現代日本人下顎大臼歯の原始的形質について

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The human lower molars show different reductional characters in the evolutional process. It may be ment the fact that the primary characters represented at the past age in the phylogentic relationship, was brought as the morphology of some development changes in the human lower molars. These original characters which have been continued the changes in the human evolutional stage, may be appeared as the condition that have been represented in the past age or have not been queit appeared in the lower molar of the recent man. Namely, the original characters do not always appear as same reductional process, and further the appearence of the original characters be found as difference variation between the dentition of several racial group or between the dentition of the individual body. This report is result that was investigated about the frequency of the appearence in some original characters in the lower molar of the recent Japanese, and about correlation coefficients between each another character or between each aproximate tooth in a individual body. The original characters were investingated in the deciduous lower second molar as well as in the permanent lower molar, because the deciduous dentition have the original character more than in the permanent dentition and are smilar to the morphology of the permanent dentition. The characters examined are as follows. 1. Dryopithecus Pattern 2. Protostylid 3. Deflecting Wrinkle 4. 6th Cusp 5. 7th Cusp The result obtained on these investigation were summarized as follows. Five characters examined have been considered as the original characters, but these were found as a fairly reductional tendency on the lower molar of the recent Japanese. However, in comparison with other racial groups in regard to these characters, Dryopithecus Pattern showed the reductional tendency of same level with the White race, and showed the reductional tendency more than in the Negro race. But other characters were seen as more frequency than other racial groups. Namely, it will be considered as special original characters that were mainly appeared in Japanese population. Deflecting Wrinkle were seen pretty frequency of appearence about m_2 and M_1, but it were not almost seen the appearence about M_2, and it will be considered as the supposition that very difference type of the reduction of Deflecting Wrinkle between M_1 and M_2 have special meaning in the phylogentic relationship. In the correlation coefficients between each character, it were found to be differences of significant (under the 5% level) between Protostylid and 6th Cusp, and between Deflecting Wrinkle and 7th Cusp about m_2, and between 7th Cusp and Groove Pattern of the occlusal surface about M_2, however it were found to be almost insignificant about M_1. In the correlation coefficients between each aproximate tooth, Protostylid, Deflecting Wrinkle and 6th Cusp were found to be the difference of significant betewen m_2 and M_1. Protostylid and 6th Cusp were found to be the difference of significant between M_1 and M_2. Two characters obtained these significant correlation will be considered as had each one another some relationship on the phylogentie or on any other evolutional process.
九州歯科学会の論文
1966-12-31

現代日本人下顎大臼歯の原始的形質について

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