Occlusal Improvement, Treatment Duration, and Stability With Clear Aligners: A Systematic Review and Meta-Analysis of Peer Assessment Rating (PAR)-Based Evidence

Clear aligner therapy is widely used as an aesthetic alternative to fixed appliances, but its ability to achieve and maintain high-quality occlusion relative to conventional braces remains uncertain when judged using comprehensive occlusal indices such as the Peer Assessment Rating (PAR) index.In this review, PAR-based occlusal outcomes and short-term post-treatment stability after comprehensive clear aligner treatment are systematically reviewed and quantitatively synthesised; outcomes are compared with those of conventional fixed appliances and aligner-only cohorts.A systematic search was conducted in PubMed/MEDLINE, Embase, Cochrane CENTRAL, and Scopus, supplemented by Google Scholar and reference screening.Eligible studies comprised randomised controlled trials (RCTs), controlled clinical studies, and prospective cohorts that reported pre-and post-treatment PAR scores (original or UK-weighted) of adolescents or adults with permanent dentition undergoing comprehensive clear aligner therapy.Primary outcomes were total PAR reduction (absolute and percentage) and the proportion of patients classified as "improved" (≥30% PAR reduction) or "greatly improved" (≥22-point reduction and/or final PAR = 0).Secondary outcomes included changes in individual PAR components, treatment duration, and PAR-based stability at follow-up.Risk of bias was evaluated using RoB 2 for RCTs and ROBINS-I for non-randomised studies, and the certainty of evidence was assessed with GRADE.Seven studies (four RCTs, two retrospective comparative studies, and one prospective aligner cohort) met the inclusion criteria.Five studies contributed to the comparative meta-analyses.Clear aligners produced large improvements in weighted PAR scores, and pooled estimates showed no statistically significant difference in overall PAR reduction compared with fixed appliances (MD -2.17 percentage points in favour of fixed appliances; 95% CI -6.74 to 2.41; I² = 73%).The proportion of patients with the outcome "great improvement" differed across the studies, with a pooled risk ratio of 0.86 (95% CI 0.69 to 1.06).In addition, nearly all participants in studies reporting this outcome achieved at least a 30% PAR reduction.Treatment duration showed no consistent difference between modalities (MD -1.48 months; 95% CI -5.45 to 2.49; I² = 96%), although heterogeneity was very high.Two non-randomised studies with follow-up PAR data reported broadly stable and low PAR scores over short-to medium-term retention; however, certainty of evidence for stability was very low due to small sample sizes, non-randomised designs, and limited comparator data.When judged by PAR-based global occlusal outcomes, clear aligner therapy achieves substantial occlusal improvement that appears broadly comparable to fixed appliances across selected malocclusions, without a consistent difference in the treatment duration.High-quality RCTs with standardised PAR reporting and long-term follow-up are needed to define the indications for which clear aligners are considered equivalent or inferior to fixed appliances from an occlusal and stability perspective.