Regeneration of the inferior alveolar nerve and mandibular incisor pulpal reinnervation was qualitatively and quantitatively examined by electron microscopy 2 days--11 months after intramandibular neurotomy in young adult cats. Fifteen millimeters central to the proximal stump moderate atrophic alterations of myelinated axons were observed 1--2 months after surgery. By 4--11 months a principally normal picture had been restored. The proportion of unmyelinated axons was increased 2--4 months after operation but had normalized by 11 months. In the distal stump the first regenerating axons were observed at 2 weeks. The regenerated myelinated axons failed to re-establish the previous fibre size range and normal axo-glial relations did not appear. A seemingly stable morphological pattern was reached 4--11 months postoperatively. In the late survival period the proportion of unmyelinated axons was subnormal. In the incisor pulps virtually all axons disappeared after surgery. By two weeks pulpal reinnervation had begun. From two months on, a structurally largely normal pulpal axon population was present except for some persisting unmyelinated axon degeneration. The findings are consistent with previous physiological data and suggest that structural normalization at proximal and preterminal levels follows upon re-establishment of peripheral contacts.
Animals Axons