A Study on the Mechanism of Pain Elicited from the Dentin

¹ Department of Dental Histopathology, the Royal School of Dentistry, Stockholm, and Research Laboratories of AB ASTRA, Södertälje, Sweden

On freshly prepared dentin surfaces produced by fracture in 18 premolars from young individuals, the gentle application of dry absorbent paper elicited pain in 54 out of 54 tests; the average duration of the pain was 24-36 seconds. Control applications using paper soaked in isotonic potassium chloride solution produced short-lasting pain (about 1 second) in only 4 out of 54 tests.

Dry absorbent paper applied to dentin surfaces exposed 1 week earlier produced pain in 2 out of 7 cases, but in all cases scraping with a probe still evoked pain. Histological examination of these teeth showed that the odontoblast layer beneath the exposed dentin was absent or greatly reduced.

It is concluded that dry absorbent paper applied to the exposed dentin stimulates the nerve fibers in the pulp or at the pulpo-dentinal border mechanically by a hydrodynamic mechanism. It is also concluded that the odontoblasts do not play any important part in the mechanism of pain elicitation from the dentin surface.

It is proposed that the pulp with its nerve fibers extending into the pulpo-dentinal zone functions as a mechanoreceptor and that most painful stimuli applied to the intact tooth or to the exposed dentin stimulate this receptor structure mechanically.