Racial diferences in tooth crown size gradients within morphogenetic fields

Summary: Teeth are arranged in morphogenetic fields,which are anatomical locations in the jaws that regulate tooth types, namely incisors, canines,premolars, and molars in primates. Each field is composed of two or three teeth (except for theisolated canine), and there is a characteristic size gradient corresponding to directionality withineach field, generally with the mesial tooth being larger and more stable than the distal, variabletooth. Focus of the present study is on racial differences in the steepness of these mesial-distalcrown size gradients. Groups with “steep” gradients have appreciable size reduction from the stableto the variable tooth, while other groups, with “shallow” gradients, have more similar crowndimensions across a field. This worldwide survey of published studies (107 groups) assessedintergroup (rather than inter-individual) variation in size gradients calculated for the incisors,premolars, and molars in each arcade. Caucasians tend to have the steepest gradients; aboriginalAustralians tend to have the most shallow gradients. Correlations among the gradients of differenttooth types are significant statistically, but modest, suggesting that microevolutionary factorshave influenced the gradients of different groups differently. Of the seven geographic groupingsevaluated, Amerindians are the most distinctive. We briefly speculate on the nature of thedevelopmental molecular signaling that determines these gradients. Key words: Tooth size.Odontometrics. Morphogenetic fields. Human variation. humana.