Ultrasound pretreatment of dentin enhances the adhesion of universal adhesives

This in vitro study evaluated the adhesion of universal adhesives to dentin following ultrasound application. The occlusal dentin of 40 molars was exposed. The teeth were assigned to groups (n = 5) according to the adhesive used (Gluma Bond Universal, Tetric N-Bond Universal, Palfique Universal Bond, Scotchbond Universal Plus) and whether ultrasound was applied to the dentin prior to adhesive application. Beam-shaped specimens were obtained. Half of the beams from each tooth were subjected to microtensile bond strength (μTBS) testing after 24 h, and the other half were tested after 6 months of water storage. An additional two teeth were used for SEM analysis of dentin topography, and 16 teeth were used for SEM evaluation of the adhesive interface. Three-way ANOVA revealed that the effects of adhesive system ( p < 0.001) and ultrasound ( p < 0.001) were significant, whereas that of storage time was not ( p = 0.261). The ultrasound × storage time interaction was significant ( p = 0.025). According to Tukey’s post hoc test, Tetric N-Bond Universal (44.5 MPa) and Scotchbond Universal Plus (40.8 MPa) resulted in the highest μTBSs. At 24 h, ultrasound application significantly increased µTBS (40.1 MPa) compared with no ultrasound (32.2 MPa) ( p < 0.05), whereas 6 months of storage did not significantly affect µTBS ( p > 0.05). SEM images revealed that ultrasound removed the smear layer, smear plugs and promoted the formation of resin tags. Ultrasound pretreatment improved the adhesion of the universal adhesives tested to sound dentin.