骨格性下顎前突症患者の咀嚼筋に関する筋電図学的ならびに組織化学的研究
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概要
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This study was designed to identify differences in the masticatory muscles between patients with mandibular prognathism and normal subjects. Electromyograms during maximum centric occlusion and in the occlusion adjusted to 5 kg by the use of a jaw force meter (NIHON KOHDEN Co.) were recorded at the masticatory muscles (masseter, anterior and posterior temporal muscles) by means of surface electrodes. The occlusal force and total contact area during maximum occlusion were recorded and calculated using an Occlusal Prescale System (Fuji Film Co.). Thirteen patients with mandibular prognathism and 20 subjects without craniomandibular dysfunction were studied in terms of their electromyographic signals and occlusal force before and after orthognatic surgery. Histochemical analysis of the masseter muscles was carried out in 9 patients and 4 normal subjects.<BR>The results were as follows:<BR>1) The masseter muscles are the main muscles during masticatory movement in subjects without biting malfunction. The anterior temporal and posterior temporal muscles change their activity according to the working side and the balancing side.<BR>2) It was found that patients had higher electromyographic activity than subjects without malfunction in a closed-jaw position before surgery.<BR>The total-contact-area and occlusal force were significantly lower in patients compared with the normal group. There was no difference in average biting pressure.<BR>3) After orthognathic surgery, total-contact-area of centric occlusion and occlusal force were increased. There were no significant differences between patients and subjects without malfunction. There were also no significant differences in average biting pressure between the two groups both before and after surgery.<BR>4) There was a period of electric-overdischarge among the patients for 2 or 3 months after operation. Concurrently, a change in load ratio among the muscles was noted.<BR>5) A so-called “type 1 fiber predominance” masseter in which type 1 fibers accounted for over 55% of muscle fibers was found frequently in the patients. In some cases, electric-myographic volume was still high even after operation. This was found particularly among patients with a high-Type 1 fiber-ratio.