Transfer accuracy of three different virtually designed CAD/CAM retainers – baseline results of a randomized clinical trial

This study aimed to evaluate the immediate three-dimensional (3D) transfer accuracy of three virtually designed CAD/CAM lingual retainers fabricated from nickel–titanium (NiTi), titanium grade 5 (Ti5), and cobalt–chromium (CoCr). The investigation represents the baseline (T = 0) phase of a registered randomized clinical trial (DRKS00028974). Sixty patients (32 females, 28 males; mean age 19.2 ± 6.9 years) were randomly allocated to receive one of the three CAD/CAM retainers. Immediately after bonding (T0–T1), intraoral scans were superimposed with the digital design to determine deviations at predefined interproximal contact points. Non-parametric Kruskal–Wallis tests with Dunn’s post-hoc comparisons were applied (p ≤ 0.05). All 60 patients completed the baseline assessment. Transfer deviations were lowest in the NiTi group (0.17 mm, IQR 0.16–0.21), followed by Ti5 (0.37 mm, IQR 0.32–0.41) and CoCr (0.35 mm, IQR 0.30–0.40). NiTi showed significantly higher transfer accuracy compared with Ti5 (p < 0.001) and CoCr (p < 0.001). No significant difference was observed between Ti5 and CoCr (p > 0.999). No adverse events occurred. Laser-cut NiTi CAD/CAM retainers demonstrated significantly higher immediate transfer precision than milled Ti5 and CoCr retainers. These findings represent the baseline phase of the ongoing randomized clinical trial; subsequent analyses will determine whether such accuracy differences translate into clinically relevant stability outcomes. Accurate passive fit of CAD/CAM retainers is essential to prevent unwanted forces on teeth. Understanding material-dependent transfer deviations may improve digital bonding workflows and guide material selection in clinical orthodontics. DRKS00028974 (registered May 2022)