Effect of bonded metal substrate area and its thickness on the strength and durability of adhesively bonded joints

In this in vitro study, the effect of substrate surface area and substrate thickness on the strength and durability of an adhesively bonded joint was evaluated. Sixty metal substrate samples were cast out of a cobalt-chromium alloy. Samples of the first group were in a disk shape of 2 mm thickness and 35 mm(2), 65 mm(2), and 95 mm(2) surface area with a U-shaped loop on the non-testing side. Samples of the second group were in the shape of disks of surface area 65 mm(2) with a U-shaped loop and thicknesses of 0.5 mm, 1 mm, or 2 mm. All samples were treated by the Silicoater MD (R) method and bonded with bisphenol-A glycidyl methacrylate (Bis-GMA) adhesive. Samples were either stored in distilled water for 3 days or thermocycled for 5000 cycles followed by storage for 180 days in water at 37 degrees C. After storage, the tensile bond strength was determined. Increasing the bonded surface area resulted in a significant drop in the initial bond strength values. However, after thermocycling and water storage, the bond strength increased with increasing bonded surface area. Increasing the substrate thickness resulted in a significant increase of the initial bond strength values. After thermocycling and water storage, there were no significant differences in the bond strength values for samples with different thicknesses.