Temporomandibular disorders: a pilot study of activation patterns and motor unit analysis of jaw muscles.

Ten patients exhibiting chronic signs and symptoms of temporomandibular dysfunction were investigated with electromyography (EMG) and compared with a group of healthy controls. A quantitative analysis of 20 individual motor units as well as single fibre recordings of the most symptomatic muscle was performed on five patients. One of these patients showed clear signs of myopathy in her right temporal muscle. Surface jaw muscle EMG of the other five patients showed co-contractions of agonists and synergists during jaw opening and closing movements. This may indicate disturbances in the integrated motor unit activity. The background of these findings may therefore be found in the function of the muscle fibre as well as in segmental and suprasegmental disturbances. Recent research has suggested a role of chemosensitive afferent endings in development of excitatory fusimotor reflexes.