THE EFFECT OF AN OCCLUSAL STABILIZATION SPLINT AND THE MODE OF VISUALFEEDBACK ON THE ACTIVITY BALANCE BETWEEN JAW-ELEVATOR MUSCLES DURING ISOMETRIC CONTRACTION

The aim of the present study was to gain an insight into the influence of a vertical bite-rise (clenching in intercuspal occlusion vs. clenc hing on an occlusal stabilization splint), the mode of visual feedback (VF; obtained from the compound masseter signal, from the compound an terior temporalis signal, or from the compound signal of both masseter and anterior temporalis muscles) and the EMG clenching level (10% MVC and 50% MVC) on the muscle balance between the masseter and the anter ior temporalis muscles. The muscle balance was quantified as the logar ithmic value of the ratio between the summated mean rectified EMG acti vity of the masseter muscles and this activity of the anterior tempora lis muscles. The muscle balance was influenced significantly by the mo de of VF (p < 0.01), the muscle balance shifting toward the group of m uscles from which VF was obtained. When VF was obtained from the masse ter muscles, a decrease in the anterior temporalis EMG activity was ob served when the vertical dimension was increased (p < 0.05-0.01). When VF was obtained from the anterior temporalis muscles, the activity of the masseter muscles was raised with respect to that of the anterior temporalis muscles during clenching with a vertical bite-rise (p < 0.0 5-0.01). When VF was obtained from both groups of muscles, the massete ric EMG activity increased, whereas the anterior temporalis EMG activi ty decreased. Hence, regardless of the mode of VF, a relatively lower activity level of the anterior temporalis muscles was achieved after i nsertion of an occlusal stabilization splint. The therapeutic effect o f a stabilization splint may therefore, at least in part, be related t o a reduced activity in the anterior temporalis muscles.