Re-innervation of rat molar tooth pulp following transection of the inferior alveolar nerve

The inferior alveolar nerves (IAN) of young male Wistar rats (b.wt. ≥ 200 g) were transected unilaterally, slightly proximal to the mandibular foramen under anesthesia with chloral hydrate (0.4 g/kg, i.p.). After various postoperative periods of time, the animals received horseradish peroxidase (HRP) applications to 3 mandibular molar tooth pulps on both sides and were fixed by transvascular perfusion 24 h later. Horizontal 60 μm sections of the trigeminal ganglion were incubated with tetramethylbenzidine hydrochloride and the cross-sectional areas of all the labeled neuronal cell bodies were measured. The average number of labeled cells on the untransected (control) side was 148 (n = 26), with cross-sectional areas ranging between 131.9 and 2129.6 μm². Of these, 42.5% fell between 300 and 600 μm². About 13.5% (n = 7) of the primary neurons innervating the tooth pulps escaped the ipsilateral neurotomy and were labeled by HRP application on postoperative day 0. With HRP application on postoperative day 3, the number of labeled neurons recovered to 56.8% (n = 7) that of the control and maintained this level up to postoperative day 75. From postoperative days 3 through 75, the cell size spectrum of labeled neurons on the transection side was similar to that of the control and no consistent tendency of alteration was observed; i.e. they were distributed between 134.4 and 2214.3 μm², with the mode being 41.5% in the range between 300 and 600 μm² (n = 19).