The effectiveness, durability and patient impacts associated with thermoformed vs direct 3D-printed retainers over a 6-month period: A randomised controlled trial / Boo Hui Shan

Boo , Hui Shan (2025) The effectiveness, durability and patient impacts associated with thermoformed vs direct 3D-printed retainers over a 6-month period: A randomised controlled trial / Boo Hui Shan. Masters thesis, Universiti Malaya.

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Abstract

Title: The Effectiveness, Durability And Patient Impacts Associated With Thermoformed Vs Direct 3d-Printed Retainers Over A 6-Month Period: A Randomised Controlled Trial Following orthodontic treatment, retainer wear is essential to prevent relapse. Thermoformed retainers (TFR) are a popular choice among patients. Advancements in 3D printing technology has enabled the fabrication of direct 3D printed retainers (3DPR), offering a more efficient and eco-friendlier alternative. This study aimed to evaluate and compare changes in post-treatment stability, retainer thickness, mechanical properties, and patients' Oral Health-Related Quality of Life (OHRQoL) between TFR versus 3DPR over six months. This is a prospective, single-centre, two-arm parallel, open-label randomised controlled trial. Thirty subjects (4 males, 26 females, mean age 22.70± 4.30 years old) were recruited and allocated equally in a 1:1 ratio to either the TFR (Erkodur, 1.0mm foil) or 3DPR (NextDent Ortho Flex resin, designed with 0.75mm thickness) groups. After debond, retainers were worn part-time at night. Intraoral scans were conducted at three time points: baseline (T0), at three months (T1), and at six months (T2). Little’s Irregularity Index (LII), intercanine width (ICW), intermolar width (IMW), arch length (AL), overjet (OJ) and overbite (OB) were measured digitally. The thickness of the retainers was measured at various locations using an electronic digital thickness gauge at T0 and T2. Mechanical properties were assessed by comparing five used retainers (T2) with unused counterparts from each group. Participants completed the OHIP-14(M) questionnaire at all time points. Intention-to-treat protocol was employed, and the trial was registered with ClinicalTrials.gov (NCT05968625). Result showed one dropout occurred in the 3DPR group. There were no significant differences in post-treatment stability between both groups in LII, ICW, IMW, AL and OJ except for OB across all time points. Comparing the median differences in post-treatment stability between TFR and 3DPR at the initial 3-month (T0-T1), subsequent 3-month (T1-T2), and the overall 6-month (T0-T2) periods, revealed no significant differences. The TFR was significantly thinner than the 3DPR at both T0 and T2. The median reduction in thickness after six months was not significant for most landmarks, except for the mesiopalatal cusp and the average reduction of the upper retainer. In terms of mechanical properties, upper and lower TFR exhibited significantly greater Martens hardness, indentation modulus, and indentation hardness at T0 and T2, along with a higher elastic index at T2. After six months, TFR exhibited an increase in the mean differences across all mechanical property parameters, whereas 3DPR demonstrated a reduction. Significant mean differences were found between groups for all parameters of mechanical properties. OHIP-14 scores showed no significant median differences between groups, except for psychological disability domain at T2. Both groups reported improvements in OHRQoL with TFR showing significant improvements in functional limitation, psychological discomfort, and total OHIP-14 score, while the 3DPR group showed significant improvements in physical pain, psychological discomfort, and total OHIP-14 score. No harm was observed. In conclusion, both TFR and 3DPR showed comparable post-treatment stability after six months of part-time wear. Thickness reductions were clinically insignificant for both. TFR demonstrated increased mechanical properties, suggesting better durability compared to 3DPR. Both groups adapted well to their retainers, leading to improved OHRQoL.

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