Effect of Surface Treatment with Zirconium Dioxide Slurry on the Bond Strength of Resin Cement to Ultratranslucent Zirconia

SUMMARY This laboratory study aimed to evaluate the effects of zirconium dioxide (ZrO 2 ) slurry surface treatment on the bond strength of ultratranslucent zirconia to resin cement using different ceramic primers. The surface morphology was evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the interface was evaluated by SEM. Additionally, the phase composition was analyzed by X-ray diffraction (XRD). Specimens of zirconia (n=120) were obtained and divided into two groups according to the surface treatment: (1) airborne particle abrasion with 50-μm aluminum oxide (n=60) and (2) ZrO 2 slurry (n=60). The 60 specimens were then further divided into three groups (n=20) according to the ceramic primer application: no primer (NP), Monobond N (MB), and Clearfil ceramic primer (CP). Four resin cement cylinders were built on each ceramic specimen. Half of the specimens (n=10) were subjected to a microshear bond strength (μSBS) test after 24 hours of storage in distilled water, and the other half (n=10) were subjected to a μSBS test after thermocycling. Additional specimens were prepared for SEM, AFM, and XRD analyses. According to the Kruskal-Wallis and Student-Newman-Keuls post hoc tests, the μSBS values were significantly higher for MB and CP than for NP ( p <0.05), and there were no significant differences in μSBS for both surface treatments associated with MB and CP after 24 hours of storage ( p >0.05). Thermocycling significantly decreased the μSBS values for all specimens, especially for the NP groups and ZrO 2 slurry treatment groups, and gaps at the interface were observed by SEM. SEM and AFM analyses showed agglomerate-type irregularities on the ceramic surface for ZrO 2 slurry treatment. XRD spectra showed that ZrO 2 slurry did not cause phase transformation. It was concluded that ZrO 2 slurry promoted irregularities on the ultratranslucent zirconia surface, not causing phase transformation; moreover, the values of μSBS were comparable to those of airborne particle abrasion with aluminum oxide. However, neither surface treatment nor ceramic primer prevented the degradation of the interface.