Influence of phosphoric acid surface treatment on shear bond strength durability of resin cement to zirconia-based ceramic conditioned with different primers

Abstract

BACKGROUND: Phosphoric acid treatment has been reported to be relevant for zirconia cleaning after contamination. However, its interaction with different primers is not well known and needs to be investigated. OBJECTIVES: To compare the shear bond strengths (SBS) of resin cement to Y-TZP after phosphoric acid pretreatment and different chemical conditioning protocols, and to test the durability of SBSs after long term storage and thermal cycling conditions. To investigate the effect of phosphoric acid 75 on the surface roughness of a yttrium-stabilized tetragonal zirconia polycrystal ceramic (Y-TZP). METHODS: Sixty bars of zirconia (30 X 5 X 2 mm) were polished and glued to acrylic tubes. Each bar received 3 different surface treatments (control, phosphoric acid and air-abrasion). The bars were randomly assigned into five groups according to different primers applied (No primer, Clearfil ceramic primer, Monobond Plus, Z-prime plus and AZ primer). After that, resin cement was mixed, injected into a mold, and light cured. The specimens were tested in shear on a universal testing machine. Half of the specimens were tested after 24 h water storage and the other half were tested after 90 days of water storage and thermocycling. Non-contact profilometer was used to assess the effect of the three surface pretreatments on surface roughness of zirconia. Mode of failure and surface roughness were evaluated with SEM. Statistical analyses were conducted with mixed-model ANOVA and chi-square tests. RESULTS: The results indicated that Monobond Plus primer showed higher SBS after phosphoric acid treatment compared to other primers used. SBS of all air abrasion groups were higher than phosphoric acid groups. Long term water storage and thermocycling led to a statistically significant decrease in SBS for all groups except Monobond Plus, Z-prime plus and AZ primer after air abrasion treatment. Surface roughness measurements showed no significant differences among the surface treatments. CONCLUSION: Monobond Plus provided the highest SBS to zirconia after phosphoric acid treatment. The findings suggest that the air abrasion is the best surface treatment after contamination of zirconia surface. Monobond Plus, Z-prime plus and AZ primer showed durable SBS after air abrasion treatment and aging process.