Objectives: To evaluate the effectiveness of probiotic drink on factors affecting dental caries. Materials and Method: A three phase study where 12 volunteers were recruited with a DMFT score >3.The unstimulated saliva samples were collected prior to the start of intervention .The saliva samples were also collected after two weeks of consumption of the probiotic drink ,Yakult (Yakult Honsha co.,Ltd) and after wash out period of two weeks .These samples were cultured to detect the Streptococcus mutans level by colony count and to detect pH using pH strips. The volunteers were also asked to maintain a diet chart to determine sugar exposure. Results: The mean of Streptococcus mutans colony count has significantly decreased from 27.17 (baseline count) to 2.50 (two weeks of intervention) respectively and has increased to 11.75 (washout period of two weeks). The mean of pH at baseline, after two weeks of intervention and after washout period were 6.08,6.92 and 7.00 respectively. The correlation coefficient of dietary sugar exposure with Streptococcus mutans count for baseline and after two weeks of intervention were -.227 and -.007 respectively. Conclusion: Probiotics when used as a regular drink reduces the Streptococcus mutans count in the oral cavity. People who have high sugar exposure can also control the oral microbiome with regular usage of probiotic with no significant variation in the salivary pH. It exhibits transient colonisation and lacks substantivity. Keywords: Probiotics; Lactobacillus casei shirota; Streptococcus mutans ; salivary pH; sugar exposure