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Task-dependence of Jaw Elevator and Depressor Co-activation

Department of Prosthodontics, University Dental Clinic, University of Erlangen-Nürnberg, Glückstrasse 11, D 91054 Erlangen, Germany;

^* corresponding author, peter.proeschel{at}rzmail.uni-erlangen.de

Elevator muscle activity per unit bite-force has been shown to be higher in chewing than in isometric biting. We tested the hypothesis that surplus elevator activity is evoked in response to a possible co-activation of jaw-opener muscles during the masticatory power stroke. In 32 subjects, digastric and bilateral masseter and temporalis activities were recorded during unilateral chewing of test foods, isometric biting on a force transducer, and during balancing of the jaw against maximum effort of depressor muscles. During elevator peak effort in chewing, the digastric activity was 113% higher than during peak effort in isometric biting. Comparison of balancing and chewing trials revealed that a 6% increase of elevator activity would suffice to compensate for this increased depressor action. Elevator activity in chewing, however, was up to 130% higher than in clenching. We conclude that depressor counteraction could have only a minor influence on the generation of surplus muscle activity in chewing.

KEY WORDS: antagonistic co-activation • masticatory muscles • EMG • force-estimation