AIM:To investigate the effects of photodynamic therapy( PDT) of different energy densities with methylene blue( MB) as photosensitizer on streptococcus mutans( S. mutans) in vitro. METHODS:Fifty-six 22 d old Wistar rats were fed with streptococcus mutans to establish dental caries. The rats were then randomly divided into 7 groups(n=8) and received different treatments: MB-PDT with irradiation time of 120 s, 240 s, 480 s, MB only, PDT only, 2 g/L NaF(positive control), and 0. 9% normal saline(negative control), respectively. The rats were trea-ted once a week for 8 weeks. CFU of S. mutans was observed by plate colony count method. The Keyes caries score method was used to observe the the development of dental caries. Tooth surface structure was observed by scanning e-lectron microscopy ( SEM) . RESULTS:MB-PDT significantly reduced the number of S. mutans in the rats oral cavity (P<0. 05). Keyes caries score showed a decreasing trend of caries incidence(P<0. 05). SEM results showed that MB-PDT irradiation could seal the demineralization holes on enamel surface. CONCLUSION:MB-PDT has bacteri-alcidal effect on S. mutans, and can close demineralized hole on enamel surface. The effect is positively related to ex-posure time.%目的:探讨以亚甲蓝( MB)为光敏剂的光动力疗法( PDT)对大鼠口腔中变异链球菌的杀伤作用,及其对龋病发生的影响. 方法:取22 d龄 Wistar大鼠56只,通过口腔接种变异链球菌构建致龋模型后,随机分成7组(n=8):MB-PDT 120 s组 、MB-PDT 240 s组、MB-PDT 480 s组、单纯MB组、单纯PDT组、2 g/L NaF阳性对照组、生理盐水阴性对照组. 然后按上述分组分别进行相应处理(激光组所用光源为810 nm的半导体激光);每周处理1次,连续处理8 周后,分别采用平板菌落计数法观察各组对变异链球菌的杀伤作用;Keyes龋齿记分法观察各组龋病发生、发展情况;扫描电镜观察各组磨牙的表面形貌. 结果:菌落计数结果显示,与对照组相比,MB-PDT 120 s、240 s、480 s 3组均可使大鼠口腔中的变异链球菌数量显著减少(P<0. 05),且随着照射时间的延长,其杀菌率不断增加, Keyes 龋齿记分也呈现逐渐降低的趋势;扫描电镜结果显示, MB-PDT各组均可有效封闭釉质表面脱矿孔,且照射时间越长,封闭效果越好. 结论:MB-PDT 对大鼠口腔中变异链球菌有明确的杀伤作用,并能在一定程度上预防龋病的发生.
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