Metrical studies of the crown components of the Japanese mandibular molars

We performed metrical studies of the mandibular crown components of molar teeth in Japanese. Materials used were 140 dental plaster casts (75 males and 65 females). The mandibular first and second molars (M I and M2) were measured using sliding calipers. Sex differences were greater in the talonid dimensions than in the trigonid dimensions, and were greater in M2 than in MI. Those of the molar reduction were also noted in the talonid dimensions. Although the trigonid mesiodistal diameter was significantly larger in M2 than 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 higher in M2 than in Ml, especially in the talonid dimensions. This result related to the fact that the talonid developed later than the trigonid in both ontogeny and phylogeny. Allometric relationships between the trigonid or talonid component to total crown size showed that males had negative allometry in the trigonid and positive allometry in the talonid, while females showed isometry in both crown components. These results indicated that the talonid was more variable under the influence of the total size variation, and related to sex difference in tooth size.