Static and dynamic responses of periodontal ligament mechanoreceptors and intradental mechanoreceptors.

1. The response properties of 39 periodontal ligament mechanoreceptors (PDLMs) and 12 intradental mechanoreceptors (IMs) related to the intact mandibular canine tooth were isolated by extracellular recording methods from the ipsilateral trigeminal semilunar ganglion. 2. The stimulus threshold and response magnitude of individual PDLMs depended on the direction of steady force applied to the intact canine tooth. Canine PDLMs as a population, however, did not have a preferred stimulus direction. IMs were activated only by a rapid mechanical transient applied to the intact tooth in any direction. The stimulus threshold and response magnitude of each IM were approximately equipotent in all stimulus directions. 3. Application of quantifiable ramp-and-hold stimulation showed that PDLMs can encode the intensity of steady forces as well as the rate of force ramps. Increasing the ramp rates decreased the total ramp discharge but increased the peak discharge frequency. IMs encoded only the rate of force ramps that were applied by percussion. Higher ramp rates increased both the total discharges and peak discharge frequency of IMs. 4. The dynamic response properties of PDLMs and IMs were clearly differentiated by sinusoidal vibratory stimulation. The maximum frequencies for entrainment of IM discharge at the stimulus cycle length (251 +/- 103 Hz, mean +/- SD) and at any periodicity including multiples of the stimulus cycle length (295 +/- 100 Hz) were significantly higher than the maximum frequencies for PDLM discharge entrainment at the stimulus cycle length (103 +/- 53 Hz) and at any periodicity (133 +/- 62 Hz). 5. The functional similarities of PDLMs and IMs, respectively, to slowly adapting type II mechanoreceptors and Pacinian corpuscle receptors in the skin are discussed. Our present findings, which complement earlier anatomic and behavioral evidence, strongly suggest that IMs subserve nonnociceptive and nonpain functions. Both PDLMs and IMs may provide a continuum of dynamic afferent inputs necessary for tactile sensibility of teeth.