Effect of print layer height on the accuracy and fit of the rapid-prototyped retainers

ABSTRACT Introduction: The purpose of this study was to comparatively evaluate the accuracy and fit of rapid-prototyped clear retainers printed at two different layer heights (100 µm and 50 µm) using a low-force stereolithography (LFS) 3D printer. Methods: Forty-two retainers were digitally designed using Maestro 3D Dental computer aided designing (CAD) software (AGE Solutions, Pisa, Italy) and rapid prototyped using an LFS printer (Formlabs Inc, Somerville, MA, USA). Half of the retainers (21) were printed at 50 µm layer height and other half at 100 µm. To assess the dimensional accuracy, linear measurements were taken from the 3D printed retainers using digital caliper (accurate to 0.01 mm) and from the digitally designed retainers using Maestro 3D Dental Studio software. The fit of the retainers was further evaluated with a scanning electron microscope. Accuracy was compared across three groups-digitally designed retainers, and those printed at 50 µm and 100 µm layer height using ANOVA/Kruskal‒Wallis tests. The reliability and internal consistency of the linear measurements were evaluated by the intraclass correlation coefficient (ICC with 95% CI) and Cronbach’s alpha, respectively. Paired t-tests were used to compare the fit of rapid prototyped retainers printed at 100 µm and 50 µm layer heights. Additionally, the printing time for each retainer was recorded. Results: There was no statistically significant difference (p value > 0.05) between the accuracy of 3D-printed retainers printed at 100 µm and 50 µm layer heights with a high reliability (ICC>0.9) and high internal consistency (Cronbach’s alpha>0.9). For comparative evaluation of the fit, no statistically significant difference (p>0.05) was observed among the retainers printed at 50 µm and 100 µm layer heights, except at the labio-gingival border and at the middle of the incisal edge of the central incisor. Time required for printing retainers at 50 µm is more than that of 100 µm layer height. Conclusion: Both rapid-prototyped retainers printed at 100 µm and 50 µm layer heights were found to be accurate for clinical use when compared to reference digital retainers with acceptable fit. As the time required for printing retainers at 100 µm is less than that of 50 µm layer height, it is better to use 100 µm layer height for rapid prototyping of the retainers.