Medical Science: Updates and Prospects Vol. 10

Clear aligner therapy (CAT) has fundamentally altered the landscape of contemporary orthodontic practice, offering patients an aesthetic and removable alternative to conventional fixed appliance systems. Despite its widespread global adoption, considerable debate persists regarding the biomechanical adequacy of thermoplastic aligners in producing predictable, complex tooth movements and achieving occlusal outcomes comparable to those of traditional bracket-and-wire mechanics. This review critically appraises peer-reviewed evidence published predominantly between 2015 and 2025, drawing on prospective clinical trials, systematic reviews, finite element analyses, in vitro mechanical studies, and comparative cohort investigations to evaluate the biomechanical principles and clinical limitations of CAT. A narrative review approach was adopted due to the heterogeneity of the clear aligner therapy literature. A comprehensive search of multiple electronic databases was conducted.

The cumulative evidence indicates that CAT demonstrates reasonable efficacy for mild-to-moderate crowding, simple tipping movements, and space closure in non-extraction cases. Its performance, however, is demonstrably compromised in scenarios requiring precise root torque control, rotation of cylindrical teeth, reliable vertical dimension management, and true bodily molar distalization. The viscoelastic properties of thermoplastic polymer materials—particularly time-dependent force decay—impose fundamental constraints on force delivery, and attachment design has emerged as a critical but imperfectly standardised determinant of treatment accuracy. Patient compliance with wear instructions remains a central confounding variable with direct and non-trivial biomechanical consequences, whilst comparative data consistently suggest that fixed appliances retain advantages in achieving ideal final occlusal quality, especially in complex malocclusion presentations.

Periodontal tissue responses appear broadly favourable with CAT relative to fixed appliances, and the risk of orthodontically induced root resorption may be marginally lower, though the evidence base requires strengthening. The management of retention following aligner therapy follows principles broadly analogous to those of fixed appliance treatment, with no established evidence for superior post-treatment stability. Emerging materials science, artificial intelligence-assisted treatment planning, and improved staging protocols continue to narrow some of these documented gaps, yet fundamental clinical limitations persist. A rigorous, evidence-informed understanding of the indications and limitations of CAT is essential for appropriate case selection, realistic patient counselling, and high-quality treatment delivery.