Can the durability of one-step self-etch adhesives be improved by double application or by an extra layer of hydrophobic resin?

Objectives This study evaluated the immediate and 6-month resin–dentin μ-bond strength (μTBS) of one-step self-etch systems (Adper Prompt L-Pop [AD] 3M ESPE; Xeno III [XE] Dentsply De Trey; iBond [iB] Heraeus Kulzer) under different application modes. Materials and methods Dentin oclusal surfaces were exposed by grinding with 600-grit SiC paper. The adhesives were applied according to the manufacturerʹs directions [MD], or with double application of the adhesive layer [DA] or following the manufacturerʹs directions plus a hydrophobic resin layer coating [HL]. After applying the adhesive resins, composite crowns were built up incrementally. After 24-h water storage, the specimens were serially sectioned in “x” and “y” directions to obtain bonded sticks of about 0.8 mm2 to be tested immediately [IM] or after 6 months of water storage [6M] at a crosshead speed of 0.5 mm/min. The data from each adhesive was analyzed by a two-way repeated measures ANOVA (mode of application vs. storage time) and Tukeyʹs test (α = 0.05). Results The adhesives performed differently according to the application mode. The DA and HL either improved the immediate performance of the adhesive or did not differ from the MD. The resin–dentin bond strength values observed after 6 months were higher when a hydrophobic resin coat was used than compared to those values observed under the manufacturerʹs directions. Conclusions The double application of one-step self-etch system can be safety performed however the application of an additional hydrophobic resin layer can improve the immediate resin–dentin bonds and reduce the degradation of resin bonds over time.