Effect of Direct Versus Indirect Bonding Techniques on Fixed Retainer Failure Rates: A Systematic Review and Meta-Analysis

Bonded fixed orthodontic retainers frequently fail, yet it remains uncertain whether laboratory-based indirect bonding, including computer-aided design and computer-aided manufacturing (CAD/CAM)-assisted techniques, reduces failure rates compared with conventional chair-side direct bonding. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, PubMed, Scopus, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Cochrane Library, Dentistry & Oral Science Source, Google Scholar, ClinicalTrials.gov, and other trial registers were searched from inception to November 2025. Randomized controlled trials (RCTs) and prospective or retrospective cohort studies comparing indirect with direct bonding and reporting retainer failure were eligible. Two reviewers independently screened studies, extracted data, and assessed risk of bias using the Revised Cochrane Risk of Bias tool for randomized trials (RoB 2) for randomized trials and the Newcastle-Ottawa Scale (NOS) for cohort studies. Hazard ratios (HRs) for first failure were pooled using a random-effects model, and heterogeneity was quantified with the I² statistic. The protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO; registration number: CRD420251003540). Fifteen studies, including 13 RCTs and two cohort studies involving 1,481 patients, were included. The pooled analysis for mandibular retainers demonstrated a significantly higher failure risk in the direct bonding group (HR = 1.41, 95% CI 1.12-1.79, p = 0.004), with low heterogeneity (I² = 14%). For maxillary retainers, no statistically significant difference was observed between bonding techniques (HR = 1.28, 95% CI 0.90-1.84, p = 0.17). Overall risk of bias was low to moderate, with inadequate blinding being the most common limitation. Updated evidence indicates a significantly higher failure risk for directly bonded mandibular retainers compared with indirect bonding, while outcomes for maxillary retainers appear comparable between techniques. Indirect bonding may therefore offer improved mandibular retainer survival, although further well-controlled trials are required to confirm this effect.