Immunohistochemical study on the sensory and autonomic nerve fibers in dental pulp and periodontium.

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Sensory innervation in the dental tissues has been studied for years in our group with the aid of the urea silver impregnation method and the transmission electron microscope. Although the methods were useful for demonstrating the distribution and ultrastructure of nerves in the dental tissues, their origin and nature remained to be further clarified. Thus, the technique of immunohistochemistry for nervous system-specific proteins was introduced to study the morphology of neural elements. With the use of antisera against neurofilament protein (NFP) and S-100 protein which are specific for neurons and glial elements, respectively, the innervation in human teeth, rat molars, and rat periodontium was discussed. With the methods devised for fixation, decalcification and immunostaining of decalcified components. The three-dimensional constitution of nerves in the human dentin and predentin was clearly demonstrated, and the sensory mechanism of human teeth was discussed. In rat molar teeth, the NFP-positive fibers in the dentin and predentin were found to penetrate directly into the dentinal tubules. However, complex nerve fibers showing three-dimensional extension as recognized in human teeth were not observed. In the periodontal ligament of rat molars, the presence of numerous Ruffini-like corpuscles was revealed in the light microscopy. These nerve terminals are considered to function as stretch receptors in the periodontal ligament. The nerve fibers showing calcitonin gene-related peptide (CGRP) were first shown to be present in the predentin of rat molars with light and electron microscopes, and the functional significance of peptidergic neurons was discussed.