Does Rubbing of Universal Adhesive Reduce the 
Negative Effect of Saliva on Adhesion?

Purpose: To evaluate in vitro the effect of saliva contamination on bond strength of a universal adhesive applied with actively (with rubbing motion) and passively (without rubbing motion).
Materials and Methods: A total of 144 bovine dentin samples were used, and the universal adhesive, Clearfil Universal Bond Quick, was either applied in accordance with the manufacturer’s instructions (passive application) or applied with rubbing motion for 10 s (active application). These 2 groups were divided into 6 subgroups according to saliva contamination (n = 12): 1. control: etch-and-rinse (no saliva); 2. control: self-etch (no saliva); 3. etching/saliva/bonding; 4. etching/bonding/saliva; 5. saliva/bonding; 6. bonding/saliva. A resin composite, Filtek Ultimate, was filled into a polyethylene mold (0.9 mm diameter, 1.2 mm height) on the surfaces. Samples were subjected to microshear bond strength testing, and five specimens from each group were examined using SEM. Resin-dentin interfaces were also observed using transmission electron microscopy (TEM). All failure modes were determined using light microscopy. Statistical analyses were performed with two-way ANOVA, the Kruskall-Wallis test, and the Mann-Whitney U-test (p < 0.05).
Results: Active-application groups showed statistically significantly higher bond strengths than did passive groups, regardless of adhesive strategy and saliva contamination (p < 0.05). Application of Clearfil Universal Bond Quick in self-etch mode with rubbing motion improved the µSBS among control groups (p < 0.05). The active application did not make a significant difference among the active groups (p > 0.05), except in group 2. Groups 2 and 5 showed significantly higher µSBS than group 3 among the passive groups (p < 0.05).
Conclusion: Rubbing the universal adhesives without any prior etching may increase the dentin bond strength. Following etching, passive application of the universal adhesive (without any additional rubbing motion) could affect the bonding to dentin in the presence of saliva.