Bond Strength of a Silorane Adhesive Using Selective Etch

An improvement in bond strength to enamel has been demonstrated with the use of phosphoric acid prior to bonding with self-etching methacrylate-based adhesive agents. No research has evaluated the effect of phosphoric-acid etching of enamel with the newer self-etching silorane-based adhesive, Filtek LS System Adhesive (3M/ESPE). Objective:  The purpose of this study was to evaluate the shear-bond strength of composite to enamel using the two-step self-etching silorane-based adhesive compared to other two-step self-etching methacrylate-based adhesives, with or without a separate application of phosphoric acid.  Method: Sixty bovine incisors were sectioned using a diamond saw, mounted in plastic pipe, and divided into six groups of ten specimens each. Filtek LS System Adhesive, Clearfil SE Bond (Kuraray), and Optibond XTR (Kerr) were applied to flattened enamel surfaces with or without the application of 35% phosphoric acid (Kerr). All specimens were light cured. The teeth bonded with LS System Adhesive were restored exclusively with Filtek LS silorane composite (3M/ESPE) and the teeth bonded with Clearfil SE Bond and Optibond XTR were restored with Filtek Supreme Ultra composite (3M/ESPE). The bonded tooth specimens were inserted beneath a mold (Ultradent) and the composite was placed incrementally to a height of 4 mm and light cured.  Specimens were stored for 24 hours in 37° distilled water and tested in shear (Instron).  A mean and standard deviation was determined per group.  Data was analyzed with t-tests/ANOVA/Tukey's to examine the effects of adhesive agent or surface treatment on the bond strength of composite to bovine enamel (alpha=0.01).  Result: Significant differences were found between the groups (p<0.01).  Conclusion:   Phosphoric-acid etching of bovine enamel significantly increased the bond strength of the methacrylate-based adhesives, but not the silorane-based adhesive. The methacrylate-based adhesives had significantly greater bond strength to enamel than the silorane-based adhesive if the enamel was etched with phosphoric acid.