Dense innervation of human radicular dental pulp as revealed by immunocytochemistry for protein gene-product 9.5.

Protein gene-product 9.5 (PGP 9.5) is a novel neurone-specific protein. At light- and electron-microscopic levels, human radicular dental pulp was heavily innervated by PGP 9.5 nerve fibres. Thick nerve bundles showing intense PGP 9.5 immunoreactivity ascended in the centre of the pulp, with some nerve fibres extending from the trunk towards the peripheral pulp at regular intervals. However, the fibres did not form a plexus (of Raschkow) beneath the odontoblast cell layer. The PGP 9.5-positive nerve fibres penetrated into the predentine and dentine beyond the odontoblast cell layer where some nerves terminated. In the predentine, PGP 9.5-positive nerve fibres were densely distributed. In tangential sections along the pulpodentinal border, the nerve fibres ran in contact with odontoblast processes. Immunoelectron microscopy revealed that all nerve fibres were immunoreactive for PGP 9.5 in the radicular predentine and dentine, and terminated in contact with the odontoblast cell processes. The distribution pattern and terminal formation of predentinal and dentinal nerves were identical to those of coronal pulp, as reported previously. The dense innervation in radicular dental pulp, overlooked in previous reports, might be responsible for dentine hypersensitivity.