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.