Effect of air-thinning a two-step adhesive layer on bond strength to tooth substrates

This study investigated the effect of air-thinning to a two-step adhesive (G2-BOND Universal) on the microtensile bond strength (µTBS) between bovine teeth (enamel, dentin) and a resin composite (G-ænial A'CHORD). The adhesive was applied with or without air-blowing before light curing on the bovine enamel and dentin surfaces finished using 320-grit SiC paper. After resin composite buildup, µTBS specimens (1.0 mm × 1.0 mm cross-sectional area) were fabricated. The µTBS values were determined 24 h, 4 weeks, and 6 months after the specimen preparation. Furthermore, the adhesive layer thicknesses were measured on the SEM photographs of the specimens' fractured site after the µTBS test. Except for the enamel specimens at 6 months, no significant differences were observed in µTBS determined at any time periods between specimens with and without air-blowing (p > 0.05). µTBS values in air-blown specimens increased from 24 h to 4 weeks, and the values in non-air-blown specimens were greater at 6 months than at 24 h. Specimens subjected to air-blowing showed significantly thinner adhesive layer than those without at any time periods (p < 0.05). Although air-blowing reduced adhesive layer thickness, it did not affect the bond strength except for the enamel specimens at 6 months.