Biaxial flexural strength of Ce-TZP/Al2O3 and Y-TZP according to grinding methods

Abstract

Purpose: The aim of this study was to determine the effects of grinding used in occlusal adjustment usually on the biaxial flexural strength (BFS) of Ce-TZP/Al2O3 and Y-TZP. Materials & Methods: NanoZr block (Ce-TZP/Al2O3 nanocomposite) and Katana zirconia block (Y-TZP) were prepared by milling with 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 process resulted in the specimens having an overall thickness of 1.20 ± 0.05 mm: 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 hours at 0.2 MPa and 134℃, and then X-ray diffractometry was applied along with measurements of surface roughness and BFS Results: After grinding, the monoclinic phase percentage increased in 3 experimental groups. It increased in Ce-TZP/Al2O3 and Y-TZP in following order respectively: group I, group II, group III and group III, group I, group II. The increase was greater for Ce-TZP/Al2O3 than for Y-TZP. The Ra value showed similar changes for both types of zirconia. Ra value of group II increased compared to control group whereas that of group I and III decreased. 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. In terms of groups, the strength increased in order of control, group II, group III, and group I. Conclusion: The grinding promotes an increase in the t-m transformation and increases the strength of zirconia. The specimens processed using the superfine diamond bur exhibited the highest BFS, and Ce-TZP/Al2O3 had a higher BFS and greater resistance to low temperature degradation (LTD) than did Y-TZP.