Obesity and temporomandibular joint disorders: a systematic review and meta-analysis                                                           

Background: Temporomandibular joint disorders (TMD) is the most common non-dental pain complaint in the maxillofacial region, which presents a variety of symptoms and signs, including temporomandibular joints (TMJ) and masticatory muscle pain, joint noise, tinnitus, headaches, irregular or restricted mandibular function, masticatory difficulty, and restricted mouth opening. When comes to the relationship between obesity and TMD, it has remained controversial and inconsistent, therefore, we first conducted this meta-analysis to estimate the unclear relationship between obesity and TMD. Methods: Searches were conducted in PubMed, Web of Science, Embase, and Cochrane Library. Subjects were divided into five groups according to BMI level in this study, including the normal weight group: 18.5 ≤ BMI < 23, obesity Ⅰ group: 25 ≤ BMI < 30, obesity Ⅱ group: BMI ≥ 30, non-obesity group: BMI < 25, and obesity group: BMI ≥ 25. Statistics analyses were conducted using Stata (15.0). The number of PROSPERO was CRD42022368315. Results: Eight studies were included in this study, and six articles with a total of 74056 participants were synthesized for meta-analysis. Compared to normal weight individuals, the obesity Ⅰ decreased the risk of TMD (OR = 0.80, 95%CI = 0.69–0.94), and it was significantly decreased by obesity Ⅱ (OR = 0.74, 95%CI = 0.56–0.97). Moreover, it was lower in obesity compared with non-obese subjects (OR = 0.83, 95% CI = 0.73–0.94). Furthermore, in obese individuals, it was much lower in obesity Ⅱ than obesity Ⅰ (OR = 0.82, 95% CI = 0.71–0.94). Conclusions: Obesity is not a risk factor for TMD, and maybe a protective factor for TMD, of which patients with larger BMI are less likely to suffer from TMD pain. Therefore, the value of BMI should be taken into consideration in the assessment of TMD.