REFLEX RESPONSES TO PERIODONTAL AND AUDITORY-STIMULATION IN HUMAN MASSETER

An investigation was made of the reflex responses evoked in the human masseter by periodontal mechanoreceptors. Weak taps were applied to th e labial surface of a central incisor tooth by an electromechanical st imulator with a flexible probe (von Frey hair). Forces as low as 0.2N evoked inhibitory reflex responses in the surface electromyograms of b oth masseter muscles. These reflexes were modulated to markedly differ ent extents in different subjects by auditory white noise, which alway s reduced the amplitude of the inhibition. The reflexes were abolished when local anaesthesia was infiltrated around the stimulated tooth an d white noise was played into the ears. Evidence is presented that the sound of the tap on the tooth, transmitted through the air, is in its elf sufficient to evoke an inhibitory reflex in masseter which is qual itatively similar to that from the periodontal receptors. Thus, in the absence of auditory masking, the total reflex evoked by tooth taps is the result of the summation of the inputs from both periodontal mecha noreceptors and auditory receptors.