Application Of IP6-PAMAM-NH₂ Collagen Extrafibrillar Demineralization System In Resin-dentin Bonds

Objecctive:In order to solve the problem of insufficient durability of resin-dentin bonding caused by the destruction of resin-dentin bonding interface structure owing to traditional acid etching bonding technology,this topic intends to introduce phytic acid（IP6）,a powerful chelating agent of small molecule,on the surface of dendrimer PAMAM-NH₂ with good solubility,to construct a system of IP6-PAMAM-NH₂ with large molecular weight（>40 k Da）and to test its ability of chelating dentin calcium ions.To study the ability of IP6-PAMAM-NH₂ complex as a pre-treatment agent for dentin bonding to achieve selective demineralization and antibacterial activity,and evaluate its influence on dentin bonding durability,so as to provide new ideas and technologies for preparing a new dentin bonding system.Methods:1)IP6-PAMAM-NH₂ polymer was synthesized,and the synthesized substances were detected and characterized by IR,gel permeation chromatography,NMR and HPLC.2)To test the ability of IP6-PAMAM-NH₂ complex as a pre-treatment agent for dentin bonding to achieve selective demineralization outside fibers.Prepare different concentrations of IP6-PAMAM-NH₂ solution,treat the surface of fresh dentin,and carry out"wet bonding"and"dry bonding"in turn.Test the bonding strength of composite resin-dentin under two technical conditions by micro-tensile test,and observe the micro-morphology of dentin collagen matrix treated by IP6-PAMAM-NH₂ by scanning electron microscope（SEM）.Atomic force microscope（AFM）was used to observe the surface roughness of dentin,and in-situ zymogram was used to evaluate the inhibition of IP6-PAMAM-NH₂ on the activity of matrix metalloproteinases（MMPs）in demineralized dentin layer.The anti-bacterial performance against S.mutans and E.faecalis biofilm on dentin surface was evaluated by living/dead bacteria fluorescent staining method,and its biological safety to dental pulp cells was evaluated by CCK-8 cell activity method.Result:The results of IR and GPC that IP6-PAMAM-NH₂ complex was successfully synthesized,and the molecular weight of the polymer met the requirement of selective extra-fibrillar demineralization（>40 KDa）.Meanwhile,The CCK-8 experiment showed that IP6-PAMAM-NH₂ has good biocompatibility.The results of micro-tensile test showed that the immediate bonding strength of the composite resin-dentin"wet bonding"and"dry bonding"in the experimental group treated with IP6-PAMAM-NH₂ solution had no significant difference with those in the phosphoric acid"dry bonding"group and phytic acid"dry bonding"group.SEM and AFM results showed that collagen fibers in dentin demineralized layer treated with IP6-PAMAM-NH₂ solution are fluffy and do not collapse,and the roughness of experimental group is greater than that of phosphoric acid group,which further confirms the practicability of the theory of selective extra-fibrillar demineralization.In-situ zymogram study showed that there was no obvious MMPs activity in dentin demineralized layer treated with IP6-PAMAM-NH₂ solution.Antibacterial experiments showed that IP6-PAMAM-NH₂ has a strong ability to inhibit the biofilm activity of S.mutans and E.faecalis.Conclusion:IP6-PAMAM-NH₂ synthesized in this research can achieve selective extra-fibrillar demineralization,achieve strong bonding strength,and will not lead to the activation of MMPs in demineralized dentin layer,effectively avoid the damage of interface structure integrity caused by traditional acid etching technology,show high antibacterial ability and biocompatibility,and have potential value in improving bonding durability of composite resin-dentin.