Tehran University of Medical Sciences Frontiers in Biomedical Technologies 2345-5837 13 1 2026 01 20 95 103 Negar Soltanian Assistant Professor, Department of Operative Dentistry, Dentistry Faculty, Urmia University of Medical Sciences, Urmia, Iran Vahid Divanpour Assistant Professor, Department of Operative Dentistry, Boushehr University of Medical Sciences, Boushehr, Iran Baharan Ranjbar Omidi Dental Caries Prevention Research Center, Qazvin University of Medical Sciences, Qazvin, Iran Monirsadat Mirzadeh Assistant Professor Community Medicine, Metabolic Diseases Research Center, Research Institute For Prevention Of Non-Communicable Diseases, Qazvin University Of Medical Sciences, Qazvin, Iran 2023 11 25 2024 06 30 Purpose: In dental operations, repairing old restorations is a typical clinical procedure. This study aimed to evaluate the micro-Shear Bond Strength (µSBS) of composite resin repairs with different adhesives and surface treatments. Materials and Methods: After preparation, ninety resin composite discs were divided into three groups of thirty at random: no surface preparation, diamond milling roughness, and sandblasting.  After 5000 heat cycles, each group was randomly divided into three subgroups of Single Bond (3M), Composite Primer (GC), and Schotch Bond Universal (3M) (n = 10). One-hundred eighty composite cylinders of the new composite were prepared by squeezing the composite into a silicon tube. The samples were then subjected to 5000 heat cycles. After thermocycling, µSBS tests were done at a cross head speed of 0.5 mm/min.  Tukey tests and two-way ANOVA were employed to analyze the data. Results: In the unprepared group, the universal bond and composite primer micro-shear bond strength were significantly higher than the single bond group (p < 0.05). In the milling group, the universal bond micro-shear bond strength was significantly higher than the composite primer and single bond group (p < 0.05). In the sandblasted group there were no significant differences in μSBS among adhesives. In single bond adhesive, the micro-shear bond strength of milling was significantly greater than the sandblasted and unprepared groups (p < 0.05). In the universal adhesive group, the micro-shear bond strength of the milling group was significantly higher than the sandblasted and unprepared groups (p < 0.05). Conclusion: The type of adhesive and the method of surface preparation have an impact on micro-shear bond strength. The greatest micro-shear bond strength was demonstrated by universal bond application combined with milling roughening. https://fbt.tums.ac.ir/index.php/fbt/article/view/889 https://fbt.tums.ac.ir/index.php/fbt/article/download/889/545