両側咬筋の筋電図活動の比較

Abstract

It is known that electromyograms of the left and right masseter muscles (LMM, RMM) during bilateral clenching reveal difference in amplitude. This study was designed to investigate the difference in electromyographic activities of LMM and RMM during bilateral clenching in many subjects and compare the difference during bilateral clenching with that during unilateral clenching and peanuts chewing. The subjects were 66 healthy volunteers, 18-56 yr of age, without clinical evidence of dysfunction of the stomatognathic system, especially without pain with occulusion. Surface electromyograms from middle portion of both masseter muscles were recorded 274 times. Several electromyograms from each subject were recorded at intervals not less than 4 months. Electromyographic activity was expressed in relative values, ratio integrated value of electromyogram of RMM to that of LMM when LMM was predominant, and ratio LMM to RMM when RMM was predominant. For recording of electromyograms, each subject was asked to make several different mandibular movements ; bilateral clenching and unilateral clenching on the left and right sides, 1st and 2nd gum clenchings on the left and right sides, and chewing to swallowing of 3, 2, 1, and 3g peanuts. Main findings were as follows. 1. The difference of electromyographic activities between LMM and RMM during bilateral clenching was recognized in all cases except only one case. In 128 cases, activities of LMM were greater than those of RMM, and mean relative value of electromyographic activities was 78.6±13.3. In 145 cases, activities of RMM were greater, and mean relative value was 78.9±13.9. 2. In unilateral clenching on the side with predominant activity during bilateral clenching, activities of the clenching side were greater in most cases (from 88.3 to 96.6%), and in clenching on the other side with lesser activities during bilateral clenching, activities of the clenching side were greater in many cases (from 60.7 to 76.0%), but greater on non-clenching side in cases from 23.2 to 38.6%. 3. Electromyographic activities during peanuts chewing were greater on the side with predominant activity during bilateral clenching. 4. Relative value of electromyographic activity on bilateral clenching was in a statistically significant positive correlation with those of unilateral clenchings and peanuts chewing, and especially well correlated with those of unilateral clenchings on the side with lesser activities during bilateral clenching. Mean relative value of unilateral clenchings on the side with predominant activity during bilateral clenching was decreased, and that of unilateral clenching on the other side with lesser activities during bilateral clenching was increased, because the difference in most cases became greater during unilateral clenching on the side with predominant activity during bilateral clenching, and the differences were decreased or reversed in many cases during unilateral clenching on the other side. These results suggest that difference of activities in both masseter muscles during bilateral clenching influences those during unilateral clenchings and peanuts chewing.