EFFECT OF FLUORIDE ON THE GROWTH OF HYDROXYAPATITE AND HUMAN DENTAL ENAMEL

A highly reproducible seeded growth method has been used to study the mineralization of calcium phosphate on human enamel and hydroxyapatite seed crystals at a pH of 7.4 and 37°C in stable supersatured solutions of calcium phosphate containing various concentrations of fluoride ion. The pH and pF values were maintained constant potentiometrically by the addition of potassium hydroxide and potassium fluoride, respectively, and the grown material was characterized chemically, by infrared spectroscopy, by scanning electron microscopy and by subsequent dissolution kinetic experiments. Low concentration of fluoride (~ 0.15 ppm) reduce the rate of crystallization in inital stages, but an enhancement of calcium phosphate mineralization is observed in the presence of higher fluoride concentrations (1-5 ppm). Whereas the stoichiometry of the first-formed surface phase corresponds to that of octacalcium phosphate in the absence of fluoride, higher molar calcium/phosphate ratios are indicated in its presence.