Polymerase chain reaction is a revolutionary development in science because it helps to determine even minute quantities of bacteria. Studies have shown high sensitivity and reliability of these machines in detecting bacteria even to a 2-fold change in the bacteria count. Few studies have evaluated the S mutans levels with polymerase chain reaction. The previous studies were based on chairside kits or other immunologic and laboratory procedures. The results of our study are similar to them and establish the efficacy of probiotics in reducing S mutans levels using a more precise and sensitive methodology: real-time polymerase chain reaction