Influence of Surface Treatment of Contaminated Zirconia on Surface Free-energy

Objectives: Influence of saliva contamination and cleaning methods on the surface free-energy of zirconia ceramics and the bond strength of resin cement were examined.
Methods: Yttrium-stabilized zirconia (IPS e.max ZirCAD) plates were used. Specimens were ground with 600-grit silicon carbide paper and airborne particle abraded with 50-μm grain size Al₂O₃ particles at 0.2 MPa. The samples were divided into five groups (n=10) as; Group 1 (control): The specimens were not contaminated, after saliva contamination, Group 2 (SC): the surface was rinsed with tap water, Group 3 (PA): the surface was treated with phosphoric acid for 30 s, Group 4 (IC): the surface was treated with Ivoclean for 20 s, Group 5 (AB): the surface was subjected to additional airborne particle abrasion (ethics approval #2011-19). The surface free energy of the ceramics surface was determined by measuring the contact angles of three test liquids. To determine the bond strength of resin cement, resin pastes were condensed into the mold on the ceramics surfaces, followed by shear tested (CHS= 1.0 mm/min). Data were analyzed by two-way ANOVAand Tukey’s test (α=0.05).
Results: γ_S^p and γ_S^h values of SC group decreased, and PA group increased substantially but remained significantly lower than those of the control group. No significant differences were found for the IC and AB groups compared with the control group. Two-way ANOVA revealed that surface treatment (p<0.01) and storage conditions (p=0.03) had a significant influence on bond strength, while there was no significant interaction between the two factors (p=0.449). AB was the most effective method of removing the contaminants and creating an effective surface for resin cement bonding.
Conclusions: A thin layer of contaminants remains on the zirconia ceramic surface after exposure to saliva, significantly impeding the bonding of the resin cement and reducing the surface free energy of the ceramics.