Comparison of dimensional accuracy between direct-printed and thermoformed aligners

Objective: The purpose of this study was to evaluate and compare the dimensional accuracy between thermoformed and direct-printed aligners. Methods: Three types of aligners were manufactured from the same reference standard tessellation language (STL) file: thermoformed aligners were manufactured using Zendura FLXTM(n = 12) and Essix ACETM (n = 12), and direct-printed aligners were printed using Tera HarzTM TC-85DAP 3D Printer UV Resin (n = 12). The teeth were not manipulated with any tooth-moving software in this study. The samples were sprayed with an opaque scanning spray, scanned, imported to Geomagic (R) Control XTM metrology software, and superimposed on the reference STL file by using the best-fit alignment algorithm. Distances between the aligner meshes and the reference STL file were measured at nine anatomical landmarks. Results: Mean absolute discrepancies in the Zendura FLXTM aligners ranged from 0.076 +/- 0.057 mm to 0.260 +/- 0.089 mm and those in the Essix ACETM aligners ranged from 0.188 +/- 0.271 mm to 0.457 +/- 0.350 mm, while in the direct-printed aligners, they ranged from 0.079 +/- 0.054 mm to 0.224 +/- 0.041 mm. Root mean square values, representing the overall trueness, ranged from 0.209 +/- 0.094 mm for Essix ACETM, 0.188 +/- 0.074 mm for Zendura FLXTM, and 0.140 +/- 0.020 mm for the direct-printed aligners. Conclusions: This study showed greater trueness and precision of direct-printed aligners than thermoformed aligners.