or to teeth with normal and healthy supporting tissues. Secondary occlusal trauma refers to changes that occur when normal or abnormal occlusal forces are applied to the attachment apparatus of a tooth or teeth with inadequate or reduced supporting tissues. Recently, the distinction between primary and secondary occlusal trauma has been challenged as meaningless since the changes that occur in the periodontium are similar irrespective of the initial level of periodontal attachment. More usefully, occlusal trauma can also be described as acute or chronic. Acute trauma from occlusion occurs following an abrupt increase in occlusal load such as occurs as a result of biting unexpectedly on a hard object. Chronic trauma from occlusion is more common and has greater clinical significance. In this chapter, occlusal trauma will mean chronic occlusal trauma.

How to Diagnose Occlusal Trauma [5] Occlusal trauma can only be diagnosed histologically. This is not possible without carrying out a block section biopsy, which is clinically impossible because it is a destructive process. When it is done, it shows increased vascularisation and permeability, hyalinisation/necrosis of the periodontal ligament, haemorrhage, thrombosis and bone resorption. Because of this, the clinician has to use clinical and radiological findings to assume that there is occlusal trauma. These include widening of periodontal ligament space, progressive tooth mobility, fremitus, occlusal disharmonies, wear facets, tooth migration, thermal sensitivity and root resorption [5].

Occlusal Trauma and Periodontitis  oes Occlusal Trauma Have a Role in the Aetiology D of Periodontal Disease? This is a key question because the answer will determine: • Whether occlusal forces influence the onset of plaque-induced inflammation. • Whether occlusal forces enhance the rate of periodontal destruction. Considerable energy has been directed at trying to determine the answer to these questions, because of the possibility that trauma from occlusion might contribute to the pathogenesis of periodontal disease. Research studies designed to examine the effects of occlusion fall into three categories: • Human cadaver investigations • Animal studies • Human clinical studies

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7  Occlusal Considerations in Periodontics

 .  Human Cadaver Investigations 1 Studies published in the 1960s and 1970s were inconclusive [6, 7]. 2.  Animal Studies (Fig. 7.1) In these studies, the variables were the level of periodontal attachment and the characteristics of an applied force, and the way in which it might be varied (see Fig. 7.2 for a summary of the results). The periodontal attachment is one of the three types: 1. A normal healthy periodontal support. 2. A healthy periodontal support but a reduced bone height. This is the experimental model equivalent to successful periodontal therapy. 3. An active plaque-induced periodontitis. The type of force that can be applied to the animal tooth is: (a) Either a jiggling force, which is produced by multi-directional displacement of a tooth in alternating buccolingual or mesio-distal directions. This is usually created in the animal by the provision of a supra-occluding onlay or by interproximal wedging. (b) Or is an orthodontic force, created by a spring and is a unilateral force that results in the deflection of the tooth away from the force.

Healthy periodontium Normal bone height

Healthy periodontium Reduced bone height

Plaque-induced periodontitis

Orthodontic force

Increased mobility Tooth movement No change in position of junctional epithelium or connective tissue attachment

Increased mobility Tooth movement No gingival inflammation No further loss of connective tissue attachment

No progression of periodontal disease

Jiggling force

Increased periodontal ligament space Some loss in crestal bone height and bone volume No loss of attachment Increased tooth mobility which is reversible upon the removal of the force

Increased periodontal ligament space Some loss in height of crestal bone height and bone volume No gingival inflammation No further loss of attachment. Increased tooth mobility which is reversible upon the removal of the force

Gradual widening of the periodontal ligament space Progressive mobility Angular bone loss

Fig. 7.1  Summary of the results from animal studies

Occlusal Trauma: Role in Aetiology of Periodontal Disease?

On

Healthy P.M. Normal Bone

169

Effect of Jiggling Forces P.M.

Mobility.

Bone.

Attachment.

Widening of PM space

Increased Mobility Reversible

Loss of Crestal bone height

No Loss of Attachment

and..... No Gingivitis Healthy P.M. Reduced Bone

Widening of PM space

Increased Mobility Reversible

Loss of Crestal bone height

No Loss of Attachment

Plaque Induced Periodontitis

Widening of PM space

Progressive Mobility

Angular Bone Loss

Loss Attachment [Bone Loss]

Conclusion: if there is Plaque Induced Periodontitis the Adaptive Capability of the PM is sufficiently reduced to induce Occlusal Trauma

Fig. 7.2  Summary of experiment jiggling forces in animal studies

Summary In 2017, a World Workshop [5] reviewing the evidence from animal studies stated: “Based on the findings of these studies, it was concluded that without plaqueinduced inflammation, occlusal trauma does not cause irreversible bone loss or loss of connective tissue attachment.” “Nonetheless, the results from animal studies suggested that occlusal trauma does not cause periodontitis, but it may be a cofactor that can accelerate the periodontal breakdown in the presence of periodontitis.” Comment • There can be very few dentists left who believe that occlusion can be a causative agent of periodontitis. But, nevertheless, it is useful to know that the evidence from studies does not support that fallacy. • It is, however, useful to gain some insight as to whether occlusal factors may influence the progress and recovery of plaque induced periodontitis.

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3.  Human Clinical Studies Few clinical studies have identified a clear relationship between trauma from the occlusion and inflammatory periodontitis in humans. There is limited evidence from human clinical studies that support the view that teeth experiencing initial occlusal discrepancies (Trauma from Occlusion) have deeper initial probing depths, have a worse prognosis and have greater mobility than those without occlusal discrepancies [8]. Tooth mobility, which may be secondary to Trauma from Occlusion, did not gain as much clinical attachment as those without mobility following periodontal treatment [9] and demonstrated significantly more clinical attachment loss during the maintenance period [10]. Multiple types of occlusal contacts, including premature contacts in centric relation, posterior protrusive contact, non-working contacts, combined working and non-working contacts, the length of slide centric relation to centric occlusion, were found to be associated with significantly deeper probing depths and a less favourable prognosis [11]. On the system level, ideal occlusion is or is not ideal for the rest of the articulatory system: the temporomandibular joints and the masticatory muscles. It has, however, been stressed that there is no such thing as an intrinsically bad occlusal contact, because the effect is a product of not only the ‘quality’ of the contact or contacts but also the frequency at which the contact or contacts are made. Also, it is widely accepted that some patients, at some times in their life, will have an articulatory system which is compromised by other factors that reduce their tolerance to a less than ideal occlusion. Factors may range from a systemic disease such as rheumatoid arthritis to the debilitating effects of chronic long-term stress. On the tooth level, an occlusion may or may not be ideal for the attachment apparatus, and the same consideration must be given to the frequency of occlusal contact, i.e. Does parafunction occur? In addition, the ability of the attachment apparatus to withstand a less than ideal occlusion may be compromised by periodontal inflammation. This leads to the second question:

Question 2  hould Occlusal Treatment Be Considered for the Patient S with Compromised Periodontal Attachment? If it is accepted that increased occlusal forces could result in a further loss of attachment for teeth with an active inflammatory periodontitis, then it follows that a

Examination

171

treatment plan aimed at preserving these teeth must address both problems. This does not mean that trauma from occlusion causes periodontitis; rather, it means that occlusal forces may exceed the ‘resistance threshold’ of a compromised attachment apparatus, thereby exacerbating a pre-existing periodontal lesion. While we know that trauma from occlusion can have an effect on the supporting tissues of the teeth, there is no evidence, at present, that trauma from occlusion is an aetiological factor in human periodontal disease. Even though occlusal trauma is not a proven aetiological factor in periodontal disease, because dentists wish to help patients keep their teeth for as long as possible in maximum health, comfort and function; it follows, therefore, that ideally dentists will ideally carry out a thorough occlusal examination on their periodontal patients. Treatment aimed at reducing occlusal forces so that they fall within the adaptive capabilities of each patient’s dental attachment apparatus might benefit those patients with periodontitis or at future risk of it. It can be argued, of course, that by resolving the periodontitis the adaptive capability of the periodontium is increased and so may be able to resist the trauma from occlusion. That is a chance the clinician might wish to take.

Examination Clinical Diagnosis of Trauma from Occlusion  Increased tooth mobility is not always indicative of trauma from occlusion. It is important, however, that hypermobility, which does occur as a result of trauma from occlusion, is detected in patients with reduced periodontal attachment. The reason for this is that trauma from occlusion may accelerate further reduction in attachment in a patient with active periodontitis. A clinical diagnosis of occlusal trauma can only be confirmed where progressive mobility can be identified through a series of repeated measurements over an extended period. This means that simple but reliable monitoring needs to be undertaken. A simple monitoring protocol is needed (Fig. 7.3). The common clinical signs of occlusal trauma are: • Increasing tooth mobility and migration or drifting (Fig. 7.4) • Fremitus • Persistent discomfort on eating The common radiographic signs of occlusal trauma are (Fig. 7.5): • Discontinuity and thickening of lamina dura • Widening of periodontal ligament space (‘funnelling or saucerisation’) • Radiolucency and condensation of alveolar bone/or root resorption

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Fig. 7.3  Trauma from occlusion: monitoring examination sheet

Date First

CI1

CI1I

CIIII

Widening or funneling of

Root

Fig. 7.4  UR 2 (12) has migrated distally. Examination of the dynamic occlusal contacts of this tooth indicates that the marked wear facet fits closely against those of LR2 and LR1 (42, 41) during a right lateral excursion of the mandible

Occlusal Trauma

173

Fig. 7.5  All radiographs show signs of occlusal trauma to differing degrees

Tooth Mobility Conventional methods for measuring tooth mobility are based on the application of a force to the crown of the tooth to assess the degree of tooth movement in the horizontal and vertical directions. Pathological mobility is defined as horizontal or vertical displacement of the tooth beyond its physiological boundaries. Normal physiological movement is thought to vary between 10 μm and 150 μm and would not be detectable on clinical examination. Clinically detectable mobility indicates some change in the periodontal tissues (i.e. it is pathological), and the cause of the mobility needs to be diagnosed. Tooth mobility can be recorded using Miller’s Index: I—up to 1 mm of movement in a horizontal direction II—greater than 1 mm of movement in a horizontal direction III—excessive horizontal movement and vertical movement

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How Can Tooth Mobility Be Measured? Manual evaluation of mobility is best carried out clinically using the handles of two instruments to move the teeth buccally and lingually. Fremitus is the movement of a tooth or teeth subjected to functional occlusal forces; this can be assessed by palpating the buccal aspect of several teeth as the patient taps up and down. Periodontometers was a research tool used in the 1950s and 1960s to standardise the measurement of even minor tooth displacement. To date, this instrument has been used in a few clinical studies and has limited practical use. Periotest® was produced in Germany in the late 1980s to provide a more reliable method for determining tooth mobility. It is designed to measure the reaction of the periodontium to a defined percussion, delivered by a tapping instrument. Again, this is of limited use in general dental practice.

Tooth Drifting or Migration Independent of the state of the supporting tissues of a tooth, if it has moved its position in the mouth, then some force has been responsible for pushing or pulling it. Clearly that force may be extrinsic such as can be seen in pencil chewers. Secondarily, a soft tissue force may be responsible as with tongue thrusting or lip position (Fig.  7.6). However, the force may be from an occlusal contact especially parafunction. A frequently encountered scenario is drifting of an upper lateral incisor. This is a common reason for referral of an adult patient to an orthodontist; a referral made usually at the patient’s request, with the aim of restoring their appearance. It is important to discover the cause of the drifting before considering any treatment. a

b

Fig. 7.6  Initial examination of the UR 1 (11), in (a) may suggest an occlusal cause of the drifting; however, as is shown in (b) the reason is the relationship with the lower lip

Treatment Considerations

175

Discomfort Upon Eating Tooth mobility can affect the patient by causing discomfort when eating. This is a further measure of tooth mobility. It will have a direct influence on treatment planning.

 reatment (Occlusal Considerations in the Treatment T of Periodontitis) Equilibration Occlusal equilibration is the modification of the occlusal contacts of teeth to produce a more ideal occlusion.

I s There a Need for Occlusal Equilibration in the Periodontally Compromised Dentition? The 2017 World Workshop [5] reviewed the literature [12–15] stated that ‘Collectively, these clinical studies demonstrated the added benefit of occlusal therapy in the management of periodontal disease, but they do not provide strong evidence to support routine occlusal therapy’.

Equilibrating Mobile Teeth In a patient with mobile teeth, it may be necessary to temporarily stabilise those teeth before equilibration is possible (Fig. 7.7a, b). If a tooth is mobile, it is very difficult if not impossible to effectively modify its shape with the aim of reducing the occlusal forces acting upon it (equilibration). a

b

Fig. 7.7 (a) The lower anteriors have been temporarily immobilised by a labial splint in order to be able to identify the premature contact. (b) It was subsequently equilibrated in order to reduce the trauma from occlusion. (Note: The adjustment to the lower anteriors was only to the labial aspect of the incisal edges: the exposed dentine was already present!)

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Equilibration and Periodontal Splinting (Fig. 7.8) Whether occlusal equilibration is indicated will depend upon: • Whether the inflammatory periodontitis has been treated successfully. If there is an inflammatory periodontal process, this should be treated initially. Subsequently, when the periodontal condition is stable, occlusal therapy may be necessary for some patients and could involve either occlusal equilibration or splinting. • The radiographic appearance of the periodontal support. Occlusal equilibration is considered an effective form of therapy for teeth with increased mobility which has developed together with an increase in the width of the periodontal ligament (PDL). Reducing the occlusal interference on a tooth with normal bone support will normalise the width and height of the PDL. Eliminating any occlusal interferences for a tooth which has a reduced bone height as a result of periodontal disease will result in bone formation and remodelling of the alveolus only to the pre-trauma level. In contrast, if the hypermobile tooth has reduced bone height but normal periodontal ligament width, then elimination of occlusal trauma will not alter the mobility of the tooth. In this situation occlusal equilibration is only indicated if the patient is complaining of loss of function or discomfort. In 1989, the World Workshop of the American Academy of Periodontology [16] issued some guidelines for situations when occlusal equilibration may be indicated: • When there are occlusal contact relationships that cause trauma to the periodontium, joints, muscles or soft tissues • As an aid to splint therapy More recently, a systematic review [17] concluded: ‘The selected studies suggest an association between occlusal adjustment and an improvement in periodontal parameters’. But they ‘suggested the need for new trials of a higher quality’ to improve ‘methodological issues’. ‘There is insufficient evidence at present to presume that occlusal adjustment is necessary to reduce the progression of periodontal disease’. In the absence of a conclusive evidence base, the decision in respect of occlusal therapy in periodontal treatment will be one for the clinician to make. Some will feel that because trauma from occlusion is not a cause of periodontal disease, reducing the frequency, direction or magnitude of that force has no place in the management of periodontitis. Others will look to the fact that the definition of occlusal trauma involves a non-pathogen breakdown in periodontal support and the limited evidence that occlusal trauma may affect the progression of periodontal disease as sufficient justification of an intervention. To return to the systematic review [17]: ‘Although it is still not possible to determine the role of occlusal adjustment in periodontal treatment, adverse effects have not been related to occlusal adjustment. This means that the decision made by clinicians whether or not to use occlusal adjustment in conjunction with periodontal therapy hinges upon clinical evaluation, patient comfort, and tooth function’.

Treatment Considerations

Clinical features

Radiographic features

Increased mobility

Increased width of PDL

177

Treatment required in addition to periodontal therapy

Treatment outcome

Occlusal equilibration

Normalises PDL width.

Occlusal equilibration

Bone fill of angular defect. Bone level stabilised. Normal width PDL

Normal bone height Increased mobility

Increased width of PDL Reduced bone height

Increased mobility Patient NOT functioning comfortably

Normal width of PDL

Increased mobility Patient functioning comfortably

Normal width of PDL

Reduced bone height

Reduced bone height

Occlusal equilibration ± splinting

No occlusal adjustment required

Patient’s comfort and function may improve. (This is not periodontal therapy, but an adjunct to it) No further deterioration

Fig. 7.8  Indications for occlusal treatment and splinting

Summary: Trauma from Occlusion in the Aetiology and Treatment of Periodontal Disease

• There is no scientific evidence to show that trauma from occlusion causes gingivitis or periodontitis or accelerates the progression of gingivitis to periodontitis. • The periodontal ligament physiologically adapts to increased occlusal loading by resorption of the alveolar crestal bone resulting in increased tooth mobility. This is occlusal trauma and is reversible if the occlusal force is reduced. • Occlusal trauma may be an exacerbating factor that can increase the rate of progression of an existing periodontal disease. • There is a place for occlusal therapy in the management of periodontitis, especially when related to the patient’s comfort and function. • Occlusal therapy is not a substitute for conventional methods of resolving plaque-induced inflammation.

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If teeth are to be equilibrated, it must be done with careful planning and great care: it is not spot grinding, which would result in the destruction of tooth morphology. The ideal technique, involving the ‘mock’ equilibration of an accurately mounted set of articulated models, is done first to confirm the viability of the exercise without damaging the teeth. This is described earlier in this book. Equilibration All these stages may be necessary

Successful stabilisation splint therapy

Study models mounted to CR on asemiadjustable articulator

Mock equilibration on duplicated study models

before equilibration of the patient’s teeth can be completed

Splinting When should teeth be splinted together in the patient with reduced periodontal support? (Fig. 7.8). The World Workshop in Clinical Periodontics [16] also, outlined some indications for splinting, not only restricted to patients with reduced periodontal support: • To stabilise teeth with increased mobility that have not responded to occlusal adjustment and periodontal treatment. • To prevent tipping or drifting of teeth and the overeruption of unopposed teeth. • To stabilise teeth after orthodontic treatment. • To stabilise teeth following acute trauma. There are two situations in which splinting may be beneficial: • Where tooth mobility is progressive with increased periodontal ligament width and reduced bone height, then splinting is indicated as part of periodontal therapy. • When patient comfort and function will be improved by splinting, then it is indicated, as an adjunct to periodontal therapy. This means that if periodontal treatment results in a stable periodontal condition which is comfortable, splinting is not needed. Probably the most important benefit of reducing the mobility of periodontally compromised teeth by splinting is to facilitate daily plaque removal by a compliant

Splinting

179

patient, and root surface debridement by their dentist or hygienist. It achieves this by eliminating the discomfort associated with applying pressure to hypermobile teeth. There is, of course, a benefit to the patient that the discomfort of eating with hypermobile teeth is also reduced. Because their teeth are much more comfortable and feel much firmer, there is a danger in splinting. That is that the patient can believe that their teeth are better supported by bone. In reality, there is no more bone that there was before splinting. Patients must understand that the need for a very high level of oral hygiene is as important as it was before splinting. The splinting of teeth does not improve the bone support, it just makes it easier to prevent further loss. The other problem that some patients believe that the apparent firmness of their teeth (often lower incisors) means that they can bite into anything. I remember a patient returning after only 3 days following the provision of a cast metal splint to stabilise her lower anterior teeth, because one tooth had debonded from that splint. She complained that ‘it was only a water biscuit’: probably the hardest biscuit in existence! Re-fixing a tooth to an existing splint is difficult and is never as a robust attachment as the original. There are various techniques to splint hypermobile teeth: 1. Fibre systems 2. Orthodontic wire 3. Cast metal adhesive splints 1. Fibre Splints (if it is a definitive splint, it is placed on the labial surface) As with all adhesive techniques, moisture isolation is very important, the best way of achieving this is by using a rubber dam (Fig. 7.9a). Next the fibre is carefully adapted and adhered to the cleaned and etched lingual surfaces of the teeth (Fig. 7.9b–d). 2. Orthodontic Wire Splint (Fig. 7.10a, b) It may be necessary to first place a temporary labial splint. This is to facilitate an equilibration of the teeth, in order to eliminate a heavy occlusal contact (see Fig. 7.7) and to stabilise the teeth. This keeps them in a ‘neutral position’ during the placement of the orthodontic wire splint. The clinician must do whatever is needed to ensure that there are no premature or heavy occlusal contact against any of the teeth after the definitive splint has been fitted. 3. Cast Metal Splints These splints require an impression because they are made by the Dental Technician. In order to ensure that it will be possible to fit them under a rubber dam, it is advisable to prepare them under the rubber dam. It is usually possible to also take the elastomeric impression needed under the same rubber dam; if an impression tray is significantly modified.

180

a

c

7  Occlusal Considerations in Periodontics

b

d

Fig. 7.9 (a) As with all adhesive techniques, moisture isolation is very important; the best way of achieving this is by using a rubber dam. (b, c) The Fibre is carefully adapted and adhered to the cleaned and etched lingual surfaces of the teeth. (d) Completed Fibre (Ribbond ©) Splint

a

b

Fig. 7.10 (a) Orthodontic wire splint placed on lingual surface. (b) Fine splint placed on labial surface. Temporary placement to stabilise teeth

Case Histories

a

181

b

c

Fig. 7.11  (a) shows the prepared teeth, after placement of a split rubber dam, and a temporary labial fibre splint. (b) shows the gingivae, at the fit appointment, immediately after removal of the rubber dam. (c) is at 2-week review; note the improvement in gingival health. Splinting has facilitated cleaning

a

b

Fig. 7.12 (a) Splinting of teeth using a cast metal splint that carries a pontic and has been successful for 40 years. (b) It has enabled the patient to wear a lower partial denture to restore the posterior occlusion

Case Histories Case 1. Useful in the Long Term? If the occlusal forces are well monitored and controlled, periodontal splinting can enable the motivated patient to keep their teeth with compromised periodontal support for a long time (Fig. 7.12a, b).

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 ase 2: Occlusal Analysis in a Periodontal Patient: Use of Mounted C Study Models Clinical Findings UR1, UR2, LL5: Class III mobile, with pus from gingival margins. Occlusal analysis • Centric occlusion not in centric relation. • Premature contact in CR between UL7 and LL7. • Fremitus between UL1 and LL1 in C.O. Treatment Plan 1. Usual periodontal therapy. 2. Occlusal therapy. (a) Mounted study models, mounted in centric relation and centric occlusion. (b) Equilibration of those models to see whether it will be possible to equilibrate the patient’s dentition to provide: • Centric occlusion in centric relation. • Atraumatic dynamic occlusion. • Elimination of incline contacts.  esults of Occlusal Analysis R See Fig. 7.13 for comparison of Clinical Occlusal Record (Occlusal Sketch) and Static (Blue) and Dynamic (Red) Centric Occlusion marked on mounted models. Explanations Analysis 1. On the models, the only incisors contacting are UR1 and LR1. Confirmed by mark on solid model, whereas in mouth the mobility of UR1 allows all other incisors to contact. Diagnosis: UR1 is in Traumatic static Occlusion. 2. No red mark on UR2 in mouth, whereas in the mouth there was because in the mouth UR2 is mobile. Diagnosis: UR2 is in Traumatic dynamic Occlusion. 3. LL5: No red mark in mouth because it is mobile. Diagnosis: Traumatic dynamic Occlusion of LL5 is confirmed. 4. LR6: There is a red mark on the buccal aspect of disto-buccal cusp, in the mouth not on the mounted models. Explanation: Semi-adjustable articulators cannot reliably replicate immediate non-progressive side shift (Bennett movement).

Conclusion In this case, occlusal analysis in the mouth and on mounted models will have helped to formulate an appropriate Treatment Plan for this patient who has some teeth with severely compromised periodontal support.

Case Histories

no red mark

183

2

2

1

1

Only 1 mark

4

4

No red mark

red mark

3 red mark

3 no red mark

Fig. 7.13  Comparison of patient’s occlusion (recorded on an Occlusal Sketch) against model occlusion. Note the 4 differences

 ase 3: Reduction of Occlusal Forces Might Facilitate C Tooth Survival History (When Patient Presented in 1989) • 34-year-old female patient • Hypermobile UL1. • She has been advised by at a Dental Hospital that it will be difficult to avoid an upper clearance (Fig. 7.14).

Examination Finding 1. Healthy looking gingivae 2. Deep pockets 3. Radiographs show significant bone loss (Fig. 7.15) 4. Previous dentist has perforated furcation of UR7 during attempted RCT 5. Occlusal analysis (a) CO not in CR (b) Premature contact between UR8 and LR7 (c) Non-working side interference on RHS (d) Poor posterior support

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Fig. 7.14  Opinion from secondary care advising poor prognosis for upper dentition (dated 1989)

Fig. 7.15  Radiograph taken 1989

Treatment Occlusal 1. Equilibrate to provide CO in CR. 2. So, eliminating premature contact between UR8 and LR7. 3. and NWS interference on RHS, 4. Provide posterior support. UR7 • Despite attempted amalgam repair and good maintenance by patient (see Fig. 7.16a–c), eventually this tooth had to be sectioned. A provisional restoration of the palatal root and an implant at UR 6 space were provided (see Fig. 7.17).

 utcome Assessed in 2017: (See Fig. 7.18a, b) O • The patient has not lost any teeth since the buccal roots of UR7. • There is no hyper-mobility. • There has been no discernible loss of periodontal support, including at UR8.

Case Histories

a

185

b

c

Fig. 7.16 (a–c) Perforation of Furcation area during RCT of UR7. Despite attempted Amalgam Repair and good maintenance by patient, this tooth had to be sectioned. See Fig. 7.18 Fig. 7.17  Taken in 2011. Compare bone levels at UR8 with those present in 1989

a

b

Fig. 7.18 (a) UR sextant (taken 2017). (b) UL sextant (taken 2017)

Case 4: ‘Perio/Endo’ Lesion LR6  resented in May 2011 P • Compromised bone support for distal root of LR6. • Good bone support at mesial root of LR6.

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Treatment (See Fig. 7.19a–e) May 2011 Separation of roots Extraction of distal root Root canal treatment of mesial root May 2012 Direct composite provisional restoration of mesial root Nov 2019 Definitive restoration of mesial root with careful adjustment of occlusion, using Shimstock. a

c

b

d

e

Shimstock

Fig. 7.19 (a) (May 2011) LR6 with Perio/Endo Lesion affecting distal root. Mesial root is supported by healthy adequate bone. (b) Root canal treatment of mesial root (June 2011). (c) Provisional restoration of mesial root of LR6 with direct composite (May 2012). (d) Definitive restoration of mesial root of LR6 (Nov 2014) with cast gold crown. (e) Occlusion of this crown on this reduced periodontal support is best checked by the use of Shimstock on the other side

Summary

a

187

b

Fig. 7.20 (a) (2008) After root resections at LR6, LR7 and UR7. (b) (2013) After restoration of the LHS with implant supported crowns

 ase 5. Use of Hemisection of Two Lower Molars to Avoid Use C of Implants on the RHS Presented • Loss of posterior occlusion on LHS. • Very compromised periodontal support on the RHS. Treatment (See Fig. 7.20a, b) 1. Root resections and endodontics of several molars as provisional restoration of RHS in 2008. 2. Provision of posterior occlusion by implant supported crowns on LHS in 2010. 3. Review in 2013 determined no need to replace compromised molars on RHS.

Summary • The periodontal support for human teeth is a complex structure, capable of a remarkable adaptation to noxious stimuli, including pathogens and adverse load. • Overall, in the presence of occlusal trauma, occlusal therapy may slow the progression of periodontitis and improve the prognosis. • Dentist should examine and record the occlusion of their patients with compromised periodontal attachment, before and after treatment. • The occlusion of periodontally compromised teeth should be designed to reduce the forces to be within the adaptive capabilities of the reduced periodontal attachment.

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Guidelines of Good Occlusal Practice

1. The examination of the patient involves the Teeth, Periodontal Tissues and Articulatory System. 2. There is no such thing as an intrinsically bad Occlusal Contact, only an intolerable number of times to (para)function on it. 3. The patient’s occlusion should be recorded, before any treatment is started. 4. Compare the patient’s occlusion against the benchmark of Ideal Occlusion. 5. A simple, two-dimensional record of the patient’s occlusion taken before, during and after treatment is an aid to Good Occlusal Practice. 6. The Conformative Approach is the safest way of ensuring that the occlusion of a restoration does not have potentially harmful consequences. 7. Ensuring that the occlusion conforms to the patient’s pre-treatment state is a product of Examination, Design, Execution and Checking (the E.D.E.C. protocol). 8. The ‘Re-Organised Approach’ involves firstly the establishment of a ‘more ideal’ occlusion in the patient’s pre-treatment dentition or provisional restorations; and then adhering to that design using the techniques of the ‘Conformative Approach’. 9. An ideal occlusion in Removable Prosthodontics is one which reduced de-stabilising forces to a level that is within the denture’s retentive capacity. 10. The occlusal objective of orthodontic treatment is not clear, but a large discrepancy between centric occlusion and centric relation should not be an outcome of treatment. 11. An ‘orthodontic’ examination of the occlusion should include: the Dynamic Occlusion; and the Jaw Relationship in which the patient has their Centric Occlusion. 12. The occlusion of periodontally compromised teeth should be designed to reduce the forces to be within the adaptive capabilities of the damaged periodontia.

References 1. Karolyi M. Beobachtungen uber Pyorrhoea alveolaris. Ost-Unt Vjschr Zahnheilk. 1901;17:279. 2. Paesani D. Bruxism theory and practice. Chicago: Quintessence Publishing Co., Inc; 2010. 3. Lobbezoo F, Ahlberg J, Manfredini D, et al. Are bruxism and the bite causally related? J Oral Rehabil. 2012;39(7):489–501. https://doi.org/10.1111/j.1365-­2842.2012.02298.x. 4. Fernandes G, Franco AL, Goncalves DA, et al. Temporomandibular disorders, sleep bruxism, and primary headaches are mutually associated. J Orofac Pain. 2013;27(1):14–20. https://doi. org/10.11607/jop.921.

References

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5. Fan J, Caton JG.  Occlusal trauma and excessive occlusal forces: narrative review, case definitions, and diagnostic considerations 2 0 1 7 WORLD WORKSHOP.  J Periodontol. 2018;89(Suppl 1):S214–22. 6. Glickman I, Smulow JB. Alteration in the pathway of gingival inflammation into the underlying tissues induced by excessive occlusal forces. J Periodontol. 1962;33:8–13. 7. Waerhaug J. The infrabony pocket and its relationship to trauma from occlusion and subgingival plaque. J Periodontol. 1979;50:355–65. 8. Nunn ME, Harrel SK.  The effect of occlusal discrepancies on periodontitis. J Periodontol. 2001;72(4):485–94. 9. Fleszar TJ, Knowles JW, Morrison EC, Burgett FG, Nissle RR, Ramfjord SP. Tooth mobility and periodontal therapy. J Clin Periodontol. 1980;7:495–505. 10. Wang HL, Burgett FG, Shyr Y, Ramfjord S. The influence of molar furcation involvement and mobility on future clinical periodontal attachment loss. J Periodontol. 1994;65:25–9. 11. Harrel SK, Nunn ME.  The association of occlusal contacts with the presence of increased periodontal probing depth. J Clin Periodontol. 2009;36:1035–42. 12. Burgett FG, Ramfjord SP, Nissle RR, Morrison EC, Charbeneau TD, Caffesse RG. A randomized trial of occlusal adjustment in the treatment of periodontitis patients. J Clin Periodontol. 1992;19:381–7. 13. McGuire MK, Nunn ME. Prognosis versus actual outcome. II. The effectiveness of clinical parameters in developing an accurate prognosis. J Periodontol. 1996;67:658–65. 14. McGuire MK, Nunn ME. Prognosis versus actual outcome. III. The effectiveness of clinical parameters in accurately predicting tooth survival. J Periodontol. 1996;67:666–74. 15. Harrel SK, Nunn ME. The effect of occlusal discrepancies on periodontitis. II. Relationship of occlusal treatment to the progression of periodontal disease. J Periodontol. 2001;72:495–505. 16. Proceedings of the World Workshop in Clinical Periodontics. Chicago. Consensus report: Occlusal Trauma. The American Academy of Periodontology 1989: III- 1/III-23. 17. Foz AM, et al. Occlusal adjustment associated with periodontal therapy— a systematic review. J Dent. 2012;40:1025–103.

8

Good Occlusal Practice in Children’s Dentistry

The difference between paediatric dentistry and most other branches of dentistry is that, in the child, the occlusion is constantly changing. Consequently ‘Good Occlusal Practice’ in children is a matter of making the right clinical decisions for the future occlusion. The clinician needs to have an awareness and be able to predict the influence that different treatment options and skeletal growth will have on the occlusion when the child’s development is complete.

In this chapter, we will discuss Good occlusal practice in Children’s Dentistry. • Decisions need to be made about the patient’s Future Occlusion.

Introduction When considering the child’s occlusion as opposed to that of the adult, the important difference is that the child’s occlusion changes, with skeletal growth. The key objective in the child patient is, therefore, to increase the chances of an optimal occlusion by predicting the effect of a clinical situation on their future occlusion. Therefore, the objectives in management are: 1. Preservation, where possible, of the primary dentition with good preventive care [1]. 2. Identification of unusual patterns of growth and/or eruption. 3. Timely referral for specialist advice/treatment if required.

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This chapter will present a range of common clinical presentations in the child patient which, when well-managed, will result in the most favourable outcome for the future occlusion.

1.  Premature Loss of Primary Teeth The primary dentition is normally fully established at 3 years of age (Fig.  8.1a) when 40% of children exhibit spacing [2]. A combined spacing of 6mm or more in either arch of the primary dentition is considered optimum to reduce the likelihood of crowding in the permanent dentition [3]. The primary dentition is important as it provides guidance for the permanent teeth into the correct position. If primary teeth are lost early, there will be a consequence for the permanent dentition and developing occlusion. Whenever there is a planned loss of a primary tooth, consideration should be given as to whether a balancing extraction is needed to prevent a centreline shift and disruption of the developing occlusion; although this will depend upon the age of the patient and the tooth that has been lost prematurely:

1.1  Primary Incisor There is no requirement to balance or compensate the loss of a primary incisor. Typically, primary incisor teeth become more spaced prior as a result of jaw growth, and therefore, space closure following enforced or planned primary incisor loss is unlikely to occur.

1.2  Primary Canine Where a primary canine is to be lost early, then a balancing extraction of the contralateral canine is recommended. Unilateral loss in all but spaced dentitions will cause a shift in the centreline in the direction of space, thereby presenting a challenge for later correction.

1.3  First Primary Molar In a crowded dentition, a balancing extraction may be beneficial and should be considered; however, there is no indication to compensate in the opposing arch.

1.4  Second Primary Molar 1. There is no requirement to balance the loss of a second primary molar as its loss will have no effect on the centreline. 2. If the second primary molar is lost early, there may be a mesial shift and tilting of the adjacent first permanent molar. This will leave less space available for the erupting permanent teeth, typically resulting in crowding with exclusion of the

1.  Premature Loss of Primary Teeth

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a

b

Fig. 8.1 (a) Primary dentition in a 5-year old [twin of child in figure b] with minimal spacing and well-aligned arched in the primary dentition. (b) Primary dentition in a 5-year old [twin of child in figure a] with cross bite on the left side and midline shift due to prolonged use of pacifier in the primary dentition

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second premolars from the dental arch. A space maintainer to preserve the space that was occupied by the second primary molar should be considered to prevent this adverse movement of the first permanent molars. When primary molars in three quadrants need to be extracted, then the equivalent molar in the fourth quadrant should be extracted, in order to keep the development and drift symmetrical in each quadrant.

Space Maintainers The appropriate utilisation of space maintenance in the primary dentition following premature loss of primary teeth can prevent a less than ideal occlusion in the permanent dentition. They are most useful when the first primary molar is lost in a very crowded arch or following the loss of the second primary molar (Fig. 8.2a, b).

a

b

Fig. 8.2 (a) Space maintenance in the primary molar region with a lingual arch space maintainer to hold LR6  in position and thereby maintain space for LR5, following early loss of LLE. (b) Space maintainer in the primary molar region with a band and loop space maintainer to maintain space for LL4 following early loss of LLD

2. Infra-occlusion

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2.  Infra-occlusion A ‘submerging’ primary molar lies below the occlusal plane as a consequence of ankylosis; this can occur in 8–14% of children [4]. The term ‘infra-occluding’ is preferred, as there is no active submergence of the tooth involved. The adjacent teeth are erupting normally whilst the ankylosed primary tooth remains static, resulting in infra-occlusion. If the permanent successor is present, the effect is usually transient, and the tooth is likely to exfoliate at or about the normal age. However, it may be an indicator that the permanent successor is missing, and this should be investigated radiographically. The significance of the ‘infra-occluded tooth’ is that there is both loss of occlusal contact with the opposing teeth and approximal contact with two adjacent teeth. In particular, there are adverse consequences where loss of contact with the adjacent first permanent molar allows it to tilt and drift mesially. This will impact on the developing occlusion between the first permanent molars and will reduce the space in the arch. When the infra-occluding primary tooth is seen to be disrupting the occlusion, then extraction of the primary unit is indicated; as long as the permanent successor is present there. Hopefully this should encourage eruption of the premolar tooth, so stabilising the occlusion. If the permanent successor is missing and the decision to preserve the submerged primary tooth is made, then restoration of the tooth with an onlay can restore the occlusal and approximal contacts. This will prevent adverse tooth movements and loss of space (Fig. 8.3).

Fig. 8.3  Orthopantomogram in a 5-year old which shows: Infra-occlusion LRD, LLD. Impaction of UR6, UL6 and resorption of URE, ULE requiring close monitoring. Developmental absence of LR5, LR4, LL4, LL5 and likely absence of UR5, UR4 requiring close monitoring

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3.  Retained Primary Teeth Primary teeth retention can be due to: • Missing or ectopic successors • Genetic or syndromal factors • Trauma • Ankylosis • Obstructions, e.g. supernumerary teeth and dental crowding A dentist needs to be aware of the normal erupting times of the permanent teeth (Fig. 8.4a, b). As a general rule, contralateral teeth will erupt within 6 months of each other. If a patient does not broadly follow these sequences, they should be investigated radiographically. a PRIMARY TEETH

Visible on Radiograph

Eruption

Incisors

Birth

6-9 months

Canines

Birth

18 months

1st Molars

Birth

12 months

2nd Molars

Birth

24 months

PERMANENT TEETH

Visible on Radiograph

Eruption

b

Central incisors

6 months

6-8 years

Lateral incisors

9-12 months

7-9 years

Canines-Mand

6 months

9-10 years

Canines-Max

6 months

11-12 years

Premolars

2-3 years

10-12 years

First molars

Birth

6 years

Second molars

4 years

11-13 years

Fig. 8.4 (a) Eruption times of primary teeth. (b) Eruption times of permanent teeth

4. Habits

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a

b

Fig. 8.5 (a) Infra-occlusion—treatment with composite Onlays LRD, LLD. (b) Infra-occlusion— treatment with composite Onlays LRD, LLD

The absence of permanent successors requires an orthodontic assessment to aid treatment planning. Following this assessment, if the decision is to maintain the primary tooth, then restoration is indicated because with good dental, the primary tooth can be preserved well into adulthood (Fig. 8.5a, b). In cases where the permanent successor is present and/or ectopic, then extraction of the retained primary tooth is often advisable as it can encourage eruption of the delayed permanent tooth avoiding deflection from its eruption path. Pathway deflection of the successor permanent teeth can result in crowding, crossbite or displacement.

4.  Habits It is common for babies and toddlers to have a sucking habit, either with dummies or digits. Where the habit is prolonged and persistent, it will result in an abnormal occlusion. Typically, this is seen as an anterior open bite, because the habit will prevent the normal eruption of the incisor teeth and the over-eruption of the posterior teeth [5]. Sucking habits can also cause posterior crossbites as a consequence of the tongue positioning towards the floor of the mouth and compressive narrowing of the upper arch (compare Fig. 8.1a, b). Other occlusal changes brought about by prolonged sucking habits are proclination of the maxillary incisors and retroclination of the mandibular incisors, resulting in an increased overjet and reduction in the overbite.

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a

b

Fig. 8.6 (a) Habit effect—Unilateral increased overjet in a 12-year old due to continued/sustained thumb sucking habit. (b) Habit breaking appliance to deter thumb sucking

As they become older, most children will naturally stop their sucking habit. If it is stopped by the time the permanent incisors begin to erupt, there will be no adverse effects to the permanent occlusion. However, if the habit persists beyond this time, then intervention may be required to prevent a lasting occlusal abnormality in the permanent teeth (Fig. 8.6a, b) [6].

5.  Ectopic First Permanent Molar As it erupts, the first permanent molar is guided by the distal surface of the second primary molar into position in the arch. In approximately 2–6% of children, the erupting first permanent molar impacts against the second primary molar, causing resorption of its distal root. This is more commonly seen in the maxillary arch and is one indicator of a crowded dentition. In some instances, it can result in the child complaining of symptoms such as mobility, pain or infection of the primary molar. Asymptomatic impaction can be detected by routine clinical examination and confirmed by radiographic examination (Figs. 8.3 and 8.7). Early treatment to disimpact the erupting first permanent molar is essential. If left, the first permanent molar will continue to resorb the primary tooth and then erupt with a rotation, resulting in mesial tipping and a less than ideal occlusion. The resulting space loss will, also, increase the likelihood of impaction for the second premolar tooth. Where disimpaction is not possible and the primary molar has to be extracted, then orthodontic treatment may be needed to upright and distalise the first permanent molar into its correct position and relationship with adjacent and opposing teeth.

6.  Premature Loss of First Permanent Molars

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Fig. 8.7  Orthopantomogram in a 7-year old—Ectopic first permanent molar (LL6) causing pressure resorption of primary molar (LLE) root

6.  Premature Loss of First Permanent Molars Where there is caries or hypomineralisation of first permanent molars, consideration must be given to their long-term prognosis. This is because early extraction of first permanent molars with a poor long-term prognosis can result in a significantly better outcome for the child, than loss of these teeth later in life. Planned early loss allows successful eruption of the second permanent molars into the position of the lost first permanent molars, followed by the eruption of third into the second molar position. This is a very good example of the principle that the treatment plan is aimed at optimising the future occlusion, rather than solely addressing the presenting condition of the needs of a tooth or teeth. Although the natural instinct of the dentist may be to restore and retain these significant teeth, an objective assessment of the long-­ term prognosis is key to the best treatment for the child patient. ‘Restoration at all costs’ is not always the best option where there is extensive caries/post-eruptive breakdown due to hypomineralisation in a first permanent molar of a child under 10 years of age (Fig. 8.8).

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Fig. 8.8  Orthopantomogram—poor prognosis first permanent molars

Restorative decisions Consider: • Long-term prognosis • Developing occlusion Treatment planning in these cases is not easy; a number of factors need to be considered. Ideally, treatment decisions will involve both paediatric and orthodontist specialists. The optimal treatment will depend upon: • Extent of the caries/enamel hypomineralisation • Presence of all other unerupted permanent teeth • Developmental stage of second permanent molars • Degree of crowding in the premolar regions • Existing incisal and molar relationships • Patient motivation In addition, careful consideration should be given to the need for balancing or compensating extractions of first permanent molars, with the aim of preserving occlusal relationships and arch symmetry in the developing dentition [7].

7.  Firm Maxillary Primary Canine

201

As discussed, the ideal time for loss of first permanent molars is between 8 and 11 years, when the bifurcation of second molars is beginning to calcify. This is especially true in the mandible. Mesial movement of second molars is more predictable in the maxillary arch. The desired outcome is for the erupting second molar to replace the missing first molar by moving forward and re-establishing the molar relationship.

6.1  Balancing Extractions Routine balancing extraction of a sound molar to preserve centreline is not indicated.

6.2  Compensating Extractions • Extraction of a maxillary molar does not require compensation by extraction of the opposing mandibular molar. • Extraction of a mandibular molar: a compensating extraction of the maxillary molar is indicated and it is likely to be unopposed for a long time. This is to prevent its over-eruption. If the maxillary first molar does over-erupt, it can interfere with the desired forward movement of the mandibular second molar. This is more likely to occur in class 1 molar relationship.

6.3  To Refer or Not to Refer? If extractions are indicated, it is never easy to know when a specialist opinion is advisable: • Class 1: The decision depends on the number of carious teeth, degree of crowding and balancing/compensating considerations. • Class 2: Space will be needed in the maxillary arch to correct a less than ideal incisor occlusion and reduce the overjet. The orthodontist may consider stabilising the maxillary first permanent molars until the second molars have erupted. Then second molars can be used for anchorage when the first molars have been extracted and the resulting space used for overjet reduction. • Class 3: Space is more likely to be needed in the lower arch to correct a less than ideal occlusion. If mandibular first molars are lost before second molars erupt, the second molars will drift mesially and occupy the space. In Class 3 molar relation cases, this may result in the need to extract a premolar unit to re-gain this space.

7.  Firm Maxillary Primary Canine Permanent maxillary canines usually erupt at 11–12 years of age. Development of the canine starts high in the maxilla. Consequently, the developing tooth has a long path of eruption, to an ideal position that is buccal and mesial to the primary canine.

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Because of this long eruption path, the maxillary canine tooth is the most common one, after third molars, to become impacted. Deviation from the normal eruption path can occur in either a buccal or a palatal direction. Palatal impactions may be as high as 3%. Because of its morphology and position, the permanent maxillary canine tooth is the ideal tooth to provide anterior guidance during lateral excursion (canine guidance). In addition, the best aesthetics are achieved with class 1 canine relation. 1. Palpation for unerupted maxillary canines should be a part of the routine dental examination of every child over 9 years old. The maxillary canine should be palpable as a bulge in the buccal sulcus between 10 and 11 years old. Ideally, the bulges should be symmetrical. If the canines are not palpable, then further investigation by radiographs is indicated to locate the permanent canine, using the parallax technique. Impacted maxillary permanent canines can cause resorption of the adjacent tooth roots so must be identified and treated early [8]. 2. If a primary canine is still firm and the permanent canine is not palpable, then specialist orthodontic opinion should be sought. The decision will be to extract the firm maxillary deciduous canine, or to retain it. a. Extraction: to encourage the permanent canines to erupt in the correct position. b. Retention: thereby, leaving the permanent canine unerupted. Regular radiographic monitoring is required. Surgical removal of the unerupted permanent canine may be indicated.

8.  Unerupted Maxillary Permanent Incisors Maxillary incisors usually erupt between 7 and 9 years of age, and contra-lateral teeth will normally erupt within 6 months of each other. The eruption of the maxillary incisor teeth is not only a significant time in the child’s dental development but also a milestone in the minds of the child, their family and friends of their general development. These teeth are vital for functioning and aesthetics. Missing or malformed maxillary permanent incisor teeth can have a major impact on the child’s self-esteem. Delayed eruption of maxillary permanent incisor teeth should be investigated with radiographs, and management depends upon the cause of failure of eruption, patient age and degree of root formation [9]. The presence of a supernumerary tooth usually a mesiodens in the anterior maxilla between the central incisors is the most common reason for the failure of eruption of the incisor teeth (Fig.  8.9a). Other causes for the failure of eruption may be trauma with dilaceration preventing eruption, hypodontia (developmental absence), ectopic eruption due to prolonged retention of primary units (Fig. 8.9b).

9. Trauma

203

a

b

Fig. 8.9 (a) Unerupted supernumerary resulting in delayed eruption of UL1 with retained ULA. (b) Retained primary teeth causing ectopic eruption of permanent successors

9.  Trauma Traumatic injury to anterior teeth is more common in children. If there is an increased overjet and inadequate lip, there is a significantly increased risk. The first priority is obviously the immediate management of the traumatised tooth/teeth. But there also needs to be consideration for long-term consequences for the developing occlusion [10]. 1. Where avulsion occurs, and the tooth is successfully replanted/treated There will be little effect for the developing occlusion, unless root resorption occurs. If orthodontic tooth movement is planned, there is an increased risk of root resorption of the traumatised tooth. 2. Where avulsion occurs and the tooth is not replanted, or is later extracted Space maintainers should be fitted to retain the space and prevent unfavourable tilting and movement of adjacent and opposing teeth. The purpose of the appliance is to preserve the pre-existing occlusal relationships and to provide an interim aesthetic outcome. 3. Where crown fracture has occurred It is important to restore contact with the adjacent teeth by rebuilding the crown form with composite restorations. Failure to do so can result in: • Tilting of the affected tooth • Tilting of the adjacent teeth • Space loss with narrowing of the arch • Over-eruption of the opposing tooth 4. Where displacement of the traumatised tooth has occurred (Fig. 8.10a, b). Orthodontic treatment may also be required to extrude, intrude, or reposition teeth following displacement.

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b

Fig. 8.10 (a) Unfavourable space loss following avulsion of UR1 as a result of accidental trauma. (b) Traumatic displacement of UR1 resulting in unfavourable space loss with mesial drift of UR2

10.  Early Orthodontic Intervention Most orthodontic management of the occlusion takes place when the permanent dentition is established, typically around 12–13 years of age. Thus, an accurate assessment of the required orthodontic movement can be made. Treatment for some occlusions should and can be provided earlier: • Functional appliances are classically prescribed between 7 and 11 years of age. This is because these appliances utilise some growth modification during active growth phases in order to reduce the more severe skeletal discrepancies. If left untreated, these discrepancies could result in adverse occlusal patterns; for example: a large overjet which carry a risk of trauma to the upper incisor teeth. • Crossbites may need early orthodontic intervention. This is particularly important where the crossbite causes an unfavourable occlusal contact, resulting in a mandibular displacement. Crossbites can also cause: –– Mobility of teeth –– Hard or soft tissue damage –– Gingival recession Simple correction of the crossbite with a removable appliance is recommended.

Summary Caring for the child patient involves the dentist examining • Teeth • Periodontal tissues • Articulatory system As part of these examinations, the occlusal relationship should be recorded together with any facial asymmetry or mandibular deviation. Although the occlusion in the primary dentition is not a reliable predictor of the occlusion of the permanent dentition, the primary dentition is, nevertheless, important. This is because the primary dentition preserves the space that is required for the erupting permanent teeth and guides them into their correct position.

Summary

205

Good dental care for the child patient has to encompass: • Immediate dental needs • Management of the developing occlusion • Identification and management of clinical situations which will have an impact on the future occlusion This management may be through early referral to a specialist and optimum restorative care to preserve valuable space and interdental contacts. One of the aims of paediatric dentistry is to stabilise the future occlusion.

Guidelines of Good Occlusal Practice

1. The examination of the patient involves the teeth, periodontal tissues and articulatory system. 2. There is no such thing as an intrinsically bad Occlusal Contact, only an intolerable number of times to [para]function on it. 3. The patient’s occlusion should be recorded, before any treatment is started. 4. Compare the patient’s occlusion against the benchmark of ideal occlusion. 5. A simple, two-dimensional record of the patient’s occlusion taken before, during and after treatment is an aid to good occlusal practice. 6. The conformative Approach is the safest way of ensuring that the occlusion of a restoration does not have potentially harmful consequences. 7. Ensuring that the occlusion conforms to the patient’s pre-treatment state is a product of examination, design, execution and checking (the E.D.E.C. protocol). 8. The ‘Re-Organised Approach’ involves firstly the establishment of a ‘more ideal’ occlusion in the patient’s pre-treatment dentition or provisional restorations; and then adhering to that design using the techniques of the ‘conformative approach’. 9. An ideal occlusion in removable prosthodontics is one which reduced de-­ stabilising forces to a level that is within the denture’s retentive capacity. 10. The occlusal objective of orthodontic treatment is not clear, but a large discrepancy between centric occlusion and centric relation should not be an outcome of treatment. 11. An ‘orthodontic’ examination of the occlusion should include: the dynamic occlusion; and the jaw relationship in which the patient has their centric occlusion. 12. The occlusion of periodontally compromised teeth should be designed to reduce the forces to be within the adaptive capabilities of the damaged periodontia. 13. Good occlusal practice in children is determined by the needs of the developing occlusion; consequentially ‘restoration at all costs’ may not be the best policy.

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References 1. Delivering better oral health: an evidence-based toolkit for prevention, 3rd edn. https://assets. publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/605266/ Delivering_better_oral_health.pdf 2. Foster TD, Hamilton MC. Occlusion in the primary dentition. Br. Dent. J. 1969;126:76–9. 3. Leighton BC. The early signs of malocclusion. Trans Eur Orth Soc. 1969:353–68. 4. Hudson AP, Harris AM, Morkel JA, et al. Infraocclusion of primary molars: a review of the literature. SADJ. 2007;62:114. 5. Proffit WR, Fields HW. The development of orthodontic problems. In: Contemporary orthodontics. London: Elsevier; 1986. 6. BOS guidelines: advice sheet dummy and digit sucking. 2012. www.bos.org.uk 7. A guideline for the extraction of first permanent molars in children. Faculty of Dental Surgery. 2009. www.rcseng.ac.uk/fds/clinical_guidelines/index.html 8. Hussain J, Burden P, McSherry. Management of the palatally ectopic maxillary canine§. Guidelines, Faculty of Orthodontics. 2010. 9. Management of Unerupted Maxillary Incisors. Royal College of Surgeons Guideline. 2016. 10. Dental trauma guidelines. International Association of Dental Traumatology. https://www. iadt-­dentaltrauma.org/1-­9%20%20iadt%20guidelines%20combined%20-­%20lr%20-­%20 11-­5-­2013.pdf.

9

Bruxism

Introduction In this chapter, we will consider bruxism. This is a phenomenon of which every dentist is aware. It is included in a book on occlusion because bruxism can adversely affect the occlusal surfaces of teeth, amongst other consequences. Given the prevalence and consequences, it is important that clinically active dentists understand: • what bruxism is • its aetiology • how it is diagnosed • management strategies • the impact that bruxism may have upon some restorative procedures The restoration of the worn dentition is the subject of the next chapter. Because some of the views expressed in this chapter may run counter to the current views of some dentists, the authors have referenced it to a greater extent than other chapters. This is so the reader can research the evidence in order to form their own view.

What Is Bruxism? Bruxism is defined as a ‘repetitive jaw-muscle activity characterised by clenching or grinding of the teeth and/or by bracing or thrusting of the mandible’ with ‘two distinct circadian manifestations; either occurring during sleep (sleep bruxism, SB) or during wakefulness (awake bruxism)’ [1]. The prevalence of SB is generally considered to be around 8–13% of the general population [2–4]. SB is more common in children (14–18%) and lower in the elderly (around 3%) [5]. Awake bruxism is more common than SB: a 2013 systematic review reported a prevalence of 22.1–31% [4].

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Bruxism may lead to tooth surface loss, masticatory muscle hypertrophy, fracture of restorations or teeth, hypersensitive or painful teeth [5–9]. The excessive forces on the teeth can lead to alveolar bone resorption, which may be visible radiographically as generalised widening of the periodontal ligament space, and increased mobility which may be transient or permanent. In the presence of periodontal disease, the trauma from the occlusion may increase the rate of disease progression. Occlusal trauma cannot induce periodontal pocketing or attachment loss in teeth with a healthy periodontium [10]. Investigations into the effects of bruxism on dental implants and implant-retained prostheses have found no increase in biological complications (e.g. peri-implantitis) but an increased risk of mechanical complications (e.g. fracture of implants/prostheses) [9].

What Causes Bruxism? A disorder is the lack of normal functioning of physical or mental processes. A parafunction is a disordered function, e.g. a normal function carried out to an excessive extent. It should be noted that the above definition describes bruxism as neither of these things, but as an activity. This is in contrast to historical perspectives which view bruxism as a dysfunctional movement, pathological condition or an ‘occlusal disease’ caused by the teeth [11]. The current understanding of bruxism is that it is a centrally controlled condition, with the activity generated by central nervous system impulses. It is not peripherally stimulated (i.e. by features of the occlusion). Current evidence does not support any causal role of occlusal factors in bruxism [7]. Bruxism may be described as primary where there is no pre-existing causative medical condition or secondary where it occurs as a result of a psychiatric or medical condition. The aetiology of sleep bruxism is the subject of some debate and is likely to be complex and multifactorial. As stated above, it is now generally accepted that the pathophysiology of SB relates to activation of the central nervous system during sleep [8, 12]. There are various risk factors that can contribute to SB, including [12]: • Exogenous risk factors: smoking, heavy alcohol intake, caffeine, medications or illicit drugs [13]. –– Psychosocial factors: there is a common professional and patient perception that stress and anxiety exacerbate SB, although results of studies have varied [2]. • Sleep disorders involving arousal from sleep (e.g. obstructive sleep apnoea). –– Comorbidities: other disorders including obstructive sleep apnoea [13] and gastro-oesophageal reflux disorder [14]. These advances in our knowledge of sleep bruxism have helped to disprove the hypothesis that SB is a result of the peripheral stimulus of an uneven or

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uncomfortable bite. In fact, there is some evidence that an occlusal interference will reduce random mandibular movement activity [15]. These are important points that will help dentists manage their bruxing patient appropriately. Especially if the fallacy of it being a peripherally stimulated event is taken further: that not only is sleep bruxism caused by some features of the patient’s occlusion but also that the activity is always pathogenic. As Frank Lobbezoo says: It should be emphasised that while the occlusion is at the receiving end of parafunctional activity it is not the cause of it [16].

Some patients with previous or current bruxism present with tooth surface loss, which can be significant. In many of these patients • In the absence of missing teeth, function e.g. chewing is not impaired. • Pulpal exposure has not occurred due to the deposition of tertiary dentine. • The periodontal support is good. Some of these patients will seek restorations for aesthetic reasons: that is the patient’s decision. Consequently, treatment should be driven by the patient’s wishes. Whilst not encouraging the need for cosmetic improvement by the unsupported view that treatment is required for mechanical or preventive reasons, it is perfectly reasonable for the dentist to design a treatment plan to restore an unaesthetic worn dentition. However, where teeth are severely worn and the patient does not wish to have treatment, the dentist must inform the patient that should further wear occur that treatment may be more complicated or that the teeth may become unrestorable. This is an indication for, at least, careful monitoring. If a patient chooses not to have treatment, the dentist must inform the patient of the risks of this, because the fact that a patient has no current concerns does not mean that they do not care about having teeth. Restoration of worn teeth for reasons of dental health will have a ‘side effect’ of improving their appearance. A protocol for restoring the worn dentition is covered in the next chapter. Photo 9.1 is a case that highlights the dilemma of when to intervene: Photo 9.1  This patient reported that he had been told by a dentist that unless he had his dentition restored his teeth would fall out

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• Obviously, it is very unlikely that his teeth will suddenly lose periodontal support. • But if some of the teeth are left much longer, they might not be easy to restore; maybe needing crown lengthening or overdentures. The key question is whether the tooth wear is ongoing through an active bruxing habit. In this particular case, the 50-year-old patient reported that this wear had occurred during his 20s, and as far as he could tell had not become worse since then. The definition of bruxism as an activity acknowledges the current perspectives that it may indeed have a function: it has been postulated that sleep bruxism may have a protective role during sleep, which may relate to airway maintenance [1, 17], or in stimulating saliva flow to lubricate the oropharynx [18].

How Do We Know If Patients Are Active Bruxists? Bruxism may involve a static clenching of the teeth, grinding or a mixture of both. There is accompanying noise in around a third of sleep bruxists [5]. Awake bruxism is more usually a static clenching without sounds [19], grinding whilst awake is generally only secondarily associated with medications or neurological disorders, e.g. dyskinesias [2]. A diagnosis of bruxism may be made by the following: • Patient report and clinical interview • Clinical examination • Intraoral appliances • Recording of muscle activity Table 9.1 shows suitable questions to ask patients along with some clinical observations. Reports by sleeping partners of grinding noises during sleep are a particularly reliable indicator of SB [20]. Questionnaire alone may not be an accurate means of diagnosis, as up to 80% of patients may be unaware of bruxism [21, 22]. Many of the given clinical observations, for example tooth surface loss (TSL), are subjective and/or may represent signs of historical, rather than current, bruxism [16]. Tooth surface loss will be a combination of: • Normal physiological functional wear • Wear associated with bruxism • Erosion from dietary or gastric sources • Abrasion Extent of tooth wear is also influenced by factors such as: • Enamel quality and quantity • The nature of any opposing restorations • Lack of posterior tooth support

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Table 9.1  Questions to elicit patient-reported history of bruxism, and suggestive clinical indicators Questions to use during history Are you aware of grinding your teeth during sleep? Has anyone told you that you grind your teeth during sleep? taking On waking, do you have your jaws clenched or thrust forward? On waking, do you experience pain or stiffness in the jaw muscles? ‘Brux Scale’ questions How often do you clench your teeth during sleep? How often do you grind your teeth during sleep? van der Meulen et al. [21] How often do you clench your teeth whilst awake? How often do you grind your teeth whilst awake? Masseteric hypertrophy Findings during clinical Muscle tenderness on palpation examination suggestive of Wear facets on occlusal surfaces either within the normal bruxism envelope of movement or at eccentric jaw positions: termed ‘bruxofacets’ Shiny spots on restorations Restoration or tooth fracture Tongue scalloping and ridging on the cheek mucosa (‘linea alba’)

Tooth surface loss cannot be used to indicate static clenching activity. ‘Bruxofacets’, i.e. tooth wear in an eccentric position of closure, may seem more convincing evidence of bruxism than wear in the intercuspal position. Tooth surface loss should, therefore, be taken in conjunction with other clinical indicators. Simple observation of wear facets on intra-oral splints would be a plausible indicator of bruxism. Some intra-oral appliances aim to detect SB, such as via the incorporation of electric devices detecting forces applied during clenching/grinding. Extra-oral devices can be used to detect temporalis and masseter activity via sensors attached to the skin (electromyography): although these sensors cannot distinguish bruxism from other orofacial movements such as swallowing or talking. The gold standard for diagnosis of bruxism, albeit outwith the scope of normal dental practice, is via polysomnography: a sleep study incorporating detection of masticatory muscle activity, audio and video recording, ECG and assessment of brain activity. It has been recommended that self-report only will provide a ‘possible’ diagnosis; a diagnosis based on this plus clinical examination will be ‘probable’ and that ‘definite’ diagnosis would require PSG or EMG recording [1]. A reasonable course of action for the clinical setting would be to take into account plausible patient report (i.e. not just based upon having been told by a previous dentist) plus observation of a combination of the clinical signs listed in Table 9.1.

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Relationship with Painful Temporomandibular Disorders Whilst many patients are unaware of having SB, in contrast, some patients may falsely believe they do have the condition, having been told by their dentist that they do. This may result from an erroneous assumption by the dentist that painful masticatory muscles are caused by bruxism. A dentist may, therefore, conclude that a patient suffering from a painful temporomandibular disorder (TMD) must be a bruxist. Evidence has shown that while significantly more patients with painful TMD than controls self-report bruxism, there may be no difference on results confirmed by sleep study [23, 24].

What Treatment May Be Indicated? Bruxism, as an activity or behaviour, does not require treatment. Where pathology results from this activity, and if both the patient and dentist decide to do so, treatment may be considered. Treatment is directed at the unwanted signs or symptoms that have arisen as a result of bruxism—not at trying to prevent bruxist activity. The reader is directed to an extensive review of management strategies by Lobbezoo et  al. [16] which was updated in a systematic review by Manfredini et  al. [25]. Irreversible adjustment of the occlusal surfaces of teeth in an attempt to reduce bruxism is not supported by the literature.

Oral Appliances Oral appliances/splints primarily aim to protect the dentition from damage caused by clenching/grinding along with reducing any grinding noises. Evidence for their effects on muscle activity is conflicting, with some studies finding reduction in muscle activity during their use and others finding an increase in some subjects. Oral appliances are also used in the management of temporomandibular disorders, where their therapeutic effect may be independent of their effect on bruxism. Soft vacuum-formed splints (Soft Bite Guards) are easy to construct and fit, although difficult to adjust and anecdotally may in some cases exacerbate bruxism. Hard acrylic stabilisation splints may reduce muscle activity and associated muscle pain [26] and may be more long-lasting than soft splints. These should be constructed with full occlusal coverage and provide balanced occlusal contact across the arch (ideally in centric relation or the retruded contact position), with canine guidance on excursions. Partial coverage anterior splints (e.g. the nociceptive trigeminal inhibition (NTI)/ sleep clench inhibitor (SCI) splint) have been used in bruxism to reduce muscle activity via reducing maximum clenching force. These should be used with caution and with careful monitoring due to the risks of tooth mobility or over-eruption of uncovered teeth and resultant occlusal changes [26].

What Treatment May Be Indicated?

213

Overeruption and occlusal changes are risks with all splints that have only partial occlusal coverage when worn for long periods of time, and this potential iatrogenic harm should be avoided. A wide range of over-the-counter splints are readily available via the internet or from non-dental outlets. Caution is advised due to concerns of unsubstantiated manufacturers’ claims of efficacy, risks of unwanted tooth movement from partial coverage and other adverse effects. Many of these appliances do not cover all of the teeth. An additional risk is that they often lack professional supervision, because the people who purchase them, sometimes as an alternative to the splint suggested by their dentist, are unlikely to tell their dentist that they have been using one [27].

Other Measures Behavioural measures include mindfulness, sleep hygiene and biofeedback. Patients with awake bruxism can be counselled as to becoming mindful of this habit in order to endeavour to reduce it. Relaxation techniques can be helpful, along with finding ways to become reminded to check they are not clenching. Examples include doing so every time they look in a mirror or by placing coloured stickers around their home/place of work to act as reminders. Patients’ companions can also help remind the patient if they observe any clenching. Simple sleep hygiene measures aim to reduce any influence of psychological stress on sleep bruxism: such as avoidance of caffeine close to bedtime and relaxation techniques before sleep, although there is little evidence for their effect [28]. Biofeedback aims to provide immediate information to the patient about their behaviour, enabling its reduction. Biofeedback has been used for awake and sleep bruxism [29], although there is no long-term evidence of efficacy. Devices are available which utilise muscle sensors with auditory, vibratory or electric stimulatory feedback. If used overnight, these would intend to disrupt the bruxism activity by arousing the patient slightly from sleep. There is a concern that this sleep disruption may lead to excessive daytime sleepiness [30]. Another possible biofeedback strategy is intervention from a sleeping partner who has been disturbed by any grinding noises! Occlusal splints may be used which release a bad taste on clenching/grinding, or introduce occlusal interferences (localised occlusal interference splint (LOIS)) [31]. The latter should be used during awake bruxism only, and with careful monitoring as tooth wear may result. Pharmacological measures may include the use of benzodiazepines, anticonvulsants, beta-blockers, antidepressants, muscle relaxants and a number of others [16]. However, a Cochrane review found insufficient evidence to support this approach [32], and these measures should only be considered when other conservative strategies have failed, and in conjunction with medical practitioners [16]. Administration of botulinum toxin (Botox) to the muscles of mastication appears to reduce the frequency of bruxism, although further investigation is required as to

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long-term efficacy [33]. There are concerns that Botox administration can lead to osteopenic changes in the condyles and sites of muscle attachment [34].

Conclusions Sleep bruxism occurs in 8–13% of the general population. Bruxism may lead to damage to teeth and restorations. Dentists should be aware of the potential aetiology, pathophysiology and management strategies in order to better advise patients. In summary: • Diagnosis of SB in the clinical setting should be made on the basis of patient history and clinical examination. For research purposes, additional sleep study should be considered. • Bruxism is now generally accepted as a centrally controlled phenomenon; it may be associated with other parasomnias leading to arousal from sleep. As such, dental interventions are unlikely to reduce the frequency or severity of bruxism. • Irreversible occlusal adjustments have no basis in evidence in the management of bruxism. • The presence of bruxism is not an indication for invasive and irreversible treatment. • Dental management of SB should be directed at protecting the oral structures from the effects of SB. The primary aim of oral splints in bruxism is to protect the dentition: the evidence for reducing muscle activity is conflicting. • Behavioural strategies include biofeedback, relaxation and improvement of sleep hygiene. • Administration of botulinum toxin (Botox) may reduce bruxism, but more research is required into long-term efficacy and possible adverse effects.

Guidelines of Good Occlusal Practice

1. The examination of the patient involves the teeth, periodontal tissues and articulatory system. 2. There is no such thing as an intrinsically bad occlusal contact, only an intolerable number of times to [para] function on it. 3. The patient’s occlusion should be recorded, before any treatment is started. 4. Compare the patient’s occlusion against the benchmark of ideal occlusion. 5. A simple, two-dimensional record of the patient’s occlusion taken before, during and after treatment is an aid to Good Occlusal Practice. 6. The conformative approach is the safest way of ensuring that the occlusion of a restoration does not have potentially harmful consequences.

References

215

7. Ensuring that the occlusion conforms to the patient’s pre-treatment state is a product of examination, design, execution and checking (the E.D.E.C. protocol). 8. The ‘re-organised approach’ involves firstly the establishment of a ‘more ideal’ occlusion in the patient’s pre-treatment dentition or provisional restorations; and then adhering to that design using the techniques of the ‘conformative approach’. 9. An ideal occlusion in removable prosthodontics is one which reduced de-­ stabilising forces to a level that is within the denture’s retentive capacity. 10. The occlusal objective of orthodontic treatment is not clear, but a large discrepancy between centric occlusion and centric relation should not be an outcome of treatment. 11. An ‘orthodontic’ examination of the occlusion should include: the dynamic occlusion; and the jaw relationship in which the patient has their centric occlusion. 12. The occlusion of periodontally compromised teeth should be designed to reduce the forces to be within the adaptive capabilities of the damaged periodontia. 13. Good occlusal practice in children is determined by the needs of the developing occlusion; consequentially ‘restoration at all costs’ may not be the best policy. 14. Bruxism is a centrally controlled behaviour: it is not an ‘occlusal disease’ or caused by the occlusion. 15. Occlusal adjustment has no evidence basis in the management of Bruxism. 16. When planning restorations, consideration should be given as to whether there is Active bruxism. 17. Management of tooth wear may simply involve protecting the dentition and ongoing monitoring.

References 1. Lobbezoo F, Ahlberg J, Glaros AG, et al. Bruxism defined and graded: an international consensus. J Oral Rehabil. 2013;40(1):2–4. https://doi.org/10.1111/joor.12011. 2. Lavigne GJ, Khoury S, Abe S, et al. Bruxism physiology and pathology: an overview for clinicians. J Oral Rehabil. 2008;35(7):476–94. https://doi.org/10.1111/j.1365-­2842.2008.01881.x. 3. Lavigne GJ, Montplaisir JY. Restless legs syndrome and sleep bruxism: prevalence and association among Canadians. Sleep. 1994;17(8):739–43. 4. Manfredini D, Winocur E, Guarda-Nardini L, et al. Epidemiology of bruxism in adults: a systematic review of the literature. J Orofac Pain. 2013;27(2):99–110. https://doi.org/10.11607/ jop.921.

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5. Lavigne GJ, Rompre PH, Poirier G, et al. Rhythmic masticatory muscle activity during sleep in humans. J Dent Res. 2001;80(2):443–8. 6. Paesani D. Bruxism theory and practice. Chicago: Quintessence Publishing Co., Inc; 2010. 7. Lobbezoo F, Ahlberg J, Manfredini D, et al. Are bruxism and the bite causally related? J Oral Rehabil. 2012;39(7):489–501. https://doi.org/10.1111/j.1365-­2842.2012.02298.x. 8. Fernandes G, Franco AL, Goncalves DA, et al. Temporomandibular disorders, sleep bruxism, and primary headaches are mutually associated. J Orofac Pain. 2013;27(1):14–20. https://doi. org/10.11607/jop.921. 9. Lobbezoo F, Koyano K, Paesani D, et al. Sleep bruxism: diagnostic considerations. In: Kryger M, Roth T, Dement W, editors. Principles and practice of sleep medicine. Philadelphia: Elsevier; 2017. p. 1427–34. 10. Lindhe J, Niklaus PL, Karring T.  Clinical periodontology and implant dentistry. Oxford: Blackwell Munksgaard; 2008. p. 349–62. 11. Seven signs and symptoms of occlusal disease: the key to an early diagnosis. 2009. Available from http://www.dentistrytoday.com/occlusion/1501%2D%2Dsp-­540653346. Accessed June 2017. 12. Carra MC, Huynh N, Lavigne G.  Sleep bruxism: a comprehensive overview for the dental clinician interested in sleep medicine. Dent Clin N Am. 2012;56(2):387–413. https://doi. org/10.1016/j.cden.2012.01.003. 13. Ohayon MM, Li KK, Guilleminault C. Risk factors for sleep bruxism in the general population. Chest. 2001;119(1):53–61. 14. Miyawaki S, Tanimoto Y, Araki Y, et al. Association between nocturnal bruxism and gastroesophageal reflux. Sleep. 2003;26(7):888–92. 15. Michelotti A, Iodice G.  The role of orthodontics in temporomandibular disorders. J Oral Rehabil. 2010;37:411–42. 16. Lobbezoo F, van der Zaag J, van Selms MK, et al. Principles for the management of bruxism. J Oral Rehabil. 2008;35(7):509–23. https://doi.org/10.1111/j.1365-­2842.2008.01853.x. 17. Khoury S, Rouleau GA, Rompre PH, et al. A significant increase in breathing amplitude precedes sleep bruxism. Chest. 2008;134(2):332–7. https://doi.org/10.1378/chest.08-­0115. 18. Miyawaki S, Lavigne GJ, Pierre M, et  al. Association between sleep bruxism, swallowing-­ related laryngeal movement, and sleep positions. Sleep. 2003;26(4):461–5. 19. Bader G, Lavigne G. Sleep bruxism; an overview of an oromandibular sleep movement disorder. Sleep Med Rev. 2000;4(1):27–43. https://doi.org/10.1053/smrv.1999.0070. 20. van der Meulen MJ, Lobbezoo F, Aartman IH, et al. Self-reported oral parafunctions and pain intensity in temporomandibular disorder patients. J Orofac Pain. 2006;20(1):31–5. 21. Carra MC, Bruni O, Huynh N. Topical review: sleep bruxism, headaches, and sleep-disordered breathing in children and adolescents. J Orofac Pain. 2012;26(4):267–76. 22. Thompson BA, Blount BW, Krumholz TS.  Treatment approaches to bruxism. Am Fam Physician. 1994;49(7):1617–22. 23. Smith MT, Wickwire EM, Grace EG, et al. Sleep disorders and their association with laboratory pain sensitivity in temporomandibular joint disorder. Sleep. 2009;32(6):779–90. 24. Raphael KG, Sirois DA, Janal MN, et  al. Sleep bruxism and myofascial temporoman dibular disorders: a laboratory-based polysomnographic investigation. J Am Dent Assoc. 2012;143(11):1223–31. 25. Manfredini D, Ahlberg J, Winocur E, et al. Management of sleep bruxism in adults: a qualitative systematic literature review. J Oral Rehabil. 2015;42(11):862–74. https://doi.org/10.1111/ joor.12322. 26. Stapelmann H, Turp JC. The NTI-tss device for the therapy of bruxism, temporomandibular disorders, and headache - where do we stand? A qualitative systematic review of the literature. BMC Oral Health. 2008;8:22. https://doi.org/10.1186/1472-­6831-­8-­22. 27. Wassell RW, Verhees L, Lawrence K, Davies S, Lobbezoo F. Over-the counter (OTC) bruxism splints available on the Internet. Br Dent J. 2014;216:E24.

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28. Valiente Lopez M, van Selms MK, van der Zaag J, et al. Do sleep hygiene measures and progressive muscle relaxation influence sleep bruxism? Report of a randomised controlled trial. J Oral Rehabil. 2015;42(4):259–65. https://doi.org/10.1111/joor.12252. 29. Needham R, Davies SJ. Use of the Grindcare(R) device in the management of nocturnal bruxism: a pilot study. Br Dent J. 2013;215(1):E1. https://doi.org/10.1038/sj.bdj.2013.653. 30. Kryger M, Roth T, Dement W. Principles and practice of sleep medicine. 4th ed. Philadelphia: Elsevier Saunders; 2005. p. 39–50. 31. Gray RMJ, Davies SJ. Occlusal splints and temporomandibular disorders: why, when, how? Dent Update. 2017;28:4. 32. Macedo CR, Macedo EC, Torloni MR, et al. Pharmacotherapy for sleep bruxism. Cochrane Database Syst Rev. 2014;10:CD005578. https://doi.org/10.1002/14651858.CD005578.pub2. 33. Long H, Liao Z, Wang Y, et al. Efficacy of botulinum toxins on bruxism: an evidence-based review. Int Dent J. 2012;62(1):1–5. https://doi.org/10.1111/j.1875-­595X.2011.00085.x. 34. Kun-Darbois JD, Libouban H, Chappard D. Botulinum toxin in masticatory muscles of the adult rat induces bone loss at the condyle and alveolar regions of the mandible associated with a bone proliferation at a muscle enthesis. Bone. 2015;77:75–82. https://doi.org/10.1016/j. bone.2015.03.023.

Occlusion and Non-carious Tooth Surface Loss

10

Introduction Tooth surface loss (TSL) can be defined as ‘surface loss of dental hard tissues by causes other than caries, trauma or developmental defects: a multifactorial condition’. The Adult Dental Health Survey 1998 found that two thirds of adults had some anterior wear into dentine: 11% had moderate wear with extensive dentine involvement and 1% had severe wear. The prevalence of TSL increases with age. A systematic review of 186 prevalence studies [1] found that the prevalence of severe tooth wear was 3% at the age of 20 years, rising to 17% at the age of 70 years. Tooth Surface Loss

• High prevalence • Probably becoming less socially acceptable Significant Demand for Management The management of this form of generalised TSL is included in this book because knowledge of occlusion is needed for both the diagnosis and, when indicated, treatment. There are, however, many other factors involved in the management of generalised TSL other than those associated with ‘occlusion’. These will also be discussed. The chapter is divided into three sections. Section 10.1 addresses: • Classification and aetiology • Distinction between physiological and pathological TSL • Examination protocols, including some examples of indices • Monitoring protocols • Restoration strategies © Springer Nature Switzerland AG 2022 S. Davies, A Guide to Good Occlusal Practice, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-79225-1_10

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Section 10.2 discusses the decision on how to create space for the restorations. Section 10.3 is composed of case histories of the restoration of the worn dentition, that illustrate: • Decisions around restoration strategies • Techniques employed

Section 10.1: General Considerations on the Management of Non-carious Tooth Surface Loss Aetiology Tooth surface loss can be due to erosion, abrasion, attrition, abfraction or a combination of these. 1.  Erosion Erosion is a chemical process in which the tooth surface is removed in the absence of bacteria. Erosive factors may be either intrinsic or extrinsic. Extrinsic sources include drinks such as fresh fruit juices, carbonated drinks, cordials and alcoholic beverages, some foods and industrial processes. Intrinsic sources include gastroesophageal reflux and eating disorders, amongst others. 2.  Abrasion External agents that have an abrasive effect on the teeth include toothbrush bristles and dietary factors. 3.  Attrition Attrition is a process in which tooth tissue is removed as a result of opposing tooth surfaces contacting during function or bruxism. These direct contacts occur during empty grinding movements: • At proximal areas • On supporting cusps • On guiding surfaces 4.  Abfractions (Stress Lesions) (Fig. 10.1a) It has been suggested that the stress lesion or abfraction is a consequence of eccentric forces on the natural dentition [2, 3]. The theory propounds tooth fatigue, flexure and deformation via biomechanical loading of the tooth structure, primarily at the cervical regions. Cusp flexure causes stress at the cervical fulcrum and results in loss of the overlying tooth structure. The lesion is typically wedge shaped with sharp line angles. Figure 10.1b shows a cervical cavity which is significantly subgingival and interestingly has caused a fenestration of the overlying attached gingiva. It is highly likely, because of the protection of the overlying soft tissue, that this lesion is an abfraction without any abrasive or erosive component. There is even more controversy concerning occlusal abfractions. Other factors such as erosion and abrasion may play a significant role in the tooth tissue loss, but a biomechanical loading may be the initial force. Non-carious tooth surface

Section 10.1: General Considerations on the Management of Non-carious Tooth

221

loss is often multi-­factorial. Figure 10.1c demonstrates multifactorial tooth surface loss aetiology: • The first molar occlusal surface displays cupped lesions into dentine and proud amalgam restorations caused by acid erosion. • The canine has a flattened tip matching the opposing tooth’s lateral excursive movement characteristic of an attritive cause. • Both the premolar and the first molar show cervical non-carious tooth surface loss: –– The molar appears smooth and rounded in keeping with cervical abrasion. –– The premolar defect is angular and deep and therefore may be due to abfraction. Fig. 10.1 (a) Abfraction V-shaped non-carious cavity noted on the labial cervical aspect of upper right lateral incisor which may be suggestive that abfraction is the cause of the tooth surface loss in the absence of other aetiological factors (Kind permission of Prof. D Bartlett). (b) An abfraction in the lower margin which has resulted in the fenestration of the Attached Gingivae. Given its location, this is unlikely to have an erosive or abrasive aetiology. (c) Multifactorial tooth surface loss (kind permission of Dr. Martin James)

a

c

b

Despite the multi-factorial aetiology of tooth surface loss, certain clinical features may suggest a major contributory factor. Flattening of cusps or incisal edges and localised facets on occlusal or palatal surfaces would indicate a primarily attritional aetiology. Traditionally, cervical lesions caused purely by abrasion have sharply defined margins and a smooth, hard surface. The lesion may become more rounded and shallower if an element of erosion is present. Once dentine is exposed,

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the clinical appearance is determined by the relative contribution of the aetiological factors. If wear is primarily attritional, then dentine tends to wear at the same rate as the surrounding enamel. Erosive lesions cause ‘cupping’ to form in the dentine, as dentine dissolves three or more times faster than enamel at pH 5 [4]. When erosion affects the palatal surfaces of upper maxillary teeth, there is often a central area of exposed dentine surrounded by a border of unaffected enamel. Tooth Surface Loss

Physiological? Pathological?

Physiological vs Pathological Tooth Surface Loss Tooth surface loss may be purely physiological (Fig. 10.2) and occurs as a natural consequence of ageing. Several factors, however, including erosion, abrasion and attrition can render tooth surface loss pathologically. As a result of this, symptoms may develop, and treatment may be indicated. Although this chapter will deal with only pathological tooth surface loss, it is important to be able to recognise that some tooth surface loss is purely physiological. It should not be assumed that all tooth surface loss is pathological.

Fig. 10.2  Purely physiological tooth surface loss

There appears to be no consensus as to what constitutes physiological tooth surface loss. It would be of assistance to practising dentists, if such criteria could be established. Pathological tooth surface loss may result in a change in the appearance of teeth, considered to be excessive with respect to the age of the patient (Fig. 10.3a–c). There may be: • Sensitivity to thermal stimuli • A loss in vertical height

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Dentoalveolar Compensation

a

b

c

Fig. 10.3 (a) Shows a young patient (18 years), who needs treatment, whereas. (b) A similar amount of TSL in an older (75 years) patient does not necessarily warrant intervention. (c) Is 45 years old and his request for treatment is justified

• A history of frequent fracture of teeth or restorations • Hypermobility and drifting

Dentoalveolar Compensation Physiological tooth surface loss is normal and results in a reduction in: • Vertical tooth height • Horizontal tooth width But in physiological tooth surface loss, vertical dimension is maintained by alveolar bone remodelling resulting in an elongation of the (dento-)alveolar process. Similarly, proximal wear is compensated by a constant forward pressure maintaining tooth-to-tooth contact. This physiological compensatory process (dentoalveolar compensation) ensures maintenance of occlusal contacts, maximising the efficiency of the masticatory apparatus. Where pathological tooth surface loss, affecting the occlusal surfaces of the teeth, has occurred, then one might expect to see a reduction in occlusal face height (vertical dimension of occlusion or VDO); or, expressed in a different way, an

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10  Occlusion and Non-carious Tooth Surface Loss

increase in the freeway space (FWS) could be anticipated. This may be further complicated by forward posturing of the mandible. It is often observed, however, that despite overall tooth surface loss, the freeway space and the resting facial height appear to remain unaltered. This is because of dentoalveolar compensation. It has been observed that in the normal adult dentition, the FWS remains constant and even in those patients who exhibit significant tooth surface loss, the VDO is unaffected in 80% and a normal FWS of 3 mm is exhibited [5]. This is important with respect to patient assessment. If restoration of worn teeth is being planned, then the extent of dentoalveolar compensation should be considered. This will be further discussed in Sect. 10.2 of this chapter. Sometimes, dentoalveolar compensation may lead to the incisal level of worn teeth being maintained at approximately the same level relative to the patients lip line, as seen in Fig. 10.4. If treatment of a patient within this group is necessary, then crown lengthening procedures may be indicated. Without doing so, restored teeth would appear excessively long-resulting in an adverse appearance (Fig. 10.4). Alternatively, restoration of the patient’s dentition may be provided at an increased VDO (reduced FWS). Some may argue that any increase in FWS should be proportionate to the degree of attrition. Nevertheless, the fundamental question is: Does it matter if the patient’s VDO is increased during the restoration of the tooth surface loss (i.e. the FWS is reduced)? The answer is different for each patient. No occlusion can be said to be ‘wrong’ rather it is the case that in certain patients, at particular times in their lives, some occlusal patterns will not be tolerated. An occlusion can only be judged by the reaction of the tissues surrounding it, so it is with the issue of an increase in VDO. The increase in OVD effected by restoration of TSL seems not to affect dentate patients in the same way as it does to edentulous patients for whom complete Fig. 10.4 Dento-alveolar compensation has resulted in the incisal edges of the significantly worn teeth to have the same relationship to the lip line

Dentoalveolar Compensation

225

denture construction needs to carefully consider the FWS. This adaptability of dentate patients may relate to the nature of the dentoalveolar process and its neuromuscular proprioception. Garnick and Ramfjord, as long ago as 1962, found that no symptoms/muscle dysfunction were experienced until the OVD was increased by of 11–12 mm (via the provision of stabilisation splints) [6].

Examination Clinical assessment of the patient with tooth wear involves extra-oral and intra-oral observations. The intra-oral examination will need to include an assessment of severity, either one of the indexes presented above, or a similar alternative. Extra-oral assessment should include assessment of the following in smile and at rest: • The position of the lip line in relation to the incisal edges • Amount of tooth show • Gingival display Radiographic examination should be considered for moderate to severe cases: Wazani, in 2012, found no PA pathology in patients with mild TSL; but that 7% of patients with moderate TSL and 20% of patients with severe wear did have PA pathology [7]. A protocol for examining a patient with TSL is presented in Fig. 10.5. This is suggested to be in addition to the normal examination of the articulatory system. This examination is designed to: • Aid in distinguishing between physiological and pathological TSL • Reveal any features that may indicate the aetiology • Indicate whether or not treatment should be carried out • Highlight any potential difficulties anticipated in treatment In addition to a general examination protocol, similar to the one suggested in Fig. 10.5 some attempts to grade the severity of the tissue that has been lost will be useful. There are many indices to help with this. Some are summarised below: 1.  Tooth Wear Index [8]: Smith and Knight 1984 (Fig. 10.6) This index requires observation of wear affecting the buccal (B), lingual (L), occlusal (O), incisal (I) and cervical (C) tooth surfaces. Patients are divided into age groups, and there is guidance as to what extent of wear is pathological according to age. For example, it was suggested that for age 36–45 years, occlusal/incisal wear >grade 2 would be deemed pathological.

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Patient 1

Date

Age

Is tooth surface loss

Normal Excessive Extreme

Is there any evidence that it is progressive ?

for a patient of this age? None Weak Strong

2

The following features suggest an aetiology of EROSION ABRASION ATTRITION

3

Known dietary habit? Known gastric reflux? Known oarafunction? Other [specify]?

4 Has dento-alveolar compensation taken place? 5 QUALTY OF LIFE ISSUES Patientis worried about: Tooth sensitivity Soft tissue comfort

Appearance Tooth or restoration fracture Loosening teeth

6 RECORDS taken and TESTS made Models

Centric Relation jaw registration Photographs

Tooth measurements taken

Ethyl chloride

Fig. 10.5  Initial examination of patient exhibiting tooth surface loss

Dentoalveolar Compensation Grade

Tooth

227

Clinical findings

surface 0 1 2

BLOI

No loss of enamel surface characteristics

C

No change in contour

BLOI

Loss of enamel surface characteristics

C

Minimal loss of contour

BLO

Bucc/ling/occlusal enamel loss, exposing dentine 1mm deep cervically

BLO

Bucc/ling/occlusal enamel loss, exposing dentine >1/3 of the surface

4

I

Incisal enamel loss with substantial loss of dentine

C

Defect 1 -2mm deep

BLO

Bucc/ling/occlusal complete enamel loss, pulp exposure or exposure of 2ndary dentine

I

Incisal pulp exposure or exposure of 2ndary dentine

C

Defect >2mm deep, pulpal exposure or exposure of 2ndary dentine

Fig. 10.6  Tooth wear index: Smith and Knight 1984

2.  Basic Erosive Wear Examination (BEWE) [9]: Bartlett 2008 (Fig. 10.7) This is a partial scoring system for severity of TSL and intended to be similar to the BPE. This index was designed to be simple to use, easy to record, and to serve as a demonstration that TSL had been examined and considered and encourage a preventive approach as opposed to a detailed examination allowing monitoring of progression. The BEWE was designed for use in epidemiological research and general dental practice. Scores are allocated in terms of surface area affected, rather than depth/exposure. The highest score in each sextant is recorded, then the scores are added. This number then gives a guide to suggested clinical management strategy. 3. Tooth Wear Evaluation System (TWES) [10]: Wetselaar and Lobbezoo 2016 (Fig. 10.8) This ‘modular’ system includes guidance on assessment, classification and management of TSL. The TWES includes multiple factors including: • A screening module with 5-point scale in each sextant. Each sextant is recorded separately. 1. No wear 2. Visible wear within enamel 3. Wear with dentine exposure and loss of crown height 2/3 • Measurement of upper and lower anterior teeth • Recording of TSL

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0

No surface loss

1

Initial loss of enamel surface texture

2

Distinct defect, hard tissue loss 50% of surface area

Risk/complexity level None

Sum of BEWE scores from all sextants £2

Low

3-8

Medium

9-13

High

≥14

Management

Routine maintenance and observation Repeat at 3-year intervals Oral hygiene and dietary assessment, and advice, routine maintenance and observation Repeat at 2-year intervals Oral hygiene and dietary assessment, and advice, identify the main aetiological factor(s) for tissue loss and develop strategies to eliminate respective impacts Consider fluoridation measures or other strategies to increase the resistance of tooth surfaces Ideally, avoid the placement of restorations and monitor erosive wear with study casts, photographs, or silicone impressions Repeat at 6 –12-month intervals Oral hygiene and dietary assessment, and advice, identify the main aetiological factor(s) for tissue loss and develop strategies to eliminate respective impacts Consider fluoridation measures or other strategies to increase the resistance of tooth surfaces Ideally, avoid restorations and monitor tooth wear with study casts, photographs, or silicone impressions Especially in cases of severe progression consider special care that may involve restorations Repeat at 6 –12-month intervals

Fig. 10.7  Basic erosive wear examination (BEWE): Bartlett 2008 Mild

Within enamel

Mod

Dentine exposure

Severe

Dentine exposure with loss of crown height, 2/3 occlusal/incisal

Fig. 10.8  Tooth wear evaluation system (TWES): Wetselaar and Lobbezoo 2016

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229

• Medical/social history • Difficulty of treatment A classification was proposed to describe TSL in terms of severity, distribution (localised/generalised) and aetiology. Localised TSL affects 1–2 sextants; generalised affects 3+. Returning to the initial examination protocol (Fig. 10.5) The first question is to help in the assessment: Pathological or Physiological (Fig. 10.9) Boxes 2 and 3 of the examination sheet (Figs.  10.10 and 10.11) consider the likely aetiology. Box 4 (Fig. 10.12) addresses the issue of dentoalveolar compensation, which can have a significant bearing on management.

1 Is tooth surface loss

Normal Excessive Extreme for a patient of this age?

Is there any evidence that it is progressive? None Weak Strong

Fig. 10.9  Question 1 of initial examination (Fig. 10.5)

2 The following features suggest an aetiology of EROSION ABRASION ATTRITION

Fig. 10.10  Question 2 of initial examination (Fig. 10.5)

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10  Occlusion and Non-carious Tooth Surface Loss

3 Known dietbry habit? Known gastric reflux? Known parafunction? Other [specify]?

Fig. 10.11  Question 3 of initial examination (Fig. 10.5)

4 Has dento-alveolar compensation taken place?

Fig. 10.12  Question 4 of initial examination (Fig. 10.5)

5 QUALTY OF LIFE ISSUES Patient is worried abour: Tooth sensitivity

Appearance Tooth or restoration fracture

Soft tissue comfort

Loosening teeth

Fig. 10.13  Question 5 of initial examination (Fig. 10.5)

Does the Patient Want/Need Treatment? This question gives rise to Box 5 (figure 1 of the examination sheet) (Fig. 10.13). It is essential as in all areas of clinical practice to carefully consider the patient’s anxieties and desires in addition to the clinical features before advice is given. Treatment planning must take into account the patient’s complaints. One study found that 60% of patients with TSL have aesthetic concerns, 40% sensitivity, 15% pain and 15% functional difficulties [11]. There are no hard and fast rules, and the need for treatment should be established after considering: • The degree of wear relative to the age of the patient • The aetiology • The symptoms • The patient’s wishes

Dentoalveolar Compensation

231

Treatment Considerations May be passive or active.

Passive Treatment 1.  Monitoring Monitoring involves taking a series of repeated examinations and certain measurements over a period of time in order to assess whether a condition is progressive. Monitoring is essential in the management of tooth surface loss as it is the only way in which TSL can be assessed as being active or static. In the literature, several methods of assessing tooth wear have been described including: • General assessment of extracted teeth • Chemical analysis • Physical methods (polarised light/indentation techniques/profilometry), scanning electron microscopic analysis • Digital image analysis These are research tools that are not applicable to clinical practice. Therefore, a monitoring protocol to assess tooth surface loss is presented (Fig. 10.14a, b). It is easy to use, and through this method, it is easy to record the progression of tooth surface loss. Monitoring is, of course, only an option when baseline measurements have been taken. This emphasises the need for the dentist to examine and record tooth surface loss. To facilitate this, a protocol for the initial examination of a patient with TSL has been presented (Fig. 10.5). 2.  Prevention This is the ‘treatment’ of future tooth surface loss. If the extent of existing tooth surface loss is considered to be acceptable, the appropriate treatment is clearly to try to prevent further TSL, which could render the patient needing restorative treatment. The form of the preventive treatment will be dependent on the aetiology of the TSL, so determining the cause is essential. For a patient whose tooth surface loss is essentially caused by erosive fluids, various aspects of prevention can be considered: 1. Reduction in frequency/severity. This could involve dietary advice for extrinsic sources of erosion; or liaison with a patient’s doctor regarding intrinsic sources, e.g. medication for reflux; support for eating disorders. 2. Enhancement of natural oral defences, e.g. stimulating saliva flow through sugar free chewing gum. 3. Enhancing remineralisation/resistance to acid, e.g. fluoride advice, tooth mousse (casein phosphopeptide). 4. Minimising mechanical factors that increase TSL, e.g. avoiding toothbrushing shortly after acid exposure. 5. Mechanical protection, e.g. splints for night-time use if sleep bruxism is suspected.

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10  Occlusion and Non-carious Tooth Surface Loss

a

Patient

Date

Age

Primary aetiology EPOSION ABRASION ATTRITION RV no:

DATE OF LAST RV

INTERVAL

AFFECTED TEETH

Tooth surface loss Dentine exposed 1 Mild, 2 Moderate, 3 Severe Sensitivity (at’s c/o) Tooth mobility CI I,II CI III Fractured/Failed restorations Hairline fracture lines OTHER NOTES

Fig. 10.14 (a) Monitoring protocol P1. Page 1 of 2

Dentoalveolar Compensation

b

233

Patient

Date

OTHER SIGNS Active bruxism? Tongus scalloping Cheek ridging T.M.J. exam

Noise Range of motion

Tenderness to palpitation Muscle tenderness

RECORDS TAKEN Photographs

Impressions

Measurements from A.D.J.

ASSESSMENT at this time Non-progressive Maybe progressive [not marked and no symptoms] Progressive [obvious] Progressive [obvious and symptomatic] TREATMENT at this time

Fig. 10.14 (continued) (b) Monitoring protocol P2. Page 2 of 2

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10  Occlusion and Non-carious Tooth Surface Loss

If the wear is primarily caused by abrasion, then examination and modification of the tooth cleaning habits will be indicated. If the wear is caused by attrition, then the patient should be advised of any possible bruxing habits. A discussion on bruxism is presented in Chap. 9. The provision of one of three different sorts of splints could be considered: • A soft bite guard can help in breaking a bruxing habit or simply will protect the teeth during the bruxing habit. • A localised occlusal interference splint is designed to help break the bruxing habit, and it can be worn easily during the day. It should not be worn at night in case the bruxism continues. A stabilisation splint reduces bruxism by providing an ideal occlusion: it also enables the clinician to locate and record centric relation [12].

Active Treatment Non-carious loss of tooth tissue may require treatment for one or more of the following reasons: • Sensitivity • Aesthetics considerations • Reduction in function • Space loss in the vertical dimension –– This may present a critical problem. Both the need for restorative treatment and the complexity of that treatment may depend upon whether or not dentoalveolar compensation has occurred. Treatment planning would, as normal, take the following form: 1. Management of acute conditions 2. Prevention 3. Stabilisation of underlying pathology, e.g. caries, periodontal disease, pulpal pathology, extraction of teeth of hopeless prognosis 4. Definitive restorations 5. Monitoring, maintenance, review To [Actively] Treat or not to Treat? The first decision is whether the condition warrants restoration. This will be a difficult decision that will be made after considering: 1. The objective findings of the examination and monitoring protocols 2. The subjective wishes, needs and understanding of the patient It is a good example of the hard and soft skills that a dentist, in common with many other healthcare professionals must have to serve the best interests of their patients.

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235

Examination Skill Set Needed for Care of TSL Patients

Hard Skills • Pathological or physiological? • Extent of tooth tissue loss • Active or passive • Dento-alveolar compensation • Temporomandibular disorder? • Active bruxist? Soft Skills • Effect of TSL on quality of life • Any possibility of body dysmorphic disorder? • Ability to reduce aetiological habits • Understanding of risks and benefits • Acceptance of limitations and features of Tx

Figure 10.15 is presented to help with some of the decisions that will need to be made.

 hich Approach to Adopt in the Restoration of the Worn Dentition W In restorative dentistry, usually two choices are considered: 1. It will either be possible to provide the restorations whilst not changing the occlusion between the other teeth (‘habitual bite’). 2. It will not be possible or desirable to do so. So, the binary choice is to adopt the Conformative Approach (Chap. 3), or not. If the conformative approach is not possible or appropriate, then the occlusion and the jaw relationship of that occlusion will change. It is generally advised that the jaw relationship in which to build the new occlusion is centric relation [syn: retruded contact position, terminal hinge axis], as this is the least likely to create an adverse reaction in the other parts of the masticatory system. This is known as the Re-Organised Approach and is discussed in Chap. 4. As will be seen in Chap. 4, it is a complex protocol that starts with finding and recording centric relation. It usually involves designing the proposed occlusal prescription by the means of a wax up on some models mounted in centric relation. The process is then to carefully copy that design in the provision of the subsequent restorations. Provisional restorations made to the new occlusal prescription are recommended prior to providing indirect restorations, e.g. using materials like ceramics or metals. Such provisional restorations may be direct composite or provisional crowns (either chairside or laboratory construction). There are examples of successful dental procedures that do not follow this strict occlusal prescriptive design and copy formula, such as orthodontics and the

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10  Occlusion and Non-carious Tooth Surface Loss

Tooth Surface Loss

Physiological

No action Pathological

Determine Aetiology

Exam + Record

Mild

Moderate

This will affect management

Severe

Management

Monitor

Explanation and patient education Prevent further loss by:

Fluoride? Splint? Diet? Habit? Further referral?

Active treatment

Restore or refer

Depends upon: • Cost • Time • Operator experience • Extent of treatment • Patient requirement

Fig. 10.15  Management of a patient with pathological tooth surface loss

Dahl approach. In the latter, the (usually posterior) occlusion develops following a combination of intrusion of teeth restored at an increased vertical dimension and overeruption of unrestored teeth. One explanation for this success is that these are procedures that take time and offer a degree of adjustment; both by patient

Dentoalveolar Compensation

237

accommodating to the new occlusal and jaw relationships and by the dentist making judicious changes. Maybe changing occlusions by evolution rather than by revolution gives the patient a greater chance of successful adaptation. Given that the worn dentition is often restored over a period of time using the adaptable adhesive material of directly bonded composite, it could be that this branch of dentistry can be successfully provided without the stages outlined in Chap. 4: The Re-Organised Approach. Best practice will still be to plan changes to the existing occlusion/jaw relationship along the lines of the traditional re-organised approach. Some clinicians, however, may opt to restore a worn dentition with direct composites by building up the worn dentition without giving much thought to jaw relationship. These clinicians will abbreviate this process, by building up the dentition (occlusion) without first analysing and planning the restorations on study models. It could be argued that a provisional phase may not be required as the composite restorations can ‘act as their own provisional restorations’ being adapted by addition, reduction and refinement as required. Of course, if the Dahl approach is used, it is then not possible to plan the final occlusal scheme of any unrestored teeth; as the eventual interocclusal relationship of these relies on uncontrollable tooth movement (intrusion/overeruption), which develops over months/years. Whilst not endorsing this approach, the aim of this book is not to be too didactic, by providing rules, or rigid answers to a set of clinical problems. The author believes in his colleagues’ personal clinical responsibility. Rather than giving all the answers, this book seeks to ask the right questions. So, a question: Is it ever justified to build up or change an occlusion/jaw relationship without a careful and detailed design phase? Surely if the patient tolerates the changes, it must be an acceptable treatment. If, however, this is a clinician’s strategy, it is suggested are be two important provisos: 1. The patient is constantly monitored for any signs of an adverse reaction to the new occlusion or jaw relationship. 2. The restorations provided can be easily adjusted. And they have been placed on teeth that have not suffered significant preparation. This then could be called the ‘Monitored Developmental Approach’. It is not the conformative approach, rather it is less prescriptive and lighter touch version of the re-organised approach.

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10  Occlusion and Non-carious Tooth Surface Loss

Choices When Restoring the Worn Dentition 1. Conformative Approach This means that the TSL will be restored, whilst not changing the occlusion between any other teeth and so not changing the jaw relationship in the three dimensions of lateral, anterior/posterior or vertical. The techniques that can be employed in restoring a patient using conformative approach are described in Chap. 3. There will be limited instances when this approach is appropriate or possible; maybe: • The restoration of the incisal edges of the lower anterior teeth which would not result in a reduction of the overjet/overbite dimensions and which does not significantly change the dynamic occlusion is one such instance. • If the TSL has occurred rapidly, e.g. erosive TSL following periods of frequent reflux/vomiting such as severe morning sickness; and there has not yet been dentoalveolar compensation. 2. Re-Organised Approach Implicit in the approach is not only that there will be a change in the jaw relationship in at least one of the three dimensions but also that the occlusal prescription to be provided will have been designed, usually on some accurately mounted models. This approach often will involve the use of laboratory made indirect restorations. It is described in Chap. 4. 3. Is there a 3rd way? Monitored Developmental Approach [13]. https://doi.org/10.1038/s41415021-3267-6 The debate of this approach centres on whether there must be a physical design to be followed. This design will usually take to form of a wax up of the occlusion of the proposed restorations, on models mounted on an articulator to a pre-determined and consistent jaw relationship. Other features of the Monitored Developmental Approach are: • The use of conventional orthodontics or the Dahl technique. • Direct restorations in adhesive material on minimally prepared or unprepared teeth are used. • A degree of adjustment of the restorations is possible, in the way that is not easy in indirect restorations. This is especially important if the Dahl technique (an unpredictable relative axial movement of teeth) is employed. • That the patient is carefully monitored, for any adverse reactions to the new occlusion, before, during and after treatment. The decisions to be taken and the techniques that can be employed in the restoration of the worn dentition are discussed and illustrated in the second half of this chapter.

Section 10.2: Creating the Space for the Restoration of the Worn Teeth

239

Section 10.2: Creating the Space for the Restoration of the Worn Teeth When space must be created for the provision of a new occlusion, the bite must be opened up. Before the restorative treatment is started, decisions have to be made how to achieve this: • Does centric occlusion (inter-cuspation position) occur in centric relation (retruded contact position or terminal hinge axis)? • If not, what is the size and nature of the slide from CO to CR? • What is the starting point of the arc along which the bite is going to be opened? • How much space is needed for the restoration? In this section, several scenarios are presented, and the restorative strategy for each is explained. These scenarios are kindly presented by Amin Aminian BDS MSc MFDS RCPS MRD RCSEd FDS RCSEd. Specialist in Prosthodontics

This slide can be: Small horizontal small vertical Small horizontal large vertical Large horizontal small vertical Non-existent Lateral

Shorthand vh hV Hv CO = CR [ICP = RCP]

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10  Occlusion and Non-carious Tooth Surface Loss

 cenario 1: Slide is vh (Small Vertical; Small Horizontal) S Restoring to premature contact in CR creates ideal space

CR

CO

Creating space: slide CR => CO vh

Pre-operative situation

Solution to space needed

By finding the Premature Contact in Centric Relation, and providing a new Occlusion that is in Centric Relation, the space needed for the restoration of UL1 is achieved. Note: It is suggested that if UR1 had not been restored by a porcelain crown that the likely consequence of the Trauma from Occlusion would have been Attrition in addition or instead of the migration that is evident.

This is a traditional Re-Organised Approach, because the space is created by increasing the OVD along an arc from centric relation (Terminal Hinge Axis)

Section 10.2: Creating the Space for the Restoration of the Worn Teeth

241

 cenario 2: Slide is Vh (Large Vertical; Small Horizontal) S Restoring to premature contact in CR creates excessive space

CO CR

Vh = excessive

Pre-operative situation

The anterior teeth exhibited marked fremitus, confirming that there was a complete absence of freedom in Centric Occlusion. If not for this Traumatic Occlusion, Centric Occlusion would be at where the dotted lines meet. Solution to space needed: The ideal space for the new occlusion is going to be created by opening the bite from a point that is between the Jaw Relationships of Centric Occlusion and Centric Relation. CO

CR

This is a Monitored Developmental Approach, because the space is created by increasing the OVD along an arc from Jaw Relationship that is neither Centric Relation or Centric Occlusion.

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10  Occlusion and Non-carious Tooth Surface Loss

 cenario 3: Slide is Vh and Is Sufficient S Restoring to premature contact in CR creates ideal space Vh=Suffcient CO CR

Pre-operative situation

Solution to space needed:

Post-operative situation

By finding the Premature Contact in Centric Relation, the space needed for the restoration of the occlusion between the anterior teeth is achieved. Note: Subsequent treatment replaced the upper central incisors and restored the posterior occlusion, whilst maintaining the occlusion of the CR premature contact.

This is the Re-Organised Approach, except that the Design Phase was done in the mouth, by restoring the Anterior Occlusion with adhesive materials. In common with all of these scenarios: The key to the success of this treatment is to determine, before starting the restoration, which jaw relation will provide the space to restore the worn dentition.

Section 10.2: Creating the Space for the Restoration of the Worn Teeth

243

 cenario 4: Slide is vh, and This is Insufficient for the Restoration S Restoring to Premature Contact in CR does not provide enough space CR

CO

Vh: but need more space

Pre-operative situation

Restoring to the Premature Contact in Centric Relation will not provide the space needed for the restoration of the lower right posterior occlusion, by implant supported crowns. Solution to space needed

  

  

Opening the bite from CR (Terminal Hinge Axis) will create the space. Re-Organised Approach

 

 

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10  Occlusion and Non-carious Tooth Surface Loss

 cenario 5: Slide is vH S Restoring to the premature contact of CR is not an option (see Case 7, in next section)

vH: too much space

Pre-operative situation CR

CO

Restoring to the vH case, represents a significant challenge, as starting from the Premature Contact in Centric Relation will result in a massive overjet. Will not provide the space needed for the restoration of the lower right posterior occlusion, by implant supported crowns.

Solution: to creating space by increasing the OVD along an arc from Jaw Relationship that is neither Centric Relation or Centric Occlusion. Use the Monitored Developmental Approach.

Section 10.2: Creating the Space for the Restoration of the Worn Teeth

245

Solution to space needed CR

CO

?

Opening the bite in the Monitored Developmental Approach does not have the consistent end point that is afforded by increasing the OVD from the starting point of the premature contact in Centric Relation. This is because in Centric Relation, also known as Terminal Hinge Axis, the head of the condyle is in its rotational phase of movement. in contrast, when opening the bite from the jaw relationship of Centric Occlusion, the TMJs are in their translationary phase. So increasing the OVD will result in further translation rather than a potentially more reproducible rotation.

Monitored Developmental Approach Needs the clinician to monitor the patient for any adverse reactions whist developing the new Occlusion. This will require the use of adjustable restorative materials, such as direct placed composite or acrylic provisional crowns.

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10  Occlusion and Non-carious Tooth Surface Loss

 cenario 6: Centric Occlusion = Centric Relation [No Slide] S Need to create space to achieve the restoration

Do we need space? Have we created space? How much?

Pre-operative situation

 

 

Solution to space needed The bite was opened along the arc from the Terminal Hinge Axis. The Design Phase was done in the mouth, by restoring the Anterior Occlusion with provisional crowns. CR CO

Post-operative situation

This is the Re-Organised Approach, because the space is created by increasing the OVD along an arc from Centric Relation (Terminal Hinge Axis), which also happens to coincide with the patient’s pre-treatment Centric Occlusion.

Case 1

247

Section 10.3: Case Histories to Illustrate Restorative Strategies Introduction In this third section of this chapter, some of the decisions that need to be taken and techniques employed to restore the worn dentition are illustrated. This is a relevant inclusion in a book on Good Occlusal Practice as the occlusion can be a factor in the aetiology of non-carious tooth surface loss, and in the success of its restoration. These cases are presented to predominately illustrate the use of directly applied adhesive composite material in the restoration of the worn dentition. Each case will be presented in the same format: Points being illustrated, then: 1. Presenting features and restorative strategy 2. Design planning, including occlusal prescription and aesthetic preview 3. Techniques employed and post-operative results The amount of detail given in each case is restricted to that needed to illustrate a point or features of the restoration. This does not seek to be a comprehensive account on how restore the worn dentition [1, 2].

Case 1 [This case is kindly provided by Ms Johanna Leven BDS, MFDS RCS(Ed) FDS (Rest Dent) RCS: Consultant in Restorative Dentistry, University Dental Hospital of Manchester] Illustrating: • Worn dentitions can sometimes be restored the using the conformative approach. • For the conformative approach to be used, the existing jaw relationship must be maintained (see appnt 6 and 7 below). • Some clinical techniques. 1. Presenting Features and Restorative Strategy a. Aetiology: mainly erosive, dietary acid and intrinsic acid b. Features: • Overall vertical dimension (OVD) remained constant as a result of patient’s metal ceramic crowns UR12. • Very little dentoalveolar compensation has occurred (Figs.  10.16 and 10.17).

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10  Occlusion and Non-carious Tooth Surface Loss

Fig. 10.16  Case 1: Frontal view of presenting condition

a

b

Fig. 10.17  Case 1: Occlusal views of presenting condition

2. Design Planning, including Occlusal Prescription and Aesthetic Preview a. Note that there is sufficient space to work in centric occlusion [ICP] b. Meaning that the restoration can be provided able to work conformatively, i.e. the worn teeth will be restored to the height of the existing crowns c. Clinic: alginate impressions, facebow and CO (ICP) record d. Laboratory: wax up worn teeth to restore full contour and to complement the occlusion between UR12 and lower incisor crowns Occlusal prescription: The planning in this case is minimal as we are using the existing jaw relationship, i.e. the conformative approach. Monitoring: It is important to emphasise that a full examination, including the articulatory system, is carried out before the decision to use the same jaw relationship (to conform) is taken. In addition, during and after the treatment, the patient is monitored for any signs of occlusal intolerance in the tooth, periodontal or articulatory systems. In summary: the new occlusion is monitored whilst it is being developed (Fig. 10.18).

Case 1

249

Fig. 10.18 Aesthetic preview

• The EDEC principle when restoring complex cases to the conformative approach • E = Examine the pre-existing occlusion • D = Design an operative procedure which allows the conformative approach • E = Execute that plan • C = Check that each stage of the restoration conforms to the occlusion of the previous stage

3. Techniques Employed and Post-operative Results In this first case to be presented, the clinician has given some details of the • Order of treatment and number of appointments • Operative techniques employed Appointment and Treatment Sequence This list is not repeated for each of the subsequent Cases. 1. Initial consultation a. Principal complaint and patient aspiration b. History i. Present complaint ii. Dental iii. Medical iv. Social histories c. Full examination i. Teeth ii. Periodontal system iii. Articulatory system d. Special tests, including radiographs e. Diagnosis f. Treatment options g. Provisional treatment plan 2. Initial records appointments a. Impressions, facebow, CO record b. Photos c. Laboratory request 3. Aesthetic preview and final TP explanation

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4. Direct composite restoration of UL123 UR3 using palatal stent 5. Direct composite restoration of LL34 LR45 using full coverage stent, composite repairs to buccal of UL56 6. Removal/repreparation of UR1 for new metal ceramic crown and also minimal chamfer preparation of LL7 for indirect composite onlay 7. Fit of UR1 crown and LL7 onlay, minor polishing/adjustment of other restorations Warning: if the decision had been taken to replace the UR1 crown before restoring the other teeth, the conformative approach would not have been possible 8. Review following completion, no further adjustments were needed 9. Further reviews at 3–6 months Note: patient not provided with an occlusal splint for night wear as the aetiology was erosive Composite build-up technique, in this case: • Monoshade nanohybrid composite used. (Note: Could have used dual shade composite to achieve enhanced morphological characteristics and translucency, but its use is more technique sensitive) • Moisture control achieved with Optragate (Ivoclar Vivodent) lip and cheek retractor and cotton wool rolls lingually. Advantages of Optragate: –– Provides good retraction and moisture control –– Can be easily removed to give the patient frequent breaks –– Allows operator to check the occlusion during treatment. Note: The patient can usually bite together with Optragate in place but if not is easily taken in and out of the mouth. Note: Dental dam is considered the gold standard; in respect of moisture control, it has the disadvantage that it needs to be removed to check the occlusion.

1.

2.



General considerations: Choice of full coverage stent vs palatal stent: Full coverage: a. Allows for full transfer of the wax up, facilitating fully guided restoration of tooth contour. b. Efficient method particularly when a number of teeth are being restored. But: • Cannot layer the composite so is only suitable for monoshade composite. • Can be more difficult to control the contact points of the restoration. • So, needs extra time removing excess composite in the polishing stage. • Can get voids in the restorations which need to be filled in. Palatal stent: a. Allows for transfer of the palatal aspect of the occlusal contour. b. Best technique for using dual shade composite to enhance morphological features and translucency. c. Less excess composite and therefore polishing stage easier. d. Better control of contact points. But: • Labial aspect is restored free hand. • So, technique is dependent on operator skill e. Generally, is more time consuming.

Case 2

251

a

b

c

Fig. 10.19  Case 1: Views of complete case

3. General advice on order of build-ups: –– For a case where maxillary incisors and canines only are being restored, this can be achieved in 1–2 visits, depending on the operator efficiency and the patient tolerance. Restoration of alternative teeth is helpful in order to control the contact points between restorations to allow some shaping and polishing. If carried out in two appointments, it is best to restore the canines first and then the incisors. –– For a full-mouth rehabilitation, the order is similar to that employed for traditional rehabilitation with crowns. Mandibular anteriors first, maxillary anteriors second, placing composite stops on posterior to prevent over eruption. Then restoration of posterior quadrants is undertaken, usually doing each side at different appointments (Fig. 10.19).

Case 2 [This case is kindly provided by Ms Johanna Leven] Illustrating: • If the conformative approach is contra-indicated because of insufficient space for an adequate thickness of restorative material, the overall vertical dimension (OVD) will need to be increased.

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10  Occlusion and Non-carious Tooth Surface Loss

• If OVD is going to be increased, some thought needs to be given to the jaw relationship of the restorations. • The use of a pronounced palatal cingulum on upper anterior teeth. • The use of stents or templates as an aid to the restorative process. 1. Presenting Features and Restorative Strategy a. Aetiology: mainly erosive b. Features: i. Marked palatal and occlusal erosion, with mild labial erosion ii. Insufficient space in the occlusion to be successfully restored conformatively Warning: These cases are sometimes unsuccessfully managed. Restoring these cupping defects conformatively in centric occlusion (CO/ICP), by applying just a smear of composite, will not provide long-term success. Composite needs to be 2-mm thick in areas of occlusal loading to be adequately strong (Fig. 10.20).

a

b

Fig. 10.20  Case 2: Presenting condition

c

Case 2

253

2. Design Planning, including Occlusal Prescription and Aesthetic Preview a. Clinic: Records taken were alginate impressions in stock trays, facebow and centric relation [RCP] record. The jaw relationship is a very important consideration, in the planning of this case, because: i. As explained the conformative approach is not an option. ii. As a consequence of the need for at least 2 mm of composite to restore the occlusal surface, the overall vertical dimension (OVD) needs to be increased. There are two options: Option A: Take a centric occlusion (CO) record (or even do not; relying on the models to be hand fitted together in the laboratory); and then increase the vertical dimension, arbitrarily, from the jaw relationship of that CO. Option B: Take a centric relation [CR] record, at the height of the increased OVD needed for successful occlusal restorations (see Fig. 10.21a–c). Discussion: Because the OVD is being increased, whichever technique is used, the patient will need to be monitored for any adverse reactions to the new jaw relationship, whilst the new occlusion is being developed. If the new occlusion is to be provided along the opening/closing arc of terminal hinge axis [CR/RCP], then it is generally considered to be likely better tolerated, comfortable and functionable. (See chapter 4 for more discussion of the features of the Re-Organised Approach).

a

b

c

Fig. 10.21  Case 2: Record of Terminal Hinge [CR] Jaw Relationship, at an increased OVD

254

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It may not be wrong, to adopt Option A, because the patient might adapt to the new jaw relationship that uses CO as its starting point. It would be wrong, however, to develop the new occlusion in that arbitrary position without carefully monitoring the patient; and being prepared to reverse or adjust the new occlusion in response to adverse reactions. The problem with using CO as the starting point is that: • It is unlikely to give a reproducible position. • There may be problems in transferring a wax up into mouth because it may be difficult to achieve the same occlusal scheme as was planned in the laboratory. • It is likely that many more adjustments will be needed. b. Laboratory following Option B as above: For the wax up of Class I or Class II cases, where there will be contact on the cingulum of the maxillary teeth, a pronounced cingulum plateau should be requested (see Fig. 10.22a). This has several advantages: • This provides the patient with a definite occlusal location that will help them adjust to their new occlusal scheme. • A wide well-defined plateau area will, also, give the patient some ‘Freedom in Centric’, so they do not feel ‘locked in’. It also ensures that the incisor teeth are axially loaded. Without this palatal plateau, the teeth then may not be axially loaded. Notes: There was no need to provide this at UR2 as it was never going to be in contact. Unless this palatal plateau of the Design Wax Up is prescribed, by the dentist, the laboratory might provide a wax up of the palatal surfaces of all the upper anterior teeth looking like the UR2. This is a good example of the principle that it is the clinician’s responsibility to give clear instructions relating to the Design of the new occlusion. a

Fig. 10.22  Case 2: [Design] Wax Up

b

Case 2

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c. Aesthetic [and Occlusal] Preview See Fig. 10.23a–e a

b

c

d

e

Fig. 10.23  Case 2: Occlusal and Aesthetic Preview, using Stent made from Wax Ups

3. Techniques Employed and Post-operative Results a. Build-up techniques: i. Stents: Using a stent is means by which the Design of the wax up can accurately Executed following the EDEC protocol, as has been illustrated in Chap. 4. ii. This case used the different types of stent in the different locations of the restoration: –– Full coverage stents were used for the posterior teeth (Fig. 10.24a–c). The technique involved building up the base of the restoration directly, and then using an injection moulding technique for the top layers, so that it is contoured using the stent. –– A transparent palatal silicone stent was used to build up the palatal aspect of the maxillary incisors (see Fig.  10.25a, b). An opaque impression putty can also be used, but it has the disadvantage that it can only be cured from the labial aspect, requiring the light to pass through the tooth. iii. In this case, the minimal labial build-ups of the upper anterior teeth were carried out free hand (Fig. 10.26).

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The E.D.E.C. Principle in the Re-Organised Approach

E = Examine • the existing occlusion [Centric Occlusion], including jaw relationship in which it occurs. • Determine which teeth occlude in C.O. • Find and Record Centric Relation [Retruded contact position, Terminal Hinge Axis]. • Record which teeth touch in CR [Premature Contact]. • Observe the direction of the slide for the Premature contact to CO. D = Design and plan the new occlusion. This may involve: • Models mounted in CR. • Equilibration of those models [Mock Equilibration], and equilibration of the patient’s existing dentition. • Design wax up. E = Execute the new occlusal prescription to the Design created above. C = Check that you are conforming to this newly designed occlusion in the definitive restorations.

a

b

c

Fig. 10.24  Case 2: Use of full coverage transparent stents to restore of lower posterior teeth

Case 3

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257

b

Fig. 10.25  Case 2: Use of transparent stent to restore of palatal aspects of upper anteriors Fig. 10.26  Case 2: Completed case

Case 3 [This case is kindly provided by Ms Johanna Leven] This case is presented in an abbreviated form to illustrate two points: • Sometimes it proves difficult or impossible to find or record a consistent jaw relationship to use as the starting point for opening the bite on the study models. • Recognising this, the clinician can proceed with an expectation on their and the patient’s parts, that more adjustments will be needed (i.e. the occlusion will be developed as a result of careful monitoring). 1. Presenting Features and Restorative Strategy a. Aetiology: attrition b. Features: i. Increased overall vertical dimension needed. ii. Class III incisor relationship when patient in CO (ICP) (see Fig. 10.27). iii. Incisor edge to edge when patient in CR (RCP) (see Fig. 10.28). iv. It was difficult to manipulate the patient into a consistent CR. This presents problems, which are compounded by the fact that a jaw relationship needed for the mounted model need to be opened to provide sufficient

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Fig. 10.27 Centric Occlusion [ICP/habitual bite]

Fig. 10.28 Centric Relation [RCP/terminal hinge axis] at increased OVD

2.

space for the restorations. It is easier if the record to be taken is on that first contact, as the patient is able to confirm consistency. Compare Fig. 10.28, which is slightly open, with Fig. 10.29 when to patient is resting on the first contact in CR/RCP. Design Planning, including Occlusal Prescription and Aesthetic Preview/build­up Review a. Although an attempt was made to record a consistent CR record (see Figs. 10.30a, b), given the muscle bracing, there was not a high level of operator confidence. b. The models were mounted to this record (see Fig. 10.30c). c. The wax up was done on these models, after having opened up the bite to accommodate the required space to the posterior restorations. d. At the aesthetic preview/build-up review stage, it was possible to refine the occlusion of the proposed definitive restoration (see Fig. 10.31).

Case 3

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Fig. 10.29 Centric relation [RCP/terminal hinge axis] at first contact

a

b

c

Fig. 10.30  Case 3: Record of a Jaw Relationship  *, at an increased OVD [*  was this CR? see text 2a Page 250 and point 2 page 252] Fig. 10.31  Note: UR2 is an implant-supported crown that was replaced by the GDP, after the restoration of the worn dentition. The patient was advised, before treatment, that this would be necessary

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Operator’s comments: I thought that I may not be able to manipulate and record a true CR/RCP in this parafunctioning patient. So, I anticipated that at the aesthetic and functional preview of the initial build-up and at subsequent review stages, I would need to make some further adjustments to the occlusion (develop the occlusion). This is because the patient is likely to ‘deprogram’ a little more once they are restored. This is very similar to the adjustments needed when reviewing a Stabilisation Splint.

What we can learn from this case: 1. If you can a. Find and record CR/RCP • Either at the increased OVD to facilitate the correct thickness of the restorations • Or, at the point of the premature contact of CR/RCP, and then open up the articulator in the laboratory, as will be needed to allow for adequate thickness of the restorative material b. Use facebow so the mounted models open/close to the same centre of rotation as the patient: from terminal hinge axis (CR/RCP) c. Do a design wax up d. from which the templates for the build-up review is made 2. If you can’t do 1 above, because of lack of: • Operator technique and experience • Laboratory support • Equipment • Patient’s neuromuscular release Use the ‘Monitored Developmental Approach’; this infers: • An expectation of having to adjust at the build-up review stage (Develop the Occlusion). In effect, this is using the build-up review stage in the same way that provisional restorations would be used in a traditional crown and bridge case (see Chap. 4). • Monitoring the patient for signs of intolerance to the new occlusion and jaw relationship, before, during and after the restorative treatment. 3. Post-Operative Results (Fig. 10.32)

Case 4

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a

b

c

Fig. 10.32  Case 3: Completed case

Case 4 [This case is kindly provided by Mr Indika Weerapperuma BDS (Brist), MSc (Manc) [Fixed/Remov Pros], PG Cert [Endo], MSDS [Ed] Hon Lecturer, University of Manchester. Kinross Dental Care,  Colombo, Sri Lanka] Illustrating: • Finding centric relation can help the design of the incisor relationship. • It is possible to build up the anterior teeth freehand, providing the provisional restorations which will establish the jaw relation for the restoration of the posterior occlusion 1. Presenting Features and Restorative Strategy a. Aetiology: localised TSL of upper anterior segment due to erosion and attrition

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b. Features: i. Overall vertical dimension—has been maintained, because ii. Dentoalveolar compensation has occurred iii. Centric occlusion (habitual bite) is a pseudo Cl III iv. Centric relation (CR) is a more retruded jaw relationship than that of centric occlusion: resulting in a Cl I incisor relationship v. o/e: no muscle tenderness, normal TMJ function, comfort and range: Nul diagnosis of TMD c. Restorative strategy is to build up occlusion along the opening/closing arc from terminal hinge axis (centric relation) because the vertical dimension of the first contact in CR does not provide enough space for the restorations (Figs. 10.33 and 10.34). Fig. 10.33  Case 4: Presenting condition

a

Fig. 10.34  Case 4: Presenting condition

b

Case 4

2.

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Design Planning, including Occlusal Prescription and Aesthetic Preview a. Clinic: CR records, facebow, and impressions b. Laboratory: Wax up of models mounted to CR (Fig. 10.35) c. Clinic: aesthetic and functional preview

Fig. 10.35  Case 4: Design Wax Up

3. Techniques Employed and Post-operative Results a. Upper 3-3 restored by direct composite at an increased vertical dimension was along opening/closing arc from terminal hinge axis (CR). These were built up freehand. b. Lower posterior occlusion restored by indirect restorations (Fig. 10.36). a

b

Fig. 10.36  Case 4: Restoration of Upper Anteriors by direct bonded composite and Lower Posteriors by indirect restorations

• • • • •

At 1 week review: No muscle tenderness TMJ NAD Eating habits normal Aesthetics satisfactory (patient happy to stay with provisional restorations) Even occlusal contacts 3 month review (patient still happy to stay with provisional restorations) Otherwise NAD

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Case 5 [This case is kindly provided by Mr Indika Weerapperuma] This case is presented to illustrate the technique of restoring alternate teeth 1. Presenting Features and Restorative Strategy a. Aetiology: Attrition b. Features: i. Significant wear of anterior teeth, in a young patient ii. Need to increase OVD to allow for sufficient space of composite build-up of upper anterior teeth (Fig. 10.37) a

b

Fig. 10.37  Case 5: Presenting condition

2. Design Planning, including Occlusal Prescription and Aesthetic Preview a. Wax up b. Palatal stent construction 3.

Techniques Employed and Post-operative Results a. Moisture control with Optragate (Ivoclar Vivodent) (Fig. 10.38) b. Use of palatal stent to form palatal and incisal surfaces c. Use of PTFE tape to isolate adjacent teeth, and aid good contact area form (Fig. 10.39) This case is presented whilst still awaiting use of Dahl technique to restore posterior occlusion, at increased OVD (Fig. 10.40b). See Case 6 for a completed Dahl result.

Case 5

a

265

b

c

Fig. 10.38  Case 5: Use of Optragate [Moisture Control], Stent [Placement of palatal and incisal composite], and PTFE tape [isolate adjacent teeth]

a

c

Fig. 10.39  Case 5: Restorative Process

b

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b

Fig. 10.40 (a) Pre-op. (b) Post restoration/awaiting dahl

Case 6 [This case is kindly provided by Mr Indika Weerapperuma] This case is presented to illustrate: • The use of a palatal stent to restore the upper anterior teeth • The restoration of the posterior occlusion using the Dahl technique 1. Presenting Features and Restorative Strategy a. Aetiology: localised TSL of upper anterior teeth, primary primarily erosive followed by attrition b. Features: i. Dentoalveolar compensation has maintained the overall vertical dimension, despite significant wear ii. Centric occlusion (habitual bite) is in a jaw relationship, resulting in an edge-to-edge incisor relationship, with consequential wear (see Figs. 10.41a–c and 10.42). iii. Centric relation (CR) results in a Cl 1 incisor relationship (see Fig. 10.43). iv. Articulatory system—NAD. c. Restorative Strategy: i. Restore patient to an increased vertical dimension, along the opening/ closing arc from terminal hinge axis (CR) which will create the space for the anterior restorations ii. Use Dahl technique to restore the posterior occlusion 2. Design Planning, including Occlusal Prescription and Aesthetic Preview a. Clinic: Find and record CR jaw relationship with aid of a deprogrammer: Facebow and Impressions. b. Laboratory: wax up of upper 3-3 at an increased height at CR c. Clinic: Aesthetic and functional preview, using template made from wax up of upper anterior teeth.

Case 6

a

267

b

c

Fig. 10.41  Case 6: Presenting condition: Centric Occlusion [not in Centric Relation] results in edge to edge incisor relationship Fig. 10.42  Case 6: Presenting condition: Significant TSL on palatal surfaces

Fig. 10.43  Case 6: Presenting condition: Finding Centric Relation [Terminal Hinge Axis] jaw relationship results in a Class I incisor relationship

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Notes: Occlusal Prescription: The pre-treatment planning for this case was not extensive; but it was carefully monitored during its development. Monitoring: 3 months post-treatment to follow up of posterior teeth achieving contact. Thereafter monitoring of any wear and tear to the composites plus occlusal (Figs. 10.44 and 10.45) 3. Techniques Employed and Post-operative Results a. Provisional Anterior Restorations by directly applied composite i. Palatal putty stent, made from design wax up, facilitated formation of the palatal surfaces and incisal edges ii. Labial form was built up with freehand technique to a size and length acceptable to the patient b. Initial reviews i. Normal TMJ comfort and function ii. No muscle tenderness iii. TMD-null diagnosis iv. Normal eating ability v. Aesthetics satisfactory c. 3 month review i. Articulatory system NAD ii. Molar and premolar occlusion achieved, through Dahl effect iii. Patient happy with aesthetics and function, and wishes to keep anterior restorations as medium-term definitive restorations (Fig. 10.46) a

b

Fig. 10.44  Case 6: Completed case, which may have been Provisional; depending on results of careful monitoring [Monitored Developmental Approach, see text]

a

Fig. 10.45  Posterior occlusion still open

b

Case 7

a

269

b

Fig. 10.46  Posterior occlusion has closed

Case 7 [This case is kindly provided by Mr Indika Weerapperuma.] This case illustrates that providing a set of rules is not appropriate; every case is different and need to be assessed. There is no ‘painting by numbers’ in dentistry. 1. Presenting Features and Restorative Strategy a. Aetiology: localised TSL of upper anterior and lower anterior segment due to primarily erosion b. Features: i. Deep overbite ii. Limited inter occlusal space c. Restorative Strategy Try to restore patient to Centric Relation (CR) (Fig. 10.47). a

b

c

Fig. 10.47  Case 7: Presenting condition: Centric Occlusion [not in Centric Relation] results in small overjet

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b

Fig. 10.48  Centric relation: note very large overjet in this jaw relationship

2. Design Planning, including Occlusal Prescription and Aesthetic Preview a. Clinic: CR records, facebow, impressions b. Laboratory: wax up of models to CR Analysis This case was done by a first year MSc student1 who thought that every case needed to follow the protocol: a. Find and record centric relation b. Ask the laboratory to wax up the new occlusion on CR mounted models (Fig. 10.48) Once the wax up was done, it became clear that this case could not be restored at CR due the significant change in jaw relationship. The design process should have stopped at the clinical stage when CR was found or at least after the models were mounted and before the wax up was done.

Case 8 [This case is kindly provided by Ms Hanah Beddis BChD (Hons), MJDF RCSEng, MSc, MPros RCSEd, FDS (Rest Dent) Consultant in Restorative Dentistry, Leeds Dental Institute This case is presented to illustrate that where dentoalveolar compensation has occurred, it may not be desirable to lengthen the teeth incisally. Where there has been dentoalveolar compensation and/or excessive gingival display, crown lengthening may be indicated in order to improve the aesthetics of worn upper anterior teeth. 1. Presenting Features and Restorative Strategy (Fig. 10.49a, b) a. Aetiology: Predominantly erosion with an element of attrition  The MSc student has given permission for this case to be used.

1

Case 8

271

b. Features: i. Short clinical crowns of maxillary anterior teeth and severe palatal tooth surface loss ii. High lip smile line exposing significant amounts of attached ging ivae. Because the incisal levels of the teeth were at a reasonable level relative to the lip line, it was not desirable to significantly increase the tooth length incisally. This would have resulted the poor appearance of excessive tooth length. c. Restorative Strategy: Perform surgical crown lengthening to upper anterior teeth before restoration of those teeth at a slight increase in OVD. The small increase in OVD was provided to accommodate indirect restoration of the severely worn palatal surfaces of the upper anterior teeth. 2. Aesthetic Preview (Fig. 10.50a) Following crown lengthening, composite restorations at a slight increase in OVD to upper right 5 to upper left 6 (Fig. 10.50b). 3. Post-operative Results (Fig. 10.51a–c) The incisal level of the teeth has not been significantly altered, but surgical crown lengthening has improved the clinical crown height and reduced the appearance of excess gingival display (Fig. 10.52).

a

b

Fig. 10.49  Case 8: Presenting condition

a

Fig. 10.50  Case 8: Small increase in OVD

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b

c

Fig. 10.51  Case 8: Completed case

Fig. 10.52  Post- and pre-op showing. Improved aesthetics, with reduction in visible attached gingivae, at the same OVD

Case 9

273

Case 9 [This case is kindly provided by Miss Alicia Patel BDS and Mr Philip Dawson BSc BDS MSc DipRestDent PgCertEd] 1. Presenting Features and Restorative Strategy a. Aetiology: multi-factorial: i. Attrition, patient knows he grinds his teeth ii. Dietary-related erosion b. Features: i. No TMD but masseters are hypertrophic ii. Skeletal Class 1, with incisor edge to edge relationship iii. Inadequate posterior occlusion due to failed restorations (Fig. 10.53) c. Restorative Strategy Option A: Increase vertical dimension along opening arc from terminal hinge axis. This is the Re-Organised Approach. Options B: Increase vertical dimension from jaw relationship of existing occlusion (Centric Occlusion). This is the Monitored Developmental Approach For a discussion of these options, see: Case 2. Sect. 10.3: Design Planning, including Occlusal Prescription and Aesthetic Preview and Case 3: What we can Learn Cases 2 and 3 were done by a consultant in restorative dentistry, whereas this case was done by fifth-year dental student, under the supervision of very experienced clinician who practised in primary care. The consultant choose the technically more difficult Option A [Re-Organised Approach], whereas the student’s case was done following Option B [Monitored Developmental Approach]. 2. Design Planning, including Occlusal Prescription (Option B) Clinic: • Impressions • Facebow • Centric Occlusion bite record

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a

b

c

d

e

Fig. 10.53  Case 9: Presenting condition

Laboratory: • Mount models in Centric Occlusion • Open articulator by about 4 mm • Design Wax-Up (Fig. 10.54)

Case 9

a

275

b

Fig. 10.54  Case 9: Design Wax Up

3. Treatment Sequence: a. Restoration of anterior teeth by the addition of composite using stents made from the design wax-up b. Restoration of the posterior occlusion to the new jaw relationship by indirect restorations c. Provision of stabilisation splint Discussion of the Monitored Developmental Approach, in this Case This treatment had not only to meet the patient’s needs for a good aesthetic and functional result, but it had to be appropriate to the operator’s level of clinical skills. The features of this treatment plan are: • It was possible to satisfy the patient’s aesthetic aspiration early in the treatment sequence. • Importantly the case was closely Monitoring: • If the students or their supervisor detected any signs of an intolerance to the new occlusion or jaw relationship, adjustments were possible, because non-invasive and adjustable materials were used, the new occlusion could be developed, and this could be done before the posterior indirect restorations were provided. • Given the history of active bruxism, the patient’s consent for long-term splint therapy was sought at the planning stage. This had the dual advantages of protecting the restorations from sleep bruxism and making the development of myaglia less likely.

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4. Post-Operative Results (Fig. 10.55) Fig. 10.55  Case 9: Completed case

Guidelines of Good Occlusal Practice

1. Not all tooth surface loss needs treatment, but effective monitoring is essential 2. Dento-alveolar compensation has often occurred in patients exhibiting marked tooth surface loss 3. The examination of the patient involves the teeth, periodontal tissues and articulatory system. 4. There is no such thing as an intrinsically bad occlusal contact, only an intolerable number of times to [para]function on it. 5. The patient’s occlusion should be recorded, before any treatment is started. 6. Compare the patient’s occlusion against the benchmark of ideal occlusion. 7. A simple, two-dimensional record of the patient’s occlusion taken before, during and after treatment is an aid to good occlusal practice. 8. The conformative approach is the safest way of ensuring that the occlusion of a restoration does not have potentially harmful consequences. 9. Ensuring that the occlusion conforms to the patient’s pre-treatment state is a product of examination, design, execution and checking (the E.D.E.C. protocol). 10. The ‘re-organised Approach’ involves firstly the establishment of a ‘more ideal’ occlusion in the patient’s pre-treatment dentition or provisional restorations; and then adhering to that design using the techniques of the ‘conformative approach’. 11. An ideal occlusion in removable prosthodontics is one which reduced de-­ stabilising forces to a level that is within the denture’s retentive capacity. 12. The occlusal objective of orthodontic treatment is not clear, but a large discrepancy between centric occlusion and centric relation should not be an outcome of treatment.

References

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13. An ‘orthodontic’ examination of the occlusion should include: the dynamic occlusion; and the jaw relationship in which the patient has their centric occlusion. 14. The occlusion of periodontally compromised teeth should be designed to reduce the forces to be within the adaptive capabilities of the damaged periodontia. 15. Good occlusal practice in children is determined by the needs of the developing occlusion; consequentially ‘restoration at all costs’ may not be the best policy. 16. Bruxism is a centrally controlled behaviour: it is not an ‘occlusal disease’ or caused by the Occlusion. 17. Occlusal adjustment has no evidence basis in the management of Bruxism. 18. When planning restorations, consideration should be given as to whether there is Active Bruxism. 19. Management of tooth wear may simply involve protecting the dentition and ongoing monitoring. 20. Dento-alveolar compensation has often occurred in patients exhibiting marked tooth surface loss. 21. The decision on how to Create Space for the restoration of the worn dentition must be taken before starting treatment. 22. The worn dentition may be restored by either the Conformative, the Re-Organised or the Monitored Developmental Approach.

References 1. Van’t Spijker A, Rodriguez JM, Kreulen CM, Bronkhorst EM, Bartlett DW, Creugers NH. Prevalence of tooth wear in adults. Int J Prosthodont. 2009;22(1):35–42. 2. Braem M, Lambrechts P, Vanherle G. Stress-induced lesions. J Prosthet Dent. 1992;67:718–22. 3. Grippo JA. A new classification of hard tissue lesions. J Aesth Dent. 1988;3:14–9. 4. Ten Cate M. In situ models, physico-chemical aspects. Adv Dent Res. 1994;8:125–33. 5. Tallgren A. Changes in adult height due to aging, wear and loss of teeth and prosthetic treatment. Acta Odontol Scand. 1957;15(24):73. 6. Garnick J, Ramfjord SP.  Rest position: an electromyographic and clinical investigation. J Prosth Dent. 1962;12(5):895–1. 7. El Wazani B, Dodd MN, Milosevic A. The signs and symptoms of tooth wear in a referred group of patients. Br Dent J. 2012;213(6):10. 8. Smith B, Knight J. A comparison of patterns of tooth wear with aetiological factors. Br Dent J. 1984;157:16–9. 9. Bartlett D, Ganss C, Lussi A. Basic Erosive Wear Examination [BEWE]: a new scoring system for scientific and clinical needs. Clin Oral Investig. 2008;12(1):65–8. https://doi.org/10.1007/ s00784-­007-­0181-­5. 10. Wetselaar P, Lobbezoo F. The tooth wear evaluation system; a modular guideline for the diagnosis and management planning of worn dentitions. J Oral Rehabil. 2016;43(1):69–80. 11. Kelleher M, Bishop K. Tooth surface loss: an overview. Br Dent J. 1999;186:61–6.

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12. Moufti M, Lilico JT, Wassell R. How to make a well-fitting stabilization splint. Dent Update. 2007;34(7):398–408. 13. Davies SJ. et al. Occlusion: Is there a third way? A discussion paper. Br Dent J. 2021;231: 16–162.

Further Reading Johansson A, Johansson A-K, Omar R, Carlsson GE. Rehabilitation of the worn dentition. J Oral Rehab. 2008;35(7):548–66. https://doi.org/10.1111/j.1365-­2842.2008.01897.x. Milosevic A. Clinical guidance and an evidence-based approach for restoration of the worn dentition by direct composite resin. Brit Dent J. 2018;224:301–10.

Good Occlusal Practice in the Provision of Implant-Borne Prostheses

11

Even those general dental practitioners who are not implant providers are likely in the future to be responsible for the maintenance of implants. The increased use of endosseous dental implants means that many dentists will encounter patients with dental implants in their everyday practice. Dental practitioners might be actively involved in the provision of implant-borne prostheses at both the surgical and restorative phases, or only at the restorative stage. This chapter is written for all dentists, because most dentists will have patients who either have or want to have implant-supported prostheses. It aims to: • Examine the subject of occlusion within implantology • Provide Guidelines of Good Occlusal Practice to be used in the design of the prosthesis that is supported or retained by one or more implants.

Implantology is based upon osseointegration.

Osseointegration For osseointegration to occur predictably, clinical guidelines were developed as long ago as 1993 to optimise success rates [1]: • The implant must consist of a suitable biomaterial with appropriate surface properties. • Adequate vital bone must be present to support the implant. • A precise surgical fit must be achieved between the bone and the implant.

© Springer Nature Switzerland AG 2022 S. Davies, A Guide to Good Occlusal Practice, BDJ Clinician’s Guides, https://doi.org/10.1007/978-3-030-79225-1_11

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• The implant must be inserted with a low-trauma technique to avoid overheating of the bone during preparation of the receptor site. • The implant should not be subject to functional loads during a healing period of 3–6 months. All of these criteria seemed to have survived except for the last: immediate loading has been accepted since the early 2000s. Although these guidelines do not mention ‘occlusion’, once integrated, dental implants must be restored sympathetically with due regard to occlusion since unfavourable loading has been cited as a major cause of failure. This chapter will present the factors that influence the occlusal schemes used for prostheses supported or retained by endosseous dental implants. Since relatively few studies have been designed with the sole aim of comparing different occlusal schemes, it is difficult to be certain what is the best occlusion for a given clinical situation. Current techniques and materials tend to be based on what has evolved over years of clinical practice and laboratory research. They are based on what is believed, rather than what is known, to be good occlusal practice in implantology. ‘Osseointegration’ is the biological process that results in a close structural relationship between vital bone and a dental implant. Successfully integrated and carefully loaded implants have been shown to be capable of being retained by the host tissues for many years. Osseointegration was first defined as ‘the direct structural and functional connection between ordered living bone and the surface of a load carrying implant’ [2]. Subsequently, it was defined as ‘a process whereby a clinically asymptomatic rigid fixation of alloplastic materials is achieved and maintained in bone during functional loading’ [3]. Obviously, the significant difference between ‘osseointegration’ and the attachment of teeth to the alveolus is the absence of a periodontal ligament. The absence of a periodontal ligament between an implant and the bone significantly reduces the patient’s sensory perception of the occlusal load.

Consequences of the Differences between Teeth and Implants The absence of a periodontal ligament is the first consideration when we are deciding what is Good Occlusal Practice in Implantology. This is because the absence of a periodontal ligament has significant consequences on the Adaptive Capability of the prosthesis to resist occlusal forces. This complete lack of adaptive capacity is the result of four factors: 1. No proprioceptive nerves 2. Much less blood supply

Consequences of the Differences between Teeth and Implants

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3. No reactive movements 4. Reduced compressive displacement [4]

1. Significantly Less Proprioception The orofacial locomotive system is unique in the body, when it is compared to all the other locomotive systems, because it has an additional layer of sensory input to the central nervous system. Whereas all of the locomotive systems have sensory nerve endings in the orofacial locomotive system has an extra layer of sensory input to the CNS from the nerve endings in the periodontal membrane. • bones • joints • muscles and associated soft tissues • epithelium This means that our patients can feel the occlusal loads that our restorations of teeth experience. This is significantly reduced or even absent when we provide an implant supported prosthesis. It also means that when a tooth is extracted, the patient experiences not only the mechanical loss of that tooth or those teeth, but they also suffer from a traumatic de-afferentation. The disability is extreme when all teeth are lost, because it is a total traumatic de-afferentation. There is some mitigation in this loss of sensory input that is described as osseoperception [5]. This suggests that there is an increased sensitivity in the sensory motor cortex to the nerve endings in the bone to occlusal forces that the alveolar implants transmit to the bone. This phenomenon whilst not being able to compensate for the loss of periodontal proprioception following tooth extraction is a useful response to disability. It is achieved through central neuroplasticity. It probably has the ability to improve jaw function for the patient who has an implant as opposed to mucosal supported prostheses. Similar learned pathways in the brain stem and sensory motor cortex can explain how people with an artificial limb can learn how to engage in activities that require a high level of sensory input (Fig. 11.1). This is an adaptation that occurs in the articulatory rather than tooth system. It does not allow any reflex protective responses, and it should be considered the ‘second best’ neural capacity.

2. Much Less Blood Supply The blood supply around an implant is significantly less than that which flows through the well-vascularised periodontal membrane. Blood is the tissue that carries the agents of the immune system, and so there is a reduced ability to react to

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11  Good Occlusal Practice in the Provision of Implant-Borne Prostheses

a

b

Fig. 11.1 (a, b) Photographer: Tony Herr. With permission from Dr. Hugh Herr. The remarkable ability to rock climb with prosthetic lower legs indicated that some ossseoperception transmitted via the attachment to the upper legs is present

pathogens. Noxious stimuli to the implant include not only pathogens but also the physical insult of occlusal overload.

3. Reactive Movements These can be considered under two headings:

Orthodontic Movement If a sustained force is applied to a tooth, then it will move. The discipline of orthodontics and the phenomenon of tooth migration are the results of this reactionary movement. Implants cannot react in this way. Reversible Hypermobility An alternative to tooth migration is the ability within the periodontal membrane to ‘hold’ the tooth less firmly. This hypermobility is probably a reaction to an interrupted long-term occlusal force.

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Consequences of Reduced Adaptive Capacity...

Reduced Compressive Displacement Teeth Implants

Vertical 25–100 μ 3–5 μ

Buccolingual 56–108 μ 10–50 μ

Because teeth are not ankylosed to the bone, they can compensate to an acute occlusal overload by a small and immediate movement. This stress breaking attachment of natural teeth rather than rigid one of osseointergration, together with the jaw jerk reflex, provides the immediate protective response to acute occlusal overload. Both are absent in implant supported prostheses.

 onsequences of Reduced Adaptive Capacity, Because C of the Absence of Periodontal Attachment A consistent message throughout this book has been that an occlusion should only be judged by the tissue reactions to it, rather than any rigid set of rules based upon some concept of mechanical perfection. We treat living systems with a very wide range of adaptive capabilities. The issue with implant-supported prostheses is that the nature of the attachment of the implant, when compared to the periodontal membrane, meaning that the adaptive capability is likely to be less than that for teeth. But what is presented are NOT RULES, rather they are Guidelines of Good Occlusal Practice in Implantology. It is up to individual clinicians to decide what type of occlusal prescription to provide. This treatment planning decision will be made after: • A comprehensive examination, including a pre-treatment occlusal analysis • An assessment of the patient’s needs Because of the reduced adaptive capability of implants, an adverse reaction of occlusal overload is likely: • To be less predictable • Happen quicker • Happen with less warning • Occur as a result of a smaller load • Occur as a result a less frequent application of occlusal load • To be harder for the patient to perceive • As a consequent difficult for the patient to avoid • To be irreversible • To be catastrophic

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11  Good Occlusal Practice in the Provision of Implant-Borne Prostheses

This list starts with the most trivial and ends up with the most severe and potentially catastrophic reactions to occlusal overload in implantology: • Screw loosening • Screw fracture • Crown fracture • Abutment fracture • Loss of crestal bone, as in ‘funneling’. This is an example of bone loss that is the result of trauma from occlusion without any inflammatory process • Implant fracture • Implant exfoliation • • • • • •

In contrast, the reactions to occlusal overload in teeth are: PDL thickening Mobility Fremitus Pain Wear facets Tooth and/or restoration fracture

Second Difference between Implants and Teeth Having considered the factors that may affect the adaptive capabilities of an implant to occlusal overload, we should now consider the mechanical consideration of the fact that implants are often, but not always, narrower than the roots of the teeth that they replace (Fig. 11.2). This means that any occlusal load applied to an implant supported crown that is not in line with the long axis of the implant will be a relatively greater force than it would be if it was applied to the wider root supporting a similar crown. Fig. 11.2  Implant v root. The crown on a tooth is supported by a much broader base than that on an implant

Second Difference between Implants and Teeth

285

The fulcrum for this force will be the crestal bone, which in common with the rest of the alveolar bone is strongest when resisting compressive forces and weakest when resisting shear forces (Fig. 11.3). The force applied to the crestal bone by an occlusal load that is outside the long axis of the implant is a shear force (Fig. 11.4). The Coronal Section is the most susceptible to Bone loss

++++

Crestal Bone is Fulcrum Point

Occlusal Load

force

Occlusal Trauma

injury

+ further the Occlusal Load is from Long Axis of the Implant... greater the Force

a

b

Fig. 11.3  An occlusal force that is distant from the long axis of the implant will result in shear force to the crestal bone

Apical force

Vertical axis

Lingual force

Tensile Force

ear

Sh

Mesial force Faciolingual axis

Shear

Shear

Distal force

ear

Sh

Compressive Force

Facial force Occlusal force In all other directions there is a vector that is a Shear Forces

Fig. 11.4  All loads that are not in line with the long axis of the implant result in a shear force. [reprinted with permission from Ch 5, Dental Implant Prosthetics, Misch C E, Elsevier]

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11  Good Occlusal Practice in the Provision of Implant-Borne Prostheses

a 1.

b 2.

3.

Occlusal Trauma +

Occlusal Load

Occlusal Trauma +++

Occlusal Load

Fig. 11.5 (a) The shorter the implant, the greater the Force potential Moment on it. (b) The increased Moment created by a reduced crown: implant ratio

The process by which bone maybe lost as a result of trauma from occlusal overload has been explained by the term ‘fatigue microtrauma’ [6] and is described as when the ‘rate of fatigue microdamage exceeds the reparative rate’ [7]. If the implant to crown ratio has been adversely affected by alveolar resorption, that has occurred before the implant is placed, then the force against the crestal bone, generated by an occlusal load outside the long axis of the implant, is even greater (Fig. 11.5). Although there is a mechanical justification in suggesting that non-axial forces should be avoided when designing the occlusion of implant supported crowns, there is little evidence that there is a biological consequence to ignoring this advice. This is why, as stated elsewhere in this chapter, the clinician does not have the comfort of scientific certainty but has to rely on clinical common sense. The evidence for the significance of non-axial forces was summarised by Koyano et al. [8]. This reviewed random controlled trials in respect of non-axial forces under three headings: 1. Difference in marginal bone levels between wide and narrow implant diameters 2. Implant angulation 3. Cantilevers None of these trials found any statistically significant differences in marginal bone levels.

Summary • Implants have less adaptive capability to occlusal force than teeth, because of the absence of periodontal membrane • The occlusal forces experienced by an implant are likely to be greater than experienced by a natural tooth, if a comparable force is applied that is not in line with the long axis of the implant.

Current Application of Oral Implants

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Current Application of Oral Implants The current application of implants is much more extensive than when implants were first utilised. In stark contrast to their initial applications (when predominantly only edentulous patients were treated with fixed dentures), implants are now inserted into: • Partially dentate patients with a healthy or compromised periodontium. • Posterior regions of the maxilla and mandible • Sites in which the bone has been augmented In addition, many different types of prostheses may now be implant-supported: • Crowns • Bridges • Precision removable dentures • Removable overdentures (mucosa and implant supported)

Implant Success Criteria for implant success have been outlined some years ago. There should be an absence of: • Mobility • Associated radiolucency • Pain • Infection or iatrogenic neuropathies. • Peri-implant vertical bone loss ––