Abstract: BACKGROUND: It has been proved in clinical and animal experiments that intraarticular injection of medical ozone can effectively improve the symptoms of temporomandibular joint osteoarthritis and slow down the progression of the disease. However, the optimal concentration and range are still controversial.
OBJECTIVE: To analyze the effects of intraarticular injection of different concentrations of medical ozone on the condylar cartilage of rats with temporomandibular joint osteoarthritis. 
METHODS: Of the 42 rats, 6 rats were randomly selected as the healthy control group, and the remaining rats were given one-time injection of sodium iodoacetate into the joint cavity to establish the temporomandibular joint osteoarthritis model. Of the 36 rats successfully modeled, 6 rats were selected as the model control group, and the remaining 30 were randomly divided into 20, 30, 40 mg/L medical ozone groups, with 10 rats in each group. After successful modeling, the rats in the medical ozone groups were given intra-articular injection of 20, 30, 40 mg/L medical ozone oxygen once a week for 3 weeks, respectively, and the model and healthy control groups were injected with equal volume of saline. One week after the final injection, unilateral temporomandibular joint tissues were taken, and the level of vascular endothelial growth factor in condylar cartilage was measured by ELISA. Hematoxylin-eosin staining and saffron O-fast green staining were performed on the contralateral temporomandibular joint tissues. The modified Mankin’s score was applied to evaluate the degree of histopathological changes in the temporomandibular joint.
RESULTS AND CONCLUSION: Compared with the healthy control group, the vascular endothelial growth factor level in the condylar cartilage of rats was significantly increased in the model control and 20, 30, 40 mg/L medical ozone groups (P < 0.05). Compared with the model control group and 40 mg/L medical ozone group, the vascular endothelial growth factor level in the condylar cartilage of rats was significantly decreased in the 20 and 30 mg/L medical ozone groups (P < 0.05). Compared with the 30 mg/L medical ozone group, the vascular endothelial growth factor level in the condylar cartilage of rats was significantly decreased in the 20 mg/L medical ozone group (P < 0.05). Histological observations showed that the modified Mankin’s scores in the 20, 30, and 40 mg/L medical ozone groups and the model control group were higher than those in the healthy control group (P < 0.05), while the modified Mankin’s scores in the 20 and 30 mg/L medical ozone groups were lower than those in the model control group and the 40 mg/L medical ozone group (P < 0.05). To conclude, intraarticular injection of medical ozone at mass concentrations of 20 and 30 mg/L significantly alleviated the progression of osteoarthritis of the temporomandibular joint in rats, especially when 20 mg/L medical ozone was injected. However, the degree of osteoarthritis in the temporomandibular joint of rats was aggravated when the mass concentration of ozone increased to 40 mg/L.

Key words: temporomandibular joint disorder, osteoarthritis, ozone, vascular endothelial growth factor