An immunohistochemical study of the pulpal nerve supply in primary human teeth: evidence for the innervation of deciduous dentine.

The innervation of pulp and dentine was studied in fully formed human deciduous teeth using antibodies to calcitonin gene related peptide (CGRP). Freshly extracted healthy teeth were divided, fixed, demineralised, cryosectioned and treated with antibodies to human CGRP which was then labelled with horseradish peroxidase. Bundles of nerve fibres passed from the apex of the root to the coronal region where a subodontoblast plexus was formed. In the cervical half of the root some nerve fibres branched away from the main bundles to supply both the odontoblast layer and the dentine. Branches from the coronal subodontoblast plexus also reached the odontoblast layer and the dentine. Most of the nerve fibres terminated in the odontoblast layer. In some areas a marginal plexus of nerves was observed between the odontoblasts and the predentine; intratubular nerve fibres arose either from this plexus or directly from the pulp. The dentine of the crown was more densely innervated than that of the root. In the crown the cervical one third had the most densely innervated dentine followed by the pulp horn and the middle third. The most densely innervated areas occurred in regions where the marginal plexus was present. Although many tubules contained a single nerve filament more complex patterns of termination were also observed. The maximum penetration of a nerve fibre into the dentine was 125 microns. The pattern of the deciduous innervation shows some similarities to the permanent dentition but among the differences is the high density of dentinal innervation in the cervical region. The latter point correlates with the clinical impression of greater sensitivity experienced by patients during invasive procedures performed without anaesthetic in the cervical area.