D. Muraviev et al., Kinetics of release of calcium and fluoride ions from ion-exchange resins in artificial saliva, SOLVENT EXT, 18(2), 2000, pp. 345-374
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 exchang
er, Lewatit S8528, and a weak base resin, Lewatit MP62, and their binary mi
xtures of different compositions in contact with solution of artificial sal
iva. The release of ions from the resins was studied by using both the "sha
llow bed" and the "limited volume" techniques varying the granulometric com
position 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 slo
wer 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 ob
served 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 re
sults obtained are explained by different diffusivities of the ions under s
tudy. The formation of a microcrystalline CaF2 layer on the surface of cati
on-exchanger beads has been shown to be responsible for the retardation of
calcium ions release from the resin phase.