犬下顎骨の発育に関する実験的研究

Abstract

An experimental study was conducted with dogs into how the functional decline due to complete removal of m. masseter on one side affects the morphological growth of the mandible. The dogs used for the experiment were 1.5 to 2 months old (1.5 to 3.2 kg.) and were operated on the left side, with the right side as control. Forty dogs were divided into seven groups, Group I undergoing the experiment for one month, Group 7 for seven months and were observed by macroscopic, radiographical, osteometrical, and splitting-line methods. The findings are summarized as follows : 1. In Group I, osseous proliferous hypertrophy was observed in the masseteric fossa and the crest of the condyloid process on the experimental side. Radiographically it was found that the osteotrabecula were arranged irregularly and loosely and the splitting lines were irregular. The osseous proliferous hypertrophy increased with the passage at time, reaching the maximum in Group 4. Radiographical examination disclosed increasingly obscure pictures, and splitting-line examination revealed an expansion of the area of irregular lines. But in Groups 5 to 7, the surface of the massetric fossa and the crest of the condyloid process tended to become smooth in the same way as on the control side, and radiographical penetration grew more difficult, while the irregular lines tended to become normal. 2. No difference was observed between the two sides in the eruption of teeth, but the formation of interdental spaces between premolars came later on the experiemntal side. X-ray penetrated through the interradicular alveolar septum of the fourth premolar and the first molar more distinctly on the experimental side. 3. In all groups, a reduction in distance or angle was observed on the experimental side in the length of the mandible (if - cd, cl. cm. goc. crc, crd), the height of the coronoid process (crd - gov, cd -crd), the height of the condyloid process (cd-gov, (cl-gov, cm-gov), the length of the condyloid process (cm-cl), the body angle of the mandible, the inclination angle of the condyloid process, the height of the mandible body of premolars (ap_2^^--a'p_2^^-, ap_3^^--a'p_3^^-, ap_4^^--a'p_4^^-). This was conspicuous especially for if-goc, crd-gov, cd-gov, cl-gov, cm-gov, cm-cl, the body angle of the mandible, and the inclination angle of the condyloid process. An increase was observed in the height of the mandible body of the molars, the angle of the processus coronoideus, and the height of the edge of the incisors. The reduction in the length and angle of the various parts are manifestations of functional morphology due to the incision of the m. masseter. The osseous proliferous hypertrophy in the masseteric fossa and the mandible body of the molars physiological defense reaction to the incision.