A Comparative Study on Sinodont and Sundadont of Japanese Teeth

It is the present situation that Sinodont and Sundadont，the two descends of Japanese group，must be considered when we conduct the comparative examination of the size and shape in Japanese teeth.This time we direct our attention to the number of the distal root canal in M I D 21 I D 2.By dividing the whole group into1-root-canal group and 2-root-canal group，we investigate whether there are any differences between these groups in the odontometrical aspect。The aim of this research is to obtain the fundamental materials by which the Japanese group is classified into Sinodont and Sundadont in the aspect of dental morphology.(1)For Japanese male，the differences of the crown width In I2and C‘between the 1-root-canal group and the 2-root-canal group are significant，while the differences of the crown thickness in P I D 11 I D 1，P I D 12 I D 1 and I/D 2.Differences of all kinds of teeth between the 1-root-canal group and the 2-root-group are not significant.(3)for the 2-root-canal group，the sexual differences of the crown width in the lower canines are significant，while the sexual differences of the crown thickness in I1，I D 22 I D 2，C，P 1，M I D 12 i D 1 are also significant.Consequently，the sexual differences of the crown thickness are more than those of the crown width.(4)for the 1-root-canal group，the sexual differences of the crown width in I1，I2，C are significant，while the sexual differences of the crown thickness in C and M2 are also significant.(5)The appearance rate of Shovel-shaped incisor in the upper incisor of the 2-root-canal group is higher than than at the root-canal group is higher than than at the root-canal group is higher than than thickness are more than those of the crown width.

It is the present situation that Sinodont and Sundadont, the two descends of Japanese group, must be considered when we conduct the comparative examination of the size and shape in Japanese teeth. This time we direct our attention to the number of the distal root canal in MィイD21ィエD2. By dividing the whole group into 1-root-canal group and 2-root-canal group, we investigate whether there are any differences between these groups in the odontometrical aspect. The aim of this research is to obtain the fundamental materials by which the Japanese group is classified into Sinodont and Sundadont in the aspect of dental morphology.(1) For Japanese male, the differences of the crown width In I2 and C' between the 1-root-canal group and the 2-root-canal group are significant, while the differences of the crown thickness in PィイD11ィエD1, PィイD12ィエD1 and IィイD21ィエD2 between these groups are significant.(2) For Japanese female, differences of all kinds of teeth between the 1-root-canal group and the 2-root-group are not significant.(3) For the 2-root-canal group, the sexual differences of the crown width in the lower canines are significant, while the sexual differences of the crown thickness in I1, IィイD22ィエD2, C, P1, MィイD12ィエD1 are also significant. Consequently, the sexual differences of the crown thickness are more than those of the crown width.(4) For the 1-root-canal group, the sexual differences of the crown width in I1, I2, C are significant, while the sexual differences of the crown thickness in C and M2 are also significant.(5) The appearance rate of Shovel-shaped incisor in the upper incisor of the 2-root-canal group is higher than that of the 1-root-canal group.