The association between traumatic temporomandibular joint bony ankylosis and depressive disorder in growing rats.

BACKGROUND

The psychological symptoms of temporomandibular joint (TMJ) ankylosis were similar to that of depressive disorder, but there were no relevant evidences to confirm that the humans or animals with TMJ ankylosis had depressive disorder. The aim of this study was to investigate the association between TMJ ankylosis and depressive disorder in the rat model.

METHODS

Thirty 3-week-old male Sprague-Dawley (SD) rats were used in this study. The damage of TMJ complexes and narrowed joint space were performed in the unilateral TMJ of test group to induce TMJ bony ankylosis (experimental side). The other TMJ of test group underwent a sham operation (sham side). The TMJs of control group did not undergo any operations. At 8 weeks postoperatively, behavioral tests, body weight, passive maximum mouth opening (PMMO), and TMJ morphological features were evaluated, and the hippocampuses were analyzed using western blotting and immunocytochemistry. The data was compared between the test group and control group by independent t-test, between the experimental side and sham side by paired t-test. The correlations between PMMO/area of bony fusion and duration of immobility, sucrose preference, CB1 receptor protein, mean optical density of CB1 receptor protein, and the number of BrdU-positive cell were evaluated using linear regression analysis. The level of significance was 0.05.

RESULTS

In the test group, the traumatic TMJ complexes with narrowed joint space developed TMJ bony ankylosis, the area of bony mass of experimental side (21.26 mm) was larger than that of sham side (1.73 mm) (p < 0.001). There were significant difference with the sucrose preference (test group: 0.36, control group: 0.76, p < 0.001), duration of immobility (test group: 127.36 s, control group: 59.41 s, p < 0.001), body weight (test group: 156.70 g, control group: 270.06 g, p < 0.001), PMMO (test group: 9.98 mm, control group: 28.79 mm, p < 0.001), CB1 receptor protein (test group: 41.00%, control group: 86.69%, p < 0.001), mean optical density of CB1 receptor protein (test group: 29.60 a.u., control group: 54.69 a.u., p < 0.001), and the number of BrdU-positive cell between the test group and control group (test group: 2133.71, control group: 4301.95, p < 0.001). PMMO was negatively correlated with the duration of immobility (r = 0.953, p < 0.001), while the area of bony fusion was positively correlated (r = 0.961, p < 0.001). PMMO was positively correlated with the sucrose preference, CB1 receptor protein, mean optical density of CB1 receptor protein, and the number of BrdU-positive cell (r = 0.955, 0.955, 0.976, 0.958, p < 0.001, all), while the area of bony fusion was negatively correlated (r = 0.970, 0.981, 0.971, 0.958, p < 0.001, all).

CONCLUSIONS

The present study verified that depressive disorder was found in the rat model of traumatic TMJ bony ankylosis. The severity of TMJ bony ankylosis correlated with the severity of depressive disorder.