EVOLUTION OF CLEAR ALIGNER BIOMECHANICS: A COMPREHENSIVE SCOPING REVIEW OF TRANSVERSE ARCH EXPANSION EFFICIENCY AND HYBRID S11 PROTOCOLS

Purpose: This scoping review evaluates the evolution of clear aligner biomechanics in transverse maxillary expansion, with a particular focus on treatment predictability, torque control, and the integration of hybrid protocols such as Smartee S11. 

Methods: A comprehensive search was conducted across PubMed, Web of Science, and Scopus for literature published from 2016 to 2026. Eligible studies included systematic reviews, clinical trials, and three-dimensional finite element analysis (FEA) studies. Data were extracted on expansion predictability, biomechanical behavior, torque control, and the effects of hybrid protocols. Risk of bias was assessed across clinical and FEA studies. 

Results: A total of 46 studies met inclusion criteria. Expansion predictability varied across the dental arch: highest in the premolar region (>90%), moderate in canines, and lowest in molars (58–70%). CAT predominantly induced dentoalveolar expansion with limited skeletal effects, characterized by tippingdominant movements. Hybrid protocols, particularly the Smartee S11 system with palatal pressure ridges and buccal attachments, improved torque control (3.42°/mm vs. 4.01°/mm in standard aligners) and reduced tipping. Mixed dentition cases showed higher expansion efficiency than adults, likely due to greater skeletal adaptability. 

Conclusions: Clear aligner therapy is effective for transverse arch expansion, especially in premolars, but posterior predictability remains limited. The integration of hybrid biomechanical systems, such as Smartee S11, enhances torque control and reduces tipping, supporting more controlled tooth movement. Digital overcorrection (10–20%) and targeted auxiliaries are recommended for improved clinical outcomes. Highquality prospective studies are needed to further evaluate long-term stability and skeletal effects.