Tritiated thymidine autoradiographic study of the effects of inferior alveolar nerve resection on the proliferative compartments of the mouse incisor formative tissues

Abstract

At 15, 30 and 60 days after denervation, 10 mice were injected (5 controls, 5 denervated) at each time period with 0.5 [mu]Ci/gm of [3H]-thymidine. Denervated teeth, after 15 and 30 days, were thinner, shorter and narrower with a chalky-white appearance; by 60 days, the teeth returned to their normal predenervated appearance. The responses of the proliferative compartments of the mouse incisor varied with time after denervation, and depended on whether comparison was made to sham controls or the control side of a denervated mouse. The pre-odontoblasts were most stable in terms of [3H]-thymidine labelling index with a significant decrease only at 60 days after surgery. This decrease may be due to an alteration of the inductive influence of the inner enamel epithelium and the nerve resection. The effects of nerve, resection on the inner enamel epithelium were a reduction in the labelling index on both control and denervated sides in comparisons to sham controls and a decrease in labelling index of the denervated side when compared to contralateral control. Significant differences between the control and denervated sides of experimental mice were evident 15 days after denervation in the outer enamel epithelium, inner enamel epithelium, and pulp fibroblasts. Indirect effects (i.e. chipping of the teeth) may mask neurotrophic influences. There also appears to be a homeostatic or compensatory mechanism for attenuation of the effects of denervation in continuously erupting teeth. The effects at the early time periods emphasize the need for a study of neurotrophic effects on the cellular compartments of the tooth in the period immediately following denervation.