Critical time of exposure of the rabbit inferior alveolar nerve to Carnoy's solution

Abstract

To reduce the recurrence of keratocysts, tanning of the epithelial lining with modified Carnoy's solution has been advocated as an ancillary procedure. This agent has occasionally been reported to induce long-lasting local neurotoxicity, when the inferior alveolar nerve (IAN) was located within the bony cavity of larger cysts. As the severity of the neurologic damage depends on the tissue penetration of the solution, a critical exposure time must be assumed. To substantiate this hypothesis, rabbit IANs were decorticated over an approximate length of 1 cm and soaked with modified Carnoy's solution for periods from 30 seconds to 10 minutes. Sensory nerve function was monitored using somatosensory evoked potentials. exposures up to 2 minutes did not result in any electrophysiologic abnormality. Exposure for 3 minutes led to either normal or rudimentary evoked potentials. After exposure of 5 minutes, and invariably after 10 minutes, the evoked potentials from the IAN were absent. Nerve segments were removed for histologic examination and the penetration depth of the Carnoy's solution was identified by staining with the Berlin-blue reaction. The involved areas were morphometrically evaluated and they reflected the electrophysiological findings. Transmission electron microscopy showed morphologic changes confined to the outer nerve sheaths (epineurium and perineurium) after exposure of 3 minutes. Exposure of 5 minutes and longer resulted in involvement of both the nerve sheaths and their axonal contents, with disruption and disintegration of the neural tissue. This study clearly supports the hypothesis that contact of a peripheral nerve (ie, IAN) with Carnoy's solution carries a time-related risk to produce acute sensory impairment. Although the thickness of nerve sheaths varies among species, it seems appropriate in the clinical setting to restrict exposure to 3 minutes whenever the IAN is unprotected.