Abstract Introduction To compare post-treatment stability and oral health–related quality of life (OHRQoL) in young adults wearing thermoformed retainers (TFR) versus direct 3D-printed retainers (3DPR) over a six-month part-time retention period. Materials and methods This single-centre, two-arm parallel randomised controlled trial allocated 30 debonded orthodontic patients (≥ 18 years) to either TFR (Erkodur PETG, 1.0 mm) or 3DPR (NextDent Ortho Flex, 0.75 mm) in a 1:1 ratio. All retainers were worn part-time (8–12 h/day). Digital intraoral scans were obtained at baseline (T0) and six months (T2) using Trios 3, and post-treatment stability was assessed digitally using Little’s Irregularity Index, intercanine width, intermolar width, arch length, overjet, and overbite. OHRQoL was evaluated at both time points using the OHIP-14(M) questionnaire. Non-parametric tests were applied following the Shapiro–Wilk assessment, and analyses were conducted using an intention-to-treat approach. Results One dropout in the 3DPR group at T2. At T2, no significant between-group differences were found in Little’s Irregularity Index, intercanine width, intermolar width, arch length, or overjet ( p > 0.05). Overbite values were statistically higher in the TFR group at T2 ( p 0.05). Total OHIP-14(M) scores improved significantly from T0 to T2 in both groups (TFR p = 0.016; 3DPR p = 0.013), with no significant between-group differences at either time point ( p > 0.05). A small but significant difference was observed in the psychological disability domain at T2, with slightly higher scores in the 3DPR group ( p = 0.020). No harm was observed. Conclusions TFR and 3DPR demonstrated comparable post-treatment stability and similar improvements in OHRQoL after six months of part-time wear. Registration ClinicalTrials.gov (Identifier NCT05968625). Protocol: The protocol was published before trial commencement
Boo et al. (Tue,) studied this question.