Reinnervation of developing rat molars.

The ability of regenerating inferior alveolar nerve (IAN) fibres to reinnervate dentine of developing rat first molar teeth was investigated. At intervals of 5, 15, 30 and 50 days after intramandibular transection of the IAN at the age of 20 days, the percentage of innervated dentinal tubules was estimated and compared with results from a series of control specimens. In addition, the myelinated axon populations of the root canal pulps were examined by light microscopy. Degeneration of almost all pulpal myelinated axons and dentinal unmyelinated axons occurred within 5 days of surgery. By 15 days after transection there was evidence of some pulpal reinnervation by myelinated axons but less than 2% of dentinal tubules showed reinnervation (control, 31.8%). At 30 days after surgery the figure for dentinal reinnervation was approximately 17.7% (control, 44.9%), and by 50 days after transection (70 days of age) mean innervation was about 70% of the level observed in control 70 days teeth, though the difference between control and experimental specimens was not significant at the 5% level of probability. The results indicate that reinnervation of dentine does occur in developing teeth after nerve transection. It is argued that the results suggest a faster and probably more complete reinnervation in young animals; and that reinnervation may be attributable more to an active than to a passive mechanism, and this may also apply to dentinal innervation during development.