Influence of a surface conditioner to pre-sintered zirconia on the biaxial flexural strength and phase transformation

Objectives. To assess the influence of a surface conditioner applied to pre-sintered yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) on the biaxial flexural strength and phase transformation. Methods. Conditioner-coated specimens (12 mm diameter x 0.8 mm thickness) were prepared by application of a slurry conditioner using a brush on pre-sintered Y-TZP discs, followed by sandblasting with 50-mu m Al2O3 after sintering (C-SB) or no further treatment (C-NT). The remaining conditioner-free specimens were subjected to sandblasting before sintering (NC-SB) or were maintained without treatment (NC-NT). Surface roughness measurements and scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray spectroscopy (SEM-EDX) were performed for surface characterizations. The phase transformation of Y-TZP was identified by X-ray diffraction (XRD), and the biaxial flexural strength was measured using the piston-on-three-ball test according to ISO 6872:2015. The data were analyzed using nonparametric KruskalWallis tests and Weibull distributions with the maximum likelihood estimation. Results. Sandblasting resulted in significantly rougher surfaces, irrespective of conditioner application. Conditioner layers were observed on surfaces in the C-NT and C-SB specimens. Monoclinic contents were present in a very small amount in the C-SB specimens. Both median biaxial flexural and characteristic strengths of all specimens exceeded ISO 6872:2015 requirements (Class 5: >800 MPa), except the NC-SB specimens which showed significantly the lowest strength (p < 0.001). Although no statistical difference was observed in Weibull modulus among the specimens (p = 0.598), the NC-SB specimens showed the highest. Significance. Surface conditioner application does not affect the biaxial flexural strength and phase stability of Y-TZP and can be considered practical for clinical use. (C) 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.