The main aim of this work was to evaluate the effect of intra-articular, sub-synovial steroid injections (IASSSI) with different doses during temporomandibular joint (TMJ) arthroscopy. Using a single-blind, randomized clinical trial, the investigators enrolled a sample of subjects who underwent TMJ arthroscopy with vs. without IASSSI for treating TMJ disorder (TMD). The predictor variable was the treatment group classified as no treatment (A - without IASSSI) or active treatments (IASSSI (B) with 2 mg or (C) 4-mg dexamethasone). Study medications were randomly assigned. Only subjects were blinded to treatment assignment. The main outcome variables included the following: 1) pain assessed up to postoperative day 30 with the McGill Pain Questionnaire and visual analog scale (VAS); 2) maximum mouth opening (MMO); and 3) analgesic and anti-inflammatory drug consumption. Other variables were demographic (age, sex) or pathologic (disease manifestations and classifications). Descriptive and bivariate statistics were computed. Statistical significance was set at p ≤ 0.5, one-tailed test of hypothesis. The sample comprised 36 patients (n = 12 per study group). In the active group with 4 mg corticosteroids, pain reduction measured by VAS (odds ratio [OR] = 0.18; p = 0.013) and McGill scale scores (OR = 0.15; p = 0.048) was significantly higher than in the control group. The McGill scale scores significantly decreased in both IASSSI groups, compared to the control group, at the final follow-up (all p < 0.012), and IASSSI was significantly associated with reduced analgesic consumption at postoperative days 7 and 14 (p = 0.003). However, there was no significant difference regarding MMO among the three groups. Within the limitations of the study, it seems that intra-articular, sub-synovial steroid injections (IASSSI) with 4 mg dexamethasone should be preferred whenever appropriate when pain relief is the priority of the procedure.Brazilian Registry of Clinical Trials (ReBec)- 28yb2g