Co-ordination pattern of masticatory muscle activities in temporo-mandibular disorders.

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The purpose of this study was to understand the co-ordination pattern of masticatory muscle activities in the temporomandibular disorders. In order to regulate the tasks producing masticatory muscle activities, bite force magnitude and direction were monitored with costom-made transducer during EMG recordings. Subjects were then asked to clench at the specific magnitudes and directions of bite force ndicated on a graphic terminal as visual biofeedback signals. Both the magnitude and the direction of bite force had significant effect on the medial pterygoid muscle activity (2-way ANOVA,p<0.05). The activity was significant higher (Student-Newman-Keuls test, p<0.05) during anteriorly or medially directed bite and lower during posteriorly or laterally directed bite. The lateral pterygoid muscle activity increased significantly (p<0.05), when the bite force direction changed from vertically to anteriorly, and to maedially. However, between the posterior and vertical direction, and betwen the lateral and vertical direction, the lateral pterygoid activity was not changed significantly. As reported previously, the masseter and the temporal muscles activities showed reciprocal pattern realted to the changes of bite force direction. These co-ordination patterns of masticatory muscle activities for controlling bite force three dimensionally could provide us the standard criterion in diagnosis of temporomandibular disorders.