日本人下顎第 3 大臼歯の形質人類学的研究
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概要
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A total of 247 of lower 3rd molar obtained from the Japanese people was subjected to measurement with reference to possible variations in their physical traits and findings were discussed in the light of anthropology, and special attention was directed to the problem of their retrogressive trend and discussed from phylogenetical viewpoint. Some of the interesting results were summarized as follows. 1. Measurement of the size of teeth revealed that almost similar reduction was observed in every direction from M_1 to M_2 and M_3 in order, but the rate of reduction was not so conspicuous as in the corresponding teeth of upper jaw. In the teeth of female, no difference in size was observed between M_2 and M_3. 2. Those teeth characterized by the dryopithecus pattern occupied only 4.1 % of the total and conversely type +_5 and type X_5 which are recognized to represent evolutive trend showed more frequent occurrence. In general, variable forms of cuspal groove were observed more frequently than retrogressive trend of cusps of the teeth. 3. The physical traits of tooth crown such as protostylid, the 6th and 7th cusps that are considered significant manifestations in anthropological viewpoint could be observed relatively frequently, accounting for 15.4%, 20.2% and 2.8% of the total respectively. This suggested that these traits are prevalent in the Japanese more than in other races. 4. Monoradicular tooth was found in 44.9%, of which 12.2% had gutter-shaped root. However, such trend of single-rootedness in the lower 3rd molar was not so conspicuous as in the corresponding molar in upper jaw. 5. When the degree of retrogression was evaluated by means of reduction proportion analysis, the lower 3rd molar exhibited the strongest trend of reduction, followed by M_2 and M_1, although was much weaker as compared with that for the corresponding tooth in upper jaw.
- 九州歯科学会の論文
- 1972-11-30