Fixation of the mandible changes masseter muscle activity associated with swallowing.

The purpose of this study was to investigate the effect of mandibular fixation on activity of the swallowing-related muscles during swallowing. Electromyograms in the masseter muscle, orbicularis oris superior muscle, suprahyoid muscles, and infrahyoid muscles were recorded from seven healthy humans. Electromyographic activity during swallowing was compared between an experimental condition with mandibular fixation and an experimental condition without such fixation. Duration of the swallowing phase was prolonged with mandibular fixation. Mandibular fixation significantly delayed the onset of masseter muscle activity during swallowing, although no other muscle groups showed a delay. The amount of muscle activity during swallowing was not significantly different between the two experimental conditions in any of the muscle groups. In conclusion, mandibular fixation decreases the masseter muscle activity at the initial phase of swallowing. This may be due to decreased need of the masseter muscle activity against force pulling the mandible.