Methods: In the present study that was conducted as “clinical trial double-blind randomized crossover”, 30 healthy dental students participated. Salivary counts of participants' Streptococcus mutans were determined by using the mitis salivarius agar environment at the base time, after 3 weeks run in period, (T1), after the completion of 3 weeks consumption (T2), and 3 weeks after discontinuity (T3) of probiotic yoghurt, ordinary yogurt (C1) or none of them (C2) by considering 3 weeks washout period. The data were analyzed in terms of intra-group and inter-groups differences by Repeated Measures and Paired-Samples T respectively. Statistical significant level was established at P<0.05.
Results: The results showed significant differences in the salivary counts of S. mutans between probiotic and control groups C1 (P=0.009) and C2 (P=0.012) at T2. However, there was no difference between C1 and C2 measures at any of the time points. Besides, a significant count reduction in the salivary S. mutans was noticed duringT1-T2 period (p= 0.028) within the probiotic group, but there was no significant difference during T2-T3 period.
Conclusions: It seemed that a 3 weeks period of probiotic yogurt consumption had an ability to reduce the number of salivary Streptococcus mutans and this effect remained 3 weeks after discontinuity.