Regenerating nerve fibres do not displace the collateral reinnervation of cat teeth

Experiments in adult cats have shown that when the inferior alveolar nerve is sectioned and regeneration blocked, there is extensive collateral reinnervation from neighbouring nerves which reinnervate the denervated teeth. In the present experiments the fate of collateral nerve fibres supplying the teeth has been investigated following regeneration of the inferior alveolar nerve. In some experiments the inferior alveolar nerve was sectioned and regeneration temporarily blocked whilst in others the nerve was frozen but not sectioned, to allow a more complete restoration of normal properties after regeneration. The jaw opening reflex evoked by electrical stimulation of the left canine and incisor teeth was abolished by left inferior alveolar nerve section or freeze but returned within 3-9 weeks due to reinnervation by collateral nerve fibres. Regenerating inferior alveolar nerve fibres were allowed to reinnervate the teeth 12-15 weeks after the initial nerve injury. Twenty seven weeks after the initial nerve injury, pulpal nerve fibres supplying the teeth which had been denervated were present in the regenerated inferior alveolar nerve as well as the ipsilateral lingual and mylohyoid nerves and the contralateral inferior alveolar, lingual and mylohyoid nerves. Except for the ipsilateral inferior alveolar and lingual nerves, these nerves do not normally include pulpal fibres from these teeth. In these experiments, therefore, after inferior alveolar nerve section or freeze, the collateral reinnervation of tooth pulps was not withdrawn following the return of regenerating nerve fibres.