This study aimed to investigate the effect of frequency on shear fatigue strength (SFS). The SFS of a resin composite bonded to dentin was determined using three self-etch adhesive systems: G-ænial Bond, Scotchbond Universal, and Optibond XTR. The staircase method of fatigue testing was used to determine the SFS at frequencies of 5, 10, and 20 Hz for 50,000 cycles. The failed bonding sites observed were classified based on the type of bond failure as follows: adhesive failure, cohesive failure in composite, cohesive failure in dentin, or mixed failure (partially adhesive, partially cohesive). A modified t-test with Bonferroni correction was used to analyze the SFS data, and a complex chi-square test was used to analyze the fracture modes. The SFS of OX was significantly greater than that of GB at both 5 and 10 Hz. However, no significant differences in SFS were found among the three frequencies (5, 10, and 20 Hz) in the three self-etch adhesive systems. Furthermore, no significant differences in bond failure mode were observed among the three frequency rates in all the three adhesives used.
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