The purpose of this study was to determine the failure mode of a posterior composite resin bonded to a glass-ionomer cement that was treated with and without a cationic vinyl functional silane coupling agent while the etch times were varied. Bond failure occurred at the glass-ionomer cement-composite resin interface (adhesive failure) in specimens that were not etched and when no coupling agent was used. When the samples were etched for 5, 15, or 30 seconds, approximately 50% failed within the glass-ionomer cement (cohesive failure). The use of the coupling agent produced a failure mode of 80% to 100% within the glass-ionomer cement. With a 15-second etch, the coupling agent produced 100% failure within the glass-ionomer cement, while only 50% of the samples without the coupling agent failed within the glass-ionomer cement. With a 30-second etch, all the samples treated with the coupling agent failed within the glass-ionomer Cement, while only 60% of the samples not treated with the coupling agent failed within the glass-ionomer cement. Without the coupling agent, groups in which the glass-ionomer cement was not etched showed a lower shear bond strength than did groups in which the cement was etched for 5, 15, or 30 seconds. With the coupling agent, the groups in which the glass-ionomer cement was not etched had lower bond strengths than did the group in which the glass-ionomer cement was etched for 15 seconds. Analysis of the data revealed all these differences to be statistically significant.