Vertical forces developed by the jaw elevator muscles during unilateral maximal clenching and their distribution on teeth and condyles.

The activity of the jaw elevator muscles (EMG) was recorded during maximal clenching in ICP and unilaterally on 2nd and 1st molars, premolars, canines and central incisors in ten subjects with complete dentitions, normal occlusal relationships, and without signs and symptoms of craniomandibular disorders. The EMG activities were converted to relative muscle force. The distribution of this relative muscle force on teeth and condyles was then calculated by means of a three-dimensional mathematical model. The results suggest that the magnitude of the muscle force is strongly associated with the localization of the biting point. Thus the greatest muscle force is produced during clenching in the intercuspal position (100%). At unilateral clenching 75% of this ICP-force is reached during rubber pad clenching on 2nd molars, 85% during rubber pad clenching on 1st molars and 45% during clenching on incisors. The calculations of the mathematical model showed then that highest bite force should be produced on 2nd molars (55% of the muscle force produced in ICP-clenching) and lowest on incisors (20%). Highest condylar load should be found on non-biting side condyles (20% of the muscle force produced in ICP-clenching) and lowest on biting side condyles (0%).