EXPERIMENTAL TOPICAL TETRACYCLINE-INDUCED NEURITIS IN THE RAT

Purpose: Recent studies have reported that tetracycline may induce chr onic inflammatory responses in the adjacent soft tissues. The purpose of the present study was to determine if dry, powdered tetracycline ev oked an inflammatory response in nerve tissue. Materials and Methods: Twenty male Sprague-Dawley rats were anesthesized and bilateral mental nerves were exposed. Half of the 40 nerves were intentionally injured by removing the epineurium, and the remaining nerves were uninjured. In a prospective, randomized, double-blind manner, equal volumes of co lor-matched, precoded tetracycline powder of Gelfoam (Upjohn, Kalamazo o, MI) powder control was placed in intimate contact with the nerves a nd sealed in polyethylene tubes. Forty-five days later the animals wer e killed and 5-mum sections of the nerves were prepared for histologic examination. The presence of epineurium, fascicular number, and fasci cular area were measured. An inflammatory response in nerve tissue and the intrafascicular and epifascicular inflammatory index was measured by counting darkly stained nuclei with a Jandel Video Analysis System (Jandel Scientific, Corte Madera, CA). Results: Experimental injury ( ie, epineurectomy) of nerves resulted in a statistically significant i ncrease in fascicular number (P = .034), but not in fascicular area. F or the intrafascicular inflammatory index, there was a significant mai n effect for drug (P = .002) and injury (P = .002). Experimental injur y in both Gelfoam control and tetracycline grouped nerves resulted in an increase in intrafascicular inflammation. There was no significant increase in intrafascicular inflammation in either Gelfoam control or tetracycline grouped nerves when the epineurium was intact. The combin ation of both tetracycline and epineurectomy resulted in the largest i ncrease in intrafascicular inflammation found among the groups studied . For epifascicular inflammatory index, there was a significant main e ffect for drug (P = .003) and injury (P = .001) that mirrored the intr afascicular inflammatory pattern. Conclusion: The results of the prese nt study suggest that dry, powdered tetracycline accentuates the infla mmatory response in intrafascicular and epifascicular nerve tissue fol lowing epineurectomy. The maintenance of epineurium inhibited the infl ammatory response in intrafascicular and epifascicular nerve tissues. Gelfoam was an inert material when placed against exposed nerve tissue . These findings suggest that tetracycline should not be placed in ext raction sockets when injury of the inferior alveolar and/or lingual ne rves are present.