The reactions of sensory nerves to restorative procedures can be classified as immediate, early and late. For each of these, the neural response depends upon the severity of pulpal injury and the stages of
inflammation and healing. Immediate responses in the first few minutes include destruction of nerve fibers in the injured dentin and pulp,
hypersensitivity of surviving fibers, release of
neuropeptides into the pulp and
neurogenic inflammation. Early responses occur during the first few days after cavity preparation, with nerve fibers sprouting in the surviving pulp and gaining increased axonal transport and
neuropeptide contents. Sensory fibers containing
calcitonin gene related peptide (CGRP) greatly outnumber those with
substance P (SP); but both types grow toward the surviving odontoblasts and associated pulp tissue surrounding the lesion. Later during subsequent weeks the nerve fibers accompany granulation tissue as it replaces acute
inflammation; and nerve sprouting subsides when
inflammation is reduced and when reparative dentin covers the injury site. An important response to
tooth injury that may regulate nerve sprouting reactions is the increased production of
nerve growth factor (
NGF) by pulpal fibroblasts near the lesion. The timing of the nerve sprouting reactions suggests that they may contribute to tooth
hypersensitivity after restorative procedures.