Heritabilities of human tooth dimensions

Genetic influences on dentognathic morphology in the Jirel population of Nepal

Patterns of genetic variation and covariation impact the evolution of the craniofacial complex and contribute to clinically significant malocclusions in modern human populations. Previous quantitative genetic studies have estimated the heritabilities and genetic correlations of skeletal and dental traits in humans and nonhuman primates, but none have estimated these quantitative genetic parameters across the dentognathic complex. A large and powerful pedigree from the Jirel population of Nepal was leveraged to estimate heritabilities and genetic correlations in 62 maxillary and mandibular arch dimensions, incisor and canine lengths, and post-canine tooth crown areas (N ≥ 739). Quantitative genetic parameter estimation was performed using maximum likelihood-based variance decomposition. Residual heritability estimates were significant for all traits, ranging from 0.269 to 0.898. Genetic correlations were positive for all trait pairs. Principal components analyses of the phenotypic and genetic correlation matrices indicate an overall size effect across all measurements on the first principal component. Additional principal components demonstrate positive relationships between post-canine tooth crown areas and arch lengths and negative relationships between post-canine tooth crown areas and arch widths, and between arch lengths and arch widths. Based on these findings, morphological variation in the human dentognathic complex may be constrained by genetic relationships between dental dimensions and arch lengths, with weaker genetic correlations between these traits and arch widths allowing for variation in arch shape. The patterns identified are expected to have impacted the evolution of the dentognathic complex and its genetic architecture as well as the prevalence of dental crowding in modern human populations.

Crown heights in the permanent teeth of 47,XXY males and 47,XXX females

OBJECTIVE

Earlier results based on dental casts and radiographs have shown that additional X and Y chromosomes influence permanent and deciduous tooth crown sizes, with 47,XYY males exhibiting greater crown heights than 46,XY males. We studied here the effect of both X and Y chromosomes on tooth crown heights.

MATERIAL AND METHODS

The series consisted of 48 47,XXY males, 22 of their male relatives, and seven 47,XXX females with five female relatives. The population controls consisted of 27 males and 33 females. Measurements of all applicable teeth except for the third molars on both sides of the jaws were made on panoramic radiographs with a sliding digital calliper.

RESULTS

Apart from a few teeth, the mean crown heights in the 47,XXY males were greater than those in the male population controls, the differences being statistically significant for one tooth in the maxilla and ten teeth in the mandible. With the exception of two teeth, the 47,XXX females had taller tooth crowns than the female population controls, the differences in the two teeth being statistically significant. The 47,XXY males had greater tooth crown heights than the 47,XXX females, except in one tooth, and the differences were significant in two teeth. The tooth crown heights of the male relatives of the 47,XXY males and the female relatives of the 47,XXX females were close to those in the general population.

CONCLUSIONS

The present results demonstrated the effect of additional X and Y chromosomes in increasing crown heights. The differences between the 47,XXY males and 47,XXX females indicated a stronger effect of a Y chromosome on tooth crown height than of an X chromosome.

Bridging the gap: Using biological data from teeth to comment on social identity of archeological populations from early Anglo-Saxon, England

Human teeth are storytellers, in that, through analysis of their size and shape osteoarchaeologists are able to 'talk' to the dead and translate biological data into social meaning. This concept has been explored in parts of the world through investigations of biological similarity and kinship, but few have focused in depth on early medieval populations who emphasized the importance of family and kinship. This paper presents the results from four early Anglo-Saxon cemeteries which highlight the utility of dental metrics in identifying biological similarity within the skeletal assemblages. 5988 mesiodistal and buccolingual measurements were recorded from the identifiable permanent dentition of adult individuals from early Anglo-Saxon cemeteries in the UK counties of Cambridgeshire and Kent. Results from statistical hierarchical cluster analysis of dental metric data revealed that it was possible to identify individuals within the cemetery sites that were more similar to one another according to their dental metrics. This similarity was not attributed statistically to biological sex or shared familial environment, as similarity between individuals could be found between males and females and few significant differences were found across the sites sampled. It was found that tooth metrics provided a meaningful biological dataset from which current theories regarding the identity of Anglo-Saxon individuals and families could be refined and improved. These types of data are useful as building blocks which help to bridge the gap between social constructs and human skeletal remains in order to substantiate interpretations about past populations in more significant ways. This work supports the need for multidisciplinary approaches to bioarchaeological investigations of past people while highlighting the utility of human dentition to enhance such areas of study.

Unexpected variation of human molar size patterns

A tenet of mammalian, including primate dental evolution, is the Inhibitory Cascade Model, where first molar (M1) size predicts in a linear cline the size and onset time of the second (M2) and third (M3) molars: a larger M1 portends a progressively smaller and later-developing M2 and M3. In contemporary modern Homo sapiens, later-developing M3s are less likely to erupt properly. The Inhibitory Cascade Model is also used to predict molar sizes of extinct taxa, including fossil Homo. The extent to which Inhibitory Cascade Model predictions hold in contemporary H. sapiens molars is unclear, including whether this tenet informs about molar initiation, development, and eruption. We tested these questions here. In our radiographic sample of 323 oral quadrants and molar rows from contemporary humans based on mesiodistal crown lengths, we observed the distribution of molar proportions with a central tendency around parity (M1 = M2 = M3) that parsed into 13 distinct molar size ratio patterns. These patterns presented at different frequencies (e.g., M1 > M2 > M3 in about one-third of cases) that reflected whether the molar row was located in the maxilla or mandible and included both linear (e.g., M1 < M2 < M3) and nonlinear molar size ratio progressions (e.g., M1 > M2 < M3). Up to four patterns were found in the same subject's mouth. Lastly, M1 size alone does not predict M3 size, developmental timing, or eruption; rather, M2 size is integral to predicting M3 size. Our study indicates that human molar size is genetically 'softwired' and sensitive to factors local to the human upper jaw vs. lower jaw. The lack of a single stereotypical molar size ratio for contemporary H. sapiens suggests that predictions of fossil H. sapiens molar sizes using the Inhibitory Cascade Model must be made with caution.

Relative tooth size, Bayesian inference, and Homo naledi

OBJECTIVES

Size-corrected tooth crown measurements were used to estimate phenetic affinities among Homo naledi (~335-236 ka) and 11 other Plio-Pleistocene and recent species. To assess further their efficacy, and identify dental evolutionary trends, the data were then quantitatively coded for phylogenetic analyses. Results from both methods contribute additional characterization of H. naledi relative to other hominins.

MATERIALS AND METHODS

After division by their geometric mean, scaled mesiodistal and buccolingual dimensions were used in tooth size apportionment analysis to compare H. naledi with Australopithecus africanus, A. afarensis, Paranthropus robustus, P. boisei, H. habilis, H. ergaster, H. erectus, H. heidelbergensis, H. neanderthalensis, H. sapiens, and Pan troglodytes. These data produce equivalently scaled samples unaffected by interspecific size differences. The data were then gap-weighted for Bayesian inference.

RESULTS

Congruence in interspecific relationships is evident between methods, and with many inferred from earlier systematic studies. However, the present results place H. naledi as a sister taxon to H. habilis, based on a symplesiomorphic pattern of relative tooth size. In the preferred Bayesian phylogram, H. naledi is nested within a clade comprising all Homo species, but it shares some characteristics with australopiths and, particularly, early Homo.

DISCUSSION

Phylogenetic analyses of relative tooth size yield information about evolutionary dental trends not previously reported in H. naledi and the other hominins. Moreover, with an appropriate model these data recovered plausible evolutionary relationships. Together, the findings support recent study suggesting H. naledi originated long before the geological date of the Dinaledi Chamber, from which the specimens under study were recovered.

Sex estimation by odontometrics of nonadult human remains from a contemporary Italian sample

OBJECTIVES

The objective was to develop an odontometric technique for sex estimation based on dental measurements from adult individuals, and to evaluate its applicability and reliability for diagnosis of sex of nonadult skeletal remains.

MATERIALS AND METHODS

This study was conducted on the permanent dentition of 132 individuals (70 males, 62 females) from the identified human skeletal collection of the Certosa Cemetery (Bologna, Italy) of the University of Bologna. Binary logistic regression equations were developed based on dental measurements of the permanent teeth of the adult individuals, and these equations were subsequently applied to the permanent dentition of nonadult individuals to estimate their sex.

RESULTS

These data show that the canine teeth of both the maxilla and mandible are the most sexually dimorphic teeth in adults, followed by the mandibular second molar, maxillary and mandibular second and first premolars, and mandibular first molar. These data provided correct assignment of sex in 80.4-94.9% of cases, which depended on the measurements used. Of the 26 nonadult individuals of the experimental sample, sex diagnosis was possible for 22, which represented an applicability rate of 84.6% of the individuals. Comparing the sex of these 22 nonadult individuals estimated by odontometrics with the known biological sex, correct assignment was obtained in 90.9% of cases.

CONCLUSION

As a method of sex estimation, odontometric analysis of permanent dentition can be used successfully for nonadult human skeletal remains in both forensic and archeological contexts.

Is the third molar maturity index (I3M) useful for a genetic isolate population? Study of a Sardinian sample of children and young adults

This work aims to assess the validity of the cut-off value (0.08) of the third molar maturity index (I_3M) for discriminating minors from adults in Sardinian population. A sample of 336 digital panoramic radiographs of healthy Sardinian children and young minors (165 females and 171 males), aged between 15 and 23 years (mean age, 19.35 years in females and 18.80 years in males), was retrospectively evaluated. The left lower third molars were analysed by applying a specific cut-off value of 0.08 determined by Cameriere et al. in 2008. The reliability and reproducibility of the test was also studied: the intra-class correlation coefficients (ICC) were 0.91 (95% CI, 0.89-0.93) and 0.88 (95% CI, 0.86-0.90), for the intra- and inter-observer reliability, respectively. The I_3M gradually decreased as the real age gradually increased in both sexes. According to the pooled results of the diagnostic test, the accuracy (ACC) was 0.86 (95% CI, 0.82-0.89); the proportion of correctly classified subjects (Se = sensitivity) was 0.82 (95% CI: 0.76-0.86); and specificity (Sp = specificity) was 0.95 (95% CI, 0.89-0.97). The positive predictive values (PPV) and the negative predictive values (NPVs) were 0.97 (95% CI, 0.94-0.99) and 0.70 (95% CI, 0.62-0.77). The LR+ and the LR- were 17.12 (95% CI, 7.27 to 40.36) and 0.19 (95% CI, 0.14 to 0.25). In spite of this, significant differences in the early mineralisation of the third molar were found between sexes as well as in the results of the diagnostic test, showing a better sensitivity in males than in females. The results showed that, although the third molar teeth are highly variable in development, and with differences between females and males as compare to other teeth, the I_3M is a reliable method to distinguish between minors and adults even in such a genetic isolate population.

Internal Tooth Structure and Burial Practices: Insights into the Neolithic Necropolis of Gurgy (France, 5100-4000 cal. BC)

Variations in the dental crown form are widely studied to interpret evolutionary changes in primates as well as to assess affinities among human archeological populations. Compared to external metrics of dental crown size and shape, variables including the internal structures such as enamel thickness, tissue proportions, and the three-dimensional shape of enamel-dentin junction (EDJ), have been described as powerful measurements to study taxonomy, phylogenetic relationships, dietary, and/or developmental patterns. In addition to providing good estimate of phenotypic distances within/across archeological samples, these internal tooth variables may help to understand phylogenetic, functional, and developmental underlying causes of variation. In this study, a high resolution microtomographic-based record of upper permanent second molars from 20 Neolithic individuals of the necropolis of Gurgy (France) was applied to evaluate the intrasite phenotypic variation in crown tissue proportions, thickness and distribution of enamel, and EDJ shape. The study aims to compare interindividual dental variations with burial practices and chronocultural parameters, and suggest underlying causes of these dental variations. From the non-invasive characterization of internal tooth structure, differences have been found between individuals buried in pits with alcove and those buried in pits with container and pits with wattling. Additionally, individuals from early and recent phases of the necropolis have been distinguished from those of the principal phase from their crown tissue proportions and EDJ shape. The results suggest that the internal tooth structure may be a reliable proxy to track groups sharing similar chronocultural and burial practices. In particular, from the EDJ shape analysis, individuals buried in an alcove shared a reduction of the distolingual dentin horn tip (corresponding to the hypocone). Environmental, developmental and/or functional underlying causes might be suggested for the origin of phenotypic differences shared by these individuals buried in alcoves.

Illegal tusk harvest and the decline of tusk size in the African elephant

Harvesting of wild populations can cause the evolution of morphological, behavioral, and life history traits that may compromise natural or sexual selection. Despite the vulnerability of large mammals to rapid population decline from harvesting, the evolutionary effects of harvesting on mega‐fauna have received limited attention. In elephants, illegal ivory harvesting disproportionately affects older age classes and males because they carry large tusks, but its' effects on tusk size for age or tusk size for stature are less understood. We tested whether severe historical elephant harvests eliminated large tuskers among survivors and whether elephants born thereafter had smaller tusks. Adjusting for the influence of shoulder height – a metric strongly correlated with body size and age and often used as a proxy for age – we compared tusk size for elephants sampled in 1966–1968, prior to severe ivory harvesting in the late 1970s and early 1980s, with tusk size of survivors and elephants born during population recovery in the mid‐1990s. In a regional population, tusk length declined by ˜21% in male and by ˜27% in female elephants born during population recovery, while tusk length declined by 22% in males and 37% in females among survivors. Tusk circumference at lip declined by 5% in males but not in females born during population recovery, whereas tusk circumference reduced by 8% in male and by 11% in female survivors. In a single subpopulation, mean tusk length at mean basal tusk circumference declined by 12.4% in males and 21% in females. Tusk size varied between elephant social groups. Tusk homogeneity within social groups and the often high genetic similarity within social groups suggest that tusk size may be heritable. Our findings support a hypothesis of selection of large tuskers by poachers as a driver of the decline in tusk size for age proxy and contemporary tusk evolution in African elephants.

Interpretative potential of dental metrics for biodistance analysis in hunter-gatherers from central Argentina. A theoretical-methodological approach

The use of dental metrics as a reliable tool for the assessment of biological distances has diversified dramatically in the last decades. In this paper some of the basic assumptions on this issue and the potential of cervical measurements in biodistance protocols are discussed. A sample of 1173 permanent teeth from 57 male and female individuals, recovered in Chenque I site (western Pampas, central Argentina), a Late Holocene hunter-gatherer cemetery, is examined in order to test the impact of exogenous factors that may have influenced the phenotypic manifestation and affected dental crown sizes. The statistical association between dental metric data, obtained by measuring the mesiodistal and buccolingual diameters of the crown and cervix, and the quantification of hypoplastic defects as a measure to evaluate the influence of the environment in the dental phenotypic expression is evaluated. The results show that socioenvironmental stress did not affect dental metrics and that only the more stable teeth (first incisors, canines, first premolars and first molars) and three variables (buccolingual diameter of the crown and both mesiodistal and buccolingual measurements of the cervix) should be included in multivariate analyses. These suggestions must be strengthened with additional studies of other regional samples to identify factors of variation among populations, so as to develop general guidelines for dental survey and biodistance analysis, but they are a first step for discussing assumptions usually used and maximizing the available information for low-density hunter-gatherer societies.

Gene networks, occlusal clocks, and functional patches: new understanding of pattern and process in the evolution of the dentition

Our understanding of the evolution of the dentition has been transformed by advances in the developmental biology, genetics, and functional morphology of teeth, as well as the methods available for studying tooth form and function. The hierarchical complexity of dental developmental genetics combined with dynamic effects of cells and tissues during development allow for substantial, rapid, and potentially non-linear evolutionary changes. Studies of selection on tooth function in the wild and evolutionary functional comparisons both suggest that tooth function and adaptation to diets are the most important factors guiding the evolution of teeth, yet selection against random changes that produce malocclusions (selectional drift) may be an equally important factor in groups with tribosphenic dentitions. These advances are critically reviewed here.

Western Saudi adolescent age estimation utilising third molar development

OBJECTIVE

The aim of this study was to establish reference data on third molar morphology/development for age estimation in Western Saudi adolescents, between ages 14 and 23 years of old.

MATERIALS AND METHODS

The orthopantomograms of 130 individuals (males and females), were examined, and the stage of third molar development were evaluated.

RESULTS

Mean ages, standard deviations, and percentile distributions are presented for each stage of development. The mean estimated age for all participants (n = 130) was 219.7 months, and this differed significantly (P < 0.05) from the mean chronological age (226.5 months). Deviations of predicted age from real age showed 28.5% of all participants had their age estimated within 1 year (±12 months) of their chronological age. Most (43%) had their age underestimated by more than 12 months and the remaining 28.5% had their age overestimated by more than 12 months of their chronological age. Differences in left-right symmetry information of third molars were detected and were higher in the maxilla (92%) than in the mandible (82%). For all molars reaching stage "H" most individuals (males and females) were over the age 18 years of old. Males reach the developmental stages earlier than females.

CONCLUSION

Third molar tooth development can be reliably used to generate mean age and the estimated age range for an individual of unknown chronological age. Further studies with large populations are needed for better statistical results.

Spatial patterns and evolutionary processes in southern South America: a study of dental morphometric variation

The purpose of this article is to examine the patterns of evolutionary relationships between human populations from the later Late Holocene (1,500-100 years BP) of southern South America on the basis of dental morphometric data. We tested the hypotheses that the variation observed in this region would be explained by the existence of populations with different phylogenetic origin or differential action of gene flow and genetic drift. In this study, we analyzed permanent teeth from 17 samples of male and female adult individuals from throughout southern South America. We measured mesiodistal and buccolingual diameters at the base of the crown, along the cement-enamel junction. The results of multiple regression analysis and a mantel correlogram indicate the existence of spatial structure in dental shape variation, as the D(2) Mahalanobis distance between samples increases with increasing geographical distance between them. In addition, the correlation test results show a trend toward reduction of the internal variation of samples with increasing latitude. The detected pattern of dental variation agrees with the one expected as an outcome of founder serial effects related to an expansion of range during the initial occupation of southern South America.

Maxillary Anterior Tooth Size and Arch Dimensions in Unilateral Cleft Lip and Palate

Objective:

To investigate differences in size of the maxillary permanent anterior teeth and arch dimensions between individuals with repaired unilateral cleft lip and palate (UCLP) and a matched control group representing the general population.

Design:

Retrospective study cast review.

Participants:

Study casts of 30 subjects due to commence orthodontic treatment following an alveolar bone graft (ABG) were collected from the Cleft Lip and Palate Units in South Yorkshire. Thirty control subjects were collected from a previously validated control group of white individuals in South Yorkshire.

Main Outcome Measures:

Casts were analyzed with an image analysis system to measure the dimensions of the maxillary permanent anterior teeth, incisor chord lengths, and the intercanine and intermolar widths. The results were analyzed statistically using paired t-tests and two-way univariate analysis of variance (ANOVA).

Results:

The mesiodistal widths of maxillary anterior teeth in the study group were smaller than the noncleft control group (p < .01). The dimensions of the cleft side maxillary incisors and incisor chord length were smaller (p < .05 and p < .01 respectively) compared with the noncleft side. The study group maxillary cleft side incisor chord length and maxillary intercanine width were narrower than the control group (p < .0001).

Conclusions:

(1) Anterior teeth are smaller mesiodistally in individuals with UCLP. (2) Maxillary incisors are smaller on the cleft side than the noncleft side. (3) UCLP subjects had smaller maxillary cleft side incisor chord lengths and intercanine widths than the control group despite pre-ABG expansion.

Morphogenetic fields within the human dentition: a new, clinically relevant synthesis of an old concept

This paper reviews the concept of morphogenetic fields within the dentition that was first proposed by Butler (Butler PM. Studies of the mammalian dentition. Differentiation of the post-canine dentition. Proc Zool Soc Lond B 1939;109:1–36), then adapted for the human dentition by Dahlberg (Dahlberg AA. The changing dentition of man. J Am Dent Assoc 1945;32:676–90; Dahlberg AA. The dentition of the American Indian. In: Laughlin WS, editor. The Physical Anthropology of the American Indian. New York: Viking Fund Inc.; 1951. p. 138–76). The clone theory of dental development, proposed by Osborn (Osborn JW. Morphogenetic gradients: fields versus clones. In: Butler PM, Joysey KA, editors Development, function and evolution of teeth. London: Academic Press, 1978. p. 171–201), is then considered before these two important concepts are interpreted in the light of recent findings from molecular, cellular, genetic and theoretical and anthropological investigation. Sharpe (Sharpe PT. Homeobox genes and orofacial development. Connect Tissue Res 1995;32:17–25) put forward the concept of an odontogenic homeobox code to explain how different tooth classes are initiated in different parts of the oral cavity in response to molecular cues and the expression of specific groups of homeobox genes. Recently, Mitsiadis and Smith (Mitsiadis TA, Smith MM. How do genes make teeth to order through development? J Exp Zool (Mol Dev Evol) 2006; 306B:177–82.) proposed that the field, clone and homeobox code models could all be incorporated into a single model to explain dental patterning. We agree that these three models should be viewed as complementary rather than contradictory and propose that this unifying view can be extended into the clinical setting using findings on dental patterning in individuals with missing and extra teeth. The proposals are compatible with the unifying aetiological model developed by Brook (Brook AH. A unifying aetiological explanation for anomalies of tooth number and size. Archs Oral Biol 1984;29:373–78) based on human epidemiological and clinical findings. Indeed, this new synthesis can provide a sound foundation for clinical diagnosis, counselling and management of patients with various anomalies of dental development as well as suggesting hypotheses for future studies.

Intercusp relationships of the permanent maxillary first and second molars in American whites

Much of a human molar's morphology is concentrated on its occlusal surface. In view of embryologists' recent attention on the determination of crown morphology by enamel knots that initiate cusp formation, we were interested in the arrangement of cusp apices in the definitive tooth. Computer-assisted image analysis was used to measure intercusp distances and angles on permanent maxillary M1 and M2 in a sample of 160 contemporary North American whites. The intent was to generate normative data and to compare the size and variability gradients from M1 to M2. There is little sexual dimorphism in intercusp distances or angles, even though the conventional mesiodistal (MD) and buccolingual (BL) crown size is 2.0% and 4.0% larger in males, respectively, in these same teeth. Dimensions decreased in size and increased in variability from M1 to M2, but differentially. Cusps of the trigon were more stable between teeth, especially the paracone-protocone relationship. Principal components analysis on the six M1 distances disclosed only one eigenvalue above 1.0, indicating that overall crown size itself is the paramount controlling factor in this tooth that almost invariably exhibits a hypocone. In contrast, four components were extracted from among the 12 angular cusp relationships in M1. These axes of variation may prove useful in studies of intergroup differences. A shape difference occurs in M2, depending on whether the hypocone is present; when absent, the metacone is moved lingually, creating more of an isosceles arrangement for the cusps of the trigon. Statistically, correlations are low between occlusal intercusp relationships and conventional crown diameters measured at the margins of the crowns that form later. Weak statistical dependence between cusp relationships and traditional MD and BL diameters suggest that separate stage- and location-specific molecular signals control these different parts (and different stages) of crown formation.

Correlations between deciduous and permanent tooth morphology in a European American sample

The expression of dental morphological characteristics is partially genetically controlled, and is assumed to be similar in deciduous and permanent dentitions. However, there are few published data comparing normal morphological variation between the two dentitions in the same individual. For the current study, data were collected from European Americans (N = 54) whose teeth were cast both as children and adults. We observed 19 trait expressions in deciduous and permanent dentitions. Deciduous traits were scored based on Hanihara's and Sciulli's descriptions, while permanent teeth were scored using the ASU dental anthropology system. The two dentitions' scores were compared using Goodman-Kruskal's Gamma (gamma) in the original, commonly used systems as well as in a new, shared scale to which the scores were converted. Observations were also dichotomized in both formats and compared using tetrachoric correlation. We expected high correlations between the two dentitions and for both statistics to yield similar results. For the original scores, gamma correlations vary from -1.0 to 0.68; tetrachoric correlations vary from 0.04 to 0.67. For the shared scale scores, gamma correlations range from -1.0 to 1.0 and tetrachoric correlations range between -0.47 and 0.8. Several traits showed no correlation in either test. Overall, categorical data analysis returned more positive moderate to high correlations than tetrachoric correlation analysis, and shared scale tests resulted in more correlations than did tests of data in the original scoring systems. These results reflect differences in commonly used scoring systems, variation in rarely occurring traits, different strengths of trait expression, and complex genetic/environmental interactions.

Genetic correlations between mandibular molar cusp areas in baboons

Primate evolutionary studies rely significantly on dental variation given the large role that teeth play in how an organism interacts with its environment (animal and plant) and conspecifics. Variation in cusp size has been shown to vary among primate taxa, although most studies to date focused on extant and extinct hominoids. Here we test the assumed hypothesis that a significant proportion of this variation in baboons is due to the additive effects of genes. We perform quantitative genetic analyses on variation in two-dimensional (2-D) mandibular molar cusp size in a captive pedigreed breeding population of baboons (Papio hamadryas) from the Southwest National Primate Research Center. These analyses show that variation in cusp size is heritable and sexually dimorphic. Additionally, we tested for genetic correlations between cusps on the same crown, between morphological homologues along the tooth row, and between cusp area and crown buccolingual width. We find that four of the six cusp pairs on the first molar have a genetic correlation of one, save for the metaconid-hypoconid and entoconid-hypoconid, which are not statistically different from zero. The second and third molars have lower genetic correlations, although the metaconid-hypoconid correlation is similarly estimated at zero and the entoconid-protoconid correlation is estimated to be one. This cross pattern of genetic and no genetic correlation does not immediately accord with the known pattern of development and/or calcification. We propose two explanative hypotheses.

Biological structure and health implications from tooth size at Mission San Luis de Apalachee

This study analyzes dental metric variation to examine the biological structure of the native population at Mission San Luis de Apalachee, a late 17th century mission located in the Apalachee Province of Spanish colonial Florida. Three topics are addressed: (1) comparison of tooth sizes among adult and subadults, (2) analysis of the bio-spatial structure of skeletons within the church area, and (3) comparison of phenotypic profiles of individuals interred within coffins in the ritual nucleus of the church: the altar region. Analyses indicate that subadults had smaller average tooth sizes than adults for the posterior dentition that was particularly evident in mandibular nonpolar molars and premolars. This disparity, also documented in two other mission populations, likely represents ontogenetic stress and resulting increased mortality among those most at risk for early death. Analysis of the spatial structure of graves failed to document biological structuring by side of the aisle or by burial row, although some gross differences were evident when front, middle, and rear church burials were compared. Individuals buried in coffins within the same row were phenotypically similar to one another. However, inter-row comparisons indicated lack of phenotypic similarity among all coffin interments. These analyses suggest maintenance of kin-structured burial for elites alone within the San Luis community.

Mineralization of the mandibular third molar: A study of American blacks and whites

The tempo of tooth mineralization is under significant genetic control, and the orderly progression of morphological changes-in concert with the long span during growth in which teeth form-makes "dental age" a useful measure of a person's degree of biological maturity. The third molar is of particular interest because (1) it is the last and most variable tooth to form and (2) it is the only tooth to complete formation after puberty, which has made it attractive in forensic and legal circles as an estimator of adulthood. Age standards are described here for mandibular third molar formation stages in a cross-sectional sample of 4,010 persons (age range: 3-25 years), with proportionate sample sizes of American blacks and whites and males and females. Formation was scored against the 15-grade ordinal scheme of Moorrees, and descriptive statistics were computed using proportional hazards survival analysis. Blacks achieved each formation stage significantly ahead of whites, but not in a uniform manner. Instead, there was an enhanced advancement in blacks during crown formation and during late stages of root formation. In both races formation proceeded faster in males, which is unique for the third molar, as prior studies suggest. Sample variance increases with the stage of formation, such that 95% confidence limits span 8 or more years for root formation stages. Consequently, the third molar provides a rough gauge of an individual's chronological age, but the considerable variability precludes any precise estimate, particularly in late adolescence where most forensic interest has focused.

Metric dental variation of major human populations

Mesiodistal and buccolingual crown diameters of all teeth recorded in 72 major human population groups and seven geographic groups were analyzed. The results obtained are fivefold. First, the largest teeth are found among Australians, followed by Melanesians, Micronesians, sub-Saharan Africans, and Native Americans. Philippine Negritos, Jomon/Ainu, and Western Eurasians have small teeth, while East/Southeast Asians and Polynesians are intermediate in overall tooth size. Second, in terms of odontometric shape factors, world extremes are Europeans, aboriginal New World populations, and to a lesser extent, Australians. Third, East/Southeast Asians share similar dental features with sub-Saharan Africans, and fall in the center of the phenetic space occupied by a wide array of samples. Fourth, the patterning of dental variation among major geographic populations is more or less consistent with those obtained from genetic and craniometric data. Fifth, once differences in population size between sub-Saharan Africa, Europe, South/West Asia, Australia, and Far East, and genetic drift are taken into consideration, the pattern of sub-Saharan African distinctiveness becomes more or less comparable to that based on genetic and craniometric data. As such, worldwide patterning of odontometric variation provides an additional avenue in the ongoing investigation of the origin(s) of anatomically modern humans.

Spanish colonial effects on Native American mating structure and genetic variability in northern and central Florida: Evidence from Apalachee and western Timucua

Standard population genetic analyses are implemented for a series of precontact and contact period samples from central and northern Florida to investigate changes in genetic variability and population affinity coincident with the establishment of Spanish missions during the 17th century. Estimates of F(ST) based on odontometric data indicate limited heterogeneity for the Apalachee samples, suggestive of some degree of within-group endogamy for this ethnic group prior to contact. This corresponds well with ethnohistoric reconstructions indicating that Apalachee were populous, partially linguistically isolated from its neighbors, and involved in persistent cycles of warfare with neighboring groups. Estimates of extralocal gene flow for the Apalachee samples indicate limited initial changes in the mating structure of these populations. After 1650, however, extralocal gene flow increases, consistent with evidence for dramatic population movements throughout northern Florida and increased Spanish presence in the province, particularly at the mission of San Luis. Inclusion of non-Apalachee outgroups does not increase estimates of genetic heterogeneity, as was expected based on ethnohistoric data. The pattern of genetic distances suggests a biological division between north and south Florida population groups, consistent with archaeological and ethnohistoric data, and similarly indicates some distinction between precontact and postcontact local groups. Differential extralocal gene flow experienced by pre-1650 Apalachee and Timucua populations suggests localized mission experience. The Apalachee, with large, dense populations, experienced limited initial changes in genetic diversity or mating structure. However, after 1650 they were apparently involved in a much more expansive mating network that may have included Spaniards and immigrant Native American groups to the region. These results are in contrast to the mission experience of the Guale Indians of the Georgia coast.

Population continuity vs. discontinuity revisited: Dental affinities among late Paleolithic through Christian-era Nubians

The present study revisits a subject that has been a source of long-standing bioarchaeological contention, namely, estimation of Nubian population origins and affinities. Using the Arizona State University dental anthropology system, frequencies of 36 crown, root, and intraoral osseous discrete traits in 12 late Pleistocene through early historic Nubian samples were recorded and analyzed. Specifically, intersample phenetic affinities, and an indication of which traits are most important in driving this variation, were determined through the application of correspondence analysis and the mean measure of divergence distance statistic. The results support previous work by the author and others indicating that population discontinuity, in the form of replacement or significant gene flow into an existing gene pool, occurred sometime after the Pleistocene. This analysis now suggests that the break occurred before the Final Neolithic. Samples from the latter through Christian periods exhibit relative homogeneity, which implies overall post-Pleistocene diachronic and regional population continuity. Yet there are several perceptible trends among these latter samples that: 1) are consistent with documented Nubian population history, 2) enable the testing of several existing peopling hypotheses, and 3) allow the formulation of new hypotheses, including a suggestion of two post-Pleistocene subgroups predicated on an age-based sample dichotomy.

Statistical genetics of molar cusp patterning in pedigreed baboons: implications for primate dental development and evolution

Gene expression and knock-out studies provide considerable information about the genetic mechanisms required for tooth organogenesis. Quantitative genetic studies of normal phenotypic variation are complementary to these developmental studies and may help elucidate the genes and mechanisms that contribute to the normal population-level phenotypic variation upon which selection acts. Here we present the first quantitative genetic analysis of molar cusp positioning in mammals. We analyzed quantitative measures of molar cusp position in a captive pedigreed baboon breeding colony housed at the Southwest National Primate Research Center in San Antonio, Texas. Our results reveal complete pleiotropy between antimeric pairs of traits--i.e., they are influenced by the same gene or suite of genes. Mandibular morphological homologues in the molar series also exhibit complete pleiotropy. In contrast, morphological homologues in maxillary molar series appear to be influenced by partial, incomplete pleiotropic effects. Variation in the mandibular mesial and distal molar loph orientation on the same molar crown is estimated to be genetically independent, whereas the maxillary molar mesial and distal loph orientation is estimated to have partially overlapping genetic affects. The differences between the maxillary and mandibular molar patterning, and the degree of genetic independence found between lophs on the same molar crown, may be indicative of previously unrecognized levels of modularity in the primate dentition.

Population history of native groups in pre- and postcontact Spanish Florida: Aggregation, gene flow, and genetic drift on the Southeastern U.S. Atlantic coast

Evolutionary trends and population history and structure are discussed for a series of late prehistoric and historic-period skeletal samples from the Georgia coast and interior (the Guale). Phenotypic dental measurement data were collected for nine samples from the late prehistoric (AD 1200-1400) and historic (AD 1608-1702) periods and subjected to population genetic and statistical analyses. The primary trends were for an increase in tooth size through time, and for an initial increase in dental variability in the early historic period, followed by a subsequent decline in dental variability in the late historic period. Given the increasing stress levels, evidenced by previous bioarchaeological analyses (Larsen [2001] Bioarchaeology of Spanish Florida, Gainesville: University Press of Florida), an environmental explanation for the increase in tooth size is unlikely. It is proposed that the early historic period witnessed aggregation and gene flow with extraregional populations, possibly African slaves or nonlocal Native American population groups. The late historic period may have experienced significant loss of phenotypic variability due to genetic drift. In both time periods, the evolutionary mechanism increased average tooth size, with independent variance effects.Because microevolutionary trends obscure patterns of gene flow and population ancestry, the data were detrended following Konigsberg ([1990a] Hum. Biol. 62:49-70), and submitted to standard population genetic analyses (Relethford et al. [1997] Hum. Biol. 69:443-465). Analysis of the precontact samples in isolation (Irene Mound, Irene Mortuary, and an aggregate coastal sample) indicated little genetic microdifferentiation (F(ST) = 0.008), limited extralocal gene flow, and a small distinction between interior and coastal samples. The inclusion of the historic data dramatically increased variability levels (F(ST) = 0.019). The analysis of extralocal gene flow indicates that the late mission period experienced significantly less external gene flow, which is consistent with historic models that suggest the social organization of the Guale during this time period may have been significantly altered. Genetic distances also indicate a primary division between inland and coastal precontact samples and a maintenance of biological populations along the coast. In other words, the coastal, early historic, and late historic period samples are phenotypically homogeneous, supporting the notion that the mission populations were drawn from the local population base. The late mission period sample was also, however, more closely related to the interior samples. This may suggest that the late mission period population was an aggregate sample composed of both remnant interior and coastal population groups.

Matrix decomposition model for investigating prehistoric intracemetery biological variation

A matrix decomposition model for analyzing prehistoric intracemetery biological variability is presented. The model, based on the correlation between interindividual biological and burial distance matrices, provides an estimate of the number of distinct burial populations interred within a single cemetery, which effectively ameliorates identifiability problems typical of general variability analyses (Raemsch [1995] Ph.D. dissertation, SUNY at Albany). Unlike other methods for analyzing intrasite variability analysis (e.g., kinship analysis and microchronology), this method is not reliant on a priori subgroup definition. Assuming a kin-structured burial pattern, a residual matrix is defined based on the raw data matrices; the proportion of negative or zero residuals to the total number of residuals provides an estimate of the number of hidden subgroupings (lineages) within the cemetery. The comparative utility of the model is demonstrated on a series of protohistoric and historic period skeletal samples from the Georgia coast, where it demonstrated that the increase in phenotypic variability during the early mission period is the result of population aggregation at the missions and not necessarily genetic admixture between local and nonlocal groups.

Differential phenotypic variability among the Apalachee mission populations of La Florida: a diachronic perspective

Phenotypic variability is evaluated in a series of skeletal samples from the Apalachee region of Florida. Based on ethnohistoric evidence, several predictive models for changes in variability are generated. If variability decreases through time, this likely represents the effect of genetic drift in populations experiencing epidemic disease and population loss. If variability increases through time, this suggests that population aggregation or genetic admixture were primary factors shaping the Apalachee population during the mission period. Dental dimensions were collected from a series of precontact (pre-1500), early mission (AD 1633-1650) (San Pedro y San Pablo de Patale), and late mission (post-1657) (San Luis) samples from the Apalachee region and were subjected to univariate and multivariate variability analyses. The results indicate that the late mission San Luis sample was significantly more variable than the Patale or precontact samples; however, the Patale sample exhibited no significant variability change in comparison to the precontact population. This suggests that the missions initially effected limited change in genetic variability in the mission populations. However, San Luis was affected by either admixture or population aggregation to such a degree that the observed variation had increased beyond earlier levels. Given the limited historic evidence for population aggregation at this mission, and the comparatively large resident Spanish population, the increased variability may be indicative of admixture at this mission, and potentially at this mission only. Based on a limited data set, however, it appears that the mission period cannot be typified by a single evolutionary or historic process.

Permanent tooth crown dimensions in prematurely born children

AIM

The aim was to examine the effect of preterm birth on permanent tooth crown dimensions.

MATERIALS AND METHODS

The data consisted of 328 prematurely born white and black children and 1804 control children who participated in the cross-sectional study of the Collaborative Perinatal Project (USA) in the early 1960s and 1970s. The dental examinations were carried out in a standardized fashion at ages varying from 6 to 12 years in 95% of cases. Tooth crown size measurements were performed on the dental casts with an electronic measuring device and readout by two experienced observers according to precise definitions generally quoted in the anthropological and genetic literature. The preterm and control groups were divided by sex and race.

RESULTS

The results show both increased and decreased tooth crown dimensions in the prematurely born children. Significantly increased dimensions were found in the means of the intercuspal distances of the first permanent molars in the white boys and in the mesiodistal dimensions (MD) of the lower lateral incisors and the upper left first molar in the black girls. By contrast, there were decreased intercuspal distances, MD and labiolingual (LL) tooth crown dimensions in the white girls and black boys. The statistical method used was the Mann-Whitney's U-test (Willcoxon Rank-Sums test).

CONCLUSIONS

The findings partly support previous reports of decreased tooth crown dimensions in preterm infants, but the increased dimensions found in the preterm white boys and black girls differ from earlier reports. Our results indicate the importance of environmental factors including neonatal factors in determining permanent tooth crown dimensions. Growth patterns, the buffering capacity and the timing of sensitive moments in tooth crown volume gain may vary between the sexes and ethnic groups and the possible effect of the accelerated growth period in preterm infants (catch-up growth) may influence the determination of permanent tooth crown dimensions.

Genetic analysis of deciduous tooth size in Australian twins

Investigations of permanent dental crown size in twins and family groups indicate a high degree of transmissible control, but little is known about the relative contributions of genetic and environmental factors to variation in size of the deciduous (primary) teeth. Here, maximum mesiodistal and buccolingual crown dimensions of maxillary and mandibular primary teeth were measured from dental models of 602 individuals, including 99 monozygous (MZ) twin pairs, 81 dizygous (DZ) same-sex pairs, 41 DZ opposite-sex pairs, and 160 singletons. Data were subjected to univariate genetic analysis with the structural-equation-modelling package, Mx using the normal assumptions of the twin model. A model incorporating additive genetic (A) and unique environmental (E) variation was found to be the most parsimonious for all tooth-size variables. Estimates of heritability for deciduous crown size ranged from 0.62 to 0.91. This study shows that variation in deciduous crown size has a strong genetic component, similar to that observed in the permanent dentition. Further studies are required to determine whether the underlying genetic mechanisms are the same for both deciduous and permanent teeth.

Dental anthropology of central-southern, Iron Age Italy: the evidence of metric versus nonmetric traits

Discrete and metric dental traits are used to assess biological similarities and differences among 13 bioarchaeological populations located on each side of the Apennine mountains in central-southern Italy and dated to the first millennium BC. An initial hypothesis, that the mountain chain might provide a significant geographical barrier for population movement (resulting in greater biological affinities among those groups on the same side), is not supported. Instead, the samples appear to cluster more on the basis of time than geography. Archaeological evidence, however, supports an association between populations on opposite sides of the mountains and thus is in accord with the dental data. As anticipated, discrete dental traits appear to be more useful than metric dental traits in assessing such population affinities. This research represents a beginning to a better comprehension of the complexity of the biological and cultural dynamics of Italian populations during recent millennia.

Genetic covariance structure of incisor crown size in twins

Previous studies of tooth size in twins and their families have suggested a high degree of genetic control, although there have been difficulties separating the various genetic and environmental effects. A genetic analysis of variation in crown size of the permanent incisors of South Australian twins was carried out, with structural equation modeling used to determine the relative contributions of genetic and environmental factors. Maximum mesiodistal crown dimensions of maxillary and mandibular permanent incisors were recorded from dental models of 298 pairs of twins, including 149 monozygous (MZ) and 149 dizygous (DZ) pairs. The analysis revealed that: (i) an adequate fit required additive genetic and unique environmental components; (ii) augmenting the model with non-additive genetic variation did not lead to a significant improvement in fit; (iii) there was evidence of shared environmental influences in the upper central incisors of males; (iv) the additive genetic component constituted a general factor loading on all eight teeth, with group factors loading on antimeric pairs of teeth; (v) unique environmental effects were mostly variable-specific; (vi) most factor loadings on antimeric tooth pairs could be constrained to be equal, indicating a symmetry of genetic and environmental influences between left and right sides; and (vii) estimated heritability of the incisor mesiodistal dimensions varied from 0.81 to 0.91.

Human dento-gnathic metric variation in mesolithic/neolithic Ukraine: possible evidence of demic diffusion in the Dnieper Rapids region

Dental and gnathic metrics from a series of Mesolithic and Neolithic cemetery samples in the Dnieper River valley (Ukraine) are compared. Both male and female Neolithic samples have larger dental dimensions, wider dental arcades, and a more robust mandibular corpus than do the Mesolithic samples. In addition, the relative variances (RVs) of bucco-lingual dental breadths (as measured by modified Levene's Tests) show an intriguing pattern of change from the Mesolithic into and through the Neolithic. Female RVs show a clear tenency to increase through time, while male RVs show more mixed tendencies. Such a pattern indicates that the increases in Ukrainian Neolithic dento-gnathic dimensions are plausibly attributable to low intensity gene flow (demic diffusion). Seen in the light of new chronometric, paleodietary, and paleolinguistic information, as well as in the context of recent archaeological models for agro-pastoralist origins in the North Pontic, these data suggest that gene flow via population interactions originating in or transient through the circum-Caucasus may have played an important role in producing the Ukrainian Neolithic dental increase.

Development defects of enamel in humans with hereditary epidermolysis bullosa

Developmental defects of enamel are often reported as a feature of the more severe forms of epidermolysis bullosa (EB). The purpose of this investigation was to determine the prevalence and character of enamel defects in each of the major hereditary EB types. Clinical evaluations were made on 237 individuals representing all of the major EB types and 58 unaffected individuals. All EB cases were categorized by phenotype, mode of inheritance and skin biopsy. The frequency of individuals having developmental enamel defects ranged from 8.6% in recessive dystrophic EB to 100% in junctional EB; 27.5% of the control population had these defects. Generalized hypoplasia characterized by either severe pitting and/or thin enamel was seen in all junctional EB cases but not in any other EB type. There was a tendency for the severe Herlitz form of junctional EB to have thin enamel while non-Herlitz junctional EB cases had less severe pitting and generally no reduction in enamel thickness. The prevalence of individuals with hypoplastic enamel bands was greater in the EB population (9.7%) than controls (1.9%). Thus individuals with simplex and dominant dystrophic EB typically have enamel defects that are similar in frequency and distribution to those of unaffected individuals. Developmental defects of enamel are a consistent feature of junctional EB, although the clinical expression is highly variable.

Maternal smoking and tooth formation in the foetus. I. Tooth crown size in the deciduous dentition

Altogether 2159 pregnancies among black and white Americans in the Collaborative Perinatal Study and dental casts from the children at the age of 5-12 years were studied to find out the effect of maternal smoking on deciduous tooth crown growth. Minor crown size reduction (2-3%) in some dimensions was found in children whose mothers had smoked during pregnancy. The possible change in dimensions seems to be influenced by sex, race and smoking habit. The critical time periods of the gestational development (16th to 19th) weeks would possibly appear from these data to be targeted by the detrimental effect of maternal smoking. It is concluded that deciduous tooth sizes seem to be greatly unaffected when compared to reduction in birthweight.

Reduction of maxillary molars in Homo sapiens sapiens: a different perspective

Crown and cusp areas, and buccolingual and mesiodistal diameters of maxillary molars of complete upper tooth rows (30 males, 30 females) were analysed in order to quantify changes in size and shape from the first to the third molar. Uni- and multivariate analyses revealed the mesial cusps, in particular the protocone (mesiolingual cusp), to be more stable than the other cusps. Although there is a gradient in size from the first to third molar, shape changes were found to be marked. Overall, the findings are in keeping with the field theory and the hypotheses of environmental constraints on later developing teeth. However, not all of the results could be entirely explained by these concepts. Functional aspects seem to account for the relative stability of the protocone and the buccolingual crown diameter. It appears that this functional complex is relatively stable despite the overall reduction of tooth size, which is probably secondary to processes occurring in the jaws and the cranium. This finding may have implications for studies on tooth reduction between populations of different time periods.

Complex segregation analysis of dental morphological variants

A set of 20 morphological variants of the dental crowns and four characteristics of the jaws are tested for probable mode of inheritance using the complex segregation analysis method of Morton et al. (Am. J. Hum. Genet. 23:602-611, 1971). Models tested include three two-allele single-locus models (dominant, codominant, and recessive) and a model employing the polychotomized normal distribution of liability (an additive polygenic model), with transmissibility estimated via maximum likelihood. Most of the traits studied are observed using ordinal scales with several grades, and many are tested using more than one dichotomy of their scale. These multiple analyses allow for an examination of such factors as trait incidence on the results of the statistical analysis. The results of the analysis yield propositions of major genes for 13 of the 24 traits examined. Two traits give good evidence of being polygenic in origin. The remaining nine characters present methodological problems that do not allow for a definite conclusion on their mode of inheritance at this time. The ability to test varying levels of transmissibility in the polygenic model allows for an estimation of the percentage of trait variance determined by familial factors. Estimates of transmissibility for all characters examined range from 0 to 1, with a mean of 0.36. These findings may suggest a large environmental role in the development of dental crown morphology. However, the possibility exists that difficulties in the ability to classify the expression of certain traits consistently result in overestimates of the environmental influences on the development of those characters.

Yugoslav Mesolithic dental reduction

Yugoslav Mesolithic dentition exhibits maximum mesiodistal reduction compared with contemporary European and North African groups. This reduction is not explained entirely by attrition, and may be seen as a continuation of the European Upper Paleolithic trend. Buccolingual dimension does not reduce as much. In fact, this dimension in premolars and molars is larger than in other groups. This observation also occurs in Natufians, who were grain collectors, hunters, and gatherers. The Yugoslav Mesolithic group was collecting and domesticating Cerelia as well as fishing and hunting. Linear enamel hypoplasias (LEH) indicate childhood stress through the fifth year, which corroborates previously reported incidence of rickets in this group. The central maxillary incisors and canines manifest higher degrees of LEH, but the appearance on the second molars suggest a more severe physiological disruption. Sex differences in distributions of alveolar resorption and calculus suggest differences in diet or nutritional stress. Previous reports indicate that females had higher incidence of osteomalacia. If so, female nutritional stress may explain the extreme mesiodistal reduction and minimal sexual dimorphism in this group.

Quantitative analysis of the molar-size sequence in human prehistoric populations of the Canary Isles

Percentage frequencies for molar-size sequence of first and second molars, as well as the statistical parameters for the individual differences between the measurements of these molars, were calculated in two human prehistoric aboriginal samples from Gran Canaria and Tenerife Islands using mesiodistal and buccolingual dimensions. Remarkable differences between the two populations, whose cultural and anthropological differences are well established, were observed. The findings support the hypothesis that quantitative analysis of molar size sequence can be useful in establishing phylogenetic relationships between populations.