Effect of Amine Fluoride on Enamel Surface Morphology

In this in vitro study, examination of the enamel surface morphology after topical application of an amine fluoride solution with different fluoride (F) content was carried out. Sound human enamel slabs were treated with an amine fluoride solution containing either 1.0, 0.5 or 0.25% F for 3 min. during 3 days. All slabs were examined using scanning electron microscopy and energy-dispersive spectroscopy (SEM/EDS) qualitative analysis. The globular precipitates were revealed in all treated specimens, regardless of F content. The distribution of the deposits was more homogeneous in groups treated with higher concentrations; however, the globules were larger and more cubical in groups treated with lower fluoride concentrations. These larger globules could be less soluble and thus serve as a fluoride reservoir for a more extended period and so they could contribute to the caries preventive effect in professional topical products with lower fluoride concentration. Following the 24-hour treatment with KOH the precipitates could be removed; however, the enamel surfaces covered with the precipitates were less degraded than the untreated enamel. The EDS qualitative analysis showed that the intensities of fluoride signals were increased with the higher concentration of fluoride in an amine fluoride solution, while the intensities of calcium signals were decreased. The enamel surface precipitates were alkali-soluble, but we were not able to demonstrate that they are pure calcium fluoride

On the Existence of the FCC Uranium

Diffusion studies in the system U - S, employing the couples U - US, U - US2 and U -- U3S5 revealed the existence of new FCC phase with the composition ranging from approx. U20S to U8S. The lattice parameter of the phase as obta ~ned in the diffusion couple is 4.95 ± 0.01 A. The same phase can be also obtained by the arc melting of the mixtures of U and US or U and S in the appropriate proportions, if followed by the heat treatment at 1900 °c during at least four hours. It is believed that this is a crystal structure modification of uranium stabilized by the addition of a small quantity of nonmetal atoms, where S and N play a mayor role. The same phase has been obtained through the addition of approximately 9 a/o of Se, Te, P, As, Sb, Bi, C and Si. Although the effect of the stabilization is not yet completely understood all samples contain a FCC phase and posess virtually the same lattice parameter as the phase containing sulphur. The experimental density amounts 14.21 g cm·:i. The calculated density is 13.21 g cm-3