Influence of alteration of occlusal relationship on activity of jaw closing muscles and mandibular movement during submaximal clenching.

The aim of this study was to investigate the relationships between occlusal contacts, responses of muscles, and jaw movements during simulated clenching. Seven healthy human males who possessed complete natural dental arches with normal occlusion, ranging from 24 to 29 years of age, volunteered for this study. Acrylic occlusal stops were fabricated for the lower jaw to simulate various occlusal conditions. Vertical movements of the lower jaw were measured by four sets of linear variable differential transformers. Simultaneously, electromyographic (EMG) activity from the bilateral masseter and anterior temporal muscles was measured. Under experimentally altered occlusal conditions, the subjects performed clenching tasks at 50% of their maximal voluntary contraction level. Analysis of EMG responses revealed clenching on the unilateral occlusal support tended to cause a unilateral activity of the ipsilateral anterior temporalis. Analysis of the movement amplitude revealed a significant difference between the experimental occlusal conditions (P < 0.05). Clenching on unilateral occlusal stops caused a larger upward movement on the contralateral side. Bilateral first premolar clenching without molar support caused a larger upward movement of the mandible in the posterior region, whereas bilateral second molar clenching did not cause a significant upward movement.