Effect of build orientation in accuracy, flexural modulus, flexural strength, and microhardness of 3D-Printed resins for provisional restorations

Purpose: This study evaluated the effects of 3D-printing build orientation on accuracy, flexural modulus (FM), flexural strength (FS), and microhardness of selected, commercial 3D-printed provisional resins (3DRs). Material and methods: PMMA CAD/CAM provisional material (Vita Temp/Vita) served as Control. Four 3DRs (Cosmos-SLA/Yller, Cosmos-DLP/Yller, PriZma-Bioprov/Makertech, Nanolab/Wilcos) were used in three printing orientations (0°, 45°, and 90°). Printed samples were cleaned with isopropyl alcohol prior to post-curing in specific post-curing units. For each group, 20 bar-shaped samples (25 × 2x2 mm) and ten disc-shaped samples (15-mm diameter, 2.5-mm thick) were obtained. The dimensions of bar samples were measured and the mean percent errors were compared to the reference (digital) values to obtain “accuracy” (n = 20). Samples were then aged in distilled water at 37 °C and half were submitted to a three-point bend test in a universal testing machine after 24 h and the other half after 1 year (n = 10). Disc samples were polished prior to microhardness evaluation (n = 10). Microstructure and elemental composition of filler particles in the 3DRs were analyzed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) (n = 3). Accuracy and microhardness were submitted to two way-, and FM and FS to three way-ANOVA, followed by Tukey's tests. Results of experimental groups were compared to a milled PMMA Control using Dunnett's tests, and Student's t-tests compared FM and FS to Control at different aging periods (α = 0.05). Results: Except for Cosmos-DLP, the 90° orientation demonstrated the best overall accuracy in all dimensions evaluated. The overall accuracy of Cosmos-SLA was not significantly different from Control and higher than other 3DRs. The FM of all 3DRs was lower than Control, regardless of orientation and aging period. After 1 year of aging, FS of 45°-Cosmos-SLA and all orientations of PriZma were not different from Control, while 90°-Cosmos-SLA was higher. Build orientation had no influence on microhardness of the 3DRs: Nanolab was the only resin harder than Control. Very few nanometric spherical filler particles were found in Cosmos-SLA, Cosmos-DLP, and PriZma, while Nanolab presented higher number of particles having irregular shapes and sizes. Conclusions: In general, although build orientation did not influence microhardness results, the 90° -orientation resulted in the best overall accuracy for most 3DRs. After 1-year water storage, Cosmos-SLA printed vertically showed the highest FS, while the PMMA Control obtained the highest FM for both aging periods.