Bonding ability of experimental resin-based materials containing (ion-releasing)-microfillers applied on water-wet or ethanol-wet root canal dentine

The objective of this study was to evaluate the bonding performance of model resin-based adhesives doped with bioactive glass or dicalcium-phosphate dihydrate microfillers to root canal dentine saturated with water or ethanol. The experimental resin was prepared by using urethane-dimethacrylate (UDMA), triethylene-glycol-dimethacrylate (TEGDMA) and hydroxyethyl-methacrylate (HEMA). This resin blend was mixed with 50 wt% ethanol to create the experimental primers. Bioactive glass 45S5 (BAG) or calcium-silicate modified dicalcium-phosphate dihydrate (DCPD) microfillers were mixed at 40 wt% to the blend. The bonding performance to root canal was assayed by push-out bond strength, SEM analysis of fractures, and interfacial confocal microscopy after filling the canals with the core composite Bis-Core (Bisco). Three-way ANOVA (bonding technique, adhesive resin and dentine third) and Student-Newman-Keuls post-hoc were used to statistically compare the results (α=5%). Filler-free adhesive applied on water-wet radicular dentine showed lower bond strength than the same resin applied on ethanol-wet dentine (p<0.05). Only the former group showed predominantly adhesive fractures whereas all other treatments led mostly to mixed failures. The presence of both fillers did not influence the push-out bond strength using ethanol-wet approach (p>0.05) but did improve using the water-wet strategy. BAG and DCPD also promoted mineral deposition and tubular occlusion in the well-hybridised fractured root surfaces especially using the ethanol-wet technique. The confocal interfacial analysis showed impaired resin infiltration only using the filler-free resin on water-wet dentine. As a conclusion, bioactive glass and DCPD micro-fillers as well as the ethanol-wet bonding were able to improve the adhesion of traditional etch-and-rinse adhesives to radicular dentine.