Mesiodistal tooth crown dimensions of the primary dentition: a worldwide survey

This analysis reports on a spatial-temporal survey of published studies of primary tooth crown dimensions in humans (80 samples). Mesiodistal data are analyzed for the 10 tooth crown dimensions. The purpose was to evaluate the numerous case reports (descriptive analyses of single samples) in the literature in order to assess patterning of variation 1) in tooth size, 2) among tooth types, 3) across sexes, 4) with space (historical affinity), and 5) with time. Sexual dimorphism is low in the primary dentition, averaging 2% across all 10 tooth types. All size distributions of the samples are positively skewed because of megadont native Australians. Europeans, who are most frequently represented in the literature, have the smallest tooth crowns of any continental grouping assessed. The method by Darroch Mosimann ([1985] Biometrika 72:241-252) of reducing size effects was used, basically standardizing the data variable-wise, and then ordinating groups on their factor scores. Principal components analysis produced just two canonical axes: overall size (68%) and a front-back (i1-i2-c vs. m1-m2) polarity (11%), based on the intergroup (not ontogenetic) covariance matrix. This second component discriminates between groups with relatively large anterior teeth (Europeans) and those where relatively more tooth substance is apportioned to the molars (Africans and Asians). Size differences predominate over shape between sexes from the same groups. Europeans have small teeth with comparatively large anterior dimensions. Asian and sub-Saharan African samples share features of average crown size but large cheek teeth. Indian and European samples show considerable overlap on both canonical axes, with average size overall but comparatively large anterior teeth. The few Amerindian samples are too variable to characterize. Based on comparisons of archaeological and living samples, tooth size reductions are documented here for Europe, India, and the Near East compared to tooth sizes of Neolithic and Mesolithic samples. The temporal changes parallel those documented elsewhere for the permanent dentition. The biological and anthropological relevance of these distributions is discussed.