Two-year bonding performance of universal adhesives with an additional hydrophobic resin coat containing 45S5 on eroded dentin surface

Purpose: To evaluate the effect of an additional hydrophobic resin coat containing 45S5 bioactive glass on bonding durability of eroded dentin after two years of water storage. Material and methods: Ninety-six human molars were assigned to 12 groups according to dentin substrate (sound or eroded dentin); Universal adhesive systems: (Clearfil Universal Bond Quick - CUQ, and Scotchbond Universal - SBU); and treatment: control, control + additional hydrophobic resin coat (Extra HL) and control + additional hydrophobic resin coat containing 45S5 bioactive glass (Extra HL 45S5). The restorations were performed using composite resin. Specimens were sectioned into resin-dentin bonded sticks for microtensile bond strength (μTBS, at 0.5 mm/min) or nanoleakage (NL) either immediately or after 2 years of storage. Data for μTBS (MPa) and NL (%) were analyzed using three-way repeated measures ANOVA (dentin vs. treatment vs. time) for each adhesive, followed by Tukey's test (α = 5 %). Results: The application of Extra HL or Extra HL 45S5 significantly improved immediate bond strength and reduced nanoleakage in eroded dentin (p < 0.00001). After two years, control groups showed reduced bond strength and an increased nanoleakage for both dentin substrate compared to Extra HL or Extra HL 45S5 (p < 0.00001). No significant differences were observed between Extra HL and Extra HL 45S5 at either time point (p > 0.05). Conclusions: An additional hydrophobic resin layer improved bonding durability in sound dentin but did not prevent bond strength loss or silver nitrate uptake in eroded dentin after two years. However, eroded dentin treated with an additional hydrophobic resin layer, whether containing 45S5 or not, showed higher bond strength values compared with the control groups. The incorporation of 45S5 bioactive glass provided no additional benefit over the conventional hydrophobic resin.