BIOMECHANICAL INSIGHTS IN ARCH EXPANSION WITH CLEAR ALIGNERS: A LITERATURE REVIEW

Clear aligner therapy has rapidly gained popularity as an esthetic and patient-friendly alternative to fixed orthodontic appliances. Among the various movements claimed to be achievable with aligners, transverse arch expansion is one of the most debated. Expansion is clinically valuable for relieving crowding, correcting crossbites, and improving arch form; however, the biomechanical basis of expansion with aligners and its predictability remain controversial. This review explores the available literature on the biomechanics of aligner-mediated arch expansion, with emphasis on the nature of the forces delivered, the determinants that influence expansion, and the clinical outcomes reported in different age groups. Evidence from laboratory investigations, finite element modeling, and clinical studies suggests that expansion with clear aligners is primarily dentoalveolar in nature, produced predominantly through buccal tipping of posterior teeth rather than true skeletal expansion. Factors such as aligner thickness, trimline design, staging protocols, patient age, and bone quality affect the extent and quality of expansion. While limited skeletal change may occur in adolescents, adults typically demonstrate only dental tipping, raising concerns regarding periodontal side effects and long-term stability. Overall, aligners can achieve expansion in certain cases, especially where the transverse discrepancy is mild to moderate, but outcomes depend on proper application of biomechanical principles, and greater skeletal changes may still require supplementary approaches.