A Comparative Study on Sinodont and Sundadont of Japanese Teeth

这是目前Sinodont和Sundadont的情况，日本团体的两个分类，必须考虑到当我们对日本牙齿的尺寸和形状进行比较测试时。This time we direct our attention to the number of the distal root canal in MイイD21イエD2.如果将整个群体划分为1-根运河群体和2-根运河群体，我们将调查这些群体之间的差异，在几何学方面。本研究的目标是通过日本群体在牙科形态学方面分类的Sinodont和Sundadont获得基本材料。（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是significant， while the differences of the Crown thickness in Py D11 y D1，Py D12 y D1 and I y D21 y D2 between the groups是significant。（2）对于日本女性来说，1根阴道组和2根阴道组之间的各种牙齿差异并不重要。（3）对于2-根运河组，下运河组的皇冠宽度的性差异是有意义的，而当皇冠厚度在I1， I-D22-D 2， C， P1， M-D12-D 1也是有意义的。从某种意义上说，皇冠厚度的性差异比那些皇冠宽度的差异要大。（4）对于单根运河组，冠宽度在I1、I2和C之间的性差异是显著的，而冠厚度在C和M2之间的性差异也是显著的。（5）2根运河组的上罪魁祸首中的Shovel-Shaped Incator的出现率高于1根运河组。

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.