[Differential Lissajous EMG of masticatory muscles and its application in man]

Difference in the activity of masticatory muscles between subjects with normal teeth alignment and occlusion and patients with disorders at the oral region was investigated using a differential Lissajous EMG method. Surface EMGs were recorded from the right and left temporal and masseter muscles during peanut and chewing gum mastications. The difference of the integrated EMGs between both sides was obtained in both the temporals and masseters, then two differences were synthesized to a Lissajous figure. The figures generally showed the following: 1) In the normal subjects, the muscle behavior varied from stroke to stroke in peanut mastication, while it was constant in chewing gum mastication. 2) Activity of some muscles of the patients was quietly weak, while that of the normal subjects was totally balanced. 3) In the patients, combination of use between the temporal and masseter muscles and contraction order among the muscles tended to be reversed compared to the normal subjects.