FORMATION OF PHOSPHATE-CONTAINING CALCIUM-FLUORIDE AT THE EXPENSE OF ENAMEL, HYDROXYAPATITE AND FLUORAPATITE

During the caries process complex reactions involving calcium, phospha te, hydrogen and fluoride ions as main species take place. In this stu dy the precipitation and dissolution reactions occurring in suspension s of enamel, hydroxyapatite (HAP) and fluorapatite (FAP) on addition o f fluoride were investigated under well-defined conditions. pH and pF were monitored; calcium and phosphate concentrations were measured at selected times; the solid phases were examined by infra-red, X-ray dif fraction and transmission electron microscopy. Precipitation of phosph ate-containing calcium fluoride crystals, CaF2(P), can cause severe re duction in the calcium ion concentration and release of hydrogen ions from the precipitated phosphate. These reactions result in considerabl e dissolution of enamel, HAP and even of FAP. More of the added minera l dissolves with 50 mmol/l fluoride than with 10 mmol/l fluoride, main ly due to the greater reduction in calcium ion concentration. This wor k shows that phosphate-containing calcium fluoride is most likely an i mportant compound to be considered in the caries process.