Masticatory muscle responses associated with unloading of biting force during food crushing

The aim of this study was to evaluate masticatory muscle responses during food crushing. Electromyograms were recorded simultaneously with mandibular movement and the sound of food fracture in eight healthy adult males at the superior and inferior heads of the lateral pterygoid muscles, the anterior belly of the digastric muscle, the temporal muscle, and the masseter muscle. After fracture of the food, silent periods of the elevator muscles and excitatory responses of the depressor muscles were observed. The latency and duration of the silent periods increased significantly with increasing incisal velocity after fracture. The mean latency of the excitatory responses of the depressor muscle was stable. After the application of anaesthetic into the temporomandibular joint capsule, the excitatory response disappeared, whereas the silent period was partly maintained. These findings suggest that the excitatory response of the depressor muscle occurs via a polysynaptic reflex arc, and that several reflex arcs are involved in the development of the silent period during food crushing. An important role for the temporomandibular joint receptors is implied.