The inhibition degree of the isolated bacteria on plaque formation of Streptococcus mutans, and the effect of these bacterial genus on the concentration of total bacteria in saliva were assessed with the following. The effectiveness of the isolated bacteria on the inhibition of plaque formation was assessed culturing Streptococcus mutans in the beaker with orthodontic wires. The mean weight of plaque produced on a wire was 152mg in the culture of Streptococcus mutans only, whereas being reduced to 4mg, 78mg, or 72mg in the combined culture of Streptococcus mutans and Enterococcus durans, Lactobacillus acidophilus, or Streptococcus oralis. The colony forming units (CFU) of Streptococcus mutans were per ml in the culture of Streptococcus mutans, only, wheras being per ml in the combined culture of Streptococcus mutans and Enterococcus durans, Lactobacillus acidophilus, or Streptococcus oralis. When saliva from children was inoculated on brain heart infusion agar, the colony forming units of bacteria were per ml of saliva. The concentration of Enterococcus, Lactobacillus, or Streptococcus inhibiting Streptococcus mutans in saliva was not proportioned to that of total bacteria replicated on brain heart infusion agar. These results indicate that the isolated bacteria inhibited the replication of Streptococcus mutans, resulting into inhibiting the formation of plaque, but the concentration of Enterococcus, Lactobacillus, or Streptococcus inhibiting Streptococcus mutans, in saliva might not affect the total bacterial concentration of saliva.