Relation of dentin sensitivity to histological changes in dog teeth with exposed and stimulated dentin

The effect of chronic exposure of dentin to the sensitivity of intradental nerves was studied in dogs. The dentin of canine and incisor teeth was exposed one week prior to the experiments in which 34 single fiber units dissected from the inferior alveolar nerve were recorded. In the teeth with acutely bared dentin 36 nerve fibers were tested. SEM of the chronically exposed dentin showed that practically no tubule apertures could be found since the surface was covered with bacteria and oral debris. This coating had to be removed by drilling and acid etching before any responses could be evoked. When compared to the teeth with acutely exposed dentin, the sensitivity of the fibers responding to drilling, probing, osmotic stimulation, and air blasts applied to the dentin was weakened in the chronic cases, in the sense that fewer units of those tested responded. However, cold evoked nerve activity only in some chronically exposed teeth, suggesting sensitization of the nerves. TEM revealed electron-dense substance in the dentinal tubules of the chronic teeth. Some of the material was evidently cellular remnants aspirated from the pulp and some of it, staining more faintly, could be extravasated plasma proteins. In the acute cases the tubules were emptier. Light microscopy showed histological injuries in the pulp-dentin border. It is concluded that the decrease in the responsiveness of the pulp nerve fibers in the chronic cases was due to the changes in the dentin.