Interaction morphology and bond strength of nanofilled simplified-step adhesives to acid etched dentin

OBJECTIVE To evaluate the effect of nanofillers incorporated into adhesives on the microtensile bond strength (μ-TBS) and interfacial micromorphology to dentin. METHODS The occlusal enamel of 5 human molars was removed and each tooth sectioned into four quarters. The exposed dentin was treated with one of the following adhesives: Adper Single Bond (SB-unfilled), OptiBond Solo Plus (OS-barium aluminoborosilicate, 400nm Ø), Prime & Bond NT (NT-colloidal silica, 7-40 nm Ø) and Adper Single Bond 2 (SB2-colloidal silica, 5nm Ø). Cylinders of resin-based composite were constructed on the adhesive layers. After 24-hour storage, the restored tooth-quadrants were sectioned to obtain stick-shaped specimens (0.8 mm2, cross-sectional area) and submitted to μ-TBS at a cross-speed of 0.5 mm/min. Data were analyzed using one-way ANOVA and Tukey's test (alpha = .05). Twenty-eight additional teeth were used for interfacial micro-morphologic analysis by SEM (16-teeth) and TEM (12-teeth). The dentin surfaces of 32 discs were treated with the adhesives (8 discs for adhesive) and laminated to form disc-pairs using a flowable resin composite for SEM/EDS analysis. For TEM, 90nm-thick nondemineralized unstained sections were processed. RESULTS SB2 showed significant higher bond strength than SB, OS and NT. The SEM/EDS and TEM analysis revealed nanofillers infiltrated within the interfibrillar spaces of the SB2-hybrid layer. Fillers were concentrated around patent tubular orifices and in the adhesive layer for OS and NT. CONCLUSION The presence of nanofillers within the interfibrillar spaces of the SB2-hybrid layer suggests its importance in the improvement of the μ-TBS.