An electrophysiological and morphological study of the innervation and reinnervation of cat dentine.

1. Experiments were carried out to determine which, if any, of the cellular processes in cat dentine are nerves. This was done by examining in the electron microscope the contents of the dentinal tubules in control teeth and in teeth that had been denervated 56 h previously. The extent of any reinnervation, and associated return of neural responses to dentine stimulation were investigated 12 weeks after denervation. 2. In five cats, the inferior alveolar nerve was sectioned on one side and the cut ends reapposed. 3. Each of the tubules in the predentine of control teeth contained one process with a cross-sectional area of 0.21-1.14 micron2 and up to eight other, secondary processes which were generally smaller. The proportion which contained secondary processes was highest (83%) near the tip of the pulp and decreased further down the side of the crown of the tooth. 4. 56 h after denervation, almost all the secondary processes had disappeared, leaving just one of the larger processes in each tubule. It is concluded that these larger processes are odontoblast processes and that all the secondary processes are nerve terminals. 5. 12 weeks after denervation, small processes were again present in some tubules. Recordings in three cats showed that inferior alveolar nerve fibres had regenerated into the canine pulp and that some of these had re-established receptor properties similar to those in normal teeth.