Comparison of Shear Bond Strength of 3D-Printed and Milled Zirconia to Resin Cement: In Vitro Study

Objective: The purpose of this study was to evaluate the shear bond strength (SBS) to resin cement of yttria-stabilized tetragonal zirconia polycrystals materials produced by subtractive and additive manufacturing. Material and Methods: Disc-shaped zirconia specimens were fabricated using either subtractive manufacturing (MZ group; Upcera ST, Shenzhen Upcera, China) or additive manufacturing (3DZ group; 3DMix ZrO₂, 3DCeram Co., France). All samples were ground using silicon carbide abrasive paper and subsequently sandblasted with 50 μm aluminum oxide particles. Resin cement (Variolink Esthetic DC; Ivoclar Vivadent, Schaan, Liechtenstein) was then applied to the zirconia surfaces with a custom-made alumina mold and the SBS was subsequently assessed. Surface morphology was analyzed using a scanning electron microscope (SEM). An independent samples t-test was employed for statistical analysis, with a significance level set at α=0.05. Results: Significant differences in surface roughness and SBS values were observed between the MZ and 3DZ groups. The MZ group (19.18±4.05 MPa) exhibited a significantly higher SBS value compared to the 3DZ group (12.78±1.65 MPa) (p<0.001). No cohesive failure was observed in the 3DZ group, which is consistent with the lower SBS values. Conclusion: Manufacturing technique affected the surface roughness and resin bond strength of the zirconia materials. SEM images showed increased porosities of additively manufactured zirconia.