Responses of pulpal nerves to cavity preparation in rat molars: an immunohistochemical study using neurofilament protein (NFP) antiserum.

The response of neural elements to a dentin injury was morphologically investigated in rat molars by use of immunostaining for neurofilament protein (NFP). An artificially formed cavity in dentin by drilling rapidly caused the displacement of some odontoblasts into the exposed dentinal tubules, while others were detached from the predentin. The subodontoblastic nerve plexus consisting of NFP-immunoreactive nerves shifted inward together with the separated odontoblasts, while a movement of the nerves into the exposed dentinal tubules was not recognized. The odontoblasts separated from the predentin degenerated and disappeared one day after the cavity preparation; at this time, the subodontoblastic nerve plexus underlying the drilled dentin was remarkably disrupted, presumably losing dentinal sensation of the drilled area. Three days after the cavity preparation, the destroyed odontoblastic layer began to be repaired by newly differentiating odontoblasts; the reparative dentin was produced from 5 to 7 days onward. Numerous NFP-positive nerves, beaded in type, gathered in the odontoblastic layer in accordance with the differentiation of the new odontoblasts. The increased beaded nerve fibers were suggested to represent peptide-containing nerves. In 10-15 days, the reparative dentin accumulated quite remarkably under the cavity area. The NFP-positive subodontoblastic nerve plexus was entirely reconstituted and also regained continuity to its surrounding plexus. The nerve fibers in the reconstituted plexus were mostly non-beaded in type as seen in the control teeth. Since dentinal tubules in the reparative dentin are not normally continuous to the primary dentinal tubules, dentinal sensation may not have been restored.