In Vitro Surface Investigation of Calcium Fluoride-like Precipitation on Human Enamel after Topical Treatment with the Organic Fluoride Nicomethanol Hydrofluoride.

PURPOSE: The topical fluoride treatment of teeth can lead to a formation of CaF2-like material, which is considered to play a significant role in caries prevention. Different types of fluoride sources are applied. The aim of this study was to analyse the in vitro fluoridation effect of the lesser known organic fluoride compound nicomethanol hydrofluoride (NH) regarding fluoride accumulation and morphological changes on dental enamel surfaces. Materials and Methods: The fluoridation effect was investigated by scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX) after treatment with fluoride solutions at a concentration of 1350 ppm F - and a pH value of 5.5. NH was tested against inorganic sodium fluoride (NaF) as reference. Fluoridation was done on pellicle-free and pellicle-covered enamel. Results: Formation of globular CaF2-like material was observed for both fluoride types. However, NH led to considerably higher calcium fluoride accumulation on the enamel surface as shown by both EDX and SEM. The globule diameters varied between 0.2 and 0.8 µm. Cross-sectional analysis revealed that the globular precipitates lay directly on the enamel surface; only the very surface-near volume was affected. No statistically significant difference of the fluoridation effect was measured with vs without saliva pre-treatment. Conclusion: The experiments showed a 6 times greater F - surface uptake on dental enamel with NH compared to sodium fluoride, thus suggesting an important role of NH during remineralization phases, fostering equilibrium between de- and remineralization.

α-Irradiation setup for primary human cell cultures.

Purpose: We present an α-irradiation setup for the irradiation of primary human cell cultures under controlled conditions using 241Am α-particles.Materials and Methods: To irradiate samples with α-particles in a valid manner, a reliable dosimetry is a great challenge because of the short α-range and the complex energy spectrum. Therefore, the distance between α-source and sample must be minimal. In the present setup, this is achieved by cells growing on a 2 µm thick biaxially-oriented polyethylene terephthalate (boPET) foil which is only 2.7 mm apart from the source. A precise and reproducible exposure time is realized through a mechanical shutter. The fluence, energy spectra and the corresponding linear energy transfer are determined by the source geometry and the material traversed. They were measured and calculated, yielding a dose rate of 8.2 ± 2.4 Gy/min. To improve cell growth on boPET foils, they were treated with air plasma. This treatment increased the polarity and thus the ability of cells attaching to the surface of the foil. Several tests including cell growth, staining for a marker of DNA double-strand breaks and a colony-forming assay were performed and confirm our dosimetry.Conclusion: With our setup, it is possible to irradiate cell cultures under defined conditions with α-particles. The plasma-treated foil is suitable for primary human cell cultures as shown in cell experiments, confirming also the expected number of particle traversals.

Nanoporous aluminum oxide membranes for filtration and biofunctionalization.

Nanoporous aluminum oxide membranes with high open porosity are prepared by anodic oxidation. Conventional self-supporting as well as mechanically stabilized nanoporous membranes are produced from aluminum plates and microimprinted aluminum foils, respectively. The mechanically stabilized membranes are characterized by very thin membrane parts stabilized by surrounding thick bridges. The minimal thickness of these thin membranes with open pores on both sides is 1 microm, with a mean pore size of the parallel open pores of 185 nm. With these two kinds of membrane the flow rates for cross filtration can be tuned over a wide range. With the mechanically stabilized membranes, substantially higher flow rates are achieved and experiments that cannot be performed with thicker membranes become possible. The biofunctionalization of the pore walls with archaebacterial tetraether lipids is realized and proved using aminated semiconductor nanocrystals. The lipid layer deposited on the pore walls also changes the filtration properties.

Ruthenium/rhodium modified gold electrodes for the amperometric detection of hydrogen peroxide at low potentials.

Electrodes of ruthenium/rhodium deposited as thin layers on gold foils were investigated. Ruthenium layers were radio frequency (r.f.) magnetron sputtered and the rhodium layers were made by vacuum evaporation. Hydrogen peroxide could be detected using the cathodic reduction at potentials lower than +170 mV or the anodic oxidation at higher potentials. Under flow injection conditions, H(2)O(2) was detected between 1 and 1000 micro M at a potential of -100 mV and between 2 and 500 micro M at a potential of +250 mV vs. Ag/AgCl/0.4 M KCl. The electrodes also showed high operational stability and selectivity against many electroactive substances. The selectivity against dissolved oxygen was investigated.