Effects of build orientation and manufacturing system characteristics in digital light processing additive manufacturing on the properties of zirconia.

OBJECTIVE: To evaluate the influence of build orientation and manufacturing system characteristics in digital light processing (DLP) additive manufacturing on the surface roughness, internal structure, and biaxial flexural strength of 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP). METHODS: Disc-shaped specimens (15 × 1 mm) were fabricated using subtractive manufacturing (SM) and two DLP-based systems with different system characteristics. Additively manufactured specimens were produced at 0°, 45°, and 90° orientations. Surface roughness (Ra) was measured using confocal laser scanning microscopy, internal structure was evaluated using microcomputed tomography (micro-CT), and biaxial flexural strength was determined using the piston-on-three-ball method in accordance with ISO 6872:2015. RESULTS: The 0° groups (LAM0 and AM0) and the SM control exhibited low surface roughness and high flexural strength (∼900-1100 MPa), with no significant differences. The 45° groups (LAM45 and AM45) and the LAM90 group exhibited increased roughness and orientation-dependent surface features, along with reduced strength (∼450-520 MPa). Notably, AM90 was an exception to this orientation-dependent pattern: despite its 90° build angle, AM90 retained high strength (922.1 ± 77.1 MPa) and a high Weibull modulus (m = 13.87), comparable to the 0° and SM groups, whereas LAM90 exhibited both reduced strength (455.7 ± 185.6 MPa) and low reliability (m = 3.20). Micro-CT revealed layer-related structural features associated with build orientation. This divergence between AM90 and LAM90 indicates that, at the 90° orientation, manufacturing system-level characteristics can outweigh the expected orientation-dependent reduction in mechanical performance. CONCLUSION: Build orientation significantly influences the surface characteristics, internal structure, and mechanical performance of DLP-fabricated zirconia. Differences between manufacturing systems may also affect outcomes, particularly under vertical (90°) build conditions; however, because the two DLP systems compared here differed simultaneously in platform size, projection resolution, and pixel pitch, these effects cannot be attributed to a single parameter and should be interpreted as reflecting combined, system-level characteristics. CLINICAL RELEVANCE: These findings suggest manufacturing-process considerations for build orientation selection in DLP-based zirconia fabrication, and indicate that system-specific characteristics may also warrant consideration. As this study used simplified disc specimens, direct clinical extrapolation should be made with caution pending validation in clinically relevant geometries.