Effects of DLP printing orientation and postprocessing regimes on the properties of 3D printed denture bases

STATEMENT OF PROBLEM: The variety of recommended postprocessing techniques and printing parameters makes it challenging to determine the best approach to 3-dimensionally (3D) printed dentures. PURPOSE: The purpose of this in vitro study was to assess the effect of printing orientations (0, 45, and 90 degrees) and postprocessing treatments (ultraviolet UV, heat, or combination) on the mechanical and surface properties of 3D printed denture base resin. MATERIAL AND METHODS: Three-dimensionally printed denture base resin specimens were fabricated at 0-, 45-, and 90-degree printing orientations, followed by 4 postprocessing techniques (UV, Heat, UV+Heat, and control). Microhardness was assessed using a Vickers microhardness tester. Additionally, the flexural strength (FS) and modulus of elasticity (MoE) were analyzed using a 3-point bend test. Wettability was measured according to the sessile drop test. The fractured surfaces were observed under scanning electron microscopy (SEM). RESULTS: FS was significantly greater (P<.001) at a print orientation of 90 degrees (73.7 MPa) compared with 0 and 45 degrees (55.2 and 61.8 MPa). No significant difference in FS was found among postprocessing treatments (all complied with the International Organization for Standardization ISO requirements). The UV group had the highest MoE (up to 2061 MPa), followed by the heat-treated groups (up to 1412 MPa). The 45-degree print orientation showed the highest contact angle (CA) in almost all groups (CA=117.6±11.7), and UV led to higher hydrophilicity (CA=33.9±12.0). The effect of build orientation on the microhardness depended on the postprocessing technique with the highest value (23.4 ±1.3) achieved by UV postprocessing in combination with the 90-degree orientation. CONCLUSIONS: The optimal FS of 3D printed denture base resin is achieved when it is printed in a vertical orientation (90 degrees relative to the platform base). Thermal annealing as a postprocessing technique combined with UV can effectively enhance FS, induce favorable wettability, and reduce stiffness.