Shear Bond Strength of Repaired Composite Using Single Bond Adhesive

Objectives: The aim of this study was to evaluate the shear bond strength of repaired composite resin restorations using one-step Single Bond Universal adhesive. Materials and Methods: Sixty cylindrical composite samples (8 x 9 mm each) were prepared from Filtek Z350 XT, light-cured and stored for 6 weeks. The surface of each sample was bur-roughened and acid-etched with 37% phosphoric acid. Samples (N = 60) were randomly assigned into 2 groups. For group 1 (the control group), silane coupling agent and bonding agent were applied in two separate steps. For group 2 (the test group), Single Bond Universal adhesive containing both silane and bonding agents was applied to the surface of the samples. Fresh composite resin was bonded to treated surfaces, and samples were cured and stored for another 6 weeks. The shear bond strength (SBS) was measured and analyzed using an independent samples t-test and descriptive statistics. Stereomicroscope examination of the samples was done to assess the mode of failure between the original and the repaired composite layers for the control and test groups. Results: The mean initial failure SBS for the test group was significantly higher than that of the control group (p < 0.001). Of the control group samples, 80% failed adhesively, while 100% of the test group samples showed cohesive failure and a mixed mode of failure when observed under the stereomicroscope. Conclusion: Single Bond Universal adhesive provides more reliable bond strength for repaired composite resin restorations compared with two-step silane and bonding agent application.