Materials and Methods: In this in vitro study, the occlusal surfaces of 80 intact human premolars were removed to expose the flat midcoronal dentin. The teeth were assigned to four groups. Two adhesive systems, Clearfil SE Bond (SE) and Clearfil Protect Bond (PB) were used according to manufacturer’s instructions as the control groups. In the experimental groups, 2% chlorhexidine was applied prior to acidic primer of two adhesives. Then, resin composite was applied. Half of the specimens in each group were submitted to shear bond test after 24 h without thermocycling, and the other half were submitted to water storage for 6 months and thermocycling before testing. The data was analyzed using three-way analysis of variance (ANOVA) and t-test (a = 0.05). 

  Results: Chlorhexidine application significantly decreased the initial bond strength (BS) of the two self-etch adhesives to dentin (P < 0.05). There was a significant reduction in BS of SE and PB after aging compared to initial bonding (P < 0.05). However, there was no significant difference between BS of the control and chlorhexidine-treated groups for the tested adhesives after aging. PB showed a lower BS than SE in two time periods (P < 0.05). 

  Conclusion: Chlorhexidine was capable of diminishing the loss of BS of these adhesives over time. However, considering the negative effect of chlorhexidine on the initial BS, the benefits of chlorhexidine associated with these adhesives cannot possibly be used.