Bilateral asymmetries in periodontal-masseteric reflex activity in man

Jaw reflexes are evoked bilaterally even when stimulated unilaterally. This bilateral cooperation is one of the characteristics of jaw reflexes. The periodontal-masseteric reflex also shows this bilateral cooperation. The mechanism underlying bilateral cooperation in the periodontal-masseteric reflex, however, still remains unclear. The present study was designed to clarify this mechanism. In order to investigate whether there are bilateral differences in the sensitivity of the periodontal-masseteric reflex, the reflexes were recorded in five healthy subjects using surface array electrodes placed bilaterally. A 0.5 N mechanical stimulation applied to the upper canine teeth evoked a reflex in the ipsilateral and contralateral masseter muscles at a background activity of 10% maximum voluntary contraction. These were obtained at a visually controlled, constant clenching level. There was no significant difference in masseter muscle background activity between sides, but the reflex response was different between the right and left sides. These results together suggest that there is no right and left difference in the response characteristic of the masseter muscle, but that a masticatory muscle feedback mechanism, from periodontal-mechanoreceptor and the masseter muscle spindle, exists.These findings suggest that the periodontal-masseteric reflex is different between the right and left sides, and that it appears to be involved in the reflex control of masticatory movement.