Sensory innervation of rat molar root pulp and dentin, apex, foramen, cellular cementum, vasculature and periodontium

Abstract

Objective

Trigeminal innervations of dental roots have only been partly investigated. The aim of this study was to document sensory innervation of rat molar roots, especially their neural patterns in periapical tissues that may affect tooth pain.

Design

Trigeminal nerve ending patterns in young and old rat molars that had been labeled by tritiated axonal-transported protein were compared by immunocytochemistry for neural peripherin, calcitonin gene-related peptide, p75-neurotrophin receptor, synaptophysin, Substance P, and neurofilament-200.

Results

Nine sensory nerve patterns were found in the autoradiograms: (1) PERIAPICAL PULP had large axons ending among odontoblasts, other axons with free endings in pulp, plus innervation of dentin on the palatal-lingual and buccal sides of each root. (2) CELLULAR CEMENTUM MATRIX (CCx) had small nerve channels extending across from periodontium to apex, plus trigeminal endings in the CCx at its apical and periodontal edges. (3) THE FORAMEN REGION had many free axons plus much vascular innervation. (4) THE APEX had a variety of axons ending along its walls. (5) NEARBY PERIODONTIUM had neurovascular clusters including trigeminal axons and Ruffini mechanoreceptors near the foramen. Immunocytochemistry showed that CGRP, peripherin, synaptophysin, and p75-neurotrophin receptor each had individual neural patterns in periapical tissues, while Substance P and neurofilament protein were more limited. Differences between lateral and accessory canals were noted.

Conclusion

The nine periapical trigeminal innervation patterns identified so far differ from crown and root shaft. They likely have important effects on tooth pain in general and on periapical pains that can be difficult to anesthetize and treat.