Irritation of Dental Sensory Nerves Promotes the Occurrence of Pulp Calcification

Introduction: Pulp calcification (PC) often appears in strong association with nerve fiber bundles, which indicates the important role of dental nerves in the formation of PC. Additionally, given that sensory nerves and calcitonin gene-related peptide (CGRP) secreted from sensory nerve fibers are involved in physiological and pathological bone formation, we aimed to determine whether chronic irritation of sensory nerves can promote the occurrence of PC. Methods: A sensory nerve irritation rat model was established via ligation of the inferior alveolar nerve (IAN), and face grooming behavior was analyzed as a measure of pain sensation. Two months post-surgery, PC was determined by imaging and histologic ana-lyses. Results: Rats in the IAN-chronic constriction injury (IAN-CCI) group showed sponta-neous pain-associated behavior after the operations and pain tolerance on the 60th postoperative day. The imaging and histological analysis showed more calcified particles in the IAN-innervated first and second molars after day 60 of the dental sensory nerve irritation. These calcified masses had a dentin-like structure that contained sparse, irregularly oriented tubules. Compared to the control and sham groups, the odontoblasts located in the periphery of radicular pulp aligned along a thicker layer of predentin; which expressed more nestin with longer and stouter processes in the IAN-CCI group. Additionally, more CGRP-positive nerves were observed in the IAN-CCI group. Conclusions: Irritation of sensory nerves promotes PC formation, and the increased density of CGRP-immunolabeled fibers probably contributes to this process. This highlights the significance of dental sensory nerves in the formation of PC. (J Endod 2023;49:402-409.)

Automated summary

In this study, a rat model of sensory nerve irritation was established by ligating the inferior alveolar nerve (IAN), and face grooming behavior was analyzed as an indicator of pain sensation. Two months after dental sensory nerve irritation, more calcified particles were observed in the stimulated teeth. These calcified masses had a dentin-like structure with sparse, irregularly oriented tubules. Additionally, more CGRP-positive nerves were found in the stimulation group. Based on these findings, it can be concluded that the irritation of sensory nerves promotes the formation of dental pulp calcification, and the increased density of CGRP-immunolabeled fibers may contribute to this process.