Influence of printing orientation on the flexural strength and flexural modulus of a 3D-printed restorative composite resin

Three-dimensional (3D) printing resins have gained popularity in dentistry due to their practicality, precision, and reproducibility. However, variations in chemical composition and manufacturing protocols may affect their mechanical properties, and evaluation methods often yield heterogeneous results. This study aimed to assess whether printing orientation influences the flexural strength and flexural modulus of a 3D-printed restorative composite. One hundred 3D-printed bar-shaped specimens (2 × 2 × 25 mm) were initially fabricated at five orientations (0°, 22.5°, 45°, 67.5°, and 90°) using an LCD printer, with 20 specimens allocated to each orientation. Thirty bar-shaped specimens fabricated from a conventional light-cured composite resin served as a reference control. All valid specimens underwent three-point bending testing. No statistically significant differences in flexural strength or flexural modulus were observed among the 3D-printed groups with different printing orientations. The conventional composite resin control group showed higher mean values for both properties than the printed groups. Within the limitations of this in vitro study, no statistically significant differences in flexural strength or flexural modulus were detected among the tested printing orientations. The conventional composite resin showed higher mean values than the 3D-printed groups. For the tested restorative resin, LCD printer, post-processing protocol, and standardized ISO bar-shaped specimens, printing orientation did not produce statistically significant differences in the evaluated flexural properties. These findings should not be directly extrapolated to clinically shaped restorations or interpreted as proof of equivalence among printing orientations.