Effect of phosphotungstic acid on surface properties and bond strength of resin cement to zirconia

Abstract Background The purpose of this in vitro study was to evaluate the effect of phosphotungstic acid pre-treatment on the surface properties of zirconium oxide ceramics and the microtensile bond strength (µTBS) between zirconium oxide ceramics and resin cement. Methods A total of 26 sintered zirconia blocks were randomly divided according to surface pre-treatment into four groups; group C (n = 6): no treatment (control), group S (n = 6): air-borne particle abrasion followed by Silano Pen treatment, group P1 (n = 7): Phosphotungstic acid 1gm/ 50 mL, and group P2 (n = 7): Phosphotungstic acid 2gm/50 mL. From each group, one zirconia block was examined using X-Ray Diffraction and scanning electron microscope. Also, one zirconia block from groups P1 and P2 was examined using Fourier-transform infrared spectroscopy. A total of 20 zirconia blocks were bonded to corresponding pre-constructed composite blocks using adhesive resin cement. Each zirconia-composite assembly was sectioned to obtain microbars of 1 mm2. A 20 microbars from each group were selected and aged (3500 thermocycles between 5°C and 55°C), then the µTBS test was performed using a universal testing machine (0.5 mm/min). The µTBS results was analyzed using one-way ANOVA test. Results Group P2 recorded the highest µTBS (23.824 ± 5.9 MPa) between all studied groups, while Group C recorded the lowest µTBS (12.19 ± 4.67 MPa). One-way ANOVA revealed a significant difference (P < 0.05) between all groups. The mode of failure was predominantly adhesive in Groups C, P1, and S, while group P2 showed cohesive and adhesive failures. Conclusions The phosphotungstic acid (2gm/50 mL) improved the bond strength of zirconia ceramics without phase transformation and composition changes.