BACKGROUND:Temporomandibular joint osteoarthritis can cause severe pain,which significantly affects the patient's quality of life and psychological health.Studies have found that medical ozone can effectively alleviate pain due to temporomandibular joint osteoarthritis,but its analgesic effect and mechanism are still unclear. OBJECTIVE:To explore the effects of medical ozone on pain relief in temporomandibular joint osteoarthritis and the potential mechanisms. METHODS:Twenty-four Sprague-Dawley rats were randomly divided into four groups(n=6 per group):control group,model group,air group,and medical ozone group.A sodium iodate-induced rat model of temporomandibular joint osteoarthritis was established in all groups except for the control group.After 1 week of modeling,rats in the air group and medical ozone group were injected with clean air and medical ozone,respectively,in the temporomandibular joint.The injection frequency for the air group and medical ozone group was once a week for three times in total.The von Frey mechanized pain measurement technique was used to assess the mechanical pain threshold of the temporomandibular joint in rats before and 28 days after modeling.ELISA was utilized to detect interleukin-1β in both serum and temporomandibular joint fluid at 28 days after modeling.Histopathologic changes of the temporomandibular joint were evaluated through hematoxylin-eosin staining.Additionally,the expression levels of hypoxia-inducible factor 1α and cyclooxygenase 2 in the temporomandibular joint were analyzed using immunohistochemistry. RESULTS AND CONCLUSION:Compared with the control group,the mechanical pain thresholds of the temporomandibular joint in the model group were decreased at 1,3,7,14,21,and 28 days after modeling(P<0.01);and compared with the model and air groups,the mechanical pain thresholds of the temporomandibular joint in the medical ozone group were increased at 28 days after modeling(P<0.01).Compared with the control group,the level of interleukin 1β in the serum and joint fluid of rats in the model group was elevated(P<0.01);compared with the model and air groups,the level of interleukin 1β in the serum and joint fluid of rats in the medical ozone group was decreased(P<0.01).Hematoxylin-eosin staining results showed derangement and degeneration of the cartilage structure in the model group and the air group,while the derangement of the cartilage structure in the medical ozone group was less than that in the model group and the air group.Immunohistochemical staining showed that the expression of hypoxia-inducible factor 1α and cyclooxygenase 2 in the temporomandibular joints of rats in the model group was elevated compared with that in the control group(P<0.01);the expression of hypoxia-inducible factor 1α and cyclooxygenase 2 in the temporomandibular joints of rats in the medical ozone group was decreased compared with that in the model group and the air group(P<0.01,P<0.05).These findings suggest that medical ozone can alleviate the pain caused by osteoarthritis of the temporomandibular joints in Sprague-Dawley rats by reducing the expression of hypoxia-inducible factor 1α,interleukin 1β,and cyclooxygenase 2.