顔面神経切除の顎・顔面成長に及ぼす影響に関する実験的研究
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The present study was attempted to elucidate the effects of unilateral facial denervation on the growth of the maxillo-facial region by means of a histochemical study of the muscles, a cephalometric analysis, by thermography, and by angiographic examination.<BR>Three-week-old Dutch-Polish rabbits and wister rats were subjected to dissection of the right facial nerve. After this denervation, the face of the rabbit deviated to the paralyzed right side, and the maxillo-facial skeleton on this paralyzed side was fairly atrophied. In contrast, the face of the rat after denervation deviated to the left side, and the rnaxillo-facial skeleton was not affected. Rabbits were able to masticate only on the unparalyzed side, whereas the rats were able to masticate on both the unparalyzed and paralyzed sides. This suggested that the mechanism of these facial deformities are related to their masticatory patterns, and so the fibers of the masseter and the orbicularis oris muscles then were investigated histochemically. These muscle fibers were classified into type 1 (slow twitch) and type 2A or type 2B (fast twitch) on the basis of the activity of the myofibrillar ATPase.<BR>The results achieved indicated that in the rabbit masseter, the right muscles had more type 2A and fewer and smaller type 1 fibers, and a lower NADH activity when compared to the left masseter muscles. This indicates a relative disuse of the right masseter muscles when chewing after right facial denervation. Type 1 fibers are best adapted for sustained contractions of moderate force which are required for chewing and postural support. Thus, a reduced proportion and diameter of type 1 fibers in the right masseter muscles may result from a sustained alteration in the patterns of recruitment of these fibers in response to the altered jaw function. The jaw deformity in the rabbit may result from a functional imbalance between the right and left masseter muscles.<BR>As for rat masseter muscles, type 1 fibers were scarce. No functional imbalance was found between the right and left muscles.<BR>In the denervated orbicularis oris muscles of both the rabbit and the rat, neurogenic changes such as type 2 predominancy and group atrophy were observed.