Neglected Interproximal Friction During Fixed Orthodontic Treatment: An Iterative Biomechanical Analysis

Introduction and aims To examine the biomechanical effects of interproximal friction on anchorage preservation during orthodontic space closure with sliding mechanics. Methods A mandibular second premolar extraction finite element analysis (FEA) model was constructed, where mesial translation of the first mandibular molar with sliding mechanics was simulated. Three ligation methods (self-ligation, passive and active continuous ligation), each with 3 friction coefficient configurations (μ) were analysed using iterative biomechanical analysis. Results Active continuous ligation minimised anchorage loss (31.5% reduction in premolar displacement vs passive continuous ligation/self-ligation at μ = 0.2) while achieving comparable molar mesial displacement (2.59-2.60 mm). After complete space closure, active ligation reduced central incisor lingual tipping by 0.80 mm and premolar distal displacement by 0.67 mm. Higher μ values reduced anterior anchorage loss. All groups exhibited two-phase displacement dynamics: rapid tooth movement during the teeth tipping stage followed by stabilised sliding during the sliding stage. Active continuous ligation groups exhibited notably higher interproximal forces than the other ligation groups. With μ = 0.2, interproximal friction in active continuous ligation was notably greater than in other groups. Conclusion Interproximal friction influenced anchorage efficacy, with greater interproximal friction enhancing grouped-teeth anterior anchorage. The concept of ‘passive range of group teeth’ is proposed, suggesting that interproximal friction may affect the expression of the bracket’s passive range. Clinical Significance Active continuous ligation enhances grouped-teeth anchorage, while passive continuous and self-ligation led to the same amount of anterior anchorage loss. However, FEA results should be complemented by additional clinical evidence before establishing more definitive conclusions.