Effects of oral sensory afferents on mastication in the miniature pig.

The performance of mastication is presumed to be influenced by afferent stimulation, but little information is available from awake, intact animals. Thirteen experiments were carried out with four miniature pigs. Electromyographic signals from the jaw muscles were recorded simultaneously with jaw movements during natural chewing of foods of differing hardnesses. Harder foods were found to be associated with higher activity levels of jaw-closing muscles and greater lateral deviation, but reduced jaw opening. The sensory supply from one side of the oral cavity was then removed by injected local anesthetic, and the recordings repeated. In addition to decreased activity levels, the jaw-closing muscles showed reduced ability to adjust to different foods. The frequency of mastication fell slightly, and the animals preferred to chew on the uninjected side. Lateral deviation was reduced, but at the same time the jaw-opening muscles usually became more active and accordingly the jaw opened more widely. These findings provide new information on the role of oral sensory afferents in regulating natural chewing patterns. The decreased activities of the jaw-closing muscles are consistent with, although they do not demonstrate, the existence of a positive feedback from periodontal afferents.