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); however, the difference was not clinically significant. Changes in post-treatment stability from T0 to T2 (ΔT2-T0) did not differ significantly between groups (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.