Occlusal outcome of orthodontic treatment: a systematic review with meta-analyses of randomized trials

BACKGROUND Several appliances or treatment protocols are marketed to either patients or orthodontists as being associated with improved orthodontic outcomes. However, clinical decision-making should be based on robust scientific evidence and not marketing claims or anecdotal evidence. OBJECTIVE To identify appliances/protocols being associated with improved outcomes of fixed appliance treatment. SEARCH METHODS Unrestricted literature searches in seven databases/registers for human studies until March 2024. SELECTION CRITERIA Randomized or quasi-randomized clinical trials on human patients of any age, sex, or ethnicity receiving comprehensive orthodontic treatment with fixed appliances and assessing occlusal outcome with either the Peer Assessment Rating (PAR) or the American Board of Orthodontics-Objective Grading System (ABO-OGS) index. DATA COLLECTION AND ANALYSIS Duplicate/independent study selection, data extraction, and risk of bias assessment with the Cochrane RoB 2 tool. Random-effects meta-analyses of averages or mean differences with their 95% Confidence Intervals (CI), followed by meta-regression/subgroup/sensitivity analyses and assessment of the quality of clinical recommendations with the Grades of Recommendations, Assessment, Development, and Evaluation (GRADE) approach. RESULTS Data from 20 small- to moderately-sized trials covering 1470 patients indicated that orthodontic treatment with fixed appliances is effective and results on average in a final PAR score of 6.0 points (95% CI 3.9-8.2 points), an absolute PAR reduction of 23.0 points (95% CI 15.6-30.4 points), a % PAR reduction of 82.6% (95% CI 70.8%-94.4%), and an absolute ABO-OGS score of 18.9 points (95% CI 11.7-26.2 points). However, very high between-study heterogeneity (I2 > 75%) was seen for both PAR and ABO-OGS. Extraction treatment was associated with significantly better occlusal outcome than non-extraction treatment with ABO-OGS (12.9 versus 16.6 points; P = .02). There was no statistically significant difference in occlusal outcome with (i) 0.018″-slot or 0.022″-slot brackets; (ii) customized or prefabricated brackets; (iii) anchorage reinforcement with temporary anchorage devices; (iv) use of vibrational adjuncts; and (v) aligners or fixed appliances (P > .05 in all instances), while small benefits were seen with indirectly bonded brackets. CONCLUSIONS Considerable between-study heterogeneity exists in the reported occlusal outcome of fixed appliance treatment, and different appliances or adjuncts have little effect on this. Standardization and/or automatization of the scoring procedures for PAR and ABO-OGS might help to improve consistency and reliability of outcome measurement in orthodontic trials. REGISTRATION PROSPERO (CRD42024525088).