[Electromyographic study of masticatory dysfunction in patients with unilateral cleft lip and palate and reversed...

Masticatory dysfunction in patients with unilateral cleft lip and palate was studied on the basis of electromyograms of the masticatory muscles. The purpose of the study was to elucidate the origin of the dysfunction by means of comparisons among electromyograms of masticatory muscles in cases of normal occlusion, reversed occlusion and reversed occlusion caused by unilateral cleft lip and palate. Subjects were 10 cases of normal occlusion (10y2m-11y10m), 10 cases of reversed occlusion (7y2m-11y2m) and 20 cases of unilateral cleft lip and palate (8y0m-14y3m). In each subject, electromyograms of the masseter and anterior venters of the temporal muscles at the isometric-contraction phase were recorded by means of the surface-electrode method with mandible loads of 1-5 kg. The electromyograms were analyzed quantitatively by means of an electromyographic device called a Turn Counter. Relations between loads and amplitude as well as numbers of turns were examined. At the same time maximum masticatory pressure and occlusal contact points were measured and then examined in comparison with electromyographic findings.

1. Correlation coefficients between loads and amplitudes as well as numbers of turns decreased among the groups in this order: normal occlusion, reversed occlusion and cleft-caused reversed occlusion. Significant differences were observed between the normal-occlusive group and the reversed and cleft-caused reversed-occlusive groups. 2. No. difference was observed between the normal-occlusive and reversed-occlusive groups in terms of correlation coefficients between total sums of amplitudes and turns of the 4 masseter muscles (right and left masseters and anterior venters of the temporal muscles) and loads. Correlation coefficients in the cleft group were significantly smaller than those in the other 2 groups. 3. Because of great differences in regression coefficient among individuals, no synergic contraction pattern of the 4 mastication muscles (right and left masseter and temporal muscles) could be specified. 4. The A/T ratio of masseters in the cleft group was significantly smaller than those in the normal- and reversed-occlusive groups. 5. Under maximum load, the activity ratio of the 4 masseter and temporal muscles was 1:1 in the normal- and reversed-occlusive groups, whereas temporal-muscle activity predominated over masseter-muscle activity in the cleft group. 6. Maximum masticatory pressure decreased in the order: normal-occlusive, reversed-occlusive, and cleft caused occlusive. No correlation with electromyographic findings was observed.(ABSTRACT TRUNCATED AT 400 WORDS)