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Objectives: The aim of this in vitro study was to evaluate the efficiency of different surface treatments on the microtensile bond strength (µTBS) of aged bulk-fill composite.Materials and Methods: Sixty bulk-fill resin-based composite (RBC) specimens in 5 x 5 x 5 dimensions were prepared. After the aging by thermal cycling for 5000 times between 5 and 55°C, substrate surfaces were abraded with SiC abrasive papers. Specimens were divided into 6 groups according to the surface treatment protocol: no surface treatment (control), control + Single Bond Universal (SBU; 3M ESPE) application, phosphoric acid etching (PA) + SBU, hydrofluoric acid etching (HF) + SBU, aluminum oxide air abrasion (AlO) + SBU, and tribochemical silica coating (TSC) + SBU. Surface roughness values were measured in five different directions using a contact profilometer (n=10). Then, specimens were repaired with a conventional RBC. After the repair, bonded specimens were cut into 1 mm2 beams and µTBS values were determined until failure at a crosshead speed of 0.5 mm/min. Specimen surfaces after surface treatments were observed by SEM. Data were analyzed using ANOVA and Tukey tests (p AlO > HF > PA = Control. Conclusions: Aged bulk-fill RBCs can be successfully repaired if effective and safe repair protocol is chosen. The highest µTBS values were obtained for the AlO and TSC. The use of universal adhesive alone is promising to facilitate the repair of bulk-fill RBCs.