Trueness and precision of direct-printed and thermoformed clear aligners after artificial saliva exposure: A comparative in vitro study

INTRODUCTION: This study aimed to compare the effect of artificial saliva (AS) aging on the trueness and precision of direct-printed aligners vs thermoformed aligners. METHODS: Four types of aligners were manufactured from the same reference standard tessellation language (STL) file: using Duran Plus (n = 12) for thermoformed ones, and TC-85DAC (n = 12), Clear A (n = 12), or OD Clear TF (OC, n = 12) resins for direct-printed ones. A printed model was used for thermoformed aligners, whereas digital design models were generated for direct-printed aligners from the reference STL file. The samples were sprayed and scanned (Trios 3; 3 Shape, Copenhagen, Denmark) before and after aging in AS at 37°C for 24 hours, 7 days, and 14 days. STL files were imported into CloudCompare software (CloudCompare, 2.13.2 version, Paris, France) and superimposed on the design or digital model (trueness) or to each other within each group (precision) using a 7 reference-point algorithm. Two-way analysis of variance was performed to evaluate the influence of saliva aging and material type. RESULTS: A significant effect of the material type was observed with a lower trueness and precision for Duran Plus aligners compared with the 3 groups of direct-printed aligners. A significant effect of AS aging, with a decrease of trueness and precision, was also noted for both thermoformed and printed aligners. CONCLUSIONS: This in vitro study demonstrated that direct-printed aligners provided higher trueness and precision than thermoformed ones. Exposure to AS decreased the trueness and precision for both types. However, further studies are needed to validate the behaviors of direct-printed aligners clinically.