In Vitro Evaluation of the Effect of Different Surface Treatments on Shear Bond Strength of New to Old Composite Restorations

Introduction: Composite resins have developed in past years, however, failures may occur which needs whole restoration repairing. this study aimed to evaluate the effect of different surface treatments on shear bond strength of new to old composite restorations. Materials and Methods: A total of 60 blocks of Z250 composite resin were divided to four groups 1) no surface preparation (control group), 2) abrasion through aerosols using 50-micron aluminum oxide particles, 3) abrasion through diamond milling with 125-micrometer particles, 4) surface preparation using hydrofluoric acid. Shear bond strength in different methods such as etching with hydrofluoric acids (with and without silanization), air abrasion, and diamond milling was compared with the control group. All data were analyzed using the Kolmogorov-Smirnov test and one-way analyses of variance (ANOVA) and Tukey's post hoc test. Results: In comparing the groups with each other, it was found that shear bond strength in Hydrofluoric acid and silanization group was significantly higher than control (P = 0.017). Conclusion: The effects of etching with hydrofluoric acid and silanization in increasing shear bond strength between aged and new composite resins are superior to control, which could be a suitable repair protocol to obtain optimal repair bond strength.