Study On The Antibacterial Activity And Mechanism Of Ag₂O/TiO₂ Combined With Dental Led Curing Light Against Streptococcus Mutans

Dental caries,one of the most important chronic diseases in the human oral cavity,which has been listed by the world health organization?WHO?as one of the three key diseases to be prevented and treated together with cancer and cardiovascular disease.Gram-positive facultative anaerobic bacterium Streptococcus mutans?S.mutans?is one of the major cariogenic bacteria.S.mutans can produce extracellular polysaccharides?EPS?to form a dense biofilm,which can protect the bacteria in the biofilm and enhance their resistance to traditional antimicrobial agents.It can also produce organic acids such as lactic acid,which can corrode teeth and cause caries.Traditional dental drugs need a long period time to against microorganism and have good antibacterial effect on the planktonic,but poor effect on the biofilm state.Therefore,it is important to develop efficient and short-term anti-planktonic and biofilm S.mutans methods.In this paper,the photocatalytic Ag₂O/Ti O₂ was synthesized and the LED curing lamp,commonly used in dental clinic was introduced to explore the photodynamic bactericidal effect and mechanism against S.mutans on planktonic and biofilm state in a short period of time.Meanwhile,we doped Ag₂O/Ti O₂ into the glass ionic cement?GIC?,a dental adhesive material already in clinical use,to explore the influence on the mechanical properties and antimicrobial properties of GIC,which provide theoretical basis for the clinical application of Ag₂O/Ti O₂.The main research contents of this project are as follows:1.Synthesis and characterization of Ag₂O/Ti O₂ microcomposite.Ag₂O/Ti O₂ microcomposite was synthesized by hydrothermal synthesis and deposition precipitation methods,and their composition,morphology and optical properties were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,energy spectrum analysis?EDS?,ultraviolet visible diffuse reflection spectroscopy?DRS?and Photoluminescence?PL?.The results showed that the synthesized sample is Ag₂O/Ti O₂ with high purity,and Ti O₂ with a diameter of 2-3 mm is uniformly distributed with Ag₂ O nanoparticles with a diameter of 5-10 nm.Compared with Ti O₂,Ag₂O/Ti O₂ has an enhanced light absorption response in the visible light range.2.Study on the antibacterial activity and mechanism of Ag₂O/Ti O₂ on planktonic S.mutans under the irradiation of dental LED curing light.Antibacterial activity of Ag₂O/Ti O₂ microcomposite on planktonic S.mutans was investigated by inhibition zone,minimum inhibitory concentration?MIC?and minimum bactericidal concentration?MBC?methods.The results showed that the Ag₂O/Ti O₂ microcomposite has antibacterial activity against the planktonic S.mutans,but the antibacterial time is longer.When the dental LED curing light was introduced,the bactericidal activities of Ag₂O/Ti O₂ against on the planktonic S.mutans enhanced significantly after irradiation 5 min.Through live/dead bacteria staining,intracellular and extracellular ractive oxygen?ROS?measurement and heat production measurement,it is indicated that Ag₂O/Ti O₂ under the illumination of LED curing light killed the planktonic S.mutans mainly by generating of ROS.3.Study the antibacterial activity and mechanism of Ag₂O/Ti O₂ on biofilm formation and mature biofilm of S.mutans under the irridation of dental LED curing light.Through crystal violet staining?colony counting?,live/dead bacteria staining and SEM observation,we found that Ag₂O/Ti O₂ exhibited significant inhibition on the biofilm formation and mature biofilm of S.mutans,and the inhibition was more significant after irradiation with LED curing light.By measuring the acid production during the biofilm formation,EPS sythesis during biofilm formation and mature biofilm and relative expression of the related gene,we found that Ag₂O/Ti O₂ and Ag₂O/Ti O₂+LED can inhibit biofilm formation and mature biofilm by inhibiting S.mutans EPS sythesis,acid production and down-regulated the related genes.4.Study on the modification of the mechanical properties and the enhancement of antibacterial activity of Ag₂O/Ti O₂ doped into dental adhesive glass ionomer cement?GIC?.The compressive strength was measured by the universal energy testing machine.It was found that the mechanical strength of Ag₂O/Ti O₂@GIC was significantly improved after doping Ag₂O/Ti O₂.In addition,the water absorption rate of Ag₂O/Ti O₂@GIC increased,and the dissolution rate decreased significantly.By colony counting and MTT staining,we found that Ag₂O/Ti O₂@GIC has a significant inhibitory effect on the planktonic S.mutans and its biofilm formation.