The objective of the current study was to evaluate the bonding durability between layers of two indirect composite materials (Cesead II and Estenia) when combined with silane primers and unfilled resin bonding agents. Disk specimens were prepared with the dentin portion of the composite materials and abraded with a silicon-carbide rotary cutting instrument. The specimens were conditioned with varying combinations of silane primer (Add-on Primer, Porcelain Liner M, and unprimed) and bonding agent (Modeling Liquid, Stain Diluent, and no-bondinga gent). After placing the enamel portion of the same brand of composite material on each surface of the dentin material, the specimens were light-exposed. Shear bond strengths were determined after 24 hours immer-sion in water and after subsequent thermocycling for20, 000, 50, 000, and 100, 000cycles. Analysis of variance-revealed that the most influential factor was thermocycling. Reduction in bond strength after thermocycling was remarkable for all groups. After100, 000 thermocycling, the combination of Add-on Primer silane material and no -bonding agent showed the greatest strength for the Cesead II material, whereas the Add-on Primer material and Modeling Liquid agent indicated the greatest bond strength for the Estenia material.
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