How stable are SLA-printed orthodontic models: a 6-month in vitro evaluation

Objectives: To evaluate dimensional stability of models fabricated using stereolithography (SLA) 3D printing. Materials and Methods: Twelve resin models were printed from a STL file using an SLA 3D printer, according to manufacturer specifications. Dimensional stability was assessed through 4752 total measurements across upper and lower arches at eight timepoints: immediately after printing (T0), 3 hours (T1), 6 hours (T2), 12 hours (T3), 24 hours (T4), 7 days (T5), 30 days (T6), and 6 months (T7). Measurements were made in triplicate with a 6-inch digital caliper: intermolar distance (central grooves and mesiobuccal cusp tips), intercanine distance (cusp tips), and mesiodistal tooth size (maximum crown width of 28 teeth). Linear mixed models (restricted maximum likelihood) were used to assess the effects of time, arch, side, measurement/tooth type, and their interactions, with dental models as a random effect. Bonferroni post hoc tests identified pairwise differences, and model assumptions were verified. Results: Significant effects of time were detected for transverse distances (P = .002) and mesiodistal tooth sizes (P < .001). These effects did not show significant interactions with arch, side, or type of measurement/tooth (P > .05). Both transverse widths and tooth sizes showed a statistically significant reduction starting from evaluation T5 (after 7 days of printing). Conclusions: Orthodontic models produced by SLA 3D printing maintain high dimensional accuracy in the short term, supporting their immediate use in clinical settings for aligner fabrication. However, delayed use or prolonged storage can lead to measurable distortions that may compromise appliance fit and treatment efficacy.