顎間距離増大後の咬筋の順応性に関する電子顕微鏡的研究

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It is generally acknowledged that masseter muscles take a great part in occlusal stability after bite opening, a means used in orthodontic treatment. Various studies of adaptation of masseter muscles have been done from different standpoints. Histological investigations however have been limited in number. An experimental investigation of adaptation of masseter muscles therefore has been done from the standpoint of finestructure. The experiment on increasing intermaxillary distance was conducted with use of anterior bite plate (Experiment I) covering only the maxillary anterior segment and complete bite plate (Experiment II) covering the anterior and posterior segments in 21 adult dogs (mongrels) for one, three, and six months. The histological and electron-microscopic findings were as follows : 1. In both Experiments I and II, muscle fibers of the masseter muscles were thinner than the normal ones in width after one month. Arrangement of the muscle fibers zigzagged. Electron-microscopically, ruptures and disappearances were observed in myofibrils in part of Z-line and I-band. Most glycogen particles disappeared. The changes in myofibrils seen in Experiment I were not observed in Experiment II. Many instances of swelling and vacuolation of mitochondria were observed. The degree of vacuolation however was slight. 2. In both Experiments I and II in the third month, most muscle fibers were thicker than those in the first month although some were still thin in part. Electron-microscopically, more significant ruptures and disappearance were observed in Z-line and I-band of myofibrils. Glycogen particles decreased as in Experiment I in the first month. 3. In both Experiments I and II in the sixth month, the width of the muscle fibers on the whole was restored to that of the normal ones. Electron-microscopically, myofibrils and mitochondria tended to be restored to near normal. Glycogen particles showed a trend toward restoration to normal in Experiment I but remained disappeared in Experiment II. 4. In both Experiments I and II, the length of sarcomere increased with time. The length of I-band in particular showed a marked increase. Based on the foregoing finding, the finestructure indicative of complete adaptation was not observed. The experiment however suggested at least a need for a longer retension of bite plate in performing the orthodontic treatment of increasing intermaxillary distance to patients who have passed the growth period.
九州歯科学会の論文
1980-11-25

顎間距離増大後の咬筋の順応性に関する電子顕微鏡的研究

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