Parotid salivary flow in response to mechanical and gustatory stimulation in man

To examine further the role of the oral receptors in the masticatory-salivary reflex, a study with eight subjects was performed. The influence on mean parotid salivation of combined alterations in frequency and force of chewing and length of the chewing object was evaluated by group comparison. Salivary flow rate was recorded using a sensitive micromanometer, and the frequency (12, 60 and 90 cycles min-1) and force of chewing (10 and 40% of maximum) were controlled by a metronome and masseter muscle EMG, respectively. The maximum instantaneous flow and the latency of the masticatory-salivary reflex were examined in three subjects. For comparison with mean salivation rate during chewing, gustatory stimulation was performed with 0.5 or 5.0% citric acid. The masticatory-salivary reflex was mainly ipsilateral, and depended upon having an object between the teeth. Salivation increased with increases in frequency and force of chewing and with the number of teeth involved, each parameter of chewing having the greatest influence when increased from a low level of action. The salivation response to chewing showed two phases; the first, presumably due to contraction of the myoepithelial cells, had a latency of 0.2-0.4 s, while the second phase occurred about 1 s later. Our results support the hypothesis that the periodontal mechanoreceptors have a major role in the parotid response to chewing. Application of 0.5 and 5.0% citric acid on the back of the tongue induced dose-dependent parotid secretions, significantly higher than those of chewing. A negative correlation was found between the maximum fluid outputs during chewing and 5.0% citric acid stimulation.