Canadian Eskimo Permanent Tooth Emergence Timing J . T. MAYHALL, P. L. BELIER AND M. F. MAYHALL Faculty of Dentistry and Department of Anthropology, Uniuersity of Toronto, Toronto, Ontario, Canada M5G 1G6 K E Y WORDS Inuit eruption Eskimos - Tooth emergence . Tooth ABSTRACT To identify the times of emergence of the permanent teeth of Canadian Eskimos (Inuit), 368 children and adolescents were examined. The presence or absence of all permanent teeth except the third molars was recorded and these data subjected to probit analysis. Female emergence times were advanced over males. Generally, the Inuit of both sexes showed statistically significant earlier emergence times than Montreal children, except for the incisors. The present results do not support hypotheses indicating that premature extraction of the deciduous teeth advances the emergence of their succedaneous counterparts. There is some indication the controls of deciduous tooth emergence continue to play some part in emergence of the permanent dentition, especially the first permanent teeth that emerge. There is an increasing volume of reports on the time of tooth emergence for human, primate and mammalian groups. These are broadening our knowledge of the diversity in the timing of the appearance of the teeth in the oral cavity and are valuable in assisting in the explanation of the diversity seen between populations. We are presenting these data on the time of permanent tooth emergence in Canadian Eskimos (Inuit) to contribute further t o the knowledge of human diversity and t o provide data that may be of assistance to the clinician. Only one comprehensive study of Eskimo tooth emergence times (Boesen et al., '76) has appeared t o our knowledge. This study was of two Greenland Eskimo populations. Unfortunately, this study does not include the times of emergence of some of the more important teeth, central incisors and first molars. Because of the increasing availability of sophisticated dental care t o Inuit throughout the world and their increasing awareness of, and demand for, good dental services, the need for such data is becoming more apparent. Although there are various definitions of the terms emergence and eruption, in this paper time of emergence refers to the moment any portion of the tooth crown pierces the gingiva and is visible in the oral cavity. This makes it possible to accurately record the AM. J. PHYS. ANTHROP. (1978)49: 211-216. event. The term eruption refers to the movement of a tooth toward its final occlusal position. Thus, eruption includes movement within the maxilla before emergence, as well as movement toward the final occlusal position after emergence. Thompson and his co-workers ('75) and Sapoka and Demirjian ('71) have stated, as have others, that tooth mineralization stages are preferable to the ages of emergence in the assessment of dental maturity because mineralization is affected much less by local environmental influences and is measurable over a longer period of time. This is undoubtedly true, but with isolated populations and lack of a source of radiographs required for determining the mineralization stages one must use readily identifiable clinical signs t o assess maturity. Further, the clinical appearance of the teeth and their relative position in the oral cavity allows the observer to make quick, accurate assessments of dental age. Initially, we considered basing the time of emergence on semi-longitudinal studies of the yearly stone models of the Eskimo children in the study, and, in fact, produced a previous study using these data (Mayhall et al., '75). However, the observations of the time of emergence were drastically limited by small sample sizes. It would have been impossible to enlarge the samples without considerable 211 212 J. T. MAYHALL, P. L. BELIER A N D M. F. MAYHALL error in the estimation of the age of emergence, and it would have required the inclusion of much larger numbers of individuals than were available in the area. Now with the use of sophisticated statistical techniques i t is possible t o determine accurately the time of emergence by being able t o include individuals without longitudinal records. MATERIALS A N D METHODS Two closely related communities in the northern Foxe Basin area of the Northwest Territories were chosen as the targets for a multidisciplinary study of the adaptability of Eskimos. Between 1968 and 1973 the settlements of Igloolik and Hall Beach were visited yearly by teams of investigators which included dental, medical and anthropological personnel. The records from the initial oral examination for each individual under 22 years of age were studied to determine the status of each tooth in the oral cavity. This was recorded as unerupted, partially erupted, fully erupted and in occlusion, congenitally missing, or extracted. These categories could be confirmed by reference to the stone models obtained at the time of examination and presently stored in Toronto. A total of 368 children were examined at least once and are included in this study. This represents approximately 95%of the total population in this age range within the communities. The subjects were classified into age categories a t the time of examination, and each tooth was recorded as present or absent in the oral cavity. The former category included any manifestation of the crown apparent, while the latter one excluded extracted and congenitally missing teeth. When all teeth had been classified, the range of the age of emergence was recorded with the upper and lower limits for each tooth - that age group by which the tooth had emerged in all subjects and that in which it had not yet emerged in any of the subjects. The categories between the extremes were then ordered in six month intervals and the analysis performed. To arrive at the mean emergence time for a tooth the probit analysis program of Dixon (’73) was used. This procedure transforms the proportion of teeth present at given ages into probits and then uses these to derive a regression line. This line is then described arithmetically and, through a series of iterations, the best slope is obtained. That becomes the basis for determining the estimated mean age of emergence and the estimated standard deviation. Since the data are “normalized” the estimated mean and the median are the same. In addition, a maximum likelihood test is performed to determine whether the various age samples are sufficiently homogeneous to be accepted as randomly drawn from a population represented by the adjusted regression line. The use of probit analysis has been successfully applied to emergence data for Pima Indians (Dahlberg and Menegaz-Bock, ’581, French-Canadians (Perreault et al., ’741, and Cree and Ojibway Indians (Mayhall et al., ’77).We have chosen the data on the children of Montreal as our reference population. We are fully aware of the problems of comparing the results of the study population with a “norm,” and we have chosen the French-Canadian sample for the comparisons because of the similarity of collection and analysis techniques. Perreault and his coworkers (‘74, ’75) demonstrate that their results differ somewhat from those of other North American studies. However, this in no way negates the use of the Montreal children as our comparative group as most populations will show some variation, and we are using them for illustrative purposes only. The important figures are those for the Eskimos which may be compared with any other population in which similar analyses and data collection techniques were used. RESULTS The comparison of the times of emergence in Eskimo males and females (table 1) shows that females are advanced in their emergence times except for those teeth emerging first: the maxillary first molars, the mandibular first molars, and the central incisors. These teeth show no statistically significant difference between the sexes in their emergence timing. Among the Inuit males the sequence of the mean emergence times for the mandible is: M,-1,-I,-C-Pm,-M,-Pm, while the maxillary sequence is: M1-I’-IZ-Pm‘-Pm2-C-M2. The sequences are the same for the females with the exception of the reversal of the mandibular second molar and second premolar. Also, i t can be seen that the pattern of the mandibular canine appearing before the maxillary first premolar generally found in females (Tanner ’62) is present in both sexes, although the difference in emergence times is quite small. Tables 2 and 3 present the results of the 213 ESKIMO TOOTH EMERGENCE TIMING TABLE I Eskimo sex differences in tooth emergence (female mean age in years minus male mean1 -. Maxilla Tooth Difference 11 - 0.50 -0.80 12 c -1.09 -0.55 -0.87 -0.03 -0.70 h l Pm, Mi M2 Mandible __ t-value Significance Difference t-value Significance 3.776 4.422 2 - 0.24 -0.34 1.391 2.083 N.S. 2 5.236 2.789 4.118 0.175 3.249 2 -0.62 - 1.35 - 1.02 +0.14 -0.33 3.269 5.021 4.789 0.829 1.591 2 2 2 N.S. I 2 > N.S. N.S. ' Statistically significant difference at 95 percent level of confidence. Statistically significant difference at 99 percent level of confidence. TABLE 2' Age of emergence o f permanent teeth - males French-Canadians ' Foxe Baain Eskimo EskimoIFrench Canadian N Mean S.D. .v Mean S.D. t-value Significance 63 38 64 67 92 50 51 7.43 8.47 11.10 9.57 10.70 5.61 11.39 0.76 0.57 1.52 1.62 1.66 0.64 1.36 103 102 74 96 96 102 88 7.33 8.24 11.11 10.19 10.04 6.22 12.14 1.11 1.12 1.12 1.14 1.13 1.14 1.13 0.504 1.227 0.051 3.369 3.722 3.552 3.868 N.S. 42 60 67 112 67 63 71 6.32 7.20 9.52 10.32 11.38 5.40 10.78 0.67 0.85 1.27 1.84 2.46 0.87 1.43 102 103 96 96 96 102 88 6.27 7.42 10.45 11.08 11.61 6.22 11.72 1.11 1.11 1.11 1.15 1.16 1.15 1.11 0.275 1.342 5.388 4.251 4.828 5.010 5.265 N.S, N.S. N.S. N.S. I 2 2 ' 2 2 2 2 2 ' From: Perreault et d..'74. Statistically significant at the 99 percent level of nignificance. analysis for the teeth of the left side and their comparison with the emergence times for the French-Canadian children. The Eskimo males generally display younger ages of emergence in the canines and posterior dentition, but there are no statistically significant differences in the incisor timing. For the females the comparisons between the Eskimo and Montreal groups are essentially the same as those for the males. Incisors show no statistically significant differences while the remainder of the dentition is advanced over the French-Canadians. The comparison of the right and left emergence times for the Eskimos revealed no statistically significant differences between the antimeres. Table 4 is a comparison of the present results with those for two other native Ameri- can groups. The Pima Indians of Arizona were studied by Dahlberg and Menegaz-Bock ('581, and we recently reported on the Indians of northwestern Ontario of Cree and Ojibway tribal affiliation (Mayhall et al., '77). Similar techniques were used in all four studies and the results should be comparable. The maxillary canine of the male Cree-Ojibway emerges before that of the Eskimo: however, in all other maxillary comparisons, both male and female, Pima and Cree-Ojibway, the Inuit demonstrate an earlier mean age at emergence. The differences tend to be greater between the female groups than the males. In the mandible, however, 8 of the 28 comparisons indicate earlier emergence among the Indians. The greatest of these differences is only 0.24 years. All occur in the first molar 214 J. T. MAYHALL, P. L. BELIER AND M. F. MAYHALL TABLE 3 Age of emergence ofpermanent teeth Foxe Basin Eskimo Maxilla I' 12 C Pm' Pm' M' M' - females French-Canadians' EakimdFrench-Canadians N Mean S.D. N Mean S.D. t-value Significance 75 86 62 1LOO 48 43 65 6.84 7.67 10.01 9.02 9.83 5.58 10.69 0.90 0.99 1.18 1.52 0.92 0.58 1.30 99 99 90 90 90 96 78 6.89 7.80 10.66 10.08 10.81 6.22 12.01 1.11 1.10 1.15 1.16 1.16 1.14 1.13 0.323 0.861 3.091 6.280 5.284 3.544 7.154 N.S. N.S. 48 69 76 55 92 55 52 6.08 6.86 8.90 8.97 10.36 5.54 10.45 0.66 0.86 1.29 0.69 1.25 0.80 1.10 96 99 90 90 90 96 78 5.98 7.07 9.62 10.44 11.18 5.95 11.32 1.12 1.12 1.11 1.15 1.17 1.16 1.11 0.575 1.330 4.233 8.693 5.028 5.828 4.621 N.S. N.S. 2 2 2 2 1 Mandible 1, I2 c Pml Pm2 M, M2 2 2 2 2 2 ' From: Perreault et el., '74. Statistically significant at the 99 percent level of confidence TABLE 4 Comparison ofmean ages ofemergence in North American natives Females Males Tooth Eskimo minus Pimal Eskimo minus Cree-Ojibway ' Eskimo minus Pima ' - 0.40 -0.27 - 0.56 - 0.51 - 0.63 - 0.37 - 0.28 -0.18 -0.11 0.23 -0.11 - 0.20 - 0.62 - 0.48 -0.63 -0.67 - 0.93 -0.61 - 0.90 - 0.22 -0.69 0.06 0.10 0.02 -0.84 -0.51 -0.05 0.15 - 0.93 - 0.07 - 0.45 - 1.26 -0.11 -0.01 0.01 -0.51 - 0.46 -0.76 - 0.90 - 0.37 0.11 -0.35 Eskimo minus Cree-Ojibway -0.57 - 0.56 - 0.66 - 0.64 - 0.23 - 0.30 - 1.21 0.24 -0.08 -0.56 - 1.33 - 0.33 0.05 - 1.19 ' From: Dahlherg and Menegaz-Bock, '58 From: Mayhall et al., '77. or incisor comparisons - the earliest teeth t o emerge. DISCUSSION The advancement of emergence times of the Eskimo females when compared with the males follows the general trends noted by previous investigators (Clements et al., '53; Dahlberg and Menegaz-Bock, '58; Lee et al., '65; Niswander and Sujaku, '60; Nanda, '60).Probably of more interest are those teeth that do not show significant differences between the sexes as seen in table 1. These include the mandibular first molar and central incisor that showed reversals in the Eskimohdian comparison. While we have not yet investigated the emergence timing for deciduous teeth, it has been pointed out previously (Tanner, '62) that deciduous teeth generally display no significant male/female differences. As the females do show earlier ages for eruption, although not always statistically signifi- ESKIMO TOOTH EMERGENCE TIMING cant, in all of the other permanent teeth, perhaps these earliest emerging ones could be considered to be in a transition period in which factors controlling emergence of the permanent teeth are replacing those that control the emergence of the deciduous teeth. Several authors (Hellman, '43; Fulton and Price, '54; Godeny, '52; Halikis, '62; Lee et al., '65) have divided the sequence of eruption or emergence into two stages and noted that there is a hiatus between them. Dental Stage I includes first molars, central and lateral incisors; while Dental Stage I1 usually encompasses the premolars, canines and second molars. The length of the hiatus between the stages in the Eskimos is reduced in comparison with the Montreal children. The male Eskimos show a hiatus between the stages of 1.10 years for the maxilla and 2.32 years for the mandible, while the comparable figures for the French-Canadians are 1.78 years and 3.00 years respectively. This reduction in the hiatus for Eskimos has the effect of spreading out the total time of active emergence of the dentition and correlates with the general growth trend among the Foxe Basin Inuit (dePeiia, '71) of a smooth growth curve with some leveling in the dramatic spurts. Among the factors influencing tooth emergence timing some have considered climate to be of some importance. However, conflicting results are contained among the papers of Friedlaender and Bailit ('601, Eveleth ('661, Houpt and co-workers ('67) and Mayhall et al. ('77) casting doubt upon what, if any, influence outdoor temperatures have on emergence times. Numerous studies have explored the role of nutrition andfor socio-economic factors on emergence times. It seems fair to summarize these studies by stating that there are no clear relationships with socio-economic status per se, and the effect of "better" nutrition afforded by the increase access to money may depend upon the composition of the dietary. The exact role of nutrition itself cannot be assessed accurately in this study due to the vast differences in the dietary of the Eskimo and the southern Canadian white. The recent Nutrition Canada Eskimo Survey report ('75) that samples Eskimos from throughout the Canadian Arctic concludes that the median caloric intakes for children up to age eight are generally higher t h a n recommended, and there is no apparent protein deficiency. Among adolescents, the boys had median 215 caloric intakes very close t o those recommended by the World Health Organization, but the adolescent girls showed median intakes below the WHO levels. The teenagers of both sexes had adequate to high levels of protein intake. Investigations of emergence timing have usually considered the effects of premature extraction of the deciduous teeth on the eruption and emergence of their succedaneous counterparts. There is lack of agreement on the effects of the premature loss of these teeth. Niswander and Sujaku ('64) studied the effects of high caries rates in deciduous teeth on the acceleration of the emergence of their permanent successors and suggested that the high rates could be a factor in determining emergence timing. However, in the Eskimo children the caries rates were low at the time of the initial examination (Mayhall, '70, '75). Butler ('62) felt that there was no consistent relationship between early deciduous tooth loss and the eruption of permanent teeth. Fanning ('62, '64) supported this conclusion in detailed studies of the effects of premature deciduous tooth extractions on the emergence of the permanent teeth. A primary factor accounting for the divergence of the Eskimo tooth emergence timing from that of other studies may be a hereditary one. Boesen et al. ('76) found that "practically unmixed' Greenland Eskimos showed no significant tooth emergence time differences from those who had a long history of Danish admixture. However, other studies of extant populations (Steggerda and Hill, '28; Dahlberg and Menegaz-Bock, '58; Eveleth, '66; Houpt et al., '67; Perreault et al., '74, '75; Mayhall et al., '77) have suggested a genetic origin of earlier or later timing. ACKNOWLEDGMENTS The authors wish to express their gratitude to the Inuit of Hall Beach and Igloolik for their interest, co-operation and encouragement in the dental studies. We would also like to thank Doctor D. L. Anderson and Doctor Frank Popovich for reading drafts of the manuscript and providing helpful suggestions. 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