The Aleut Dentition: A Correlative Study of Dental Characteristics in an Eskimoid People [Reprint 2014 ed.] 9780674429499, 9780674499423

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The Aleut Dentition

The A l e u t Dentition A Correlative Study of Dental Characteristics in an Esk i m o i d P e o p l e

C o e n r a a d F. A .

Moorrees

1957

C a m b r i d g e , Massachusetts

H a r v a r d U n i v e r s i t y Press

© Copyright 1957 by the President and Fellows of Harvard College

Distributed in Great Britain by Oxford University Press, London

Library of Congress Catalog Card Number: 57-7615

Printed in the United States of America

Preface

An expedition sponsored by the Peabody Museum of Harvard University was sent to the Aleutian island chain in 1948 to conduct a comprehensive study of the inhabitants. Particular attention was to be directed toward a study of the historical development of their culture and language, their racial and genetic diversity, and the factors responsible for the decline in the number of Aleuts. Also evidence was to be gathered to determine whether the population had migrated to the Islands from Siberia or from Alaska, and whether the islands of this long-stretching chain had ever been employed as "stepping stones" for the peopling of the New World from the Old World. The relative isolation of the present population and the rich archeological sites gave promise of making this endeavor worthwhile. The initiative for studying the Aleuts came from Dr. William S. Laughlin who had accompanied Dr. Ales Hrdlicka on his last trip to the islands in 1938. In a sense, therefore, the researches planned were a continuation of those of the late Dr. Hrdlicka. The personnel of the 1948 expedition consisted of two archeologists, Allan G. May and Charles I. Shade; a linguist, Gordon H. Marsh; a cardiologist, Frederic Alexander; two physical anthropologists, William S. Laughlin and Stanley M. Garn, and the author who served as an odontologist. Dr. Laughlin was also the field director of the team.

vi

Preface

Funds for the expedition were provided by the Viking Fund Incorporated of New York (The Wenner-Gren Foundation) and the Office of Naval Research. In addition assistance was received from the United States Navy, Coast Guard, and Army which provided, among other services, transportation to and from the Aleutians, and also made it possible to visit a great many of the islands. Preparations for the expedition were carried out in the Peabody Museum, and I should like to acknowledge our gratitude to Dr. John Otis Brew, Director of the Museum, and to the late Dr. Earnest A. Hooton, Professor of Physical Anthropology, for the valuable guidance they provided. Personally, I am most indebted to the late Dr. Percy R. Howe who, as Director of the Forsyth Dental Infirmary for Children, permitted me to join the expedition staff. It was characteristic of Dr. Howe to support with wholehearted enthusiasm any research endeavor which would open new and broad perspectives. To his successor, the late Dr. Howard M. Marjerison, who was Director of the Forsyth Dental Infirmary from 1950 to 1955,1 am most grateful for his encouragement in conducting an exhaustive analysis of the material gathered and for providing all the support that could be desired to facilitate this task. During the entire period of this undertaking I profited greatly from my association with Professor Hooton. His unflagging interest in the progress of the study did much to relieve the drudgery that is unavoidable in any investigation of this type. Lastly I want to pay tribute to all of my companions on the trip for the good fellowship they provided. Their good spirits and the friendliness of the Aleuts made the three months spent in the subarctic an unforgettable experience. The adventurous landings on small islands, the hunts for skeletal remains, the chasing and catching of seal pups on the Pribilof Islands for the purpose of obtaining their cardiograms and, yes, even the innumerable wheelbarrows full of dirt to be emptied for the archeologists, are still pleasant memories of this voyage in the summer of 1948. C. M. Boston, Massachusetts, 1957

Acknowledgments

The chapter on the Aleut dietary was written in collaboration with Tomi K. Hibbett, former Chief of the Nutrition Department, the Forsyth Dental Infirmary for Children. Penelope Peckos, the present Chief of this Department, and Dorothy Callahan, Nutritionist, Massachusetts General Hospital, Boston, Massachusetts, also lent considerable assistance in the preparation of the dietary analyses. Chemical tests on the three water samples brought back from the Islands were carried out by Elias Elvove, Senior Chemist, Division of Chemistry, National Institute of Dental Research, Bethesda, Maryland, through the courtesy of Dr. Trendley Dean, the Director of the Institute. The detailed laboratory studies on the morphology of Aleut teeth were made with the assistance of Kale vi Koski, Dr. Odont., former Fellow in Orthodontics, Forsyth Dental Infirmary, who is at present the Chief of the Orthodontic Department, University of Helsinki Dental School, Helsinki, Finland. Dr. Koski made the measurements on the teeth and dental arches, and carried out the statistical analyses of these data. He also collaborated in drafting the chapter on odontometry and in preparing the section that deals with the dental arch in Chapter 8. Richard H. Osborne, Ph.D., of Columbia University, studied

viii

Acknowledgments

the data on torus mandibularis and mandibular prognathism and worked out the genetic analysis of this material. The section on the histology of Aleut teeth, in Chapter 9, was written in collaboration with Reidar F. Sognnaes, D.M.D., Ph.D., Charles A. Brackett Professor of Oral Pathology and Associate Dean of the School of Dental Medicine, Harvard University, Boston, Massachusetts. Valuable suggestions for this study were contributed by Stanley M. Garn, Ph.D., former Anthropologist, Forsyth Dental Infirmary, at present Associate Professor of Anthropology, Antioch College and chief of the Department of Physical Growth, Fels Research Institute, Yellow Springs, Ohio. The preparation of the final draft was carried out by Mary R. Crawford. Veikko O. Hurme, D.M.D., Director of Clinical Research, Forsyth Dental Infirmary, served in the onerous capacity of critical reader of the manuscript and furnished a number of editorial suggestions. Ruth W. Howe (Mrs. Percy R. Howe), Consultant to the Nutrition Department, and Charles E. Hatch, D.M.D., Chief of the Central Clinic, both of the Forsyth Dental Infirmary, also have offered many valuable contributions to the manuscript. Barbara Voss, former Librarian of the Forsyth Dental Infirmary and Ruth H. Burgess, her successor, as well as Margaret Currier, Librarian of the Peabody Museum, Harvard University, Margaret G. Palmer, Librarian of the School of Dentistry, University of Pennsylvania, and Theo Ε. de Jonge, Privaat Docent, Municipal University of Amsterdam, Holland, were most helpful in securing the bibliographic material utilized. To all the people named above, in addition to several others whose names have not been specifically mentioned, the author wishes to express his deep gratitude for their collaboration and for their interest shown in this investigation.

Contents

1

The "Aleut," his environment, history, and appearance

2

The objectives of a dental study in populations of different racial stocks

3

Collection of data and statistical treatment of observations

4

The Aleut dietary (in collaboration with Tomi K. Hibbett)

5

Morphologic characteristics of the dentition, torus mandibularis, and gingival pigmentation in the Aleuts Shovel shape of incisors Cusp numbers of mandibular second premolars Cusp numbers of maxillary molars Carabelli's cusp of maxillary molars Cusp numbers and groove patterns of mandibular molars Taurodontism Supernumerary cusps Supernumerary and missing teeth Exostoses of the maxillae Pigmentation of gingiva and oral mucosa A general discussion of the morphological aspects of the dentition of Aleuts

6

The odontometry of Aleut teeth (in collaboration with Kalevi Koski)

1 5 8 12 20

77

χ

Contents

7

Tooth emergence in the Aleuts

102

8

Tooth position and occlusion in the Aleuts Occlusion Crowding The ratio between the size of the maxillary and mandibular teeth as a possible cause of malocclusion The dental arch Wear of the teeth

114

9

Dental disease in the Aleuts Peridental disease Dental caries

134

Appendix. Comparative odontometric data of different populations

155

References

175

Notes

191

Index

193

T h e A l e u t Dentition

1 The

Aleut," Η is Environment

History, and Appearance A chain of treeless, rocky, volcanic islands, usually well hidden by fog and rain but otherwise favored by a mild climate, can be located on the globe at the same latitude as London, but on the 180° meridian (Fig. 1). These islands, the Aleutians, were inhabited at least 4000 years ago by Eskimoid people who came from the Alaskan mainland (Laughlin and Marsh, 1951). The first inhabitants are now referred to as Pre-Aleut by Hrdlicka (1945), or as Paleo-Aleut by Laughlin and Marsh. One thousand years ago a second main migration period began, which brought a different strain of Eskimoids to the islands. The new invaders did not reach the western end of the island chain in great numbers, and therefore the original inhabitants there were not subjected to as great a degree of admixture as those of the eastern islands. Thus, the Western Aleut has retained more of the PaleoAleut morphologic type and, consequently, differences can still be observed between Eastern and Western Aleuts today. Laughlin (1949) does not even consider the contemporary Aleuts as belonging to a single homogenous population, but recognizes the "Eastern" and "Western" Aleuts as two "breeding isolates." His hypothesis is based on existing anthropometric, serologic, ethnologic, and linguistic differences between the two groups. The dis-

2

The Aleut Dentition

tribution of blood groups, furthermore, confirms the racial origin of the Aleut as Eskimoid, and indicates only a slight degree of white admixture. Contact with white men dates from Bering's discovery of the islands in 1741 and the subsequent arrival of Russian fur traders, or promishlenniki, who were attracted by the great number of fur-bearing animals. The persistent hunting of sea otter, seal, and fox, however, caused a depletion of the herds in many localities. Thus the search for new hunting grounds necessitated betterorganized expeditions into more distant parts of the area. Companies were established in order to cope with these greater demands and finally a merger of two large private companies, the Shelekof-Golikof and the Muilnikof, resulted in the formation of the Russian American Company in 1799. This company had a virtual monopoly on the management of the new Russian possessions which lasted until the purchase of Alaska by the United States of America in 1867 (Andrews, 1947). During the Russian administration the population acquired Russian names and became members of the Russian Orthodox Church. It is of interest to note that the Russians recognized the existence of cultural differences between the two groups of Aleuts and established two separate districts for their administration in 1826. The islands from Attu to Atka were incorporated in the Atka district and the islands east of Atka were incorporated in the Unalaska district. The dividing line was thus drawn directly east of Atka island. The same geographic division of the island chain was used by Laughlin for his classification of the Eastern and Western Aleuts. The arrival of the Russian fur hunters not only signaled the beginning of the depletion of the animal herds, but resulted in a marked decline in the number of Aleuts through massacres, disease, and warfare. The pre-Russian Aleut population is estimated at 20,000 to 25,000 (Collins, Clark, and Walker, 1945). Laughlin and Marsh (1951) record that of this large Aleut population only 1200 remain, "over half of whom reside outside their aboriginal homeland, in the Pribilof Islands and in the Komandorskie Ostrava (Commander Islands)." On the island of Umnak probably

Environment, History, and Appearance

3

22 villages once existed, with a total population of 2000, whereas in 1950 there was only one village, Nikolski, with a population of 59. The decline of the Aleut population continues even today owing to a high incidence of disease, such as tuberculosis and venereal disease, and an unsatisfactory economic situation. According to Alexander (1949) the diseases mentioned are especially serious deterrents to the well-being of the populace and result in a high mortality rate and a low mean age of death. Furthermore, no proper use can be made of the economic resources that are still present on the Islands and in their immediate vicinity. A more profitable exploitation will entail financial assistance and guidance in the use of modern techniques and equipment. Laughlin and March (1951) have already pointed out that "with proper attention, medical and social, the Aleuts could be made vigorous and enabled to make more extensive use of the vast economic resources of the Aleutian Islands which were so successfully exploited by their ancestors." During our visit to the Aleutian Islands in 1948, a total of 156 Aleuts of all ages was found. They lived in Nikolski village on Umnak Island and in Atka village on Atka Island. The inhabitants of Attu were not permitted to return to their homes after World War II and now live in Atka. Laughlin and Marsh (1951) have given the following general physical description of the Aleut: "In common with all other Eskimo-speaking peoples the Aleuts have a large head, large face and lower jaw, tall relative sitting height, medium to submedium stature primarily due to short legs, small hands and feet, and a generally Mongoloid physiognomy particularly noticeable by the epicanthic fold, straight black hair, scanty beard, and narrow nasal root." (Figs. 2 to 7) Furthermore, east-west differences are listed by Laughlin (1949) as follows: "Both the male and female Western Aleut have a shorter stature and a steeper forehead slope than the Eastern Aleut. The head breadth of the latter not only exceeds that of the Western Aleut, but of all other Eskimo. Easterners have a higher cephalic index and are, therefore, more round-

4

The Aleut Dentition

headed than Westerners. Easterners also exceed Westerners in having a greater bizygomatic breadth, greater face height, and a higher frequency of blood groups Ο, Β and type N." Statistical significance could be demonstrated, however, only for head breadth. Laughlin attributes the existence of these differences, as has been mentioned previously, to a greater persistence of Paleo-Aleut traits in the Western Aleut and, in the case of bloodtype N, to a greater degree of non-Aleut admixture in the Eastern group. The family relationships of the Aleut population of Nikolski and Atka village are shown in two genealogies prepared by Gam (1949) (Figs. 8 and 9). It should be borne in mind that Eastern and Western Aleuts are found together in these genealogies because some of the Western Aleuts actually live in Nikolski and some of the Eastern Aleuts in Atka village.

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Morphological Characteristics

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26

The Aleut Dentition

ridges are only faintly developed. As in the maxilla, the mandibular lateral incisors have slightly more ridge formation than the central incisors. Sex differences are consistently present in the shoveling of incisors and canines, the males showing a preponderance of the more pronounced degrees. Interpopulation differences for shovel shape were also found, the Eastern Aleuts invariably displaying a more marked form of the trait in all classes of teeth studied than the Western group. No statistical tests were carried out to determine the level of significance of sex and east-west differences, because the available data were too few to warrant a meaningful interpretation. The findings have been plotted on the genealogies of the Aleut population, but because of the small number of siblings and the great variation in expression of this trait, no study of the mode of inheritance could be attempted. Ridge formation was also observed on the labial surfaces of a few Aleut maxillary incisors, resulting in what Dahlberg (1949) has termed "double shovel shape." In contrast to the lingual shoveling the labial shoveling frequently showed a greater accentuation of one of the two marginal ridges. The presence of labial ridges was not associated with the more pronounced degrees of shoveling of the lingual surfaces. The lingual surfaces of the incisors were also studied for the presence and size of the tuberculum dentale and of median ridges. The tuberculum dentale is generally absent in Aleut incisors and, therefore, no relationship could be demonstrated between the tuberculum and the degree of shoveling. According to de Jonge Cohen (1935) the lingual surfaces of maxillary incisors are of two basic types and the Aleut incisor resembles Type II (Fig. 13). In the few instances where a tuberculum was discernible, its shape conformed to Type Β in the classification of Mühlrciter-de Jonge Cohen (1928), but was ill-defined (Fig. 14). Median ridges are seldom present on the lingual surfaces of the maxillary incisors of Aleuts and are only barely elevated when they do occur. During the examinations of the Aleuts it became apparent,

Morphological

Characteristics

27

from a study of worn incisors in which the dentin was exposed, that the dentin participated in the marginal ridge formation. Discussion The comparison of data on Aleuts with those on other populations is of limited value because of the subjective method of appraisal used in this and all other studies. Some basis exists for comparing the findings on shovel-shaped incisors with the observations made on populations which likewise show a marked ridge and fossa formation in these teeth because of the probability that an approximately similar scale of grading was used in these studies. The degree of shovel shape is likely to have been overrated in describing populations with only slight expression of this characteristic, a fact which necessitates great caution in attempts to use such data for comparisons of populations. As in all other populations of predominantly Mongoloid stock, the occurrence of shoveling of the maxillary incisors is high in the Aleut, approximating that in the Chinese (Hrdlicka, 1920) who have the highest prevalence of the trait according to Dahlberg (1945). The percentage of pronounced degrees of shovel shape of central incisors is higher in the Aleut (63 percent) than in Hrdlicka's (1920) Eskimo group (38 percent). Such differences can be expected because the Aleuts may have originated from an Eskimoid group with particularly marked shovel-shaped incisors, or because their relative isolation on the Islands may have favored a high degree of specialization. Geographical differences exist in the shovel shape of central incisors within the Eskimo population, judging from Hrdlicka's findings in Alaska (38 percent) and those of Pedersen (1949) in East Greenland (84 percent). Predominance of the marked forms of shovel shape in the Aleut males conforms to the observations reported by Hrdlicka on Whites, American Negroes, and Hawaiians (1920) and on Sioux Indians (1931), and by Goldstein (1948) on Texas Indians. The findings do not agree with those of Hrdlicka (1920) on Chinese, and of Dahlberg (1949) on the Pima Indians.

28

The Aleut Dentition

In the Aleuts and East Greenland Eskimos (Pedersen) the lateral incisors showed a higher percentage of marked shoveling than the central incisors. This is not surprising because the lateral incisor is narrower than the central incisor and is thus likely to give the impression of a more pronounced shovel, while in reality the ridge can be of the same height as in the central incisor. No difference in the frequencies of marked shovel shape between the central and lateral incisors was observed in Pecos Indians (Nelson, 1938) and Pima Indians (Dahlberg, 1949). The usefulness of the shoveling of the maxillary incisors as a means of differentiating between Mongoloid groups has yet to be demonstrated. Further analysis of this problem will require the utilization of a uniform and objective method of classification of this trait. This analysis may also facilitate the determination of the mode of inheritance of shovel shape, which could not be studied in the Aleut material and which is not known at present (Gates, 1946; Lasker, 1950). Hrdlicka (1920) stated that the development of shovel shape and tuberculum dentale are unrelated. This is confirmed by the absence of the tuberculum in the majority of Aleut maxillary incisors, while the incidence of shovel shape is relatively high in this population. A similar conclusion was reached by Pedersen from his study of the East Greenland Eskimo dentition. In contrast to the near absence of median ridges in Aleuts, Pedersen noted that the median ridges appear in a rather high proportion of East Greenland Eskimo incisors, but to varying degrees of height. These ridges are conspicuous in anthropoids (Hrdlicka, 1920, 1921) and in Krapina skulls (de Terra, 1905). What little factual evidence there is concerning the incidence of median ridges in the maxillary incisors of contemporary man suggests, in general, that distinct ridges are rarely observed. Their racial significance remains to be established. Thus, of the morphologic features of maxillary incisors discussed above, it seems that only shovel shape has significance for racial classification. Shoveling of incisors is part of the Mongoloid master pattern in the dentition and the prevalence of mark-

Morphological Characteristics

29

edly shovel-shaped incisors in the dentition of a population indicates preponderantly Mongoloid origin. THE NUMBER OF CUSPS OF THE MANDIBULAR SECOND PREMOLAR The mandibular second premolar is known to have either two or three cusps in both man and the anthropoids. De Terra (1905) considers the three-cusped premolar as a progressive or specialized form that has arisen to compensate for the reduction in size of the lingual cusp of the mandibular first premolar. De Jonge Cohen (1917) objects to the usual classification into a two- or three-cuspal type, because actually more than three cusps are always present. Following Bolk's (1922) "dimere" theory3 he assigns the formula 1P2/3D4 to the bicuspal premolar and calls it sextitubercular, since two smaller cusps can be observed adjacent to each of the main cusps. Reduction of the mesiolingual cusp (No. 3) results in a quintitubercular form 1P2/D4 commonly referred to as the tricuspal second premolar. Notwithstanding the fact that the quintitubercular second premolar exhibits a reduction of one lingual cusp (No. 3), de Jonge Cohen still considers it a progressive type because the size of the two remaining lingual cusps is increased. Neither the hypothesis of de Terra or of de Jonge Cohen gives a clear-cut answer to the question of whether the threecusped mandibular second premolar is the ancestral or the modified form. Thomsen (1955) has been able to formulate a more satisfactory hypothesis of the problem, based on her studies of the occurrence of missing teeth in the population of Tristan da Cunha. It may be recalled that the frequency of missing teeth in man's dentition is greatest for the last or most distal tooth of any group (lateral incisors, second premolars, and third molars), with the exception of the mandibular incisors where the central incisor, instead of the lateral, is more frequently found to be agenesic. Thomsen stated her hypothesis concerning the ancestral form of cusp numbers of the mandibular second premolar as follows: "It seems strange, however, that whereas in other groups

30

The Aleut Dentition 3 _Q)
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Morphological

Characteristics

59

greater prevalence of torus, but also a greater frequency of the more pronounced tori. Torus mandibularis in the Aleuts was located at the level of the root tips of the teeth and, generally, extended from the second premolar to the canine, but it may well have reached beyond these limits in a few instances. In general, the tori on the left and right sides of the mandible were equally well developed. In only one instance, that of a 43-year-old feTable 13. Frequency of occurrence (percentage) of torus mandibularis at different a g e levels in male and female Aleuts belonging to the all inhabitants group. (The figures irfparentheses'refer to the numbers of individuals studied.) Age group (years) Torus mandibularis

1-9

10-19

20-29

30-39

40-49

50-65

69.6 (16)

86.9 (20)

71.4 (15)

47.1 (8)

53.8 (7)

36.4 (4)

Trace

8.7 (2)

0

4.8 (1)

5.9 (1)

0

9.1 (1)

Slight

21.7 (5)

8.7 (2)

14.3 (3)

11.7 (2)

7.7 (1)

9.1 (1)

Marked

0

4.4 (1)

9.5 (2)

35.3 (6)

23.1 (3)

36.3 (4)

Extreme

0

0

0

0

15.4 (2)

9.1 (1)

Total number of individuals 23

23

21

17

Absent

13

11

male, was its presence unilateral. Asymmetrical development was found in five Aleuts, but undoubtedly many more such differences would have been observed if an exact technique of evaluation had been employed. In order to investigate a possible causal, environmental relationship between torus formation and function of the masticatory apparatus, the association between wear of the teeth and the presence of torus was studied. The degrees of tooth wear, although not a precise measure of function, still give some indication of the amount of use to which the dentition has been sub-

60

The Aleuf Dentition

jected. No association between these two factors was found in the Aleut. The findings on torus mandibularis in the Aleuts strongly suggest that the presence or absence of torus mandibularis is not a purely functional response. Among these findings may be listed: (1) lesser prevalence in females, (2) preponderance of the more marked degrees of torus in males, (3) absence of any association with tooth wear as a measure of function, (4) different frequencies of torus in Eastern and Western Aleuts, and (5) the occurrence of torus in Aleut children. Since it was apparent that other factors are involved in its causation and, since torus appeared in a fairly large number of Aleuts of all ages, its genetic aspects were investigated. On plotting the data on genealogical charts designed by Garn (1949), a familial incidence of torus became evident and a further genetic study was conducted by Dr. Richard H. Osborne of Columbia University. Osborne was able to formulate a hypothesis concerning the mode of inheritance of torus mandibularis in the Aleut. He found that, "at least three independent loci affecting torus development must be assumed to satisfy all cases represented in the pedigrees of the two Aleutian populations, clearly indicating a complex rather than a simple mode of inheritance. However, the data are not sufficient to determine how complex the mode of inheritance may be. The evidence is, furthermore, insufficient to determine whether a cumulative or major gene modifier mechanism is operating" (Moorrees, Osborne and Wilde, 1952). One should bear in mind that this particular mode of inheritance found for torus mandibularis may apply only to the Aleut populations and, in the absence of confirmatory data, it should not be assumed to exist in other population groups (Muller, 1949). Discussion Torus palatinus. The complete lack of torus palatinus in the Aleut, an Eskimoid population, is interesting in view of its frequent occurrence in Eskimos from St. Lawrence Island (Woo). Pedersen also found it "quite often present" in the East Green-

Morphological Characteristics

61

land Eskimos. Fürst and Hansen, on the other hand, observed the palatine torus to be "not so frequent" in Eskimos from Greenland. Further studies of the prevalence of torus palatinus in the Eskimo may reveal whether these variations are incidental or part of a geographical pattern. Association between torus mandibularis and torus palatinus. The data presented clearly suggest that no association exists in the living Aleut between torus palatinus and torus mandibularis. This conforms to observations made on the Bushmen by Drennan (1937) and on the Bantu by Shaw (1931). Differences between the two types of tori have also been revealed in their bone structure. Microscopic inspection of bone sections shows that spongiosa is present in torus palatinus (Weidenreich; Thoma, 1937; Woo), while the mandibular torus is made up entirely of compacta (Fürst and Hansen; Weidenreich). Thus, the two types of tori seem to form independently of each other, a characteristic which, however, does not exclude their appearing together in a population as in the Norwegian Lapps (Schreiner). Sex differences. The greater prevalence of torus mandibularis and the greater representation of the more pronounced forms in Aleut males conforms to Hrdlicka's observations on 5632 mandibles of White, Negroid and Mongoloid origin. The findings concur also with those of Danielli on Ostiaks, of Schreiner on Norwegian and Eskimo material, and of Ihara (1950) on Japanese. Yet a preponderance of tori in females was found by Akabori in 244 Japanese and by Schreiner in 308 Norwegian Lapp mandibles. Thus, if Hrdlicka's extensive series represents the general trend, we should be aware of its possible reversal in a specific population as observed by Akabori and Schreiner. Age differences. The occurrence of torus mandibularis in Aleut children is contrary to most previous findings, but it is by no means unique. Fürst observed the torus in the skulls of "quite young children and young individuals." Schreiner (1935), studying the skulls of Norwegian Lapps from seven villages, reported a frequency of 12.9 percent of torus mandibularis in 62 children

62

The Aleut Dentition

as against 32.5 percent in 308 adults. However, all children with tori originated from two villages. The prevalence of torus mandibularis in children from these two villages alone was 34.8 percent. The percentage of adults with tori was also higher in these two communities (48.7 percent) than it was for the rest of the population (17.1 percent). The latter figure has been calculated from Schreiners original tabulations. Hrdlicka examined 119 mandibles of Western Eskimos up to 10 years of age and, in contrast to the findings of the present study, of Fürst, Hansen, and of Schreiner, he found torus in only three instances all above 5 years of age. In view of the observations made by Schreiner on Norwegian Lapps, an evaluation of Hrdlicka's results would be possible only after a study of the frequency of torus mandibularis in adults of the same population. Very few tori have been found in children by other observers, which is not surprising because these studies have dealt exclusively with skeletal material in which the young are sparsely represented. As it was remarked earlier, the opportunity to study torus in children is much better on the living subjects. In order to obtain additional evidence on the incidence of torus mandibularis in Aleut children, a study of a closely related Aleut population living in the Pribilof Islands was conducted in collaboration with Dr. Edwin Wilde, Physician for the Fish and Wildlife Service, stationed at St. Paul Island, Alaska. Wilde examined 127 Aleut children, none older than 17 years of age, from the Pribilof Islands and found torus mandibularis in 30.7 percent. He used the same method of grading and classification as that employed in the present study and checked the accuracy of his grading technique by examining adults from Atka and Nikolski who were employed during the sealing season on the Pribilof Islands and who had been previously graded by the author. The prevalence of torus mandibularis in children from the Pribilof Islands was found to approximate that in children from Atka and Umnak Islands. The data have been pooled for presentation in Table 14. For the total series of Aleut children between 1 and 17 years of age, the frequency of torus mandibularis is 23.9 ± 3.3 percent (Figs. 24 and 25).

Morphological

63

Characteristics

This additional material points out again that torus mandibularis can be present in the young, at least in an Aleut population (Moorrees, Osborne and Wilde, 1952). It is, however, quite likely that the final degree of development of torus is not expressed until the adult age is reached. Location. Schreiner, Miyasita (1935), and data as to the most frequently observed limits of torus mandibularis. The anterior canine root (Schreiner, Miyasita) or the (Akabori). All three writers agree that

Akabori have provided anterior and posterior limit is either near the first premolar root tip the posterior limit is

Table 14. Frequency of occurrence (percentage) of torus mandibularis in Aleut * children from 1 to 17 years of age. (The figures in parentheses refer to the numbers of children studied.) Torus mandibularis

Both sexes

Males

Females

3.1 (5)

3.5 (3)

2.6 (2)

9.8 (16)

11.6 (10)

7.8 (6)

Marked

4.9 (8)

5.8 (5)

3.9 (3)

Extreme

0.6 (1)

0

1.3 (1)

5.5 (9)

3.5 (3)

7.8 (6)

76.1 (124)

75.6 (65)

76.6 (59)

163

86

77

Bilateral: Trace Slight

Unilateral: Trace & slight Absent Total number of children

* From the Aleutian and Pribilof Islands.

most often found near the second premolar root tip. Fürst and Hansen have remarked that this torus is very constant in its location and their statement is in complete agreement with the findings on living Aleuts. Van den Broek relates that torus mandibularis never passes the mylohyoid line and the place of

64

The Aleut Dentition

origin or insertion of the muscles below the line is always free from bony exostoses. The bilateral form of torus mandibularis is the most common, according to Akabori. When differences occur, the torus on the right side is generally larger (Akabori; Lasker, 1947). Schreiner concluded that as a rule the left and right tori are of identical size. He examined 100 mandibles with torus and found only seven with a unilateral torus, all of which were very small. In the Aleut the location of torus mandibularis and its bilateral occurrence conform, in general, to the findings of other investigators. Torus mandibularis in previous generations. The figure expressing the prevalence of torus mandibularis in the living Aleuts (35 percent) differs greatly from that obtained by Hrdlicka (63.4 percent) from his study of 238 skulls representing older Aleut generations. Three factors may have influenced these results. First, some very slight tori may have escaped detection in the living Aleut because of overlying soft tissue and, therefore, more tori can be reported on skeletal material of the same population. Second, White admixture could have lowered the incidence in the now living Aleuts on the assumption that fewer Whites have tori than Mongoloids. This statement is conjectural since the amount of White admixture and the mode of inheritance of this trait in the Aleut and his racial mixtures are not known. Third, Hrdlicka's Aleut skeletal material dates roughly from A.D. 1000 to 1800 and in view of the results of other investigators, it is possible that torus occurred more often in the older generations. It has been shown, for instance by Fürst and Hansen, that tori were more frequent in Scandinavian mandibles from prehistoric times and the Middle Ages (17.0 percent; η = 164) than those from "later times" (12.0 percent; η = 110). A similar conclusion can be obtained by comparing the prevalence of torus (60.4 percent) in 169 Neolithic Japanese mandibles (Kiyono and Miyamoto, 1926; Kintake, 1928) to that in recent Japanese (26.6 percent, Akabori).

Morphological

Characteristics

65

It is most likely that the greater prevalence in older Aleut generations and the technique of evaluation are the two factors chiefly responsible for the greater frequency of torus mandibularis in the skeletal material reported by Hrdlicka than that found in the contemporary Aleut. Geographical distribution. Torus mandibularis has been observed in many contemporary populations but, in general, the prevalence is low in European (7.5 percent) and American Whites (6.1 percent) and in American and African Negroes (11.3 percent) according to Hrdlicka (1940). Its frequency is the highest in Mongoloids, although varying among the subgroups. Eskimoids have the greatest percentage of occurrence (71.6 percent, Akabori) followed by Chinese (27.0 percent, Miyasita), Japanese (26.6 percent, Akabori) and American Indians (13.5 percent, Hrdlicka). Among American Indians, the findings range from 4.0 percent in female Florida Indians to 27.6 percent in male Pueblo Indians (Hrdlicka). The frequency also differs among Eskimoid groups, varying from 84.8 percent in Greenland Eskimos (Fürst and Hansen) to 40.0 percent in Alaskan Eskimos (Hrdlicka). The prevalence of torus mandibularis in Aleuts (35.2 percent) is close to that in Alaskan Eskimos. Causation. A controversy regarding the influence of genetic and environmental factors underlies the various hypotheses concerning the origin of torus mandibularis. The same difference of opinion also exists with respect to the causation of torus palatinus. The formation of torus mandibularis in Icelanders was visualized by Hooton as a reponse to functional demands, due to hard food substances or heavy use of the teeth. Kajava, in his study of Finnish Lapp material, supports this contention after observing an association between torus and wear of the teeth as a measure of function. Hrdlifcka, in one of the latest and most complete reviews to date on exostoses, strongly supports the functional hypothesis. Perier, on the other hand, has stated that if the torus is caused by stress, it should be located on the external, rather than the internal, surface of the mandible in order to reinforce the bone.

66

The Aleut Dentition

Furthermore, it has been shown that the bone lamellae of torus mandibularis and of torus palatinus are transverse to the stress lines (van den Broek; Woo). The occurrence in children and the absence of a relationship with attrition led Fürst and Hansen to the conclusion that torus mandibularis originally may have arisen through mechanical causes, but that it now has become a racial characteristic, although a variable one. Shaw likewise supports the genetic explanation of the formation of torus mandibularis and Drennan even utilized this torus, together with other racial characteristics, to show that Bushmen have Mongoloid affinities. Knap (1953) considers mandibular and maxillary tori "characteristic of the Mongolian race." Three other hypotheses have been brought forward in answer to this problem. Grimm (1938) found a negative correlation between torus and the linea mylohyoidea. The more marked the latter, the smaller the torus, especially the tubercular type. He classified this negative correlation as "clear proof" that variations in the soft tissue layers of the bone are responsible for the formation of the tubercula mandibularis. Schreiner assumed that because of a deficient diet and especially avitaminoses, a high sensitivity of the bone leads to the formation of tori. As a result, various other exostoses, in addition to those in the palate and mandible, are found in the skeleton. Unfortunately, this hypothesis has not been subjected to critical study, but it is worthy of future attention. Van den Broek related the cause of torus mandibularis to "chemical irritation of the mucous membrane." Weidenreich found torus more closely associated with robustness than with weakness of the jaw bone and suggested that the protuberances (tori mandibularis and maxillaris) are pillars left after the reduction of the formerly much bulkier alveolar processes in the course of human evolution. He considers tori early hominid characteristics, and not late acquisitions. It is rather difficult to explain the different frequencies of torus mandibularis in the Eastern and Western Aleuts on the basis of functional stimuli. In the light of available information,

Morphological

Characteristics

67

one can assume that the form and kind of food and also the chewing habits are practically identical in these two groups. Furthermore, no evidence was obtained during the visit of the expedition to the Islands that the Eastern Aleuts performed certain tasks with their jaws and teeth which taxed their masticatory apparatus appreciably more than the corresponding organs of the Western Aleuts. From Schreiners study of interpopulation differences in adult Norwegian Lapps an inverse relationship between torus development and function can be inferred. Schreiner reported a statistically significant difference (C.R. = 3.3) between the prevalence of torus in 150 Sea Lapps (48.7 percent) and 37 Nomad Lapps (21.6 percent). More Sea Lapp children were found to have tori than was the case with Nomad Lapp children, but at the same time he observed that the Sea Lapps did not utilize their dentitions as much as the Nomad Lapps. From the results of the Aleut study and the review of the literature, it seems obvious that there is a sufficient number of reasons to make the hypothesis of a functional causation of torus mandibularis difficult to accept. This conclusion is derived from findings pertaining to bone histology and architecture, occurrence in children, sex differences, absence of association with wear of the teeth, and different frequencies of torus mandibularis in populations having comparable diets and habits of mastication. In the present study evidence is presented, on the basis of a familial incidence and results of a genetic study, which suggests strongly that torus mandibularis is an inheritable trait. According to Lasker (1950) the trait has a "high penetrance because of the tendency toward bilateral symmetry in individuals." Evidence from other sources may in time support the hypothesis of genetic causation of torus mandibularis. General conclusions. Torus mandibularis is most frequently, although not exclusively, found in Mongoloid populations. If its prevalence is high in a population and the more marked degrees of its development prevail, the torus is seemingly indicative of

68

The Aleut Dentition

Mongoloid ancestry. Unless future investigations prove the contrary, torus mandibularis may be considered as one of the criteria of the Mongoloid master pattern as defined in Chapter 2. With respect to torus development, the Aleuts conform to this pattern. At present no conclusions can be drawn as to its possible value for the differentiation between populations of Mongoloid stock. PIGMENTATION OF GINGIVA AND ORAL MUCOSA Oral pigmentation, or melanoplakia, generally occurs in the darkskinned populations. However, Becker (1927) demonstrated microscopically the presence of melanin even in the oral mucous membranes of Whites which showed no clinical evidence of pigmentation. It is not surprising, therefore, that non-Whites exhibit oral pigmentation in association with greater amounts of pigment in hair and skin. Oral pigmentation is most frequently observed in the gingival margin near the incisor and canine teeth and may even be present in the partially or totally edentulous (Dummett, 1945). It may occur as a line, as a triangular area conforming to the shape of the interdental papilla, or as a combination of both. Interdental pigmentation is usually observed near the canines, to a lesser degree in the gingivae of the more posterior teeth, and on the lingual side of the mouth (Dummett, 1945). These pigment deposits are not retricted to the gingivae but are also found in submucous tissues. Monash (1932) noted, when examining Negro babies, that oral pigmentation may be present shortly after birth. Yet there is usually a relative paucity of general pigmentation in the Negro at birth and oral pigmentation is correspondingly slight. Skin pigmentation increases during the first years of life and is accompanied by an increase in oral pigmentation. It is of interest to note from Monash's report that, "in infants the pigmentation is first observed on the palatal and lingual surfaces and not on the buccal surface, whereas in adult life the latter surface is very often found pigmented with the former surfaces free."

Morphological

Characteristics

69

In persons of a similar skin color, but of different racial origin, no appreciable difference occurs in the amount or character of the oral pigmentation (Monash). Dummett (1945) similarly found a close relationship between skin color and oral pigmentation, yet was able to show that oral pigmentation may be absent in Negroes with a very dark skin color. Dummett (1946) concluded that physiologic pigmentation is not limited to any race, but is a common characteristic of the dark-skinned populations. A darkish pigmentation in the mouth may also result from diseases (Addison's disease), ingested chemicals (lead, bismuth, mercury, and silver salts), and from mechanical deposits of exogenous origin, such as charcoal from tooth powders or coal dust in mines (Prinz and Greenbaum, 1939). This incidental pigmentation affects only certain individuals in a population and, therefore, is of no concern as a source of error in a racial study. Oral pigmentation is of value only as a means of determining whether a population is of non-White stock. Since this determination can be made adequately without inspection of the oral cavity, oral pigmentation has no practical importance for racial differentiation. Present Study Gingival pigmentation was observed in the field and recorded under one of four categories: absent, diffuse, triangular area, and linear. In addition, the amount of melanin deposition was graded as trace, slight, or marked. Evaluation of the amount of diffuse pigmentation which occurred together with spots or lines was attempted but found impractical. Observations were made separately for the maxilla and mandible. Results are summarized in Tables 15 and 16, and show that some form of gingival pigmentation was noticed in Aleuts of all ages. In the maxilla the total percentage of individuals with gingival pigmentation was 61 percent and in the mandible 63 percent. No distinct difference in the occurrence of pigmentation was observed between the young Aleuts (5 to 10 years) and the adults.

The Aleut Dentition

70

Table 15. Frequency of occurrence (percentage) of pigmentation of the maxillary gingiva in male a n d female Aleuts belonging to the all inhabitants group.

(The figures in parentheses refer to the numbers of individuals studied.) Degree of occurrence Pattern of pigmentation

Trace

Slight

Marked

All three degrees combined

Diffuse only

21.9 (7)

43.8 (14)

26.9 (32)

Triangular area

57.1 (4)

34.4 (11) 42.9 (3)

0

5.9 (7)

Linear

27.3 (9)

45.5 (15)

27.3 (9)

27.7 (33)

Absent

0

0

0

39.5 (47)

20

29

23

Total number of individuals

119

Table 16. Frequency of occurrence (percentage) of pigmentation of the mandibular gingiva in male a n d female Aleuts belonging to the all inhabitants group.

(The figures in parentheses refer to the numbers of individuals studied.) Degree of occurrence Pattern of pigmentation

All three degrees combined

Trace

Slight

Marked

Diffuse only

28.6 (8)

32.1 (9)

23.5 (28)

Triangular area

50.0 (9)

22.2 (4)

39.3 (11) 27.8 (5)

Linear

37.9 (11) 0

37.9 (Π) 0

24.2 (7)

24.4 (29)

0

37.0 (44)

28

24

23

Absent Total number of individuals

15.1 (18)

119

Morphological Characteristics

71

Localized melanin deposits occur in the Aleut either as triangular concentrations in the interdental papillae or as straight or festooned lines which follow the gingival margin. The triangular or linear deposits were found mostly in the incisor regions, but in some instances extended to the molar regions. It was also noticed that the localized deposits occurred only in the buccal mucosa of the maxillae. Separate tabulations of the type and extent of gingival pigmentation have not been made for the sexes or for Eastern and Western Aleuts because it was felt that the results obtained by utilizing subjective criteria did not warrant detailed analysis. There is no clear evidence that either the maxilla or mandible exhibits a greater proclivity to gingival pigmentation. No attempt was made to study pigmentation of the tongue, floor of the mouth, cheeks, or the hard and soft palates of the Aleut. Discussion The findings recorded in Tables 15 and 16 are only approximations of the true incidence of gingival pigmentation in the Aleut due to the subjective method of appraisal employed in this study. Comparative material is scarce and seems to be limited to reports on Japanese and Negroes. Fujibayashi (1938) observed pigmentation in 5 percent of 1729 Japanese, a markedly lower figure than that reported for the Aleuts. In his series the incidence for females (53 percent) was slightly higher than that for males (47 percent). In 72 percent of 50 Negroes, Dummett (1945) found "some degree of melanogenous pigmentation." Prinz and Greenbaum noted that gingival pigmentation is "never observed in children," but findings on the Aleut children, Negroes (Dummett and Monash), and on Japanese (Fujibayashi) contradict this statement. No data on other populations of Mongoloid or Negroid stock are available and therefore, an interpretation of the significance of melanoplakia in the Aleuts is impossible.

72

The Aleut Dentition

A GENERAL DISCUSSION OF THE MORPHOLOGICAL ASPECTS OF THE DENTITION OF ALEUTS In preference to further discussion of each dental character separately, an attempt will be made to review these characters in a broader perspective by indicating possible trends which underlie their occurrence, and which are superimposed on the basic pattern of man's dentition. This method of approach may give the reader a better understanding of the fundamental differences between the dentitions of populations. It may also lead to a clearer comprehension of the differences between the dentitions of Eastern and Western Aleuts, which have been frequently demonstrated, but were classified as "not statistically significant" except for torus mandibularis. Before proceeding with this specific aim, a discussion of Dahlberg's (1949) interpretation of Butler's (1939) "field concept" and its application to the human dentition is appropriate. This concept postulates that all the teeth are part of a system, not separate evolutionary units, and also that "the evolution and variation of that system are of an orderly nature." It permits the schematization of the occurrence of various dental traits, especially with regard to their anatomical location. According to Dahlberg, dental characteristics are manifested to a maximum degree in certain key teeth in each of the four morphologic tooth groups: incisors, canines, premolars, molars. The key teeth in these groups are morphologically relatively stable. The farther away a tooth is from the key tooth in its own group, the more unstable, or variable, it will generally be. The third and second molars, the second premolars, and the maxillary lateral incisors are the least stable teeth, exhibiting a greater tendency to variations in size and in the expression and retention of basic patterns than the first molars, first premolars, and maxillary central incisors. These more variable teeth are also frequently absent, a condition noted and labeled by Bolk (1912), "terminal reduction." The only exception to the observation that the more posterior

Morphological Characteristics

73

or distal teeth are more variable than the anterior or mesial key teeth in each tooth group, is the mandibular incisor group. In the mandible the central incisors are considered more variable than the lateral ones. The "field" is, thus, an anatomical area wherein some influence is effective during development. It can be visualized as a magnetic field, which decreases in intensity with increasing distance from the center of magnetic energy. Not only each tooth group, but each characteristic feature within a group, has its own individual field, which accounts for differing tendencies in the degrees of modification exhibited by these autonomous characteristics. According to this concept, none of the various anatomical traits in man's dentition are completely interlinked. As an illustration of this hypothetical law, one can point out that the incidence and degree of development of Carabelli's cusp is independent of the number of cusps in the maxillary molars, even though Carabelli's tuberculum is only an accessory cusp. For the same reason, a reduction in cusp numbers in the maxilla does not necessarily imply that the same degree of reduction will be found in the mandibular molars (de Terra, 1905). Besides this complex aggregate of subfields, the dentition as a whole is controlled by a center with a wider area of influence. Figure 26 has been reproduced from Dahlberg (1945) to facilitate comprehension of the application of Butler's "field concept" to the variations of the morphologic characteristics of the human teeth. Dahlberg (1949) apparently influenced by this hypothesis of Butler, classified the characteristic features of the dentition as primary and secondary. The primary characters are the fundamental traits of the dentition, for example, Carabelli's cusp and the Dryopithecoid pattern of the mandibular molars. The secondary characters, on the other hand, tend to mask or suppress the primary characters, especially in the more variable members of each tooth group as, for instance, in the modification of the Dryopithecoid pattern into a " + " groove pattern. Actually, the secondary characters are simplifications of the primary characters. Since Dahlberg contends that the primary

74

The Aleut Dentition

characters can be intensified and that simplifications also occur on the "stable" teeth, the designations primary and secondary do not greatly clarify the description of specific trends in the dentition of a racial subgroup. However, it appears more profitable to consider the differences in the dentitions of individuals as being due to various combinations of intensifications, simplifications, or retentions of the basic characters. It can be further expected, and partly demonstrated, that populations show specific and generalized patterns in all tooth groups toward either intensification or simplification of dental traits. Examples of intensifications are: marked shovel-shaped incisors, large cusps of Carabelli, hypertaurodontism and marked mandibular tori. Simplifications are: " + " groove patterns in mandibular molars; reduction in the number of cusps of mandibular second premolars, maxillary and mandibular molars; and reduction in the number of teeth. This concept agrees in principle with that of Dahlberg and will be used in this study because it affords the most simple portrayal of evolutionary trends which underlie the formation of dental characters in the Aleuts. When the findings are grouped on the basis of intensification, simplification, or retention, as in Figure 27, the Aleut dentitions show intensification in possessing marked forms of shovel-shaped incisors as well as of torus mandibularis. Retention is evident in the relatively great prevalence of four cusps in the maxillary second molar and five cusps in the mandibular second and third molars and, possibly, of hypotaurodontism of pulp chambers in the mandibular molars. Simplification is observed in the near absence of Carabelli's cusp, the high incidence of " + " groove patterns in mandibular molars and the high incidence of bicuspal mandibular second premolars. This last observation conforms, however, to the trend toward modification of dental characters observed in other populations. In general, however, the Aleut dentitions are modified to a lesser extent from the hypothetical basic human pattern than the dentitions of other racial groups. A similar observation has been

Morphological

Characteristics

75

made for the American Indians (Dahlberg, 1949), and East Greenland Eskimos (Pedersen, 1949). The findings on the Eastern and Western Aleuts were analyzed in the same manner to determine whether differing trends toward intensification or modification exist in the dentition of these two groups. A review of the material studied indicates that the Eastern Aleuts exhibit more intensification of basic characteristics than the Western Aleuts. They show, for instance, greater frequency of marked shovel-shaped incisors and of marked mandibular tori. The retention of a Ύ " groove pattern in the first molars, of five cusps in the other two mandibular molars, and of four cusps in the maxillary second molars, is likewise greater in the Eastern Aleuts. It is only in a greater prevalence of the bicuspal form of the mandibular second premolar and of the tricuspal form of the maxillary third molar that the Eastern Aleuts show a trend toward simplification in the morphology of their dentition. Thus, despite the fact that interpopulation differences between the Eastern and Western Aleuts were statistically significant only for torus mandibularis, a grouping of the findings on the basis of intensification or retention of basic characters demonstrates rather distinctive trends for each subgroup. These differing trends strengthen Laughlin's hypothesis (1949) that the population of the Aleutian Islands consists of two different breeding isolates. There is still, however, no fully satisfactory explanation of why these trends exist. One might conjecture that the contemporary Western Aleuts have more White admixture than the Eastern Aleuts. In favor of this hypothesis is the fact that Whites as a group show, in general, a marked tendency toward simplification and little tendency toward intensification of the basic traits in their dentitions. Furthermore, the greater frequency of the cusp of Carabelli likewise suggests a greater degree of White admixture in the Western Aleuts. Since the prevalence of Carabelli's cusp is, however, low in the total Aleut population and since the degree of its development does not differ in individuals of the two

76

The Aleut Dentition

subgroups, the slightly greater statistical frequency in the Western Aleut is actually not very meaningful as a criterion of White admixture in the Aleut population. If, on the other hand, one assumes, like Laughlin, that the contemporary Western Aleuts are less admixed with the later Eskimo migrants, and have retained their Paleo-Aleut traits to a greater extent, then one might conclude that the Paleo-Aleut dentition must have shown a marked tendency toward simplification and little tendency toward intensification. The later Eskimoid invaders must have possessed opposite trends in order to effect the change from a simplified Paleo-Aleut dentition to that of the contemporary Eastern Aleuts, who show retention and intensification of the basic characters. Since Paleo-Aleut skulls are available for study, one could attempt to determine which of the aforementioned two possibilities is supported by facts. It should also be remembered that in this study the method of grouping for Eastern and Western Aleuts may have affected the findings, since only very accurate genealogic records on several generations could ensure proper ethnic classification of the living Aleut population. The present study of morphologic aspects of the Aleut dentitions alone does not offer sufficient data to explain why different trends toward intensification or retention of basic characters exist in the dentitions of Eastern and Western Aleuts. Further studies of the dentition are needed to determine whether these differences are due to White admixture, the survival of Paleo-Aleut traits, the admixture with people from the second Eskimoid invasion, or any possible combination of these three factors.

6 The Odontometry of Aleut Teeth Tooth measurements offer one distinct advantage in the study of populations in that they furnish a source of accurate and objective data which can be subjected to statistical analysis. Yet little progress in dental anthropometry has been made because data have been obtained on relatively few populations. In the studies available the samples have usually been small, the measuring techniques have varied, and proper statistical treatment of the data frequently has been omitted. The authors could locate only ten publications which dealt with this subject and furnished sufficient statistical treatment of the original material to make the findings useful for comparison.4 Consequently, we still cannot determine with any certainty whether the size of the teeth is associated with the racial origin of a population. The history of odontometry has been thoroughly discussed in a recent publication on the teeth of Norwegian Lapps by Selmer-Olsen (1949) and a repetition here seems unnecessary. The interested reader is referred to this excellent work. Present Study Measurements were made on the plaster casts of the Aleut dentitions and on a small number of extracted teeth obtained during the expedition to the Islands. Only permanent teeth were utilized, as the number of casts of deciduous teeth was too small

78

The Aleut Dentition

for a meaningful analysis. No measurements were made of permanent teeth which had not erupted fully, or of teeth in which the extent of caries or the degree of tooth wear had caused a loss of the original dimensions. Malformed teeth, confined in the Aleut dentitions to the vestigial forms of the maxillary lateral incisors and third molars, were also excluded from measurement. Dr. Kalevi Koski made all measurements, using a sliding caliper equipped with a vernier scale. The caliper points were carefully sharpened to make accurate measuring possible. In order to perfect the technique and to establish the unit of measurement at 0.1 millimeter, certain casts and teeth were measured independently by the senior author. Methods of Measurement Methods for the measurement of tooth crowns have been presented by Hrdlicka (1923), Martin (1928), Remane (1930), Weidenreich (1937), and others. The choice of the most suitable method depends on the specific purpose of the study and the material available. Slightly different techniques are used in measuring extracted teeth, teeth on plaster casts, in skulls, and in the mouths of the living. In addition, methods of measurement generally differ in anthropologic studies as contrasted with Odontologie ones. In anthropologic studies each tooth is studied individually for its anatomic characteristics and dimensions. In Odontologie, and notably orthodontic, investigations which are concerned with the positions of the teeth in the dental arch, the exact size of a tooth is of less importance than the metric relations that it has with its neighbors. For the present study, which is primarily of an anthropological nature and in which the material consisted mainly of plaster casts, the tooth dimensions defined in detail below have been used: 1. Mesiodistal crown diameter: the greatest mesiodistal dimension of the tooth crown, measured parallel to the occlusal and labial surfaces. This definition, labeled the "greatest length" by Remane (1930), can be considered satisfactory because it describes the anatomy of the individual teeth and is not dependent

Odontometry

79

on the position of the teeth in the dental arch. In general, however, investigators have followed Remane's definition for the "mean length," according to which the points of contact with neighboring teeth are utilized as landmarks for measuring the mesiodistal crown diameter. In certain instances, especially those in which the molars and premolars are in normal position in the dental arch and in surface contact with their neighboring teeth, an identical measurement would be obtained by measuring the greatest or mean length of Remane. But if the greatest diameter is not found along the midline of the crown at the points of contact with neighboring teeth, measuring the greatest length will yield results which are slightly in excess of those obtained with the other technique. In practice, certain difficulties are met in locating the proper measuring points on incisors and canines. In principle, mesiodistal crown diameters of incisors and canines should be measured in a plane perpendicular to their long axis. Since this method cannot always be used when measuring teeth shown in plaster casts the mesiodistal diameters of the tooth crowns are often determined in a plane perpendicular to the occlusal plane. It is also not always possible to measure the greatest distance between the mesial and distal surfaces of tooth crowns because the proper landmarks frequently cannot be reached when holding the beaks of the sliding calipers perpendicular to the occlusal plane. The somewhat shorter distance between the actual contact points is obtained instead. However, the resultant errors are not very great as has been pointed out by Selmer-Olsen. For the sake of consistency, the mesiodistal crown dimensions of extracted teeth were obtained in the same manner as for the teeth on dental casts. Mesiodistal crown diameter has been referred to frequently as crown "length" (Remane, Weidenreich, Nelson, 1938; Pedersen, 1949) and almost as frequently as crown "breadth" (Martin, Mühlreiter, 1870; de Terra, 1905; Selmer-Olsen). It seems strange to find both "length" and "breadth" used as synonyms for the same dimension and Selmer-Olsen is quite correct in stating that, in this instance, "length" is a misleading term. Actually neither

80

The Aleut Dentition

length nor breadth are completely satisfactory substitutes for "mesiodistal crown diameter" and, therefore, it is better to discontinue their use. 2. Labiolingual crown diameter: the greatest distance between the labial and lingual surfaces of the tooth crown in a plane perpendicular to that in which the mesiodistal diameter was measured. This definition for obtaining the labiolingual crown diameter seems to be accepted by most investigators. The labiolingual crown diameter was not obtained for incisors because, as a rule, it cannot be ascertained whether these teeth have erupted sufficiently to make the greatest labiolingual dimension measurable. Pedersen also omitted this measurement for the incisors. 3. Crown height: the distance between the tip of the mesiobuccal cusp and the deepest point of the cemento-enamel junction on the vestibular side measured along a line parallel to the long axis of the tooth. This definition is similar to the one given by Black (1902) and Weidenreich (1937). 4. Root length: the distance between the apex of the mesiobuccal root and the deepest point of the cemento-enamel junction on the vestibular side measured along a line parallel to the long axis of the tooth. Black used essentially the same method for measuring root length. No measurement was made when pathological changes were observed at the root tip. Bending of the roots was not considered. The manner in which this measurement is obtained varies among the following investigators: Remane, Weidenreich, Nelson, and Selmer-Olsen. Findings The comments which can be made in discussing the odontometric findings on the Aleuts are few, dealing mostly with sex differences in crown size and with the amount of variation observed in the dimensions of tooth crowns. In contrast to the observations on the morphology of Aleut teeth, the statistical analyses of the crown measurements are reported for the number of teeth measured and not by individuals studied, conforming to the procedure used by most investigators (Tables 17 to 25, 29, 30, and A - l to A-8, appendix).

81

Odontometry Table 17. Mesiodistal crown diameters of permanent maxillary teeth of Aleuts (mm). Tooth

Sex

H

& 9

8.45

H

a" 9

7.29

C

cf 9

8.03

Pi

cf 9

7.15

c? 9

6.65

Ml

d" 9

10.37

MT

& 9

10.00

Μ3

& 9

9.16

S.E.jif

S.D.

C.V.

Range

Number

C.R.

8.07

0.05 0.05

0.48 0.44

5.68 5.45

7.1-9.5 7.2-8.7

97 65

5.4

7.08

0.05 0.05

0.45 0.41

6 17 5.79

6.1-8.1 6.3-8.1

88 59

3.0

7.67

0.04 0.05

0.36 0.37

4.48 4.82

7.1-9.0 6.8-8.5

81 57

6.0

6.96

0.04 0.05

0.35 0.33

4.90 4.74

6.2-8.0 5.8-7.5

77 37

3.2

6.61

0.06 0.07

0.45 0.41

6.17 6.20

5.7-8.1 5.1-7.8

62 37

0.4

10.05

0.01 0.07

0.71 0.42

6.85 4.18

9.0-12.0 9.3-11.0

53 36

2.7

9.84

0.10 0.09

0.68 0.60

6.80 6.10

8.0-11.5 8.7-11.4

51 41

1.2

8.99

0.17 0.13

0.89 0.50

9.71 5.56

7.1-11.2 7.8-10.2

27 15

0.8

Mean

Table 18. Mesiodistal crown diameters of permanent mandibular teeth of Aleuts (mm). Tooh

Sex

II

& 9

5.23

H

cf 9

6.09

C

a" 9

7.20

PI

d" 9

7.01

Ρ2

d1 9

7.17

ΜΙ

d" 9

11.56

M2