Bond strength of a total-etch and two self-etch adhesives to dentin with and without intermediate flowable liner

To evaluate the effect of flowable resin composite application on the microtensile bond strength of a total-etch and two self-etch adhesive systems to dentin.

Occlusal surfaces of 30 human third molars were ground to obtain flat dentin surfaces. One of the following adhesive systems was applied to the dentin surface following manufacturers' instructions: Admira Bond, Futurabond DC and Clearfil SE Bond. For each adhesive, half of the specimens received a layer of flowable composite (Amaris Flow) applied into dentin and light-cured (experimental groups). The other teeth received no liner and served as control group. For all teeth, resin composite (Amaris) was applied in 2 mm thickness to form a crown segment 5-6 mm height and each increment was light-cured. The restored teeth were stored in water at 37 degrees C for 24 hours. Each tooth was serially sectioned in a longitudinal direction in order to obtain several bonded slabs (1.0 mm2 in cross-section). Each slab was attached to the set-up by their lateral sides and placed in a universal testing machine. Tensile load was applied at cross-head speed of 0.5 mm/minute until failure. Data were analyzed by two-way ANOVA and Tukey's test at 5% significance level.

Placement of a low-viscosity resin after adhesive application increased the microtensile bond strength for all tested adhesive systems. However, such increase was not significant (P > 0.05). The percentage of cohesive failure was increased in specimens with flowable resin liner.