effect of milk and yogurt on streptococcus sobrinus counts and caries score in rats

background: an anti-cariogenic diet containing probiotics can be effective in caries prevention. this animal study compared the effects of milk and yogurt on streptococcus sobrinus counts and caries score. materials and methods: a total of 36 male rats were infected with s. sobrinus (27,607) and divided into three groups. group a and b received 200 ml of milk and 100 g of yogurt per day, respectively, and a control group received 2.5 ml of ncp number 2 diet twice daily for 21 days. after killing the animals, their lower left jaws were removed and sonicated to quantify the colonies of s. sobrinus . dental caries was scored using keyes technique. data were analyzed using anova and kruskal-wallis, mann-whitney and wilcoxon-signed rank tests. statistical signifi cance was set at p < 0.05. results: the mean (±standard error of the mean) of s. sobrinus colonies in the milk, yogurt and control groups were determined at 119666.67 (±20733), 46416.666 (±12846) and 163,250 (±33493), respectively. microbial counts decreased in the yogurt group compared with the milk and control groups ( p = 0.004 and p = 0.000; respectively). there were signifi cant differences between caries scores of smooth surfaces in the milk and yogurt groups compared with the control group ( p = 0.000 and p = 0.000, respectively). both milk and yogurt signifi cantly reduced caries score of fi ssured surfaces compared with controls ( p = 0.004 and p = 0.000, respectively). conclusion: considering the limitations of this study, yogurt administration reduces s. sobrinus counts. in addition, yogurt and milk regimens reduce the caries scores of smooth and fi ssured surfaces. key words: dental caries, milk, streptococcus sobrinus , yogurt