Effect of Aging and Different Surface Treatments on the Repair Microshear Bond Strength of a Nanohybrid Composite Resin

<b>Objectives:</b> Repair of composite resin restorations is a challenge specially when the restoration undergoes aging; thus, this study aimed to assess the effect of aging and different surface treatments on the repair microshear bond strength of IPS Empress Direct nanohybrid composite resin. <b>Materials and Methods:</b> This in vitro, experimental study evaluated 48 IPS Empress Direct composite resin samples in two groups of aged and nonaged (n=24). The samples in both groups were finished and polished with Sof-Lex discs. Composite samples in the aged group were subjected to 5000 thermal cycles. The two groups were then divided into two subgroups (n=12) for surface roughening by a diamond bur or sandblasting with aluminum oxide particles. Composite cylinders were then bonded to the composite samples, and underwent microshear bond strength test in a universal testing machine. Data were analyzed by two-way ANOVA and t-test (alpha=0.05). <b>Results:</b> The results showed no significant difference in the microshear bond strength of bur and sandblasted subgroups, irrespective of aging (P>0.05). In the aged subgroups, however, irrespective of the method of surface treatment, the bond strength was significantly lower than that in the subgroups that did not undergo the aging process (P<0.05). <b>Conclusion:</b> Micromechanical retention is the most reliable method to achieve a high repair bond strength in IPS Empress Direct composite resin. Surface roughening by bur is safe and cost-effective, and can be used instead of sandblasting for composite restoration repair.