An investigation was made of the reflex responses evoked in the human masseter by periodontal mechanoreceptors. Weak taps were applied to the labial surface of a central incisor tooth by an electromechanical stimulator with a flexible probe. Forces as low as 0.2N evoked inhibitory reflex responses in the surface electromyograms of both masseter muscles. These reflexes were modulated to markedly different extents in different subjects by auditory white noise, which always reduced the amplitude of the inhibition. The periodontal origin of the reflexes was confirmed by the abolition of the reflexes when local anaesthesia was infiltrated around the stimulated tooth, and white noise was played into the ears. Our evidence suggests that the auditory modulation of the inhibitory responses was due to bony conduction of a shock wave and also due to the sound of the tap entering the ear.

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