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A novel technique for fluorapatite synthesis and the ..

28/01/2011 · One of the most common methods for the synthesis of hydroxyapatite and fluorapatite ..

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and F in carbonate-rich fluorapatite

In order to further confirm the phase composition and crystallinity of these synthetic crystals produced with or without the presentation of EDTA, we have conducted powder X-ray diffraction pattern analysis (). All of the diffraction peaks can be readily indexed to a pure hexagonal phase with the lattice constants a = 9.381 and c = 6.912 , which is in accordance with that of synthetic fluorapatite. However, the crystals prepared under low pH () have a better crystallinity than those of prepared at neutral pH () and at high pH (). Several of the peaks in are much broader than those seen in . This is reasonable as the crystals prepared under pH 4.0 with the presence of EDTA are much larger than those prepared under pH 10.0 without EDTA.

Reaction mechanisms of synthesis and decomposition …

The excellent biocompatibility of HA nanostructures has resulted in many studies focusing on their synthesis. This is mainly achieved by using surfactants, glutamic acid, EDTA, polyaspartate, biological proteins, etc. to control the nucleation and growth of crystals under varying synthetic conditions. However, there is little literature specially reporting the synthesis of 1-dimension fluorapatite nanostructures. In comparison to hydroxyapatite, the incorporation of fluoride makes the fluorapatite structure more stable, therefore, the reaction progresses more easily under relatively simple and mild reaction conditions.

for synthesis of dimethyl carbonate

Two methods were used to synthesize FA nanostructures. One is without the stabilizer EDTA, under ambient pressure, and usually produced short FA nanorods. This is a modification of our previous reported method of synthesizing hydroxyapatite nanorods. One hundred and four point six milligrams hydroxyapatite powder and 8.4 mg sodium fluoride were mixed with 100 mL distilled water. The suspensions were stirred continuously and HNO3 was added until the powder dissolved, after which the pH was adjusted to 2.4. Ammonium hydroxide was then added dropwise to 20 ml the above solution with continuous stirring until the desired pH between 6 – 11 was reached. The suspension was sealed in a plastic tube and kept in a water bath at 70°C for 5 days. In order to obtain the longer FA nanorods similar to those seen in human enamel, EDTA-Na4.4H2O was used to stabilize the Ca, allowing the slow release of Ca2+. The reaction is performed under mild hydrothermal conditions (121 °C, 2 atm) to dissociate the Ca2+ from EDTA-Ca complex. Typically, 1004.6 mg HA, 9044.8 mg EDTA-Na4.4H2O and 84 mg NaF were added to 100 mL distilled water. The suspension was stirred continuously and the pH was adjusted to 4–12 using HNO3. The temperature of the solution was raised to 121 °C at a pressure of 2 atm for six hours. All final suspensions were centrifuged and washed with distilled water (pH 7.4) 3 times. The resulting pellets were dried in vacuum before use.

We set out to mimic this natural anti-caries ability of teeth by developing new, effective anticaries materials using fluorapatite nanorods or nanowires. The advantage of these nanorods or nanowires is that the physico-chemical composition is the same as the hydroxyapatite crystals in the dental hard tissues. They also have the ability to release fluoride ions as the site specific pH drops which will help in preventing caries and aid in remineralisation. Further these nanorods / nanowires may be used directly to form a matrix to be placed in boney areas where there has been, for example, malunion, defects, and/or where bone augmentation is desirable. They could also be introduced into scaffolds containing the signaling molecules of bone, dentin, enamel, cementum and / or blood vessels for the repair of the type of conditions referred to earlier. Recently Yamagishi et al. has reported that it is possible to use the fluoridated-apatite to repair early caries lesions directly. We believe that the shape and chemical composition of well defined synthetic fluorapatite nanorods / nanowires have the potential to be layered over carious lesions.

The Scientific World Journal - Hindawi Publishing …

It should be noted that the F signal is not strong in energy-dispersive X-ray spectra (). This is because of high energy TEM electron beam damage during the EDS data acquirement. Fluorine is a light element and is easily released when bombarded by the high energy electron beam. However, 19F MAS-NMR data clearly shows the strong and sharp peak of 19F resonance at −103 ppm (). This is the typical 19F chemical shift of fluorapatite. Furthermore chemical analysis of these synthetic crystals also confirmed that the ratio of Ca/P/F is close to the theoretical value of Ca5(PO4)3F.

In natural tooth enamel fluoride is always present in the carbonated hydroxyapatite mineral and plays a key role in the prevention of tooth decay. In this study we aimed at mimicking this natural anti-caries ability of the tooth by developing new, effective anticaries materials using fluorapatite nanorods or nanowires. We therefore investigated the conditions necessary to synthesize fluorapatite nanorods of different size, shape and composition for future use either directly or indirectly, that is by incorporation into dental materials, in the treatment and prevention of caries. By controlling the chemical conditions, nanorods of desirable chemical composition and dimension were produced. The mechanism of how these structures were formed is also proposed.

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but increasing interest is being directed to fluorapatite ..

Several plant species have the ability to convert soluble fluorides taken up from soil into carbon–fluoride compounds, such as monofluoroacetic acid, monofluoro-oleic acid, monofluoropalmitic acid and monofluoromyristic acid (Marais, 1944; Ward et al., 1964). Two well known Australian species that synthesize monofluoroacetates are spp. (Aplin, 1968) and Georgina gidgee ( F.M. Bailey) (Oelrichs & McEwan, 1961); other species include spp. (Australia), spp. (Africa) and (reviewed by Weinstein, 1977). The function of monofluoroacetate in the plant is unknown. The assumption that its synthesis by the plant is a response to high concentrations of available inorganic fluoride in soil or water (Preuss et al., 1970) is not supported by the finding that some plants containing monofluoroacetate grow in soils with low fluoride concentrations (Hall, 1972).

a magnesium- and carbonate-substituted fluorapatite will be ..

In summary, the present work shows we are able to synthesize FA nanorod / nanowire of different composition, shape and size at low temperature or mild hydrothermal conditions by simply controlling the pH and using EDTA as a stabilizer in the precipitation solution. These nanorods and / or nanowires may have potential use in dentistry and medicine.

Biomimetic Synthesis of Fluorapatite Coating - …

Hydrogen fluoride (hydrofluoric acid) is an important industrial compound, with an estimated annual world consumption in excess of 1 million tonnes (Greenwood & Earnshaw, 1984). Hydrogen fluoride is manufactured from calcium fluoride and is used mainly in the production of synthetic cryolite, aluminium fluoride (AlF3), motor gasoline alkylates and chlorofluorocarbons; however, the demand for chlorofluorocarbons is decreasing as a result of efforts to restrict their use. Hydrogen fluoride is also used in the synthesis of uranium tetrafluoride (UF4) and uranium hexafluoride (UF6), both of which are used in the nuclear industry (Neumüller, 1981). It is also used in etching semiconductor devices, cleaning and etching glass, cleaning brick and aluminium and tanning leather, as well as in petrochemical manufacturing processes. Hydrogen fluoride may also be found in commercial rust removers (Upfal & Doyle, 1990).

"Biomimetic Synthesis of Fluorapatite Coating ..

Cooke (1976) studied the effect of fluoride (200 mg/litre) on common sunflower () seeds grown in sand culture. No effect on total dry weight was observed; however, there were significant reductions in leaf growth. Keller (1980) grew Norway spruce () cuttings in sand and watered with 100 mg fluoride/litre during winter until bud break. Watering with sodium fluoride significantly depressed the carbon dioxide uptake of shoots. Although the previous year’s needles did not show signs of injury, most of the new needles were killed immediately after flushing with fluoride. Exposure to fluoride significantly increased the susceptibility of plants to sulfur dioxide in subsequent fumigation experiments. Zwiazek & Shay (1987) grew jack pine () seedlings in sand culture at 3 or 15 mg fluoride/kg dry weight. Wilting was the first sign of fluoride injury and occurred in approximately 50% of plants after 25–26 h at 15 mg fluoride/kg and 2–6 h later in only 7% of plants exposed to 3 mg/kg. Fluoride-induced injuries to mesophyll and guard cells were similar to those caused by drought and included the appearance of lipid material in the cytoplasm during early stages of injury, suggesting cell membrane damage. Plants exposed to 3 mg/kg for up to 168 h showed significant reductions in water content. Respiration was significantly reduced after 24 h, but not after longer exposure times, while photosynthetic oxygen release was significantly reduced at 48 and 91 h but had recovered after 168 h (Zwiazek & Shay, 1988a). Zwiazek & Shay (1988b) reported that 3 mg fluoride/kg significantly reduced growth (as measured by fresh weight) and acid phosphatase activity and increased total organic acid content of jack pine () seedlings.

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