Investigation On Inhibition Of Photodynamic Therapy On Cariogenic Streptococcus Mutans Of Oral Biofilm

Dental caries is harmful to human health of the third kind of disease,secondonly to its health risks of cardiovascular disease and cancer.The direct cause of dentalcaries is that cariogenic Streptococcus mutans and other microorganism formeddental plaque in oral biofilm and acid metabolism activity carried out.Therefore,itcan prevent dental caries for adoption of appropriate means to affect the oral bacteriabiofilm metabolism and interfere with dental plaque formation or the promotion ofdissociation of dental plaque.Although it has been universally recognized of fluoridein caries prevention,but the use of the safety of fluoride and fluoride-resistant strainsof Streptococcus mutans bring a new topic for caries prevention.It is an urgent needof solve the problem to looking for a more safe and effective method of cariesprevention.Photodynamic therapy(PDT) has become one of the basic treatment of cancer.Inrecent years,PDT has also achieved remarkable effects of non-tumor diseaseparticularly for the treatment of bacterial and viral diseases.In view of the foreignlaboratory have been carried out the experimental studies for PDT on a singlecariogenic bacteria,but not on artificial caries model,this study from the point ofview of caries prevention to explore the effect of PDT to cariogenic Streptococcusmutans of oral biofilm of artificial caries model.Objective:To build an artificial caries model consistent with the physiological environmentand used it in PDT anti- caries experiments.To discuss the effects of PDT on themainly oral cariogenic biofilm bacteria (Streptococcus mutans).To analysis theimpact of different doses of PDT photosensitizer to bacteriostasis and select the doseof laser energy for PDT anti- caries.To investigate the anti- caries mechanism of PDTcombined with DiO,Hoechest33342 two fluorescent probe at cell level.To provideacademic and experimental evidence on PDT anti- caries for clinical practice.Methods:1.An artificial caries model was built consistent with the physiological environment with Streptococcus mutans.The growth curve of oral cariogenic biofilm and thesurface micro-hardness of enamel blocks were determined subsquently.2.Selected doses of PDT anti- caries:Applying different doses of 635nm diode laserenergy and different doses photosensitizer to achieve bacteriostasis effects forPDT anti- caries.3.Observed the effects of PDT to bacterial metabolism through the experiments ofinhibition of bacterial growth and acid metabolism of PDT.4.Analyzed the impact of PDT on the tooth surface hardness and calcium content bymicro-hardness analysis and atomic absorption spectrometry.5.Investigated the anti- caries mechanism of PDT combined with DiO,Hoechest33342 two fluorescent probe at cell level.Results:1.Oral bacterial biofilm growth at 48h reached a mature stage.After cariogenictreatment,the enamel surface micro-hardness value(MHV) of artificial cariesgroup was significantly lower than that of the control group(P＜0.05).2.When the diode laser energy dose of 12.47 J/cm~2,the growth of Streptococcusmutans of artificial caries model were significantly inhibited (P＜0.05).When thephotosensitizer HMME moderate dose (20μg/ml),PDT can be effectively playedthe bactericidal effect to Streptococcus mutans of oral biofilm in artificial cariesmodel (P＜0.05).3.After PDT treatment against dental caries,the number of Streptococcus mutans(CFU/ml) of oral biofilm in artificial caries model significantly reduced(P＜0.05),the bactericidal rate up to 99.36%;the ability of S.mutans acidproduction decreased significantly (P＜0.05).4.MHV descending order of the experimental groups:simple laser＞PDT anti-cariestreatment＞simple HMME＞0.05% chlorhexidine＞0.9% saline.The dissolution ofcalcium concentration from small to big as following order:simple laser＜PDTanti-caries treatment＜0.05% chlorhexidine＜simple HMME＜0.9% saline.Therewere significant different compared between the experimental groups (P＜0.05).5.During the process of HMME-PDT anti-caries,HMME optional combined withcariogenic S.mutans showing red fluorescent;the same field of vision,when added green fluorescent membrane probe DiO,the cell surface displayed greenfluorescent;when at the same time also added Hoechest33342,while bluefluorescence in the bacement could be seen,but no Hoechest33342 combinationwith S.mutans.Conclusions:The artificial caries model formed in this study had the performance of earlyeanemal caries and could be used for the experimental research of PDT anti-caries.HMME-PDT doses selected through the experiments were:HMME 20μg/ml,diodelaser 10mW,90s,12.74J/cm~2.PDT can effectively kill S.mutans of artificial cariesoral biofilm and inhibit acid production of S.mutans.PDT can reduce the amount ofcalcium dissolution of the teeth,thereby significantly improve the surface hardness ofthe teeth Will help slow down or prevent the process of dental caries.The target ofHMME-PDT anti-caries located on the membrane of the S.mutans cells.Singletoxygen and other reactive oxygen substances(ROS) produced after laser irradiationdirectly damage bacterial cell membrane system,affecting their metabolism,leading tobacterial death,thereby made anti-caries effect.HMME-PDT is an effective method indental caries prevention,it has broad application prospects in dentistry.