This study aimed to assess the nature of outcomes and outcome assessment methods used in clear aligner therapy (CAT) clinical trials, and to evaluate their sample and study characteristics.

An electronic search of MEDLINE (via OVID), Embase, Web of Science, and the Cochrane Library was conducted to identify randomized controlled trials and controlled clinical trials involving CAT from database inception to 12th January 2026. Extracted data included participant demographics, sample size, and dropout rate. Study characteristics including publication year, setting, study duration, number of arms, overarching comparisons, and treatment stage were recorded. The type of clear aligner, wear protocol, and compliance assessment methods were also documented. Primary and secondary outcomes were identified and categorized into domains.

Of 869 records screened, 103 trials were included, with 73.8% published in 2020 or later. Most studies involved adults (83.5%), had ≤ 40 participants (44.7%), were conducted in educational settings (61.2%), and were single-centered (69.9%). Most trials compared CAT with fixed appliances (63.1%) and focused on the first 6 months of therapy (53.4%); only 20.4% assessed the full treatment period. Across studies, 50 distinct outcomes were identified. The most frequently investigated domains were dental and periodontal health (36.9%) and patient-reported outcomes (35.9%), with fewer studies addressing treatment efficiency (15.5%), material properties (4.9%), and compliance (2.9%).

CAT trials showed heterogeneity in both outcome selection and measurement tools. Most studies focused on short-term oral health outcomes, while the full course of treatment, objective treatment effectiveness, compliance, and long-term stability were less frequently assessed.