DYNAMIC PLASTICITY OF DENTAL SENSORY NERVE STRUCTURE AND CYTOCHEMISTRY

Hypersensitive dentine responds to normal changes in touch or temperat ure with abnormal pain sensations. This paper reviews studies that hav e shown dynamic changes in sensory nerve structure, cytochemistry and location after tooth injury, suggesting that those changes contribute to dentine hypersensitivity. Nerve fibres containing calcitonin gene-r elated peptide (CGRP) are the main type of sensory fibre to innervate dentine. Evidence that many of those dentinal nerve endings originate from small myelinated fibres is presented here. The location of CGRP n erve terminals correlates with the pulpal gradients of nerve growth fa ctor that have been demonstrated in normal teeth by in situ hybridizat ion histochemistry. When shallow cavities are drilled into the outer d entine of rat molars a five-to-eight-fold increase in pulpal nerve gro wth factor precedes the extensive structural changes in the sensory ne rve fibres in pulp and dentine near the injury. Those nerve growth fac tor and sensory nerve reactions eventually subside if healing occurs, but both continue if inflammation continues. Evidence correlating pulp al inflammation with long-term changes in central trigeminal pain path ways is reviewed. There can be extensive neuroplasticity after tooth i njury, both within dental pain fibres and in central pain pathways. Th e timing of those alterations of nerve structure, location, and cytoch emistry is consistent with their involvement in mechanisms of dentine hypersensitivity.