Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 22 0 2025 02 18 3097 3097 Maryam Hoorizad Ganjkar Restorative Department, Faculty of Dentistry, Tehran Medical Sciences, Islamic Azad University, Tehran, Iran Negin Nasoohi Restorative Department, Faculty of Dentistry, Tehran Medical Sciences, Islamic Azad University, Tehran, Iran Mahshad Lesani Restorative Department, Faculty of Dentistry, Tehran Medical Sciences, Islamic Azad University, Tehran, Iran Neda Sanaee Restorative Department, Faculty of Dentistry, Tehran Medical Sciences, Islamic Azad University, Tehran, Iran 2019 04 14 2020 07 27 Objectives: 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. Materials and Methods: 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). Results: 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). Conclusion: 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. https://fid.tums.ac.ir/index.php/fid/article/view/3097