Retention after orthodontic treatment aims to maintain tooth position and prevent relapse, yet no consensus exists on the optimal fixed retainer design. Rectangular and round (multistrand) wires are commonly used, but evidence comparing their effectiveness on stability, periodontal health, and survival remains inconsistent. This meta-analysis aimed to compare the clinical efficacy of rectangular and round wire fixed retainers on tooth alignment, periodontal health, and failure rates.

PubMed, Scopus, Web of Science, and the Cochrane Library were systematically searched from inception to 8 January 2026 for randomized controlled trials directly comparing rectangular and round wire retainers. Meta-analysis was conducted using R 4.5.0 with R Studio 2024.12.1 + 563. A random-effects model was applied, using mean differences (MDs) with 95% confidence intervals (95% CI) for continuous outcomes and risk ratios (RRs) with 95% CI for dichotomous outcomes. Statistical heterogeneity was assessed using I-squared (I ² ) statistics and forest plots.

Nine studies including 994 participants were analyzed. Rectangular wires showed a statistically significant difference in maintaining lower incisor alignment measured by Little's Irregularity Index at 9 months (MD = 0.22 mm, 95% CI: 0.16–0.28, P < 0.001) and 12 months (MD = 0.20 mm, 95% CI: 0.02–0.39, P = 0.03), but not at 3, 6, or 24–36 months. Heterogeneity at 12 months was high (I ² = 73.2%). No significant differences were found in retainer failure rates at any follow-up interval, including 6, 12, or 24–36 months, and no significant differences were observed in gingival index, plaque index, or intercanine width at any follow-up.

Rectangular wire retainers may provide a modest short-term advantage in anterior alignment at 9–12 months, while both wire types show comparable long-term outcomes, periodontal effects, and failure rates. Large-scale randomized controlled trials with long-term follow-up are warranted.

The study protocol was registered on PROSPERO (CRD420261295135).