IRCT2012090510747N1 IRCT 2012-11-23 Vice chancellor for research ,Dental Faculty of Islamic Azad University of Tehran Comparison of the effect of ordinary yogurt drink with probiotic yogurt drink on the level of salivary Streptococcus Mutans Comparison of the effect of ordinary yogurt drink with probiotic yogurt drink on the level of salivary Streptococcus Mutans of dental student of Islamic Azad University in 1390 2011-11-06 anticipated 30 Complete https://irct.ir/trial/11165 interventional Randomization: Randomized, Blinding: Double blinded, Placebo: Used, Assignment: Crossover, Purpose: Prevention. 2-3 Condition 1: level of salivary streptococcus mutans. Condition 2: Enamel Caries. Intervention 1: Intervention Study Groups: a group that received probiotic yogurt drink. The considered yogurt drink was a production of Pegah Company and contains Lactobacilus Acidophilus and Bifidobacterium Bifidum. Each participant has been asked to take 200 cc amount of probiotic yogurt drink 10 minutes after dinner meal and not to brush their teeth for an hour after that. Intervention 2: Control group 1: a group that received regular yogurt drink.The considered yogurt drink was a production of Pegah Company. Each participant have been asked to take 200 cc amount of regular yogurt drink 10 minutes after dinner meal and not to brush their teeth for an hour after that. Intervention 3: Control group2: a group that did not use any yogurt drinks. The control group has been asked not to use any yogurt drink or probiotic products in three weeks through the study.