Study On Preparation And Application Of A Novel Polyurethane Antibacterial Self-adhesive Resin Cement

The prosthesis could be bonded to the surface of abutment teeth by cement through chemical bonding,mechanical locking or both,so as to maintain the durability and stability of the prosthesis.However,due to secondary caries,more than 50%of the restorations will fail to bond within ten years.Resin cement provides better adhesive and anti-aging properties than traditional cement to improve the retention rate of restorations.Polymerization shrinkage and hydrolysis will also appear in the resin material,resulting in the continuous expansion of the adhesive interface damage.At the same time,the adhesion,proliferation and acid production of bacteria will destroy the dentin and lead to secondary caries,further exacerbating the damage and failure of the adhesive interface.How to reduce the interface damage and improve the bonding system has become a current clinical problem.Polyurethane(PU)can play an elastic buffering role relying on the combination of soft chain and hard chain,in effectively offsetting the shrinkage stress caused by polymerization shrinkage and reduce the volume change.Different ratios of PU can also increase the hydrophobic properties of the material,which are conducive to reducing the damage of the adhesive interface.Based on the above functions of polyurethane materials,the research group plans to build up a novel type of PU resin cement system to reduce the polymerization shrinkage of the material by its elastic buffering capacity,maintaining the stress balance of the adhesive interface,and improve the hydrolysis resistance of the cement by virtue of its hydrophobic performance to ameliorate the long-term stability of the bonding system.There is no antibacterial property of the traditional resin cement to resist the adhesion and erosion of bacteria.The quaternary ammonium salt antibacterial agent is often used to enhance the antibacterial ability of resin materials due to its great contact-active antibacterial properties.In this experiment,the modified quaternary ammonium salt antibacterial agent-dimethylaminohexadecyl methacrylate(DMAHDM)was added to study its antibacterial properties against common cariogenic bacteria in the oral cavity,in order to provide a new idea and research basis for the improvement and development of low-shrinkage antibacterial cement.In chapter 2,four PU polymers with elastic buffer function were prepared by modifying PU polymers with acrylate and adjusting the ratio of polyester and polyether PU.The products were characterized by ~1H NMR and FTIR.The elastic buffering capacity of the four PU products was evaluated by testing the tensile strength and elongation at break;The best proportion of PU resin cement was selected by testing the water absorption and dissolution value,degree of conversion,static water contact angle,thermal stability,mechanical properties,polymerization shrinkage and micro-tensile strength of the material.The cytotoxicity,marginal microleakage and aging properties were studied.The results showed that the maximum tensile strength of the four groups of PU was 28.37 Mpa,and the elongation at break was 58.38%;Compared with the commercial group,the water absorption and dissolution value of each experimental groups were lower,the degree of conversion rate and water contact angle were higher,and polymerization shrinkage of the PU3 was better than the control group(P<0.05).After thermal cycles,the decrease of the micro-tensile strength and mechanical properties of the experimental group were significantly lower than those of the commercial control group(P<0.05).PU3 group was selected as the resin cement with the best comprehensive performance.In order to further optimize the mechanical and adhesive properties of the cement,PU self-adhesive resin cements with different diluents was prepared in Chapter 3.Their degree of conversion,water contact angle,mechanical properties,polymerization shrinkage,micro-tensile strength and aging properties were compared with the commercial group.The results showed that the PU1:1 self-adhesive cement group has the best comprehensive properties,and some properties could be close to or better than the commercial group.The surface pretreatment of tooth tissue is an important factor that affects the bonding strength.In this experiment,according to the different pretreatment methods of the three bonding systems of etch-and-rinse,self-etch and self-adhesive,a comparative study was conducted on the bond strength of enamel and dentin whether to etch and whether to apply primer and adhesive.The results showed that the micro-tensile bond strength value of the etch-and-rinse system in adhesive/dentine interface was the highest,however there was no significant difference between the self-etch and self-adhesive groups(P>0.05).After etching treatment,the bond strength of the etch-and-rinse system did not change significantly(P>0.05),but the self-adhesive group decreased to a certain extent(P<0.05).In the adhesive/enamel interface,the bond strength of the etch-and-rinse group was much higher than that of the self-adhesive group(P<0.05).The bond strength of self-adhesive cement was significantly improved by etching(P<0.05).It was suggested that the bond strength of self-adhesive resin cement can be enhanced by"selective acid etching"(only etching enamel).A great adhesive interface should not only reduce the polymerization shrinkage,improve the bonding performance and hydrolysis resistance,but also possess antibacterial properties to reduce secondary caries caused by bacterial aggregation and proliferation,and improve the durability and stability of the adhesive interface.Quaternary ammonium salt is a contact antibacterial agent in oral materials,but its chain length is too short to play an effective antibacterial role.In Chapter 4,16 units of long-chain DMAHDM antibacterial monomers were synthesized and mixed with different mass fractions into PU resin cement to evaluate their effects on the properties of PU cement by testing the degree of conversion,water contact angle,mechanical properties,polymerization shrinkage and adhesive properties.The antibacterial properties of DMAHDM with different proportions were evaluated by early attachment,MTT,Live/dead bacterial staining and CFU counts.The results showed that with the addition of DMAHDM,the mechanical and adhesive properties of PU cements decreased slightly,and there were statistical difference between the 4%and 5%groups compared with the 0%group(P<0.05).The antibacterial performance promoted with the increase of DMAHDM.The 3-5%groups could regulate the bacterial activity and quantity at a lower level and achieve better antibacterial effect.However,there were no significant difference among the 3-5%groups(P>0.05)in the early attachment and MTT.The CFU counts from 3%to 5%groups decreased with the decelerated trend,therefore the 3%group can achieve great antibacterial effect on the premise of great mechanical and adhesive properties.In summary,the following conclusions are speculated according to the experimental results:1.Polyether-polyester mixed PU resin cements showed low polymerization shrinkage and great adhesive performance,which could reduce the damage of adhesive interface and the occurrence of microleakage.2.Great hydrolysis resistance was presented in the novel PU self-adhesive resin cement,which was superior to the commercial group self-adhesive resin cement.The selective acid etching of enamel can enhance the adhesive property of resin cement,and maintain the great marginal sealing effect and long-term stability of the restoration system.3.The antibacterial property could be endowed by DMAHDM to PU resin cement to greatly reduce the bacterial concentration and activity on the surface of cement,thus improving the ability of the cement to resist secondary caries.The resin cement system containing 3%DMAHDM showed the best comprehensive performance.