Influence of Printing Orientation on the Flexural Strength of Different Light-Cured Resins Manufactured with Two 3D Printers: In Vitro Study.

Three-dimensional printing is rapidly growing in applied dentistry. In order to print faster, increase workflow, and minimize the consumption of resin material, it is important to use the right printer and the correct printing orientation. The objective of the present report is to analyze the flexural strength of specimens realized with two different dental light-curing resins (Keyguide and C&B) obtained from two different Digital Light Processing (DLP) 3D printers. Different printing orientations (0°, 45°, and 90°) were evaluated. 3D Builder, MeshMixer, RayWare, and Chitubox software were used to design the resin specimens. A total of 15 Keyguide and 15 C&B specimens in the shape of a rectangular parallelepiped, with dimensions of 2 mm × 2 mm × 25 mm, were obtained with the Sprintray Moonray S 3D printer, and the 15 Keyguide and 15 C&B specimens presented the same characteristics as those printed using the Moon Night printer. Prior to sample printing, a calibration protocol (tolerance test and dimensional accuracy test) was performed using RayWare software. This procedure allowed compensation for resin shrinkage or expansion, thus ensuring dimensional consistency in all printed samples. Each resin specimen, after printing and post-processing (MoonWash 2 and MoonLight 2), was subjected to a mechanical test with a universal testing machine. After breaking the specimen, the flexural strength values were recorded with computer software (Bluehill, Instron Corporation, Canton, MA, USA). According to the results obtained, the printing orientation of the specimens does not affect the flexural strength of the two materials examined. However, at the maximum load, some differences emerged for both materials printed with the Moon Night printer, depending on their build angle. Both light-cured resins tested had a higher maximum load resistance when printed with the newer Moon Night printer. This result could be due to the Moon Night printer's better construction characteristics compared to those of the Sprintray or to issues related to the dimensional calibration of the specimens.