Effect of Electric Current-assisted Application of Adhesives on their Bond Strength and Quality

Purpose: To assess the effect of the application of different electric currents on dentin bonding and resin infiltration of self-etching and etch-and-rinse adhesives. Materials and Methods: Two hundred four sound third molars were selected and divided in groups according to the adhesive (self-etch [CSE, Clearfil SE Bond, Kuraray Noritake], universal [SBU, Single Bond Universal, 3M Oral Care], and etch-and-rinse [SB2, Adper Single Bond 2 (SB2), 3M Oral Care]) and electrical current used (0, 5, 10, 15, 20, 25, 30, and 35 μA). Light curing was performed for 10 s with an LED-curing unit at 1000 mW/cm2. Composite blocks were constructed of nanofilled composite in increments of 2 mm, which were light cured for 20 s. Specimens were sectioned into sticks with a cross-sectional area of ~1 mm2 and stored in distilled water at 37°C for 24 h. Microtensile bond strength (μTBS) testing (n = 8) was performed using a universal testing machine at a crosshead speed of 0.5 mm/min until failure. The bonding quality (n = 2) of adhesives applied with or without 35-μA electric current was evaluated using confocal laser scanning microscopy. Bond strengths were analyzed with two-way ANOVA and Tukey's test (α = 0.05). Results: CSE presented the highest μTBS for all electrical currents tested. For CSE and SBU, electrical currents from 0-20 μA showed the lowest μTBS. Electrical currents from 0-10 and 20-25 μA yielded the lowest μTBS for SB2. CSE and SB2 applied under 35 μA showed a greater number of resin tags in dentin tubules. Fluorescein penetration into the hybrid layer was found for SBU applied without electric current. Conclusion: The application of adhesives using 35-μA electric current improved the bond strength and quality of the adhesive interface. Keywords: bonding efficacy, adhesives, electric current, microtensile, dentin