EXPERIMENTAL OCCLUSAL INTERFERENCES .2. MASSETERIC EMG RESPONSES TO INTERCUSPAL INTERFERENCE

In 12 subjects, a rigid unilateral intercuspal interference (minimum m ean height of 0.24 mm) was placed on either the right or left mandibul ar second premolar and first molar (sagittal physiological equilibrium point of the hemimandibular dental arch). During brisk and forceful c lenching on the interference, bipolar surface electromyograms were obt ained from the right and left masseter muscles. On the side opposite t he interference, myoelectric clenching activity was significantly redu ced. Correlation analyses showed that the interference elicited a non- linear (complex) co-ordination of the amplitude, but not the duration, of bilateral masseteric clenching activity, i.e. frequently there was significant motor facilitation on the side of the interference, and s ignificant motor inhibition on the side opposite the interference. The oretical considerations predicted that brief clenching on the interfer ence would easily lead to frontal plane rotatory motions of the mandib le which, indeed, occurred clinically.