Formation Of A Rough Inorganic Dentin Interface For Dentin Dry Bonding

Objectives: The durability of resin dentin bonding remains an unsolved challenge in adhesive dentistry.Inspired by enamel etching bonding strategy,we aimed to explore a dentin dry bonding protocol utilizing citric acid and sodium hypochlorite as etching agents to create a rough inorganic dentin interface for resin dry bonding to dentin.Methods: Dentin surfaces were treated with 10% citric acid and 5.25% sodium hypochlorite to create a rough inorganic dentin interface by demineralizing the dentin surface and removing the exposed dentin collagen.Phosphoric acid etched dentin surfaces served as controls.Dentin surfaces were air dried and characterized using scanning electron microscopy（SEM）,fourier-transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,atomic force microscopy（AFM）,and microhardness tests.The effect of resin dry bonding to dentin was evaluated by microtensile bond strength test,in situ zymography fluorescence technique,and confocal laser scanning microscope.Results: SEM and AFM micrographs showed that the collagen interfibrillar spaces were preserved and dentinal tubules were patent without collagen collapse after air drying compared with the control group.The microhardness of the dentin surface treated with citric acid and sodium hypochlorite was comparable to that of natural dentin.FTIR and XRD suggested the formation of an inorganic dentin surface.The microtensile bond strength results showed a significant difference after thermocycling,indicating the better durability of resin dentin bonding compared with the control group（P<0.05）.Furthermore,no fluorescence was detected,indicating that MMPs remained silent within hybrid layers,and no micropermeability or gap was found at the hybrid layer interface.Conclusion: Within the confines of the current research,it may be concluded that citric acid and sodium hypochlorite-based dentin dry-bonding protocols eliminated collagen fiber exposure,which could increase bonding strength after thermocycling,reduce MMP activity in situ,and promote bonding interface integrity.Therefore,citric acid and sodium hypochlorite as potential alternative etching agents can improve the resin–dentin bond durability.