The remarkable evolution of contemporary dentin adhesive systems has focused on simplifying the clinical steps. Factors, such as time and simplification of the clinical steps have led to the increased use of simplified-step adhesives in association with resin materials.Conventional (three-step) and simplified-step adhesive systems are currently available for etch and rinse systems. The bonding protocol of three-step systems requires separate acid-etching of the enamel and dentin surfaces, the application of a primer containing hydrophilic resin and solvents to etched dentin, and the subsequent application of an adhesive containing resin monomers to both enamel and dentin 1) . However, in order to simplify the bonding protocol, manufacturers have attempted to produce several one-bottle dentin bonding systems that combine the primer and adhesive resin in a single solution.Simplified-step adhesive systems have replaced their predecessors in most clinical applications because of their reported versatility, ease of use and time-saving protocols. Most of these products are composed of hydrophilic and hydrophobic resins dissolved in a high vapor pressure organic solvent, such as ethanol or acetone, which chase the water and bring the monomers into intimate contact with the exposed collagen fibers 2) . These adhesive systems This study compared the effect of an activator, intermediate bonding resin and low-viscosity flowable resin on the microtensile bond strength of a self-curing composite resin used with two-step total etching adhesives. Twenty extracted permanent molars were used. The teeth were assigned randomly to nine groups (n=10) according to the adhesive system and application of additional methods (activator, intermediate adhesive, flowable resin). The bonding agents and additional applications of each group were applied to the dentin surfaces. Self-curing composite resin buildups were made for each tooth to form a core, 5mm in height. The restored teeth were then stored in distilled water at room temperature for 24h before sectioning. The microtensile bond strength of all specimens was examined. The data was analyzed statistically by one-way ANOVA and a Scheffe' s test. The application of an intermediate bonding resin (Optibond FL adhesive) and low-viscosity flowable resin (Tetric N-flow) produced higher bond strength than that with the activator in all groups. Regardless of the method selected, Optibond solo plus produced the lowest μ TBS to dentin. The failure modes of the tested dentin bonding agents were mostly adhesive failure but there were some cases showed cohesive failure in the resin.