Balancing strength and translucency: The role of microstructure in additive and subtractive dental zirconia

To elucidate the effect of microstructure on the strength and translucency of dental zirconia fabricated using additive (AM) and subtractive manufacturing (SM) technologies.

Twelve 3Y-TZP discs were fabricated using AM with two print orientations (0°: group AM0; 90°: group AM90; n = 6), and six via CAD/CAM machining (group SM). Density, composition, roughness, translucency parameter (TP), and biaxial flexural strength (σ) were evaluated. Fractographic analysis was conducted and defect size estimated. Based on the preliminary σ results (n = 6), the optimal print orientation was identified. Nine additional specimens were prepared for each of the AM90 and SM groups for Weibull σ analysis (n = 15). Differences in Weibull modulus were assessed via non-overlapping 95 % confidence intervals. An one-way ANOVA followed by Tukey's post-hoc test and an independent samples t-test were used (α = 0.05).

The relative density was consistent across all groups (>99 %). The tetragonal and cubic phases were comparable among groups, with proportions exceeding 82 wt% and 17 wt%, respectively. Group SM exhibited significantly higher roughness (1.18 µm) than AM0 (0.71 µm) and AM90 (0.51 µm). Group SM exhibited the highest TP values, while groups AM0 and AM90 had statistically similar TP values. AM0 showed the lowest σ value (411.60 ± 73.99 MPa) and larger defects. Groups AM90 and SM (n = 15) possessed comparable σ values (969.85 ± 123.13 MPa and 989.72 ± 107.78 MPa, respectively) (p = 0.6417) and Weibull moduli (9.17 and 10.62, respectively).

SM zirconia showed higher translucency and roughness, while defects reduced translucency in AM zirconia. Flexural strength was lower for AM0 due to larger defects, whereas AM90 matched SM strength.