Alteration in mandibular posture by vibration of posterior fibres of the temporalis muscle

Abstract

Introduction: Vibration causes reflex muscle shortening because of excitation of muscle spindle primary afferents. Although this is subordinate to voluntary control, responses have been demonstrated in jaw elevator and (unexpectedly) in jaw depressor muscles. Forward posturing of the mandible is a common habit. The only part of the perioral musculoskeletal system that actively retrudes the mandible is the posterior part of the temporalis muscle. This study set out to investigate the effect of vibration of this area on the horizontal position of the mandible during a jaw registration procedure. Method: In a randomized cross‐over study, the posterior fibres of both left and right temporales of 17 subjects were vibrated synchronously at 180 Hz. Interocclusal wax jaw registrations were recorded for each subject with and without vibration applied. Position of the mandible was assessed by mounting pairs of casts using these registrations and measuring their position relative to intercuspal position. Results: In 17 subjects, the effects of vibration on mandibular posture were: no change in one; protrusion in two; and retrusion in 14. A sign test returned a value of P < 0·01. Discussion: Reasons for the protrusion seen in two subjects are discussed. These may be anatomical or methodological. However, vibration of the posterior part of the temporalis muscle retruded the mandible in a significant majority of cases.