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Kinetics of hydroxyapatite dissolution during incubation with sucrose and Streptococcus mutans and its application to cariogenicity testing.

The kinetics of acid production from sucrose fermentation by Streptococcus mutans has been investigated. The rate of acid production, expressed as nmoles H+ produced per minute per milligram bacterial protein, was shown to be saturated at a sucrose concentration of 2 mM, a concentration below the taste threshold. Similarly the rate of calcium release from hydroxyapatite when added to the same system, expressed as nmoles Ca++ released per minute per milligram bacterial protein, was also saturated at a sucrose concentration of 2mM. The Michaelis constant (Km) for both processes was 0.2 mM sucrose. These results indicate that the rate-limiting step in this in vitro system was the production of organic acids by fermentation. In vitro tests to determine the cariogenicity of foods containing saturating sucrose concentrations are of limited value and the low Km value obtained here shows that most foods would contain saturating sucrose concentrations. Hence, as part of a cariogenicity test these foods should be diluted to allow comparison at non-saturating sucrose concentrations. Further, the low Km value could help explain the poor correlation reported between sucrose intake and caries incidence.