EDTA Functionalized Silica Nanoparticles-Based Extrafibrillar Demineralization In Improving Dentin Bond Durability

Objective Although the immediate strength of dentin adhesion has achieved satisfactory results,dentin bonding durability faces challenges,compared with stable enamel bonding.In this study,silica nanoparticles（SiO₂,50 nm）with the diameter larger than the gap zone of collagen fibrils was selected to construct Ethylenediaminetetraacetic acid（EDTA）functionalized silica nanoparticles（SiO₂-EDTA）.To explore the effect of SiO₂-EDTA as dentin conditioning agent on dentin extrafibrillar demineralization and investigate the improvement of dentin bond stability and durability.Methods The first part was to synthesize and characterize the SiO₂-EDTA.SiO₂-EDTA were synthesized by(N-[3-（Trimethoxysilyl）propyl]ethylenediamine triacetic acid（TMS-EDTA）and SiO₂,and characterized by Flourier transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,thermogravimetric analysis（TGA）and transmission electron microscopy（TEM）.The second part was to investigate the effect of SiO₂-EDTA as dentin-conditioning agent on dentin extrafibrillar demineralization based on SiO₂-EDTA.The capacity of SiO₂-EDTA and EDTA to chelate calcium ions from dentin was examined by inductively coupled plasma-atomic emission spectrometry（ICP-OES）.The dentin surfaces conditioned with SiO₂-EDTA and EDTA were detected by field emission scanning electron microscopy（SEM）,TEM and microhardness testing.The third part was to investigate the promotion effect of SiO₂-EDTA on durability of dentin bonding.In dentin bonding experiment,there were four groups:EDTA（wet）,EDTA（dry）,SiO₂-EDTA（wet）and SiO₂-EDTA（dry）.The collected teeth were cut with a low-speed diamond saw to remove the crown enamel,exposed the dentin surface of middle crown and polished with silicon carbide paper.Then ultrasonically cleaned in deionized water and dried for later use.EDTA and SiO₂-EDTA were used as dentin demineralization conditioning agent to condition the dentin surface for 1 min and 2 min,respectively.After rinsing the dentin surface,the part of the dentin surface adopted wet-bonding strategy,with filter paper to absorb excess water on the dentin surface,so that the dentin surface retained appropriate moisture,and then the surface bonded with adhesive（Adper Single Bond 2）and applied composite resin（Filtek Z350 XT）on it.The other part of the dentin surface adopted dry-bonding strategy,directly blowing dry the surface with water-free and oil-free air for 5 s,and then bonded with adhesive and applied composite resin on it.The above four groups were divided into two subgroups:immediately group and thermocycling group.In microtensile bond strength（μTBS）test,using universal testing machine to measure theμTBS value of each group to access the effect of each group on dentin bond strength.The matrix metalloproteinase（MMPs）activity at bonding interface accessed by laser confocal microscopy（CLSM）.The nanoleakage at bonding interface of each group was evaluated by nanoleakage test.Results TGA,XPS and FTIR results indicated that EDTA has been bonded to the surface of silica nanoparticle.The results of ICP-OES showed that SiO₂-EDTA had the ability to chelate calcium ions from dentin,although its chelation was significantly lower than that of EDTA group（P<0.05）.The SEM results showed that regardless of critical-drying or air-drying,the dentin surface conditioned with SiO₂-EDTA was rough and filled with cracks,while the dentin surface conditioned with EDTA was smooth after air-drying.TEM results indicated that the demineralization depth of SiO₂-EDTA is shallow than that of EDTA,and the intrafibrillar minerals still stained within collagen fibrils when the time of conditioning time was extended.The microhardness of SiO₂-EDTA group was comparable to that of the control group,and both were significantly higher than EDTA group（P<0.05）.In the dentin bonding experiment,regardless of wet-of dry-bonding strategy,the bond strength of SiO₂-EDTA group was comparable to EDTA（wet）group（P>0.05）.Compared with EDTA,SiO₂-EDTA reduced the activity of MMPs and nanoleakage along the resin-dentin bonding interface.Conclusion This study demonstrated that the constructed SiO₂-EDTA as conditioning agent could achieve dentin extrafibrillar demineralization and promoted the stability and durability of dentin bonding.The SiO₂-EDTA of 50 nm is larger than the gap zone（intrafibrillar minerals are mainly deposited here）could achieve dentin extrafibrillar demineralization and the application of dry-bonding strategy could obtained acceptable bond strength.After aging,SiO₂-EDTA can reduce the MMPs activity and nanoleakage at the resin-dentin bonding interface and improve the interface stability.In conclusion,SiO₂as a dentin-conditioning agent for extrafibrillar demineralization provides a possibility to promote the life of restoration bonding.