Contribution of capsaicin-sensitive innervation to the continuous eruption of the rat mandibular incisors

A major component of tooth innervation is made of capsaicin-sensitive primary afferents (CSPA). These fibers play a key role in tooth pain and inflammation; little is known, however, about the role of CSPA in tooth eruption. The aim of this study was to examine the role of the capsaicin-sensitive afferents in the process of eruption of intact rat incisors. CSPA fibers in several rat groups, were subjected to one of the following experimental procedures: systemic chemical ablation, systemic ablation followed by chemical sympathectomy and localized activation. The observed effects on incisor eruption were compared to those made on controls. The total amount of eruption in control/naive rats, measured over a total period of 144h, was 3.18 +/- 0.07mm and decreased to 2.43 +/- 0.08mm (n=7; p<0.001) following systemic ablation of CSPA. Further decrease to 2.24 +/- 0.08mm (n=7; p<0.001) was noticed when chemical sympathectomy was added to CSPA ablation. The average rate of eruption was 1.7 +/- 0.25mm following CSPA activation, compared to an average of 0.8 +/- 0.07mm for controls (n=7; p<0.001). Capsaicin sensitive fibers play an important role in tooth homeostasis, and intact neural supply is required for tooth growth under normal conditions.