Force system of 3D-printed orthodontic aligners made of shape memory polymers: an in vitro study

Abstract

This study aimed to report forces and moments delivered by 3D-printed aligners. Tera Harz TC-85 resin and Zendura FLX (ZF) thermoformed sheets (0.76 mm) were used. Rectangular strip specimens (50 × 10 × 0.6 mm) were produced for a three-point bending test (3PB) at different temperatures. Full anatomical aligners were produced for 3D force measurements on different teeth and directions at 37 °C, using a custom-made device. ZF exhibited flexural forces between 1.7 and 2.3 N, while TC-85 from 0.3 N to 2.7 N, with temperature affecting TC-85 more significantly. At lower temperatures, TC-85 was stiffer than ZF, but at higher temperatures, it became less rigid. The 3D-force measurements indicated comparable values for both materials. Force ranged from 0.3–1.7 N and moment from 4.8–9.4 Nmm. The study concluded that TC-85 3D-printed aligners deliver biologically compatible forces for orthodontic movement and offer better control over thickness. Highlights The 3D-printed Tera Harz TC-85 resin revolutionises aligner production. Tera Harz TC-85 aligners generate forces within the orthodontic accepted range. Shape recovery of TC-85 can enable adaptability and larger incremental step size. The 3D printing offers greater control over aligner design and thickness.