Comparative analysis of fit, mechanical properties, and surface characteristics in subtractive- and additive-manufactured zirconia crowns

Abstract Background This study presents different zirconia additive manufacturing (AM) materials and technologies while assessing the fit, hardness, and shear bond strength of crowns produced by AM and subtractive manufacturing (SM) methods, as well as their surface characteristics. Methods Zirconia crowns were fabricated using a 5-axis SM and five AM approaches, including four digital light processing principles and one stereolithography (SLA) technique. Each method utilized varying slurry delivery and light-curing mechanisms. The replica technique measured marginal and internal gaps (axial, line angle, and occlusal) between the crowns and abutments. The Vickers hardness and shear bond strength of crowns bonded with resin cement were assessed. Surface characteristics were analyzed with scanning electron microscopy (SEM) post-printing and sandblasting. The fit, hardness, and shear bond strength of crowns were manufactured through AM and SM methods. Sixty crowns were fabricated (10 per group). Statistical analysis was conducted using one-way analysis of variance (ANOVA) with Tukey post-hoc testing (α = 0.05). Results The marginal fits were 48.45 µm and 42.83 to 81.95 µm for the S and AM groups, respectively. Significant differences were observed between groups (< 0.001), although all measurements fell within the clinical acceptance range (120 µm). The Vickers hardness measurements revealed that the SM group had a hardness of 1473.87 HV, whereas those of the AM groups ranged from 1441.94 to 1532.53 HV, showing statistically significant differences ( P < 0.001). Shear bond strength measurements displayed 7.97 MPa and 6.97 to 8.97 MPa for the SM and AM groups, respectively, with no significant differences between the groups. SEM analysis of the crown surfaces revealed agglomerated zirconia particles with various grooves after sandblasting. Conclusions Zirconia crowns produced through the AM and SM methods demonstrated clinically acceptable marginal fit and ideal hardness exceeding 1200 HV. Some AM groups demonstrated higher hardness and shear bond strength than the SM group. The diverse physical and mechanical properties of various zirconia AM technologies suggest their selective use in specific clinical situations. Certain AM techniques, such as SLA spreading demonstrated comparable or even superior results to those of SM in terms of fit and hardness, indicating their potential as viable alternatives in clinical settings.