Dynamic control of human mastication

It has been established that the masticatory movements in animals dependent on sensory feedback from various receptors and that the level of this feedback alters during chewing. In a couple of recent studies, a similar modulation in the strength of the feedback has been suggested to take place in human mastication. Objectives: The aim of this study is to determine the modulation of feedback from the periodontal mechanoreceptors and muscle spindles whose contribution has not been studied on masticating subjects. Methods: Thirty one young healthy volunteers 'masticated' on a simulator and mechanical stimuli were delivered to the left upper central incisor tooth each time the jaw passed through the mid-open position.  Application of the stimuli was repeated after locally anaesthetizing the involved tooth to dissect the contribution by the periodontal mechanoreceptors and expose the contribution of the muscle spindles. Results: We found that the inhibitory reflexes that originate from the periodontal receptors significantly decreased (p<0.05) during jaw opening and stayed the same (p>0.05) during jaw closing. On the other hand, the excitatory reflexes that originate from the muscle spindles significantly reduced (p<0.05) in strength during mastication. Discussions and Conclusions: This study has shown that the inhibitory reflexes that are activated by rapidly changing forces on the teeth preserve their strengths during jaw movement and hence help protect the teeth and supporting structures from becoming damaged. The excitatory reflexes that originate from the muscle spindles on the other hand are reduced in strengths during jaw movement to allow mastication to take place.  Since during normal mastication both of these receptors are stimulated, the exact control of the jaw muscle activity will depend upon their relative activation.

Kemal S. Türker has received the Marie Curie Chair of the European Union.