On the Occlusal Surface Patterns of Cusps of Maxillary Molars in the Recent Japanese especially Reduction of Metacone
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There is a distinct tendency in recent man, to enlarge the protocone at the expense of the paracone, the metacone and especially also of the hypocone. We ('56) observed the reduction of the hypocone among recent Japanese and arrived at the conclusion that the Japanese seem to be highly specialized in a trend toward a reduction in the cusp pattern on the maxillary molar.However, there is a tendency in fossil man, to decrease the metacone and in the majority of cases it is much more reduced than the hypocone. For example, in Sinanthropus the metacone of the maxillary third molar is reduced in length and in breadth to the same extent, and in some cases, even inferior to the hypocone. Also it is evident that in Neanderthal group the metacone is much more involved in the reduction than the hypocone. This paper offered the statistical data on the reduction of the metacone among recent Japanese.From the observation of the 515 plaster models obtained from the maxillae of the inhabitants of Nagano Prefecture we studied the reduction of the metacone on the occlusal surface of the maxillary molars. As shown in Fig. 1, we grouped them into two classes, i. e, marked or slight; and got the following result concerning their frequency and so on.1. Comparison between the first and the second maxillary molars as to the reduction shows that the frequency is higher in the latter than in the former, as is shown in Table 1. The difference, however, is rather small compared with that of the reduction of the hypocone.2. In each individual, the degree of reduction of the metacone in the maxillary first molar tends to correlate with that in the corresponding maxillary second molar. The same is seen concerning the comparison between the right and the left side, but they do not exactly agree with each other.3. As to the degree of reduction in the metacone and the hypocone no remarkable correlation is seen between the two of the first maxillary molar; whereas in the case of the maxillary second molar one stands in contrariety to the other. Namely, where the marked degree of reduction is seen in the metacone, that of the hypocone is mostly in the slight degree, and where the hypocone shows marked reduction, the corresponding reduction of the metacone is generally slight.4. The frequency of the maxillary molar of which the occlusal surface is mesiodistally compressed is approximately 1% and 7% in the maxillary first and second molars, respectively, of the total number of teeth examined.
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日本人類学会 | 論文
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