Friction in Orthodontics Revisited: A Scoping Review and Meta-Analysis Challenging the Friction-Driven Paradigm: Evidence for Binding-Dominated Resistance to Sliding

Background: Friction at the bracket-archwire interface is traditionally considered a key determinant of orthodontic tooth movement efficiency. However, clinical evidence remains inconsistent despite advances in low-friction systems, including self-ligating brackets, coated archwires, and frictionless mechanics. Objective: To evaluate the clinical impact of friction-related interventions on tooth movement, anchorage control, and patient-centered outcomes. Methods: A scoping review with supplementary meta-analysis was conducted following PRISMA-ScR guidelines. Electronic searches of the Cochrane Library (1 systematic review: CD003453), PubMed (128 primary studies), and Google Scholar (approximately 2,500 results, screened to 45 relevant studies) were performed. Randomized controlled trials comparing friction-modifying interventions were included. Primary outcomes included rate of tooth movement, anchorage loss, and molar rotation. Secondary outcomes included pain and treatment duration. Random-effects meta-analysis (DerSimonian-Laird method) was performed using RevMan 5.4; this method was chosen due to expected clinical heterogeneity. Risk of bias was assessed using Cochrane RoB 2, and certainty of evidence was evaluated using GRADE. Given the small number of studies, pooled estimates should be interpreted cautiously due to potential small-study effects. Results: Nineteen RCTs were included in quantitative synthesis. Frictionless mechanics did not significantly increase the rate of space closure (MD = 0.15 mm/month; 95% CI: -0.08 to 0.38; P = 0.20; I-squared = 68%) but resulted in significantly greater molar rotation (MD = 6.1 degrees; 95% CI: 4.8 to 7.4; P < 0.001; I-squared = 45%). Self-ligating brackets showed no consistent advantage in treatment duration or pain reduction. Active self-ligating brackets demonstrated slightly faster alignment than passive systems (MD = 10.24 days; 95% CI: 2.80 to 17.68). Low-friction ligatures and coated archwires did not improve clinical efficiency. Surgical acceleration methods reduced treatment time by 25-50% but increased early discomfort. Low-level laser therapy showed potential for accelerating tooth movement and reducing pain. Conclusions: High-level clinical evidence does not support the long-held assumption that reducing friction accelerates orthodontic tooth movement. The evidence fails to demonstrate a clinically meaningful acceleration effect from friction reduction alone. Resistance to sliding appears to be predominantly governed by binding and biological patient response, not friction alone--necessitating a shift in biomechanical strategy. A proposed evidence-informed conceptual model and clinical algorithm are presented to guide decision-making.