Inheritance of tooth size in Liverpool families

Variability in permanent tooth size of three ancient populations in Xi'an, northern China

OBJECTIVES

This paper compares permanent dental dimensions between three ancient populations that belonged to the same biological population throughout a temporal range of 2000 years to detect temporal trends and metric variation in dentition.

MATERIALS AND METHODS

The samples analysed were dental remains of 4502 permanent teeth from 321 individuals, which were excavated from three archaeological sites: Chang'an (1000-1300 years BP), Shanren (2200 years BP) and Shaolingyuan (3000 years BP) in the Xi'an region (northern China). For each tooth three standard measurements were taken: Mesiodistal (MD) diameter of crown, labiolingual or buccolingual (BL) diameter of crown and length of root (LR).

RESULTS

Three ancient population samples generally displayed the same dental dimensions (p>0.05), whereas some tooth types varied. The Shaolingyuan had larger canine and the smallest maxillary second molars and the Chang'an had the largest mandibular first molars in the MD dimension. The Shanren had the smallest maxillary third molars and mandibular central incisors, and the Chang'an had the smallest maxillary lateral incisors in the BL dimension. In the LR measures, statistically significant differences of five tooth types showed that the Chang'an were smaller than the Shaolingyuan and the Shanren. Comparisons of coefficients of variation for teeth showed that the length of root and third molar usually displayed greater variation.

CONCLUSIONS

Decreasing or increasing trend for crown size does not occur between the ancient populations, while changes in crown size of a few tooth types fluctuate. The root size is more variable than the crown size and is likely to reflect a degenerated trend in a few tooth types.

Differentials of Yayoi immigration to Japan as derived from dental metrics

A major influx of new people, today termed Yayoi, migrated from the East Asian continent into the Japanese archipelago during the Aeneolithic and Protohistoric periods and interbred with the preexisting Jomon people. This study classifies ancient and more modern Japanese into natives or immigrants using discriminant analysis based on dental measurements in order to reconstruct the initial impact of the immigrants and the temporal and geographical differentials of mixture with the preexisting people. The results suggest that the earliest immigrants diffused into central Japan, including the Kanto region. The proportion of immigrant origin in the protohistoric Kofun was less in eastern Japan (72%) as compared to western Japan (81%-90%). The proportion of the immigrants in the Kanto District decreased during the medieval period (63%) and increased again in the early modern Edo and later modern times (75%), which might indicate that the gene flow still was occurring from west to east even in these times. Assuming the estimated proportions of either group reflect the intermixture ratio, the recent Japanese people may be regarded as hybrid of the native and immigrant groups with the following approximate ratios: 1:3 for the Kanto Japanese, 2:3 for the Ryukyu Islanders and 7:3 for the Hokkaido Ainu. These estimations support the "dual structure model" formed by Hanihara (1991) for explaining the population history of Japan.

Relations between the mesiodistal crown diameters of the primary and permanent teeth of Hong Kong Chinese

Relations between these diameters were studied on serial dental casts of 112 Hong Kong Chinese (61 males, 51 females) taken at mean ages of 5.68 and 12.31 yr. Size relations were studied in terms of correlation coefficient, difference, and ratio between corresponding pairs of individual teeth and corresponding groups of teeth in both dentitions. The coefficients of correlation were low to moderate (0.2-0.8), with those between groups of teeth consistently higher. As for size differences, incisors and canines were larger in the permanent dentition in both arches by 1.2-2.0 mm. Premolars were smaller than their primary predecessors except for the upper first premolar. When the absolute values of the differences were ranked, the second premolar-second primary molar differences were the greatest (2.0-2.8 mm) while those between the first premolar-first primary molar were the smallest (0.3-0.7 mm). When tooth groups were assessed, the permanent teeth were larger than their predecessors in the anterior segments but smaller in the posterior segments. The leeway space was larger in the mandibular arch (2.2 mm) than in the maxillary arch (0.3 mm). When diameters of five teeth on one side of the arch were combined, the permanent exceeded the primary by 3.5 mm in the upper arch but only 0.5 mm in the lower. The ratios between the permanent and primary tooth sizes showed the same trend as the differences.

Phenotypic selection on the dentition in a Late Archaic population of Ohio

Significant phenotypic selection acting on the buccolingual diameters of the permanent first and second molars is established for a Late Archaic population in Ohio. Directional selection appears to be acting on an index that increases the size of the maxillary first (UM1) and mandibular second (LM2) molars and decreases the size of the maxillary second (UM2) and mandibular first (LM1) molars. Variance selection is fundamentally disruptive but results in a more integrated (highly correlated) set of characteristics in the after-selection sample.

Dental size traits within families: path analysis for first molar and lateral incisor

Previous works on the inheritance of dental traits have traditionally followed Fisher's model for family data under the assumption that phenotypic similarity between relatives is due solely to genetic factors. This study uses recent causal models that incorporate the contribution of nonrandom environmental sources of variation to familial resemblance on dental size. Path analysis was applied to observed interclass and intraclass correlations of sex-specific parent-offspring and sib pairs in 293 Pima Indian families from the southwest United States. The mesiodistal dimension of an early-forming and stable tooth (first molar) was contrasted with a late-forming and variable tooth (upper lateral incisor) for genetic and familial environmental components of variation. Parameters were estimated according to the XTAU models of Rice et al. (1980) and linear constraints placed upon the parameters were tested. The proportion of variance accounted for by genetic and environmental transmissible factors is estimated to be 52% for the first molar and 35% for the lateral incisor. Neither X-linkage nor sex-specific environmental effects are required to explain the transmission of dental size. Nontransmissible environmental effects that account for sibling correlations are detectable. Furthermore, sex differences are found in correlated sibling environments for the lateral incisor but not the first molar, to explain in part male-female differences in the distributions of the upper lateral incisor size.

Crown dimensions of deciduous teeth from pre-Columbian Peru

The mean mesiodistal and buccolingual diameters are presented for the deciduous teeth from Pre-Columbian Peru. Generally, the deciduous teeth from Pre-Columbian Peru are larger in most dimensions than the deciduous teeth of modern populations of European descent and smaller than those of modern Australian aboriginals. Differences in crown dimensions between the Pre-Columbian Peruvian deciduous teeth and those from Prehistoric Inamgaon and Mesolithic Europe are inconsistent. However, the maxillary and mandibular second molars are larger in the Peruvian population while the incisors are smaller. Since comparative data for prehistoric deciduous teeth are rare, this paper adds valuable data to the growing literature on deciduous crown dimensions.

Inheritance of tooth size in Australian aboriginals

The purpose of this study was to clarify the question of inheritance of tooth size, with particular reference to the role of the sex chromosomes. Data were obtained from the dental casts of Aboriginals living at Yuendumu in the Northern Territory of Australia, who had participated in a longitudinal growth study extending over 20 years. The compilation and verification of comprehensive genealogical records gathered over a number of years enabled the analysis of family data. Product-moment correlation coefficients between different full-sibling and half-sibling pairs were calculated for permanent tooth size. Values of individual and average correlation for both mesiodistal and buccolingual tooth diameters conformed with the theoretical correlations expected assuming polygenic inheritance. However, no evidence of sex chromosomal involvement was found.

The anthropological value of minor variants of the dental crown

The incidences of 31 minor variants of the dental crown were scored from dental casts of samples taken from six European populations. Although several variants showed significant sex bias in one or other sample, only one (pits instead of furrow on premolar2) consistently favoured one sex. Associations between the variants were sought. Although few consistent associations were demonstrated, there was a possible tendency for extra cusps to occur together throughout the dentition. Distance statistics calculated between the samples were compatible with the expected genetical relationships of the samples, but only modern samples could be used since variants were destroyed by attrition in archeological samples. Before such distances can be considered reliable, it is necessary to know: (i)the extent to which environmental factors such as diet influence variant expression. (ii)whether or not variant bearing teeth are selectively destroyed by caries, which in civilised populations render a high proportion of most dentitions unscoreable.