樋状根歯に関する形態学的研究
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概要
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The lower molars present the various degenerative traces in the evolutional process. They have two roots in its standard type, one mesial and one distal. As a sign of regressive tendency, however, their roots are also reduced to single by fusing gradually each other. It is supposed that the fused root exhibits a variational type from two roots to single root. So-called the fused root, which fuses only the buccal side and is separated by the vertical gutter in the lingual side was named "Gutter Shaped Root" by Nakayama (1941). In the present study, measurements were undertaken for the dimensions of the gutter shaped root teeth occurring in the lower molars and examined in detail the morphology of their crown and root, as shown Figs. 1-5. 1. The percent frequency for occurrence of those teeth was 0% (0/257) in the first molar, 30.0% (107/357) in the second molar and 10.6% (65/613) in the third molar respectively. They were fused almost in the buccal side. 2. The occlusal surface pattern of the teeth presented the X pattern in the majority. Comparing with two rooted teeth, they showed strong trend of decrease of the y Pattern and increase of the X pattern. 3. Measurement of the size of the teeth showed some reduction in the crown, and increase in the neck and root as compared with double rooted teeth, but upon the whole, the teeth did not show trend of reduction. The bifurcated point of the root was situated by the crown side in comparison with two rooted teeth. 4. Measurement in cross section of the root showed almost similar values in the middle of the root as double rooted tooth, while the root area showed trend of reduction and increase in the root canal area around root apex. 5. The width and depth of the non-fused side gutter in cross section presented reduction proportion to the fused degree of the root. The type of fused side surface was not related to the fused degree in the middle of the root, but the root canal presented trend of fusing in proportion to the fused degree of the root around root apex. 6. The root canal types were related to type of the non-fused side gutter or the fused side surface in cross section of the root. It is suggested that the root canal types are influenced by the gutter depth of the fused side surface. 7. The root type could be discriminated by roentgenogram, but that of the root canal types was difficult. 8. Those teeth had the apical foramen between one and seven, of which the two number was most, 32.8%. The number of the foramen decreased in proportion to the fused degree of the root, and their opening ends centered at the fused portion from the mesial or distal portion. 9. Those teeth are a kind of evolutional type which presents the devolutive process from two roots to single root. It has been supposed that those teeth do not only present reduction in the degenerative process but also present more eminently degenerative phenomenon by action of some secondary factor from morphological point of view.
- 九州歯科学会の論文
- 1976-01-31
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