Comparative Assessment of Dimensional Accuracy and Fit of Aligners Manufactured by Direct Printing and Thermoforming: An in vitro Study

Objective: The objective of the study was to compare the accuracy and fit of direct-printed and thermoformed aligners. Methods: The in vitro study included a pre-treatment scan as a reference model. Thirteen successive treatment stages were digitally planned and exported as STL files. Based on the treatment plan, 39 aligners were manufactured for three groups: Group 1, direct-printed aligners with TA-28 resin; Group 2, thermoformed polyurethane (PU) aligners; and Group 3, thermoformed polyethylene terephthalate glycol-modified (PET-G) aligners. All aligners were subsequently scanned, and the resulting STL files were superimposed on the baseline models. The dimensional accuracy and fit of the aligners were evaluated. The groups were compared using the Kruskal-Wallis test, followed by Dunn-Bonferroni post-hoc comparisons, with significance set at p≤0.05. Intra-rater and inter-rater reliability were evaluated via intraclass correlation coefficients. Results: Group 1 exhibited greater dimensional accuracy, as evidenced by the lowest mean deviation compared with Groups 2 and 3 (p<0.001). Pairwise comparisons indicated significant differences between Group 1 and Group 2 and between Group 1 and Group 3 (p<0.001); however, no significant difference was found between Groups 2 and 3 (p=0.489). Landmark-based deviation analysis indicated that Group 1 demonstrated the least deviation across all nine evaluated anatomical landmarks (p<0.001). Group 3 showed slightly greater deviations than Group 2 for most landmarks. Conclusion: Direct-printed aligners fabricated using TA-28 resin exhibited significantly higher dimensional accuracy and a better fit than thermoformed aligners manufactured from PU and PET-G.