Effect of printing technology and orientation on the accuracy of three-dimensional printed retainers.

Objectives: To evaluate the impact of printer technology and print orientation on the accuracy of directly printed retainers.

Materials and methods: Digital retainers were printed with two different printing technologies: digital light processing (DLP) and stereolithography (SLA), using two different orientations: 0° and 90°. After printing, the retainers (n = 40) were scanned using cone-beam computed tomography. The DICOM files were then converted into standard tessellation language (STL) files. Comparison of the printed retainers with a master file was done by superimposition using a three-dimensional (3D) best-fit tool in Geomagic software. A ±0.25 mm tolerance was set to detect differences between the superimposed files. Statistical analysis was conducted (Kruskal-Wallis and Wilcoxon-Mann-Whitney tests, with Bonferroni correction).

Results: The lowest median average deviation was observed for the DLP horizontally printed models (median, [interquartile range (IQR)] = 0.01 mm, [-0.01, 0.02]) followed by the SLA horizontally printed retainers (median, [IQR] = 0.05 mm, [0.03, 0.07]). The highest median inside the tolerance levels ratio was observed for the horizontally SLA printed retainers (median, [IQR] = 78.9%, [74.4, 82.4%]) followed by the horizontally DLP printed retainers (median, [IQR] = 78.2%, [74.5, 80.7%]).

Conclusions: Both technologies (DLP and SLA) showed 3D printed results compatible with orthodontic clinical needs. Printing orientation was more important than printer type regarding its accuracy. Additional studies are needed to evaluate the accuracy of direct printed appliances clinically.