Application Of Etch-Crosslink Technique In Improving The Long-Term Stability Of Dentin Bonding

PART ?Resin repair has always been the first choice for both medicine and patients with dental defects.However,Comparing to mature enamel bonding,there are still many problems with dentin bonding.During the bonding process,the exposed collagen fibers in the mixed layer are easily degraded by the activated MMPs and cathepsins.Therefore,domestic and foreign scholars try to improve the durability of the dentin adhesive by using MMPs inhibitors and protein cross-linking agents.In this thesis,calcium ion pretreated NDGA was used to cross-link demineralized dentin collagen to verify its mechanism and influence on adhesion performance.Firstly,the NDGA was pretreated with calcium chloride to prepare a solution of a certain mass fraction,and the absorption peak intensity of the solution was directly observed by ultraviolet-visible spectroscopy.The dentin slices completely demineralized by 48 h 10% phosphoric acid solution were treated with crosslink agent,and then we observed the reaction mechanism of NDGA and type I collagen by XPS.The demineralized dentin slices treated by exogenous enzymatic degradation cross-linking agent were used to measure the mass of loss,HYP content release and elastic modulus before and after enzymatic hydrolysis to analyze the anti-enzymatic properties,and then the cross link collagen morphology was observed by TEM.Finally,UV-VIS study validated the assumption that NDGA might form bisquinone bond between two adjacent o-quinone groups,resulted in NDGA polymer matrix in which dentin collagen fibrils were embedded.And the XPS verified the chemical combination of calcium and phenolic hydroxyl of NDGA.These results confirmed that calcium ions couldeffectively improve the mechanical properties and anti-enzymatic properties,and the collagen fibers were more closely arranged.Finally,this experiment clarified the binding of type I collagen and NDGA under the regulation of calcium ions and its crosslinking reaction mechanism from the molecular level,and verified its stability effect on the cross-linking of dentin collagen.PART ?Study on the effect of biomodified etchant to the dentin bondProtease inhibitors and crosslinkers can improve the service life of resin dentin adhesive materials,but the application of crosslinkers alone undoubtedly increases the clinical steps.Previously,the research group had prove that adding procyanidins to etching agents could significantly improve its mechanical properties and anti-enzymatic properties.Therefore,in this study,we evaluated the effects of in situ enzymatic activity and dentin bonding durability after application of NDGA modified etchants.Divided into four groups: 10% H3PO4 ? 10% H3PO4+DMSO ? 10% H3PO4+0.5%NDGA?10% H3PO4+1% NDGA,treated the demineralized dentin with the above solution as an acid etching crosslinkers,and then we dealed with resin adhesive,and cutted perpendicular to the adhesive plane,fixed on the slide,added gelatin enzyme and incubation in the incubator,we observed under excitation wavelength of 488 nm using a laser confocal microscope endogenous enzymes activity.Similarly,other above bonded resin dentin slices were immersed in the 0.1mg/ml collagenase-containing artificial saliva in the dark at 37°C for one month,replaced every 3 days.and the other slices were cutted into small cylindrical specimens of 0.8mm*0.8mm.The instant and long-term micro-tensile bonding strength ware tested by universal testing machine to verify its mechanical properties.SPSS16.0 software was used for two-way ANOVA of the microtensile strength of dentin bonding.From CLSM,we observed strong green fluorescence in control group,this indicated that the fluorescein-bound gelatinases at these sites were strongly hydrolyzed by endogenous enzymes of dentin collagen fibers.The fluorescence intensity of 10%H3PO4+ 1%NDGA was the weakest,indicating that the corresponding endogenous enzymeactivity was the weakest.The results of micro-tensile strength showed that the adhesive strength of resin dentin was the strongest in the 10% H3PO4+1%NDGA modified acid etchant group,these results indicated that the modified acid etchant of high concentration could effectively reduce the in situ enzyme activity and improve the adhesive strength of resin dentin.