Comparative Analysis of Fit, Mechanical Properties, and Surface Characteristics in Subtractive and Additive Manufactured Zirconia Crowns

Background: This study aims to present different zirconia 3D printing materials and technologies, and to evaluate the fit, hardness and shear bond strength of crowns produced by additive (AM) and subtractive (SM) manufacturing methods, along with an assessment of surface characteristics. Methods: Zirconia crowns fabricated using one 5-axis SM and five AM approaches, including four different digital light processing (DLP) principles and one stereolithography (SLA) technique, each with varying slurry delivery and light-curing mechanisms. The marginal and internal gaps (axial, line angle, occlusal) between crowns and abutments were measured using the replica technique. Vickers hardness and shear bond strength between the crowns and resin cement was evaluated. Surface characteristics were analyzed with scanning electron microscopy (SEM) after printing and sandblasting. Results: Marginal fit analysis revealed that the marginal fit was 48.45 µm for the milling group and ranged from 42.83 to 81.95 µm for the additive manufacturing groups, with significant differences between groups (<0.001), but all within the clinical acceptance range (120 µm). Vickers hardness measurements showed the milling group had a hardness of 1473.87 HV, while the additive manufacturing groups ranged from 1441.94 to 1532.53 HV, with statistically significant differences (P<0.001). Shear bond strength measurements showed 7.97 MPa for the milling group and 6.97 to 8.97 MPa for the additive manufacturing groups, with no significant differences between groups. SEM analysis of crown surfaces revealed agglomerated zirconia particles, with various grooves observed after sandblasting. Conclusions: Zirconia crowns produced by both AM and SM methods demonstrated clinically acceptable marginal fit and ideal hardness above 1200 HV. Some additive manufacturing groups exhibited higher hardness and shear bond strength compared to the milling group. The diverse physical and mechanical properties of various zirconia 3D printing technologies suggest their selective use based on specific clinical situations.