Quantifying molar tooth shape in primates using geometric morphometrics

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The occlusal shapes of molars in Macaca fuscata fuscata were analyzed by means of geometric morhpometrics. The central pit was selected as the origin, and the following points were selected as landmarks the cusp tips, the mesial and distal pits, and the intersection between central groove and buccal/lingual groove, and the most prominence points of occlusal outline. The two dimensional and three dimensional vectors for the landmarks were measured.Two dimensional measurements were made for the three permanent molars (M1, M2 and M3), and they were analysed by the Procrustes and thin-plate spline analyses. Sexual differences in molar shape were very small, but centroid size was significantly different between the two sexes. Sexual differences in size and shape of the molars were more conspicuous in the later-developed molar than in the early-developed molar. There were small differences between M1 and M2 in shape, but M2 had significantly larger centroid size than M1. The shape change from M1 to M3 is represented by mesiodistal elongation and buc colingual compression of the distal half of the crown.The occlusal shape differences between maxillary fourth deciduous premolar (dp4) and first permanent molar (M1) were analyzed by the thin-plate spline analyze. Three dimensional vectors of 8 landmarks were measured when the central pit was selected as the origin. The centroid size of the dp4 was significantly smaller than the M1 (P<0.01). The dp4 had shallower pits and well-developed metacone than M1, but the location of cusp tips on the occlusal plane did not different among the two molars.