To develop the cariogenicity test for sugar substitutes and foods in vitro, the growing system of mutans streptococci was examined in this study. Four strains of mutans streptococci were cultured under aerobic or anaerobic conditions, and the time course of changes in pH value, cell growth and insoluble glucan synthesis were analysed. In all bacterial strains, either pH decrement, cell growth and insoluble glucan synthesis showed slightly higher values under anaerobic conditions compared with those under aerobic conditions after 5 to 7 hours of incubation. However, a difference of oxygen conditions did not have remarkable effects on data after a long incubations over g hours. After 23 hours of incubation, sorbitol was fermented by all strains of mutans streptococci used in this study, especially by Streptococcus mutans. Yet, after 9 hours of incubation, the fermentation was not very notable, but the difference in fermentability from sucrose was shown clearly. These results suggest that the optimal incubation time for evaluation might be approximately g hours under the conditions used in this study.

The time course of changes in pH and cell growth showed a similar pattern, so the capacity to grow mutans streptococci in sugar substitutes and foods were evaluated directly and indirectly. In addition, we analysed insoluble glucan synthesis in this test system. The capacity of sugar substitutes and foods to form dental plaque were assessed by the integration of data from the three ways of analysis in this test system.

Maltitol, xylitol and a food sample were tested by this system､ The results suggested that either two sugar substitutes or a food sample were non-cariogenic.