Calcium Dissolution and pH Modulation in Plaque Fluid

Example 3

Dissolution of calcium compounds in plaque fluid was simulated using multicomponent thermodynamic speciation modelling, implemented using the software Geochemist's Workbench. The initial plaque fluid composition was modeled after starved plaque fluid from caries-free individuals. To simulate the low pH conditions following eating the initial pH was set to pH 5. Precipitation was suppressed for all minerals except for the mineral being modeled.

FIG. 1 is a plot of pH versus the amount of mineral added for the highly soluble and poorly soluble forms of calcium generated from the software model. The plot shows that addition of alpha-tricalcium phosphate and calcium carbonate to simulated acidic plaque fluid results in an increase in pH from pH 5 to pH 6 or above when saturation is reached. Addition of soluble calcium results in a decrease in pH.

FIG. 2 is a graph of HA saturation level versus the amount of mineral added for the highly soluble and poorly soluble forms of calcium. The plot shows that addition of alpha-tricalcium phosphate or calcium carbonate to simulated acidic plaque fluid results in an increase in hydroxyapatite supersaturation. At the solubility limit of alpha-tricalcium phosphate or calcium carbonate, hydroxyapatite supersaturation is at least five orders of magnitude greater than with addition of soluble calcium.