Abstract
Three aspects of metric variation in the permanent dentition of humans are often simply accepted as true. The first is that formation of the permanent dentition occurs within morphogenetic fields broadly associated with tooth type and jaw. The second is that dental development of among females is characterized by a higher degree of ontogenetic buffering relative to males. The third is that expression of sex dimorphism in permanent tooth size is expressed uniformly among well-nourished human populations. This study tests these assumptions through an examination of mesiodistal and buccolingual dimensions of all non-canine permanent teeth, except third molars, among 2,709 living individuals of 15 ethnic groups from South Asia. With sexes pooled, only one in four contrasts of variance among key versus distal teeth within dental fields are significantly heterogeneous, while one in four contrasts yield higher levels of variance among key teeth relative to their distal counterparts within a dental field. Such results weaken considerably orthodox applications of Butler’s dental field theory. When samples are the unit of analysis, male samples are marked by fewer dental fields with significantly heterogeneous levels of variance between key and distal members, while males and females are affected equally by significantly heterogeneous variation between key and distal members when dental fields are the unit of analysis. Such results suggest males and females are equally buffered against environmental perturbations that affect odontometric variation. One-way ANOVA indicates that a tooth’s position within a dental field ac-counts for 15.5% to 23.1% of the observed varia-tion in tooth size, while two-way ANOVA reveals that when sex is added as a second factor, the percentage of variance in tooth size explained increases from 16.7% to 30.8%, an improvement of 27.2%. Such results indicate sex dimorphism in tooth size varies in both patterning and in magnitude among these samples, thereby explaining why discriminant functions developed for one population often perform more poorly when applied to other populations.
Highlights
Three aspects of metric variation in the permanent dentition of humans are often accepted as true
Over the last 70 years a consensus has emerged that dental development in humans is characterized by a series of developmental fields that correspond broadly to tooth type by jaw (Butler 1939; Dahlberg 1945, 1951), that odontogenesis is marked by a greater degree of developmental buffering, or “canalization,” among females relative to males (Garn et al 1965, 1966; Nichol et al 1984; Niswander & Chung 1965), and that expression of sex dimorphism is uniformly expressed across adequately nourished human populations (Kieser et al 1985)
A similar observation was made by Keene (1982), whose concept of the morphogenetic triangle emphasized the dynamism in the formation of the individual cusps until coalescence among the cusps fuses them in place. Given these expectations, it has been widely assumed that the key tooth within each morphogenetic field ought to possess the highest heritabilities, while the non-key teeth ought to be marked by lower heritabilities
Summary
Three aspects of metric variation in the permanent dentition of humans are often accepted as true. Over the last 70 years a consensus has emerged that dental development in humans is characterized by a series of developmental fields that correspond broadly to tooth type by jaw (Butler 1939; Dahlberg 1945, 1951), that odontogenesis is marked by a greater degree of developmental buffering, or “canalization,” among females relative to males (Garn et al 1965, 1966; Nichol et al 1984; Niswander & Chung 1965), and that expression of sex dimorphism is uniformly expressed across adequately nourished human populations (Kieser et al 1985) This study tests these assumptions through assessment of mesiodistal and buccolingual dimensions of all noncanine permanent teeth except third molars among 2,709 living individuals of 15 ethnic groups from South Asia
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