The Study Of The Effect Of Incubated Concentrations Of Photosensitizer In HMME-Mediated Photodynamic Therapy On Anticaries

Dental caries is a progressive disease influenced by external factors which damages the enamel, dentin or cementum. Its essence is a bacterial infectious disease. The formation of acid products through the metabolism activity within dental plague is a directed factor in the development of dental caries. Dental plague contains many cariogenic bacterium, for example, Streptococcus mutans (S.mutans), Actinomyces viscous, Streptococcus sangius and Lactobacilli has been currently implicated as the primary aetiological agent. So to inhibit S.mutans growth by appropriate method is an important path to the prevention of dental caries. The result of experiment in vivo shew that HMME-mediated photodynamic therapy can inhibit S.mutans effectively. PDT is thought to be positive in the protection of dental caries. In the period of establishing the caries rat model for further study, the rat's teeth were treated with different concentrations of HMME-mediated PDT once a week for four weeks, recorded the changes of S.mutans and observed the effects of PDT on the development of dental caries. The anticaries result of PDT was compared with sodium fluoride. The experiment was preliminary discussed the proper concentration of HMME photodynamic effect in the role of caries prevention.Objectives:①To investigate the effects of different concentrations of HMME with the laser had the wavelength of 532nm on the growth of S. mutants in vitro, and prepared for the fllowing animal experiment.②To study the effect of different concentrations of HMME-mediated PDT on the growth of primary cariogenic S.mutants and the development of caries in rats, then find the suitable dose of photosensitizer. It will be provided theoretical basis and experimental evidence for PDT used for the prevention of caries in clinical.Methods:①The suspension of Streptococcus mutans incubated with different concentrations(5μg/ml,10μg/ml,20μg/ml,40μg/ml,50μg/ml,60μg/ml) of HMME for five minutes, then irradiated by the semiconductor laser whose wavelength is 532nm and output power was 120mw and the density power was 140mw/cm2. Finally, the viable counts of S. mutans recorded by counting colony forming unit were compared among the HMME-PDT groups, photosensitizer-only group, laser-only group, and blank control group. ①Wistar rats, whose molars were inoculated with Streptococcus mutans (S. mutans), were fed with caries-inducing diet 2000 in order to establish the caries rat model. These rats were divided into five groups, whose molars were treated respectively with 10μg/ml HMME-PDT (group A),20μg/ml HMME-PDT (group B), 40μg/ml HMME-PDT (group C),0.2 g/L sodium fluoride as positive controls (group D), and with 0.9% sterile physiological saline as negative controls (group E) once a week for four weeks and recorded the changes of S. mutans every week. The rats were then killed. The surface morphology of dental caries of the rats was observed by scanning electron microscope.Result:①The experiment in vitro shows that the viable counts of Streptococcus mutans of different consentrations of HMME-PDT are reduced significantly(P<0.05). The counts are reduced gradully with HMME concentration increasing from 5μg/ml to 40μg/ml, but there were no significant decreasing trends found when the HMME concentration continued increasing.②Animal experiment shows that the colony count in each group shows no significant difference in the first and second weeks (P>0.05). The colony counts of group 20μg/ml HMME-PDT and 40μg/ml HMME-PDT are significantly reduced compared with group 0.9% sterile physiological saline in the third week (P<0.05). In the fourth week the colony counts of group 10μg/ml,20μg/ml and 40μg/ml HMME-PDT are significantly reduced compared with group 0.9% sterile physiological saline (P<0.05 or P<0.01). Meanwhile the colony count of group 40μg/ml HMME-PDT is significantly lower than both group 10μg/ml and 20μg/ml HMME-PDT(P<0.05).③The tooth enamel of both group 40μg/ml HMME-PDT and 0.2g/L sodium fluoride are found to be damaged most slightly, and the tooth surfaces of the two groups are relatively smooth.④The hardness of buccal enamal of groups 20μg/ml,40μg/ml HMME-PDT and 0.2g/L sodium fluoride have no significant difference (P<0.05), but are significantly high compared with group of 0.9% sterile physiological saline (P<0.05). The hardness of lingual enamal in each group shows no significant difference (P<0.05).Conclusion:In vitro, the experiment shows that only the presence of photosensitizer or only the presence of the laser is almost no killing effect on Streptococcus mutans, but the combination of the two factors has a significant effect on Streptococcus mutans. The viable counts of Streptococcus mutans are reduced gradully between 5μg/ml HMME and 40μg/ml HMME. But over this range the effect of PDT on bactericidal was no significantly increased. The rat caries model simulating the developing of human dental caries is used for the experiment study of PDT. The group of 40μg/ml HMME-PDT kills Streptococcus mutans of rat oral effectlively. PDT can clean the tooth surface and control the dental plague attaching to tooth surface, meanwhile reducing the extent of the damage, so PDT is the key of anti-caries. In addition, PDT can improve the surface hardness of the rat's tooth, that can slow or stop the process of dental caries. HMME-PDT will provide a new effective method for the prevention of dental caries.