The Effect of Fluoride Application on Fluoride Release and the Antibacterial Action of Glass lonomers

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Abstract
The aim of this study was to investigate whether the release of fluoride and the antimicrobial effect of freshly mixed glass ionomers could be prolonged by application of fluoride on aged material. Test slabs of freshly mixed and aged (14 d in water) conventional and silver glass ionomer (Ketac-Fil and Ketac-Silver, Espe, Seefeld, Germany) and composite (Silux Plus, 3M, St. Paul, MN) were fitted into the bottom of a test tube. A layer ofS. mutans Ingbritt cells was centrifuged onto the test slabs, and the samples were incubated for 20 h in 1.7% sucrose solution. After the incubation, pH, F, and Ca contents of the fluid phase, and F, Mg, P, and K contents of the cells were determined. The aged glass-ionomer samples were then covered with toothpaste (0.1% F) or with fluoride gel (1.25% F), and the composite samples with fluoride gel. After being thoroughly rinsed, S. mutans cells were incubated on the samples as above. The pH fall was significantly inhibited by freshly mixed glass ionomers, and there were changes in cellular cation and phosphorus contents. Large amounts of fluoride were found in the fluid and cells. For old glass ionomers, no inhibitory effect on pH fall could be seen. Fluoride release had decreased to a low level. Application of fluoride toothpaste on the material resulted in a small increase in the release of fluoride and slight inhibitory effects on bacteria. After application of fluoride gel, the fluoride contents of the fluid phase and cells were as high as in freshly mixed samples, and the inhibitory effect on pH fall and electrolyte metabolism was even more pronounced than initially. Fluoride release from old glass ionomers and their antimicrobial effect could be significantly increased by application of fluoride gel on the material.
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