Direct 3D-Printed Clear Aligners: Materials, Biomechanics, and Clinical Application—A Narrative Review

Direct three-dimensional (3D) printing of clear aligners has introduced distinct material, manufacturing, mechanical, and biological considerations. This narrative review aims to critically synthesize evidence on the materials science, additive-manufacturing technologies, processing variables, biomechanics, biological safety, and clinical performance of directly printed clear aligners, while comparing these findings with conventional thermoformed appliances and identifying the principal evidence gaps. Resin chemistry, printing parameters, appliance geometry, and post-processing collectively influence dimensional accuracy, mechanical behavior, and biological performance. Direct printing permits programmable spatial thickness and other design variables, and several laboratory studies report favorable geometric accuracy and distinct force-system characteristics; however, these findings are highly dependent on the material–printer–process combination and test conditions. Clinical evidence remains limited and heterogeneous, and patient-reported comfort and esthetic outcomes are sparsely reported. In conclusion, directly printed aligners provide important manufacturing and design capabilities, but current evidence does not establish uniform clinical superiority over thermoformed appliances. Standardized material characterization validated manufacturing protocols, prospective clinical studies, and longer-term aging investigations are required before the relative clinical performance of the two approaches can be determined.