| Objective:Caries is a dental hard tissue progressive disease that caused by complex factors from the oral cavity, which is characterized by high incidence and wide distribution.The World Health Organization has its parallel with the cancer and cardiovascular diseases prevention for the three major human diseases. Investigation etiologies of dental caries, to find effective ways and means of prevention of dental caries are the focus of foreign scholars.To explore effects of different parameters of photodynamic therapy on preventing dental caries, changes of endodontic tissue in rats, and provide applications for further clinical guidance. Using Streptococcus mutans in vitro cultured bacterial suspension, optimize the laser parameters, the photosensitizer incubation time and concentration, so as to select three group laser parameters, the best photosensitizer incubation time and photosensitizer concentration to carry out photodynamic therapy on dental caries formation in rats.Methods:(1) Recovery of S. mutans at room temperature, bacteria were routinely grown overnight in tryptic soy broth (TSB) under aerobic conditions at 37℃using a constant temperature incubator in order to the number of colonies to reach 1×108CFU/ml, set aside.(2) The bacterial suspension of S.mutans were added into 96 well plate, 100μl each well, in accordance with the experimental design for laser radiation, optimizing photosensitizer incubation time, concentration and laser parameters. According to colony-forming unit (CFU) result after irradiation, we selected parameters for the further experiment on rat caries model.(3) Wistar were infected with S.mutans and fed diet 2000 # to establish the caries rat model.The rat's teeth were treated with 17mwHMME-PDT group,34mw HMME-PDT,68mwHMME-PDT,0.9%NS,0.2% NaF, only laser, only photosensitizer once a week. HMME was used as the photosensitizer and semiconductor laser as the light source. The rats were killed after five weeks.(4) Keyes counts were used to measure the inhibitory effect of dental caries. The hard tissues of rats were evaluated by Scan electronic microscopy (SEM).Using pathological section to evaluate changes of pulp tissue.Results:(1) The colony counts of S. mutans in 96 plates after PDT in vitro experiment showed that incubation 3min, the concentration of 40μg/ml was the best photosensitizer parameters, and 17mw,34mw,68mw was the appropriate laser parameters.(2) Keyes score results of the smooth surface and fissure E-class caries in rats showed that different power density PDT group' score and fluoride groups' were significantly lower compared with the negative control groups' (P<0.05); on the smooth surface and fissure Ds-level caries, in comparison with the negative control group' score, in addition to pit and fissure Ds level caries 17mw HMME-PDT groups'Keyes scores were not significantly different (P>0.05), Keyes score of the rest of the PDT group and the sodium fluoride group were lower (P<0.05);on smooth surface and fissure E-class, Ds-class caries, Keyes caries scores were not different among the simple laser irradiation group, simple photosensitizer group and negative control group (P>0.05). Dm level caries of smooth surface were not detected in different power density PDT group and sodium fluoride group, but were detected in simple laser irradiation group, simple photosensitizer group and negative control group. Keyes caries score of Dm level for pit and fissure caries, compared with the negative control groups', Keyes scores of the different power density PDT group and sodium fluoride group were significantly lower(P<0.05), both which showed a strong role in prevention of dental caries (P<0.05); Dx level for smooth surface caries, all groups were not detected. Dx level of pit and fissure caries were only detected in the negative control group.Keyes score results in rats (smooth surface E-class, Ds-level caries; fissure E-class, Ds level, Dm-level caries), compared with the positive control group', Keyes score of 17mwHMME-PDT group were higher (P<0.05), Keyes score of 34mwHMME-PDT group were not statistically different (P>0.05), Keyes score of 68mwHMME-PDT group were lower (P<0.05); in comparison with 17 mwHMME-PDT group', Keyes score results of 34mwHMME-PDT group and 68mwHMME-PDT group were both lower (P<0.05), showing strong anti-caries effects; Keyes score results of 68mwHMME-PDT group in comparison with the 34mwHMME-PDT group'were lower(P<0.05). With the power increasing, Keyes scores were gradually decreased.(3) Scanning electron microscopy images after exposure to PDT suggested varying degrees of changes in the teeth after the different laser power density irradiation. The enamel surface of negative control were roughness and had pits, scratches and hole-like demineralizing area, these holes were deep and uneven; enamel surface were smooth and still had a little strip pits, scratches, hole-like demineralizing area after laser irradiation alone; after 17mwHMME-PDT group laser irradiation, the enamel surface became more smooth and had a little strip pits; after 34mw HMME-PDT group laser irradiation, the enamel surface were more smooth and had a very little strip pits; after 68mwHMME-PDT group laser irradiation, the enamel surface were smooth and flat, having a small amount of point-like depressions and scratches, the melting structure in some parts of the enamel could be seen.(4) Pathological section showed that different laser power density irradiation teeth, pulp tissue may show capillary expansion, inflammation, congestion changes and so on. After laser irradiation,17mwHMME-PDT group and 34mwHMME-PDT group showed capillary expansion, congestion, whereas 68mwHMME-PDT showed more capillary expansion, congestion, but no found inflammatory corpuscle infiltration; The scoring of 17mwHMME-PDT group and 34mwHMME-PDT group compared with negative control were not different (P>0.05);The scoring of 68mwHMME-PDT group were highly compared with negative control (P< 0.05).Additionally, with the laser power increasingly, Pulp scores were increased gradually.Conclusions:(1) HMME-mediated PDT was efficient at killing S.mutans of bacterial suspensions in vitro, killing result had a relationship with the photosensitizer incubation time, the photosensitizer concentration and the irradiation power density.(2) The different power density of photodynamic laser irradiation rats' teeth could cause varying degrees of change in tooth surface. The greater power density, the more distinct changes could be found in the structure of the tooth surface. (3) The different power density of photodynamic laser irradiation rats'teeth could cause different degrees changes in pulp tissue. The greater power density was likely to cause pulp hyperemia, edema and other pathological changes.(4) HMME-mediated PDT had significantly inhibitive efficacy on Caries Development in Rats, its inhibitive effect presented close correlation with the power density of laser. So looking proper power density during treatment is very important. |
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