Kinetics of release of calcium and fluoride ions from ion-exchange resins in artificial saliva

The paper reports the results obtained by studying the kinetics of release of anti-carious ions, such as Ca2+ and F-, from a carboxylic cation exchanger, Lewatit S8528, and a weak base resin, Lewatit MP62, and their binary mixtures of different compositions in contact with solution of artificial saliva. The release of ions from the resins was studied by using both the 'shallow bed' and the 'limited volume' techniques varying the granulometric composition of the resin fractions in the range of bead diameters from 0.42 to < 0.050 mm. It has been shown that the kinetics of Ca2+ release is far slower than that of F- ions. The release of F- ions from the resin mixtures of different compositions is essentially not affected by the presence of the cation exchanger in the Ca-form in the mixture. An opposite situation is observed for the release of Ca2+ ions, which appears to be far slower in the presence of the anion exchanger in the F-form in the resin mixtures. The results obtained are explained by different diffusivities of the ions under study. The formation of a microcrystalline CaF2 layer on the surface of cation-exchanger beads has been shown to be responsible for the retardation of calcium ions release from the resin phase.