頬舌 2 根を有する人類下顎第一小臼歯の 1 例

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I found a case of the human lower right first premolar which had 2 separate roots in male of 45 years old. In this case, the roots are separated into the buccal and the lingual side by the deep fissure. In the mesial surface of the root, the fissure begins about 1/3 below the cervical line and runs toward the apex along the nearer side of the lingual than the central part of the root. Therefore, the root separates completely into bucco-lingual side at the upper 1/3 part of the apex. The distal surface of the root is almost flat, and there is a vertical shallow groove on the cental part of the root, and it separates completely into bucco-lingual root at the upper 1/3 part of the apex. The buccal root is slightly longer than the lingual root as a whole. In the lower premolar, the root is sometimes separated into two or three. And in case of two roots, they are separated into buccal and lingual side, or mesial and distal side. As for frequency of the supernumerary roots, it does not occur constantly. In the end I should like to say that the factors of supernumerary root of the lower premolar should be not only in the theory of atavism from phylogenetic problem, but also in ontogeny as being the result of a morphological disturbance that occurred in the dental lamina. But, I think this case is not ascribed to atavism of the tooth.
九州歯科学会の論文
1976-03-31