顎関節内障患者における咀嚼運動時の咀嚼筋活動について

Abstract

It has been reported that the absolute muscle activity of working-side masseter muscle and non-working temporal muscle is significantly lower than that of healthy subjects during mastication in patients with internal derangement of the temporomandibular joints. Also, it has been observed that the raw muscle activity of lateral pterygoid muscles is lower. Although it seems obvious that use of normalized muscle activity is more appropriate than raw muscle activity, there have been few reports of determination of normalized muscle activity in such patients. The purpose of the present study was to investigate the normalized muscle activity of masticatory muscles during mastication in patients with internal derangement of the temporomandibular joint. The subjects were 11 adults with unilateral internal derangement of the temporomandibular joint (patient group) and 11 adults with normal occlusion without temporomandibular disorders, matched by age and sex with the patient group (control group). Each subject unilaterally masticated standardized hard gummy jelly (patient group, affected side; control group, right side). We recorded movements of the mandibular central incisor point at a sampling frequency of 89.4 Hz, and recorded muscle activities of the anterior temporal, masseter, anterior digastric and inferior lateral pterygoid muscles at a sampling frequency of 2.56 kHz, using a six-degrees-of-freedom jaw-tracking and EMG recording system. Each subject performed 5 maximum opening and closing movements, in order to determine normalized muscle activities. Also, occlusal forces and occlusal contact areas at maximum clenching in centric occlusion were determined. Each measured parameter was tested for differences in mean between the groups. During affected-side mastication in the patient group, the normalized muscle activities of the non-working side temporal muscles, the working-side masseter muscles and the working-side lateral pterygoid muscles showed significantly lower values than those of the control group. There was no significant difference in contact area between the groups, but the maximum occlusal force in the patient group was significantly lower than that of the control group. These results suggest that the activity of masticatory muscles was adjusted so that excessive load was not applied to the temporomandibular joints during mastication in patients with internal derangement of the temporomandibular joint.