MODEL FOR THE EXAMINATION OF EVOLUTIONARY TRENDS IN TOOTH DEVELOPMENT

Through the use of serial computerized tomography (C-t) scans, two dis tinct developmental stages can be identified in mature teeth. C-t scan s thus provide a non-destructive method for assessing growth within in dividual teeth, as well as for comparison of the development of modern and fossil teeth. The second deciduous molar (DM2) and first permanen t molar (M1) resemble one another morphologically, despite differences in size and developmental rates. Thus, they provide an excellent mode l for studying variation in growth within an individual. To test the C -t method, we first examined a recent archaeological sample and then e xamined teeth from Skhul I. Serial C-t scans were used to compare two distinct developmental stages represented by the dentine-enamel juncti on (DEJ) and outer enamel surface (OES), respectively, in mandibular D M2 and M1 of 31 archaeological specimens. The difference in form and s ize between these two surfaces in and between teeth was calculated fro m intercusp distances measured at the DEJ and OES using the form dista nce matrix. Intercusp distances at the DEJ and OES of these teeth were then compared to their counterparts in the DM2 and M1 of Skhul I, tak en here as representative of early anatomically modern Homo sapiens sa piens. Form differences between paired DM2 and M1 at the DEJ were smal ler than those at the OES, supporting the hypothesis that differences between the two teeth increase throughout development. The increase in intercusp distances from the DEJ to OES was found to reflect the angu lation of cusps relative to one another, rather than enamel thickness. Form differences between the Skhul DM2 and M1 were smaller than those observed in the recent series, and the recent M1 differed more than t he DM2 from its fossil counterpart. The similarities found between the Skhul permanent and deciduous teeth and the recent DM2, may reflect a similar growth pattern. This would contribute to earlier crown comple tion in the fossil M1. (C) 1997 Wiley-Liss, Inc.