[Investigation of an electromyogram and a mandibular movement in prognathia of mixed dentition compared with normal occlusion].

Abstract

A quantitative analysis of EMG activity in temporal and masseter muscle and of mandibular movement was performed in prognathia (n = 20) and normal (n = 30) occlusion. EMG recordings were analyzed during rest position, maximal clenching and maximal clenching with a cotton-roll. Mandibular movement was examined for path of closure, amount of freeway, maximal velocity of jaw opening and closing, condylar test and amount of maximal vertical jaw opening. The results of the investigation revealed the following. Normal occlusion and prognathia were classified into two groups by path of closure. One group was going toward the upper front and another toward the upper back. The former was indicated in 77% of normal occlusion and 65% of prognathia cases examined. Amount of freeway space was the same in both groups. Maximal velocity of jaw was significantly (p less than 0.05) faster for prognethia than for normal occlusion. Condylar test was significantly (p less than 0.05) greater for prognathia than for normal occlusion. Temporal muscle activity was greater for normal occlusion than for prognathia. During maximal clenching, temporal muscle activity was greater than masseter activity in the normal occlusion. A tendency toward negative correlation was found between temporal muscle activity during maximal clenching and the mandibular plane angle, facial height and gonial angle. The same tendency was found between masseter muscle activity and the mandibular plane angle, facial height, ramus-height and gonial angle. These results prove that it is important to examine muscle activity and mandibular movement to make treatment planning.