Responses of intradental nerve fibres to stimulation of dentine and pulp.

In the present work responses of intradental nerve fibres to stimuli that induce fluid flow in dentinal tubules as well as to direct mechanical irritation of the exposed pulp were studied on 9 young adult beagle dogs. Under pentobarbitone anesthesia 31 single functional intradental fibre units were dissected from the mandibular nerve. Stimuli were applied to the lower left canine tooth. Exposed dentine surface was irritated by scraping, air blasts and dry absorbent paper and the pulp mechanically with a von Frey hair. Ten fibre units responded to stimulation of dentine. Six of them were also tested with mechanical irritation of the pulp and were all responsive. Fifteen of twenty fibres responded to mechanical stimulation of the pulp. The mechanosensitive nerve fibres were all A-type according to conduction velocities (mean 25.6 +/- 8.1 (SD) m/s). It is concluded that there exist mechanosensitive intradental A-nerve fibres in the dog which are activated by stimuli that induce fluid flow in dentinal tubules. Nerve fibres of this type could be responsible for dentine sensitivity in man. Consequently, the present study gives support to the hydrodynamic hypothesis of dentine sensitivity. Moreover, mechanosensitive nerve fibres could also be responsible for the pain symptoms of pulpal inflammation, because pulpitis may also create suitable circumstances for their activation.