The Study Of The Inhibition Of Photodynamic Therapy On The Early Root Caries

Objectives:Root caries is a common chronic bacterial infection disease which hazards the elderly oral health. The incidence of root caries is rising in our country. Root caries can develop into pulpitis or periarthritis in a relatively short period of time. Root caries has become a social problem. The plaque biofilm which attached to the root is the main cause of the root caries,so clear the plaque biofilm is the key to prevent root canes.Photodynamic therapy is a new method which use a specific wavelengths of light to activate photosensitizer, can kill pathogenic microorganisms or diseased tissue.To select the best effect of photodynamic therapy parameters on three main root caries pathogens in mixed suspension using the wavelength of532nm semiconductor and HMME as photo-sensitizer. Then establish early root caries models in vitro, explore the inhibitory effect of PDT on early root caries by observing the destruction of plaque biofilm the dissolubility of calcium and root caries surface morphology, to provide experimental basis for clinical applications of PDT in inhibition of early root caries.Methods:1.Revive A. viscosus,S.mutans and L.acidophilus as the experimental bacteria, anaerobic culture48h, adjust the concentration of mixed bacteria suspension into1×108CFU/mL.2.Combine different irradiation time (30s、60s、90s) of532nm semiconductor and various concentration of HMME (20μg/ml、40μg/ml、60μg/ml) to deal with the mixed bacteria suspension to select the best effect of photodynamic therapy parameters.3.Collect25premolars pulling for orthodontic and whole saliva, use the A. viscosus,S.mutans and L.acidophilus as the experimental bacteria to establish early root caries model.Use the best effect of PDT parameters to deal with the model then colony conting, evaluate the killing effect of PDT on the cariogenic bacteria in dental plaque biofilm of early root caries model. 4.Use atomic absorption spectrophotometerto measure the dissolubility of calcium of early root caries model after PDT, evaluate the inhibition of PDT to early root caries.5.Observe the effect of PDT on morphology of root surface in SEM.Results:1.The tablet colony count results of mixed bacteria suspension experiment showed the best effect of PDT parameter: the concentration of HMME is40μg/ml, and the time of532nm semiconductor is60s in continuous irradiation.2.The results of killing effect of PDT on the cariogenic bacteria in dental plaque biofilm of early root caries model shows that: compared with normal saline negative control group, PDT group can significantly decrease the cariogenic bacteria(P<0.05), the sterilizing rate reach up to98.70%.3.The results of the dissolubility of calcium measured with AAS showed that: Compared with normal saline negative control group, Laser group and Chlorhexidine group can reduce the dissolubility of calcium(P<0.05). The dissolubility of calcium in each point in time in PDT group were significantly decrease(P<0.05).4.The SEM showed that in PDT group:cementum surface structural integrity, no bacterial adhesion, fissure and pit decreases, and the fracture healing, tiny calcification around the deposit.Conclusion:l.The concentration of HMME is40μg/ml, and the time of532nm semiconductor is60s in continuous irradiation, PDT has a significant killing effect on the cariogenic bacteria in dental plaque biofilm of early root caries.2. PDT has a significantly effect to decrease the cariogenic bacteria in dental plaque biofilm of early root caries, not only prevent the root surface of bone continue to demineralization,but also promoted the root surface of bone remineralization. PDT can effectively restrain the early root caries, it has a wide prospect in clinical application in root caries prevention.