Effect of Combined Orthodontic–Periodontal Therapy Versus Periodontal Therapy Alone on Periodontal Parameters in Adults with Periodontitis: A Systematic Review and Meta-Analysis

Objectives: To compare combined orthodontic–periodontal treatment with periodontal therapy alone on probing pocket depth (PPD) and clinical attachment level (CAL) in adults with periodontitis. Methods: Three databases and two trial registries were searched (October 2025, updated October 2026; PROSPERO: CRD420261392570). Mean differences (MD) were pooled using random-effects models (REML, Hartung–Knapp) with 95% prediction intervals (PI); risk of bias (RoB 2.0, ROBINS-I) and certainty (GRADE) were assessed. Results: Seven studies (four randomized controlled trials [RCTs]; n = 605) were included for PPD and six for CAL. Combined treatment yielded a modest additional PPD reduction (MD 0.49 mm, 95% CI 0.26–0.71; I2 = 75.4%; PI −0.05 to 1.02), not significant in RCTs alone (MD 0.46 mm, 95% CI −0.08 to 0.99). The CAL difference was not significant (MD 0.42 mm, 95% CI −0.01 to 0.84; I2 = 91.7%). In exploratory subgroup analysis, studies with mean baseline PPD > 5 mm showed a larger difference (MD 0.67 mm; I2 = 0%). Certainty was low (PPD) and very low (CAL). Conclusions: Low-certainty evidence suggests a modest additional PPD reduction with combined treatment; evidence for CAL is very uncertain. The larger effect with deeper baseline pockets is hypothesis-generating and needs confirmation in adequately powered trials.