STATIC AND DYNAMIC-RESPONSES OF PERIODONTAL-LIGAMENT MECHANORECEPTORSAND INTRADENTAL MECHANORECEPTORS

1. The response properties of 39 periodontal ligament mechanoreceptors (PDLMs) and 12 intradental mechanoreceptors (IMs) related to the inta ct mandibular canine tooth were isolated by extracellular recording me thods from the ipsilateral trigeminal semilunar ganglion. 2. The stimu lus threshold and response magnitude of individual PDLMs depended on t he direction of steady force applied to the intact canine tooth. Canin e PDLMs as a population, however, did not have a preferred stimulus di rection. IMs were activated only by a rapid mechanical transient appli ed to the intact tooth in any direction. The stimulus threshold and re sponse magnitude of each IM were approximately equipotent in all stimu lus directions. 3. Application of quantifiable ramp-and-hold stimulati on showed that PDLMs can encode the intensity of steady forces as well as the rate of force ramps. Increasing the ramp rates decreased the t otal ramp discharge but increased the peak discharge frequency. IMs en coded only the rate of force ramps that were applied by percussion. Hi gher 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 cy cle length (251 +/- 103 Hz, mean +/- SD) and at any periodicity includ ing multiples of the stimulus cycle length (295 +/- 100 Hz) were signi ficantly higher than the maximum frequencies for PDLM discharge entrai nment at the stimulus cycle length (103 +/-53 Hz) and at any periodici ty (133 +/- 62 Hz). 5. The functional similarities of PDLMs and IMs, r espectively, to slowly adapting type II mechanoreceptors and Pacinian corpuscle receptors in the skin are discussed. Our present findings, w hich complement earlier anatomic and behavioral evidence, strongly sug gest that IMs subserve nonnociceptive and nonpain functions. Both PDLM s and IMs may provide a continuum of dynamic afferent inputs necessary for tactile sensibility of teeth.