Effect of diazepam on temporomandibular joints in rats with increased occlusal vertical dimension.

Anxiolytic agents, mainly benzodiazepines, have been used to treat symptomatic disorders of the temporomandibular joint (TMJ). Our aim was to evaluate the effect of diazepam on the TMJ of rats with increased occlusal vertical dimension (iOVD). Forty male rats were randomly assigned to 4 groups: control rats were given sham iOVD plus saline solution daily for 7 days. The first experimental group was given sham iOVD plus diazepam 2.5mg/kg/intramuscularly daily for 7 days (diazepam alone group); the second had iOVD induced in molars for 7 days plus saline daily for 7 days (iOVD alone group); and the third had iOVD induced in molars for 7 days plus diazepam 2.5mg/kg/intramuscularly daily for 7 days (iOVD plus diazepam group). At the end of each experiment the animals were killed and their bilateral TMJs were removed, randomly stained with haematoxylin and eosin and sirius-red, and immunoassayed. The thickness of condylar cartilage and of fibrous, proliferating, mature, and hypertrophic layers, number of collagen fibres, and the articular area were measured. Proinflammatory cytokines (interleukin (IL)-1α, IL-1β, IL-6, and tumour necrosis factor (TNF)-α) were also measured. ANOVA and Tukey's tests or the Kruskal-Wallis test were used to compare data among groups (α=5%). Condylar cartilage was thicker in the control group than in the other groups, the diazepam alone group being thicker than the other 2 experimental groups. There were fewer collagen fibres in the 2 groups given diazepam than in the other 2 groups, and there were no significant differences in the area of cartilage among groups. The controls had lower concentrations of all cytokines (p<0.05) than the 3 experimental groups, except for IL-6. Both iOVD groups had higher concentrations of IL-1α, IL-1β, and IL-6 than the diazepam alone group. Diazepam alone was associated with increased concentrations of all cytokines except IL-6. We conclude that both iOVD and diazepam induced significant changes in rats' articular cartilage.