The effect of autoclave aging with different surface polishing systems on the surface properties, phase transformation and fracture strength of monolithic zirconium

Aim: This study was carried out to evaluate the effect of autoclave aging with different surface polishing systems on the surface properties, phase transformation and fracture strength of monolithic zirconium. Material and Methods: The 48 samples of Prettau Zirkonzahn monolithic block were prepared as discs with a diameter of 15 mm and a thickness of 1.2 mm, in accordance with international standards (ISO 6872) with Computer Aided Design / Computer Aided Manufacturing (CAD / CAM). The sample thicknesses were checked with a digital caliper. After sintering, the samples were allowed to cool at room temperature. Glaze powder and liquid mixed in accordance with the manufacturer's instructions were applied to all samples in a thin layer and fired using the Ivoclar Vivadent Programat P300 oven. Examples; control, Meisinger polish kit and OptraFine polish kit applied. No procedure was applied to 16 samples in the control group after glazing. The remaining samples were etched at 20000 rpm in the form of a back and forth sweeping motion under water cooling with an aerotor for 20 seconds by the same researcher with blue banded burs containing 100 µm diamond particles recommended for zirconium restorations. The 16 samples that were etched were polished with the Meisinger polish kit, and the remaining 16 samples were polished with the OptraFine polish kit. After polishing, each group was divided into two groups (N=8). The samples in one group were kept in distilled water for 24 hours, and the samples in the other group were aged in a steam autoclave at 134°C under 2 bar pressure for five hours in accordance with the ISO 13356 standard. The surface of all samples was evaluated with a profilometer. Then, their microhardness was analyzed by Vickers microhardness test, three-dimensional surface images were analyzed by Atomic Force Microscope (AFM), surface properties were analyzed by Scanning Electron Microscopy (SEM), crystal structures and phase transformations were analyzed by X-Ray Diffractometry (XRD). Finally, the fracture strengths were evaluated with the piston technique on three balls. Results: The effects of surface polishing applied on monolithic zirconium specimens on surface roughness, microhardness and fracture strength were very significant (p<0.01), and the effect on phase transformation was significant (p<0.05). The highest surface roughness was detected in the group that applied the Meisinger polish kit. The effect of autoclave aging on the phase transformation was significant (p<0.05), while the effect on surface roughness, microhardness and fracture strength was statistically insignificant (p>0.05). Conclusions: It was determined that the surface polishing systems applied to the monolithic zirconium samples affected the surface properties, phase transformation and fracture strength, while the autoclave aging process did not affect the surface properties and fracture strength, but affected the phase transformation. Key Words: Monolithic zirconium, surface polishing systems, autoclave aging, surface properties, phase transformation, fracture strength