This study was performed to evaluate the effect of Streptococcus oralis on the formation of artificial plaque and the replication of Streptococcus mutans. S. mutans was incubated alone and in the combination with S. oralis in the beaker with wires. The produced plaque weight and the viable cells of S. mutans were compared between those cultures. Various factors were studied about the effect on the formation of plaque and the replication of S. mutans. Followings are the results.
1. Lower amount of plaque was produced and fewer cells of S. mutans were replicated at the mixed culture of S. mutans and S. oralis than S. mutans alone.
2. When 10 mM glucose was added, the plaque weight was increased in the culture of S. mutans alone. But in the mixed culture ol" S. mutans and S. oralis, the plaque weight was not increased when 10 mM of glucose was added.
3. When 10 mM fructose was added, the plaque weight was increased in the culture of S. mutans alone or combined S. mutans and S. oralis.
4. In the mixed culture of S. mutans and S. oralis with different concentration, the more S. oralis exist, the less plaque and the fewer viable cells of S. mutans were observed.
5. The plaque weight and the viable cells of S. mutans were more decreased in the mixed culture of S. mutans and S. oralis than S. mutans alone after 12 hours.
6. When Staphylococcus epidermidis consuming hydrogen peroxide was added to the mixed culture of S. mutans and S. oralis, the plaque weight and the viable cells of S. mutans were increased.
7. When 10,000 units of catalase were added to the mixed culture of S. mutans and S. oralis, the plaque weight and the viable cells of S. mutans were increased.
8. In culture of S. mutans, the more concentration of hydrogen peroxide was added, the less plaque and the fewer viable cells of S. mutans were produced.
These results indicate that S. oralis inhibited the formation of plaque and the replication of S. mutans, and this may result from the formation of hydrogen peroxide by S. oralis.
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