Because this study choosed the children who had at least two carious teeth at the same time that avoided bias on different oral circumstance , different oral habit ,and different dietetic habit.

• 分析认为，本实验选择的对象是一人有两颗以上龋齿的儿童，这就避免了不同口腔环境、口腔习惯和饮食习惯造成的偏倚。