Metrical studies of the crown components of the Japanese mandibular molars

We performed metrical studies of the mandibular crown components of molar t eeth in Japanese. Materials used were 140 dental plaster casts (75 males an d 65 females). The mandibular first and second molars (M I and M2) were mea sured using sliding calipers. Sex differences were greater in the talonid d imensions than in the trigonid dimensions, and were greater in M2 than in M I. Those of the molar reduction were also noted in the talonid dimensions. Although the trigonid mesiodistal diameter was significantly larger in M2 t han in M I (P < 0.01), the talonid dimensions were significantly larger in M I than in M2 (P < 0.01). The variability of the crown dimensions was high er in M2 than in Ml, especially in the talonid dimensions. This result rela ted to the fact that the talonid developed later than the trigonid in both ontogeny and phylogeny. Allometric relationships between the trigonid or ta lonid component to total crown size showed that males had negative allometr y in the trigonid and positive allometry in the talonid, while females show ed isometry in both crown components. These results indicated that the talo nid was more variable under the influence of the total size variation, and related to sex difference in tooth size.