Effect of high-speed sintering on the microstructure, mechanical properties and ageing resistance of stereolithographic additive-manufactured zirconia

Digital light processing (DLP) demonstrates significant application potential in the fine printing of dental zirconia. However, its complicated print process and post-treatments, such as sintering, are time consuming and sensitive to technical details. Therefore, the feasibility of using a high-speed sintering (HS) method for the fabrication of DLP-based zirconia was investigated in this study. Zirconia samples fabricated using DLP and conventional subtractive manufacturing techniques were all sintered following the different protocols: HS and conventional sintering (CS). Then, the density, Vickers hardness, fracture toughness, surface micro-topography, phase assemblage, and ageing resistance were assessed. The results showed that samples fabricated using the HS technique presented moderate Vickers hardness, fracture toughness, and ageing sensitivity in comparison with the other groups of specimens; moreover, they exhibited moderate initial cubic phase content and average grain size. Conversely, specimens sintered using the CS protocol with a peak temperature of 1580 °C showed high ageing sensitivity and unbalanced mechanical properties. The DLP- and SM-fabricated specimens showed similar trends for the studied properties. Overall, sintering parameters can significantly affect the macro- and micro-properties of DLP specimens, and the proposed HS method showed potential for producing DLP-based zirconia that is acceptable for clinical applications.