Transfer accuracy and chairside efficiency of rigid- and flexible-printed versus double vacuum-formed lingual indirect bonding trays: a prospective cohort study

This study aimed to compare bracket-transfer accuracy, chairside time, and early bond failure among rigid 3D-printed (RP), flexible 3D-printed (FP), and double vacuum-formed (DV) lingual indirect bonding trays. Thirty-three consecutive adults (n = 11) were prospectively enrolled. After virtual setup and tray fabrication, brackets were bonded following a standard protocol. Post-bonding intraoral scans were superimposed on the planned setup, and six positional discrepancies (mesial-distal, in-out, height, rotation, tip, and torque) were quantified for each tooth. One-sample Wilcoxon signed-rank tests compared observed errors with clinical limits (0.5 mm, 2.0°). Kruskal-Wallis and pairwise Mann-Whitney U tests assessed inter-tray differences. 818 brackets (RP = 280; FP = 259; DV = 279) were analysed. Median translational errors were ≤ 0.10 mm for RP/FP and ≤ 0.07 mm for DV; all were below the 0.5 mm threshold (P < 0.001). Median pure-rotation errors remained ≤ 1.0° for all trays. Tip met the 2.0° limit except for FP in the lower-anterior segment (P = 0.184). Torque rarely met the limit, with RP-upper-anterior being the sole exception. DV outperformed RP and FP in mesial-distal accuracy across upper and lower-posterior regions (P ≤ 0.002). All tray systems delivered clinically acceptable translational accuracy, but DV trays provided the most precise mesial-distal positioning. Selecting a tray architecture that balances rigidity and elasticity can markedly improve chairside efficiency without compromising bracket-placement accuracy.