Abstract
Many TMJ patients who have occlusal interferences often complain of pains in the sternocleidomastoid muscle. The pain occurs mainly in the insertion of the muscle (SCM-I) rather than in the middle of the muscle (SCM-M). In order to investigate a causative mechanism of pain in the sternocleidomastoid muscle in relation to occlusion, the activities of sternocleidomastoid and masticatory muscles were studied by means of EMG during functions in relation to the occlusal contact on six normal subjects. EMG activities of temporal, masseter, SCM-I and SCM-M were recorded by surface and needle electrodes.
EMG activity was recorded from SCM-I in accordance with the activity of the masticatory muscles during tapping, clenching, and mastication. On the other hand little activity was registered from SCM-M. The amplitude of the EMG of SCM-I increased as the occlusal force increased. During chewing the sternocleidomastoid muscle was functioning more actively on the working side than on the non-working side.
