Objectives: The purpose of this study is to investigate the effect of grinding, polishing, sandblasting, and sintering on biaxial flexural strength and the microstructure of two different commercial types of zirconia ceramics. Methods: Two types of zirconia ceramics were used in this study, YZ blocks from Vita and LAVA blocks from 3M ESPE. Disc-shaped specimens were fabricated and randomly divided into six groups (n=10); Sintered (Control), Ground, Polished, Sandblasted, Ground/Fired, and Simulated veneer firing (four cycles). Biaxial flexural strength was tested using an Instron at a crosshead speed of 0.5 mm/min. The microstructure was examined using an SEM with EDS for elemental analysis. The weight% of the monoclinic phase was determined using X-Ray diffractometry. The statistical analysis was performed using ANOVA and Tukey multiple comparison (p<0.05). Results: There is no significant difference between YZ and LAVA in the mean strength among all the groups. The “sandblasted” and the “polished” groups in both materials show a higher mean strength than that of the “sintered” (control) group (p<0.05).  “Ground and fired” showed the lowest mean strength in both materials (p<0.05). There is no significant difference in the mean strength between the “Simulated veneer firing” and the “sintered” group. “Sandblasted” group show the highest weight percent of monoclinic phase. In all groups that were subjected to a firing cycle the monoclinic phase was negligible. Biaxial Flexure Strength (MPa)

Material	Sintered	Ground	Polished	Sandblasted	Ground/Fired	Veneer Fired
YZ	812.39	810.58	979.24	1081.28	652.21	772.99
LAVA	842.07	808.54	1004.27	1133.22	632.07	840.49

 

Conclusion: Sandblasting and polishing increases the mean strength values of both materials tested. A simulated firing cycle after grinding led to significant degradation in strength values.