Fit analysis of 3D-printed versus thermoformed clear aligners for labial tooth movement using micro-CT: an in vitro study

This study examined the fit of 3D-printed and thermoformed clear aligners (CAs) on activated tooth models using micro-computed tomography (micro-CT). Three evaluation models were prepared: a passive model (P0.0) and two activated models (A0.3 and A0.5, where the upper right central incisor was labially displaced by 0.3 and 0.5 mm, respectively). Three CA material groups were tested: 3D-printed CAs made from TC-85 resin (3DP), thermoformed multi-layer CAs with a copolyester-elastomer combination (TM), and thermoformed single-layer CAs made of polyethylene terephthalate glycol (TS). CAs (n = 10) were fitted to corresponding models and scanned using micro-CT. Gap widths were measured at various tooth positions and measurement points in sagittal sections on all sides under passive and active states. Nonparametric analyses (Kruskal-Wallis tests with Bonferroni-corrected Mann-Whitney U post hoc comparisons) were performed with α = 0.05. The 3DP group exhibited significantly greater overall gap widths than the thermoformed groups (p < 0.001), with no significant effect of activation level (p = 0.350). In contrast, both the TM and TS groups showed significant increases in gap width with increasing activation (p < 0.001). Fit patterns differed by tooth position and measurement point, particularly in activated models, demonstrating distinct material-dependent adaptation behaviors.