Effects of artificial aging on the biaxial flexural strength of Ce-TZP/Al2O3 and Y-TZP after various occlusal adjustments

The aim of this study was to determine the effect of aging on the biaxial flexural strength (BFS) of Ce-TZP/Al2O3 and Y-TZP after occlusal adjustment. NanoZr block (Ce-TZP/Al2O3 nanocomposite) and Katana zirconia block (Y-TZP) were prepared by milling with the aid of CAD/CAM into disk-shaped specimens. For each type of zirconia, 16 specimens were prepared without grinding for the control group (diameter of 16 mm and thickness of 1.20±0.05 mm, mean±SD), while 48 specimens were prepared for 3 experimental groups (n=16 each; 16 mm in diameter and 1.50±0.05 mm thick) with different types of surface grinding: superfine diamond bur (group I), zirconia stone bur (group II), and zirconia stone and fine polishing bur (group III). These specimens underwent an aging process in a steam autoclave for 5 h at 0.2 MPa and 134 °C, and then X-ray diffractometry was applied along with measurements of surface roughness and BFS. After occlusal adjustment, the monoclinic phase percentage increased in 3 experimental groups. Overall the increase was greater for Ce-TZP/Al2O3 than for Y-TZP. The Ra value showed similar changes for both types of zirconia. Following the aging process, Y-TZP showed a greater increase in the monoclinic phase percentage, but the change was not statistically significant. The Ra value showed similar changes in both types of zirconia, with no significant differences between before and after the aging process. The results of the BFS test showed that applying the aging process after grinding significantly increased the strength of both types of zirconia, with Ce-TZP/Al2O3 being significantly stronger than Y-TZP. The specimens treated by a superfine diamond bur exhibited the highest BFS in the four tested groups. Ce-TZP/Al2O3 had a higher BFS and greater resistance to low-temperature degradation than did Y-TZP.