Thirty-Day Thermomechanical Ageing of 3D-Printed and Thermoformed Orthodontic Aligners: A Comparative Force Analysis

OBJECTIVES: To investigate the effect of thermomechanical ageing on the force system of three-dimensional (3D)-printed orthodontic aligners compared with conventional thermoformed aligners and to evaluate the thickness characteristics of both aligner types. MATERIALS AND METHODS: Ten aligners were fabricated from 3D-printed Tera Harz TC-85 resin, and 10 from thermoformed Zendura FLX (ZF). All aligners underwent thermomechanical ageing for up to 30 days. Forces transmitted to the maxillary right central incisor (Tooth 11) in a resin model were measured before ageing (Day 0) and after thermomechanical ageing (Days 2, 7, and 30) using Fuji pressure-sensitive films to assess contact normal forces and an orthodontic measurement and simulation system (OMSS) to measure resultant 3D forces. Aligner thickness was evaluated using a digital caliper and microcomputed tomography. RESULTS: TC-85 aligners generated significantly higher initial normal contact forces than ZF aligners (149.7 ± 25.6 N vs 69.8 ± 9.0 N). Both materials exhibited significant force decay following thermomechanical ageing. Orthodontic measurement and simulation system analysis demonstrated comparable preageing resultant forces for both materials (0.1 ± 0.07 N to 0.5 ± 0.09 N), with no statistically significant difference in facial force components at baseline. Facial forces remained relatively stable over time, whereas lingual resultant forces decreased significantly. Thickness analysis demonstrated pronounced thinning in ZF aligners (≈0.5 ± 0.05 mm) and thickening in TC-85 aligners (≈1.0 ± 0.09 mm). CONCLUSIONS: TC-85 aligners produced higher initial normal contact forces than ZF aligners, consistent with their greater postmanufacturing thickness and reported improved adaptation to the dental model; however, both materials exhibited force decay over time. Although preageing resultant forces were comparable between materials, the reduction in lingual resultant forces may adversely affect the predictability of tooth movement during prolonged aligner wear. CLINICAL SIGNIFICANCE: The current findings underscore the significant impact of aligner material, thickness, and manufacturing method on force stability and consistency in clear aligner therapy.