The effects of unilateral and bilateral chewing, empty clenching and simulated bruxism, on the masticatory-parotid salivary reflex in man.

In man, parotid flow has been recorded, using modified Lashley cups, in response to mechanical stimulation of the teeth by repeated chewing and clenching manoeuvres. The rectified and integrated masseter electromyographic activity was used as an indirect measure of the stimulus intensity where necessary. Following the observation that "empty clenching' failed to evoke a parotid salivary response, a series of three experiments has been undertaken to address the following questions. (1) Is a lateral component of force required to evoke a flow during empty clenching? (2) Does contralateral inhibition of salivary secretion explain this observation? (3) What is the threshold for the masticatory-salivary reflex? The results suggest that: (i) empty clenching together with a lateral component of force does not result in a secretion above resting flows; (ii) there is no evidence for the existence of contralateral inhibition of salivary secretion; and (iii) the threshold for the masticatory-salivary reflex is lower than 5% of comfortable chewing forces. We are still unable to offer an explanation for the lack of parotid secretion during empty clenching.