EFFECT OF AGING ON THE SHEAR BOND STRENGTH OF ZIRCONIA CERAMIC WITH DIFFERENT SURFACE TREATMENTS

Statement of the problem: Zirconia is an acid etching resistant ceramic and may cause difficulty in obtaining a safe bond with it. The aim of this study is to evaluate the effect of aging on the shear bond strength of zirconia ceramic after being subjected to different surface treatments.
Materials & Methods: Forty zirconia samples were constructed in the form of discs by copy milling. All the samples were 5mm in diameter and 1mm in thickness. The samples were divided into four groups according to the type of surface treatment they were subjected to, group1: control, group 2: subjected to etching using hydrofluoric acid 9% , group 3: sandblasting using 50µm Al2O3 particles and group 4 : silica coating using 50µm Al2O3 and 50 µm SiO2 particles. The samples were cemented on the occlusal surface of molar teeth using Rely XTM U200. Each group was further subdivided into two subgroups according to the type of test: shear bond strength before aging, shear bond strength after aging. The samples of the second subgroups were thermocycled (5– 55 °C/5,000 cycles) as aging procedure. Shear bond strength was measured. Data were tabulated and statistically analyzed using one-way analysis of variance (ANOVA).
Result: Results showed that the highest shear bond strength before aging was recorded by the silica coated samples while the lowest shear bond strength was recorded with the hydrofluoric acid etched samples. There was no statistical significant difference between all the tested different surface treated samples regarding shear bond strength before aging except the silica coated samples. After aging, the most affected samples with decrease in the shear bond strength were the control samples while there was no significant difference for the tested surface treatments.
Conclusion: Silica coating recorded the highest shear bond strength. Hydrofluoric acid etching and sandblasting are not reliable methods of surface treatment for production of safe and strong bond with zirconia. Aging has a significant effect on the control zirconia samples which showed decrease in the shear bond strength.