犬下顎第一後臼歯に 4mm 咬合挙上の金属冠を装着した場合の下顎骨分裂線について

Abstract

Since when Prof. Nakayama emphasized the meaning of existence of the irregular splitting lines, publicizing his views that the line systems indicate the direction of growth, while the irregular splitting lines are the signs of disorder of the growing direction due to collision of internal growth strengths, or the physiological load or other external influences, in other words, the irregular splitting lines are the direct functional manifestation that may be interpreted as a sort of direct defence reaction of the tissue itself, his theory has been verified by the senior students of this laboratory on the various tissues, too. With the results of these research works in mind, the author have pursued the changes of the splitting lines of mandible after bite-hight was raised in the grown up dogs (1 to 2 years post natal) and observed the appearance or disappearance of the splitting line systems, especially of the irregular splitting lines, with the 19 specimens of 10 age stages ranging from 1 and 2 weeks, 1, 3, 5, 7, 9, 11, 13 and 15 months after mounting of the metal crown on the first molar. Following conclusions have been obtained by these experiments : 1) The overload to the tooth caused by the raised occlusion is prominently observed as the increase of the irregular splitting lines at the alveolar border, apex of the root, insertion parts of masticatory museles, pre-molar alveolar border and the transitional part between body and ramus of the mandible. 2) The splitting lines at the portion in contact with the apex of root of the experimented first mandibular molar is seen for a longer period of time in the lateral surface than in the medial surface. This is considered to be due to the occlusional condition whereby the first maxillar molar pressed the experimented first mandibular molar from lateral side to the medial side, resulting in that the portion in contact with the apex of root affects stronger external influence to the lateral side. 3) The fact that the insertion parts of muscles expanded the area of the irregular splitting lines earlier than the other parts is interpreted that it is the result of the raised occlusion directly influencing each insertion part externally as the excessive force of the masticator to lift the mandible, and the appearance or disappearance of the irregular splitting lines group thereafter is the state of the fluctuation of masticatory force to lift the mandible reflecting in the insertion parts of the masticator. 4) That the effect of the raised occlusion appeared in the alveolar border and transitional part between body and ramus of mandible seems to be that the former is the mandibular tissue's adaptation trying to let the engapped upper and lower anterior teeth parts between maxilla and mandible contact each other, and the latter is because the said transitional part is the center of distortion caused by the excessive occlusion force as it occupies the supporting position in the occlusion.