Adhesion of a total-etch phosphate ester bonding agent

This study evaluated the shear bond strengths of a phosphate ester bonding agent, Clearfil Photo Bond, using different phosphoric acid gels to etch dentin. The study also tested the shear bond strength of the Clearfil Liner Bond system. Sixty extracted human molars were ground to expose mid-coronal dentin and were randomly assigned to six treatment groups. The first group was left unetched as a control. In the next four groups, dentin was etched with phosphoric acid gels: K-etchant (40% with silica thickener); Uni-Etch (polymer-thickened 32%); All-Etch (10%, polymer thickener); or Ultra-Etch (10%, silica thickener). Specimens in the sixth group were etched with 10/20 Ca, a gel with 10% citric acid and 20% calcium chloride. All specimens were bonded with Clearfil Photo Bond and XRV Herculite resin composite. Specimens in the final group also received SA Primer and Protect Liner. After thermocycling, shear bond strengths were determined using an Instron universal testing machine. Mean shear bond strengths ranged from 1.3 MPa (control) to 15.9 MPa (Clearfil Liner Bond). The shear bond strengths of specimens that had been etched with phosphoric acid gels were in the range of 5-8 MPa, and were not significantly affected by either acid concentration or thickener type. SEM examination showed that phosphoric acid demineralized dentin to a depth of 5 microns, while 10/20 Ca demineralized dentin to a depth of only 1-1.5 microns.