Elemental depth profiling of fluoridated hydroxyapatite by X-ray photoelectron spectroscopy

Structural and chemical changes that arise from a fluoridation of synthetic hydroxyapatite in neutral and acidic fluoridation agents are investigated. For synthetic hydroxyapatite (Ca5(PO4)3OH = HAp), the elemental depth profiles were determined by X-ray photoelectron spectroscopy (XPS) to reveal th...

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Published inarXiv.org
Main Authors Mueller, Frank, Zeitz, Christian, Mantz, Hubert, Karl-Heinz Ehses, Soldera, Flavio, Hannig, Matthias, Huefner, Stefan, Jacobs, Karin
Format Paper
LanguageEnglish
Published Ithaca Cornell University Library, arXiv.org 09.06.2008
Subjects
Calcium fluoride
Chemical composition
Crystal structure
Depth profiling
Fluorapatite
Fluoridation
Hydroxyapatite
Mathematical models
Organic chemistry
Penetration depth
Photoelectrons
Predictions
Reagents
Slaked lime
Spectrum analysis
X ray photoelectron spectroscopy
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Summary:Structural and chemical changes that arise from a fluoridation of synthetic hydroxyapatite in neutral and acidic fluoridation agents are investigated. For synthetic hydroxyapatite (Ca5(PO4)3OH = HAp), the elemental depth profiles were determined by X-ray photoelectron spectroscopy (XPS) to reveal the effect of fluoridation in nearly neutral (pH = 6.2) and acidic agents (pH = 4.2). Due to the high surface sensitivity of the technique, the depth profiles have a resolution on the nm scale. With respect to the chemical composition and the crystal structure XPS depth profiling revealed very different effects of the two treatments. In both cases, however, the fluoridation affects the surface only on the nm scale which is in contrast to recent literature, where a penetration depth up to several microns was reported. Moreover, evidence is given that the actual fluoridation depth depends on the pH value. Recently, a qualitative three layer model was proposed for the fluoridation of HAp in an acidic agent. In addition to the elemental depth profile, as presented also by various other authors, we present a quantitative depth profile of the compounds CaF2, Ca(OH)2 and fluorapatite (FAp) that are predicted by the three layer model. The analysis of our experimental data exactly reproduces the structural order of the model, however, on a scale that differs by nearly two orders of magnitude from previous predictions. Our results also reveal that the amount of Ca(OH)2 and FAp is small as compared to that of CaF2. Therefore, it has to be questioned whether such narrow Ca(OH)2 and FAp layers really can act as protective layers for the enamel.
ISSN:2331-8422