The relationship between the pressure applied to the exposed pulp and evoked discharge of the intradental nerve in the cat.

Abstract

To elucidate the mechanism of dentin sensitivity, the threshold intensity of mechanical stimulation of the intradental nerve was determined. Two small cavities which just reached the pulp surface were drilled in the canine tooth of anesthetized cats. Various hydrostatic pressures (0-50 mmHg) were then applied in step increments (5 mmHg) to one of the cavities as a stimulus and the threshold of mechanical stimulation was determined by recording the action potential from a dissected single fibre obtained from the inferior alveolar nerve. The second cavity functioned as a pressure vent so that pulp tissue could be easily displaced. Units were identified as active intradental fibres by applying an electrical stimulation between the two cavities. Most of the units identified were considered to be A a fibres based on the conduction velocity (16.3±8.6 m/sec, n=33). Twenty four of 33 units responded to the pressure, with thresholds ranging from 10 to 45 mmHg (Mean±SD: 25.7±10.8 mmHg). This value was 1.6-4.7 times greater than normal intrapulpal pressure (5.5 mmHg) or inflamed intrapulpal pressure (16.3 mmHg), which suggests that the threshold pressure determined here is sufficient to deform intradental nerve endings of 2-3 μm. These results suggest that Aσ intradental nerve endings may not be mechanoreceptors within the physiological range.