Etching of Translucent Zirconia: Effect on Roughness and Flexural Strength

Objectives: There are currently no laboratory protocols available for etching zirconia. Our goal was to investigate the effect of various etching conditions on roughness parameters and flexural strength of translucent zirconia.
Methods: Disc-shaped specimens were sectioned from blanks (Zpex Smile, Tosoh USA), sintered at 1450°C/2h and randomly assigned to 7 groups (n=20). Roughness parameters were measured on polished specimens by atomic force microscopy in contact mode before and after treatment. Crystalline phases were investigated by x-ray diffraction (XRD). Two groups were left as-sintered as controls, one was tested in air, the other in water. All other treatment groups were tested in water. The same etchant based on a mix of acid solutions was used for all experiments. Two groups were etched in an ultrasonic bath at room temperature for either 10 or 20 minutes. Two groups were etched at 40°C with or without ultrasonic action. The last group was etched at 65°C for 10 minutes without ultrasonic action. The mean biaxial flexural strength was tested on a ball on ring-of-balls fixture.
Results: XRD revealed no change in surface crystalline phases after etching. R_ms roughness was significantly higher for all etched groups compared to polished controls, however, there were no significant differences in R_ms among etched groups. The mean biaxial flexural strength was highest for the control group tested in air (744.0±125.6MPa) and lowest for the control group tested in water (644.0±164.5MPa), but this difference was not statistically significant (p>0.05). There were no significant differences in mean biaxial flexural strength among etched groups (p>0.05).
Conclusions: Translucent zirconia was successfully etched at 25°C for 10 minutes using a specially designed mix of acidic agents. Etching led to an increase in roughness ranging between 3 and 6-fold, compared to polished specimens, but had no significant effect on mean flexural strength.