Study On Dopamine Modified Dentin Adhesive System To Improve Bonding Quality

Caries are very popular among the population and can seriously affect human health.Composite resins have been widely used as clinical restoration materials.They are aesthetic,convenient for clinical operation and nontoxic.The weak link of composite resin restoration lies in the dentin-adhesive interface.The dentin is demineralized after etching and the collagen is exposed,but the adhesive monomer cannot completely penetrate into the demineralized collagen fibers,resulting in a weak layer which is easily destroyed by enzymatic hydrolysis.Secondary caries are the most common reason for the restoration failure.Fissures are formed between the dentin and the composite resin,causing microleakage and leading to the growth of bacteria.Therefore,increasing the stability and durability of the adhesive can effectively control the occurrence of secondary caries and prolong the service life of the restoration.Mussels are marine organisms that can obtain long-lasting adhesion in a humid environment and attach to the surface of any natural or synthetic substrate through the adhesive protein secreted by the mussel byssus.Inspired by the phenomenon of mussel adhesion in nature,dopamine hydrochloride is used to modify the dentin adhesive system from three aspects:dentin primer,dentin adhesive matrix and filler,in order to improve the dentin adhesive performance.In the second chapter,inspired by the marine mussels,we synthesized biomolecule analogue N-3,4-dihydroxyphenylethylmethacrylamide monomer(DMA),which contained the catechol group and the acrylic group,providing chemical crosslinking for different materials.The shear strength,microleakage,degree of conversion,contact angle and biocompatibility were evaluated.¹H NMR and FTIR results showed that DMA monomer was successfully synthesized.Thermal stability experiment showed that the initial decomposition temperature of DMA monomer could meet the requirement of dental applications.The shear strength of the three commercial adhesives was significantly improved after applying DMA primer,but the difference in concentration and solvent had no effect on the shear strength.After applying the DMA primer,the wettability of the dentin surface could be improved,and the adhesive could penetrate into the demineralized dentin collagen matrix more easily.However,the degree of conversion of the adhesive was decreased.The microleakage experiment showed that the DMA primer could decrease the microleakage.And the DMA primer showed no negative influence on cell proliferation.In the third chapter,for the convenience of clinical operation,we directly mixed the DMA monomer into the experimental dentin adhesive,and then introduced the2-isocyanatoethyl methacrylate(IEM)monomer into the adhesive with an isocyanate group(NCO)and an acrylic group in the opposite end.On the one hand,the NCO group could react with the water in the dentin,and the acrylic group could undergo free radical polymerization with the adhesive monomer which could compensate for the decreased degree of conversion caused by DMA.On the other hand,the NCO group could also react with the NH₂of the dentin collagen,forming chemical bonding and enhancing the bonding strength of the adhesive.Different proportions of DMA monomer and IEM monomer were mixed into the experimental adhesive to prepare dual-component adhesive.Its physical and chemical properties were evaluated through thermal stability test,contact angle,degree of conversion.The mechanical properties were evaluated through immediate and aging shear strength tests.ATR-FTIR characterization,SEM characterization,HYP release and dry weight loss of dentin collagen were evaluated for the crosslinking effect of dentin collagen.MTT test and live/dead cell staining were used to evaluate the biological safety of the dual-component adhesive.The thermal stability test showed that its initial decomposition temperature could meet the requirements for dental application.The immediate shear strength of the dual-component adhesive was improved compared with the control group,and the shear strength after aging was increased.ATR-FTIR showed that the IEM monomer could form a covalent bonding with the amino group of dentin collagen.After the application of IEM,the degradation of dentin collagen was significantly reduced,which was manifested in the significant reduction of the release of HYP and the dry weight loss of dentin collagen.The results of MTT experiment and live/dead cell staining showed that the dual-component adhesive had excellent biocompatibility.The dual-component adhesive could form a chemical bonding with the hydroxyapatite and collagen matrix of the dentin.Together with the micro-mechanical retention,it could form a stable bonding interface and prolong the service life of the restoration.In the fourth chapter,HA-PDA-Ag-PDA filler was prepared and characterized(SEM,TEM,XPS,FTIR,XRD).The HA-PDA-Ag-PDA filler was mixed into the experimental adhesive in the proportion of 0.5 wt%,1 wt%,and 2 wt%to prepare a dual-functional dentin adhesive.The antibacterial property of the adhesive was characterized using S.aureus and S.mutans.The remineralization performance was mainly characterized by SEM observation and surface hardness test of the adhesive.The influence of HA-PDA-Ag-PDA filler on the shear strength and contact angle of the experimental adhesive was also evaluated.Finally,the cytotoxicity of the dual-functional dentin adhesive was evaluated by MTT experiment,live/dead cell staining and the release of silver ions.The antibacterial rate in the 2 wt%group reached over 99%for both kinds of bacteria tested.In the SEM pictures,a significant reduction in the number of live bacteria was observed in the experimental group.The bacteria in the control group shrank less and had a more complete round shape.However,in the experimental group,more obvious shrinkage of the bacteria,cell membrane damage and leakage of the cell contents was noticed.The higher the content of the filler was,the more severe damage occurred.Bacterial live/dead staining experiment showed that it was difficult to see the green live bacteria in the 1wt%and 2 wt%groups,however,the red dead bacteria increased.After immersing in artificial saliva for a specific time(1 d,7 d,14 d,28 d),apatite crystals could be observed on the surface of the dual-functional adhesive sample by SEM.The EDS result was consistent with the SEM result.The functional adhesive also demonstrated good biocompatibility.In summary,we use dopamine to modify the dentin adhesive system from three aspects of dentin primer,adhesive matrix and filler to improve the durability and stability of dentin adhesives.Therefore,our study has paved the way for future clinical applications to prevent the occurrence of secondary caries and could provide new ideas and experimental foundations for dentin bonding materials.