Pain in the sternocleidomastoid muscle and occlusal interferences

The EMG of the sternocleidomastoid muscle and the masticatory muscles during function has been observed in relation to opposing occlusal contacts. The purpose was to investigate the possible developmental mechanism of pain which can occur in the muscles. Six subjects with normal function and ten patients were studied. EMG activities of temporal, masseter, sternocleidomastoid (insertion) and sternocleidomastoid (middle) were recorded by surface and needle electrodes. EMG activity was recorded from the insertion of the sternocleidomastoid during activity of the masticatory muscles in tapping, clenching, and mastication. On the other hand little activity was registered from the middle of the sternocleidomastoid. 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. On the patients, EMG activities of the muscles were of low amplitude and low frequency with no synchronization with the chewing movement, suggesting hyperactivity of the muscle.