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Self-glazed zirconia is a novel dental material fabricated with a combination of subtractive and additive manufacturing techniques. However, how the marginal and internal fit of these restorations compare with conventionally fabricated zirconia is unclear. The purpose of this in vitro study was to evaluate the marginal and internal fit and internal accuracy of single crowns made from self-glazed zirconia compared with those made from milled zirconia. A metal die was scanned, and a crown was designed using a computer-aided-design program. The computer-aided-manufacturing milling method (conventional technique) was used to produce 10 zirconia crowns, and additive manufacturing was used to produce 10 self-glazed zirconia crowns. Internal and marginal fit measurements were made by using the silicone replica method; marginal fit was also measured by using the direct-view technique. An independent t test was performed to compare both types of crowns and test the null hypothesis (α=.05). For the occlusal, internal, and total mean distances, significant differences were found between self-glazed and milled zirconia crowns (P <.001). With the direct-view technique, a significant difference (P =.004) between the 2 techniques was found in the marginal area. The accuracy for the axial and occlusal areas combined for self-glazed and milled zirconia was 27 μm and 49 μm, respectively. Both techniques produced crowns with clinically acceptable marginal and internal fit. The self-glazed zirconia crowns had higher accuracy of internal fit than milled zirconia crowns. [ABSTRACT FROM AUTHOR]

To minimize technical complications, implant-supported fixed dental prostheses must fit well. The fit of complete-arch veneered zirconia frameworks has not been fully evaluated. The purpose of this in vitro study was to evaluate the fit of screw-retained zirconia implant-supported complete-arch maxillary frameworks for fixed dental prostheses before and after porcelain veneering. Ten stone casts simulating an edentulous maxilla and provided with 6 abutment analogs were produced. For each stone cast, 1 zirconia framework was fabricated by computer-aided design and computer-aided manufacturing. The fit was analyzed by using a coordinate measuring machine in 3 dimensions (x, y, and z axes) using best fit by virtual matching of center point coordinates before and after porcelain veneering. Also, the horizontal distances between implant position pairs P1–P6, P2–P5, and P3–P4 were measured. Furthermore, an optical microscope was used to evaluate vertical fit at the terminal abutments after porcelain veneering. Before the porcelain veneering procedure, the frameworks had a mean horizontal misfit of 27.7 μm in the x-axis and 12.0 μm in the y-axis. In the vertical dimension (z-axis), the mean misfit was 2.4 μm and the mean 3D misfit value was 32.3 μm before veneering. Porcelain veneering increased the mean misfit by 0.2 μm in the horizontal plane (x and y axes), 0.4 μm in the vertical plane, and 0.4 μm in 3D; the difference before and after veneering was not statistically significant (P >.05). The mean ±standard deviation vertical misfit at the terminal abutments was 9.2 ±2.9 μm, optically recorded after porcelain veneering. The measured horizontal distances between implant position pairs P1–P6, P2–P5, and P3–P4 increased to 0.9 μm, 2.0 μm, and 1.9 μm, respectively, after porcelain veneering. The difference for the implant position pair P2–P5 was statistically significant (P <.05). Screw-retained zirconia implant-supported complete-arch maxillary frameworks for fixed dental prostheses have a fit well within the range of 30 μm in the horizontal plane and 10 μm in the vertical plane. The porcelain veneering procedure did not affect the fit of the frameworks. [ABSTRACT FROM AUTHOR]

Monolithic dental prostheses made of 3–6 mol% yttria-stabilized zirconia (3–6YSZ) have gained popularity owing to their improved material properties and semi-automated fabrication processes. In this study, we aimed to evaluate the influence of mechanical surface treatments, such as polishing, grinding, and sandblasting, on the residual stress of 3–6YSZ used for monolithic prostheses in association with crystalline phase transformation. Plate specimens were prepared from five dental zirconia blocks: Aadva Zirconia ST (3YSZ), Aadva Zirconia NT (6YSZ), Katana HT (4YSZ), Katana STML (5YSZ), and Katana UTML (6YSZ). The specimens were either polished using 1, 3, or 9 μm diamond suspensions, ground using 15, 35, or 55 μm diamond discs, or sandblasted at 0.2, 0.3, or 0.4 MPa. The residual stress, crystalline phase, and hardness were analyzed using the cosα method, X-ray diffraction (XRD), and Vickers hardness test, respectively. Additionally, we analyzed the residual stress on the surfaces of monolithic zirconia crowns (MZCs) made of 4YSZ, 5YSZ, and 6YSZ, which were processed using clinically relevant procedures, including manual grinding, followed by polishing using a dental electric motor on the external surface, and sandblasting on the internal surface. Residual stress analysis demonstrated that grinding and sandblasting, particularly the latter, resulted in the generation of compressive residual stress on the surfaces of the plate specimens. XRD revealed that the ground and sandblasted specimens contained a larger amount of the rhombohedral phase than that of the polished specimens, which may be a cause of the residual stress. Sandblasting significantly increased the Vickers hardness compared to polishing, which may possibly be due to the generation of compressive residual stress. In the case of MZCs, compressive residual stress was detected not only on the sandblasted surface, but also on the polished surface. The difference in the residual stress between the plate and crown specimens may be related to the force applied during the automated and manual grinding and polishing procedures. Further studies are required to elucidate the effects of the compressive residual stress on the clinical performance of MZCs. [Display omitted] • Influence of polishing, grinding, and sandblasting on 3–6YZ was studied. • The residual stress, crystalline phase, and hardness were analyzed. • Sandblasting resulted in compressive residual stress on the surface. • Ground and sandblasted specimens contained more rhombohedral phase. • Sandblasting increased the Vickers hardness compared to polishing. [ABSTRACT FROM AUTHOR]

Monolithic dental prostheses fabricated from 5 mol% yttria-stabilized zirconia (5YZ) have been developed to improve the translucency of conventional 3 mol% yttria-stabilized zirconia. In this study, we aimed to evaluate the influence of airborne-particle abrasion (APA) and low-temperature degradation (LTD) on the mechanical properties of 5YZ in association with the crystalline phase transformation. In total, 120 disc-shaped specimens of two brands of 5YZ (Lava Esthetic and Katana UTML) were prepared. The specimens were divided into four groups (n = 15 for each group): (i) control, (ii) APA, (iii) LTD, and (iv) APA + LTD groups. APA was performed with 50 μm alumina particles, and LTD was induced by autoclaving at 134 °C for 50 h. The biaxial flexural strength of the specimens was assessed using a piston-on-three-ball test according to ISO 6872:2015, and Vickers hardness was determined using a microhardness tester. The crystalline phase was analyzed by the Rietveld refinement of X-ray diffraction patterns. APA significantly increased the flexural strength of the Lava Esthetic specimens, whereas LTD hardly affected the strength of both materials. APA and APA + LTD significantly increased the Vickers hardness of both materials. According to Rietveld analysis, the pseudocubic phase was predominant in both materials, i.e., 66 mass% and 81 mass% in the Lava Esthetic and Katana UTML specimens, respectively. APA induced the rhombohedral phase at approximately 37 mass% in both materials, while LTD induced the monoclinic phase at 2.8 mass% in the Lava Esthetic specimens and 0.9 mass% in the Katana UTML specimens. APA + LTD weakly affected the amount of the rhombohedral phase but slightly increased the amount of the monoclinic phase. These findings suggest that APA may improve the mechanical properties of 5YZ, particularly hardness, via the generation of the rhombohedral phase. In contrast, the influence of LTD on the mechanical and microstructural properties of 5YZ was limited. [Display omitted] • We tested properties of two dental zirconia products stabilized with >5 mol% yttria. • Pseudocubic phase was predominant in both materials. • Airborne-particle abrasion (APA) and low-temperature degradation (LTD) were applied. • APA and APA + LTD significantly increased Vickers hardness of both materials. • APA and APA + LTD induced the rhombohedral phase at about mass 37% in both materials. [ABSTRACT FROM AUTHOR]