Optimal sandblasting conditions for conventional-type yttria-stabilized tetragonal zirconia polycrystals

Objective: To assess the influence of sandblasting conditions applied to conventional-type yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) on surface roughness, phase transformation, and biaxial flexural strength. Methods: Commercially available Y-TZP (Lava Frame, 3M Dental Products) disks were used after sintering (specimen dimensions: 14 mm in diameter and 1.2 mm in thickness). The surfaces of specimens were ground, and then sandblast treatments were conducted at different pressures (0.20, 0.25, 0.30, 0.35 and 0.40 MPa) and distances (1, 5, 10 and 20 mm) with 50 μm alumina particles. Surface roughness measurements were performed and scanning electron microscopy (SEM) images were taken for surface characterizations. Phase transformation of Y-TZP was identified by X-ray diffraction (XRD). Biaxial flexural strength was measured using the piston-on-three-ball test. Results: The surface roughness increased significantly by increasing the sandblasting pressure, and microcracks were observed at high sandblasting pressure at 0.40 MPa. The shortest sandblasting distance (1 mm) was not effective to increase the surface roughness compared with other sandblasting distances. A tetragonal to monoclinic phase transformation was observed after grinding. The degree of the phase transformation tended to increase with sandblasting pressure, and significant effect was independent of the sandblasting distance. The biaxial flexural test showed improved mechanical strengths for the samples after sandblasting at 0.20–0.35 MPa, with the maximum strength at 0.25 MPa. Sandblasting at 0.40 MPa decreased the strength as compared with 0.25 MPa. Significance: The surface roughness increased with increasing the sandblasting pressure, whereas there was an optimal sandblasting pressure range to increase biaxial flexural strength of Y-TZP.