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PubMed1988

Kinetics of dissolution and growth of calcium fluoride and effects of phosphate.

The rate of growth of pure calcium fluoride crystals is controlled by a surface polynuclear mechanism when the supersaturation is less than 4.4. The surface free energy is found to be 120 mJ/m2. The dissolution process is also controlled by a surface process. Both of these processes are very strongly inhibited by phosphate ions. Calcium fluoride-like materials contaminated with phosphate are formed when calcium fluoride is precipitated in phosphate-containing solutions or suspensions. The physical and chemical properties of these materials have been investigated and compared with the corresponding properties of pure calcium fluoride. The former dissolve much faster than pure calcium fluoride in solutions containing phosphate, but an inhibitory effect is still shown. It is suggested that the calcium fluoride-like material formed on dental enamel during treatment of enamel with acidified solutions of high fluoride content is a phosphate-containing calcium fluoride.

Calcium Fluoride↗
PubMed1977

Calcium fluoride formation on enamel and its influence on uptake of fluoride in the apatitic lattice.

Human dental enamel was exposed to a pH 4 buffer containing 150 parts/10(6) fluoride. It was found that due to the arising degrees of saturation with respect to calcium fluoride and apatites, surface enamel dissolved coincident with a formation of calcium fluoride. The calcium fluoride redissolved while it kept the liquid saturated with respect to this salt. During this second period, fluorapatite was formed while hydroxyapatite dissolved. Finally, all calcium fluoride was dissolved and the unreacted fluoride was taken up in the apatitic lattice. The results are discussed with reference to the conditions of the oral cavity and enamel solubility experiments.

Apatites↗
PubMed1994

Dissolution of various calcium fluoride preparations in inorganic solutions and in stimulated human saliva.

The aim of the present study was to examine the dissolution of various preparations of calcium fluoride in inorganic solutions and in human saliva. Calcium fluoride was prepared by mixing either 0.25 or 0.02 mol/l calcium chloride with 0.5 or 0.04 mol/l sodium fluoride. After preparation, the salts were washed in 1 mmol/l calcium chloride solution and in distilled water. A commercial product, calcium fluoride Suprapur (Merck), was used for comparison. The solubility of the salts was examined in distilled water, in a 2-mmol/l sodium phosphate solution, and in whole human saliva, produced by chewing paraffin. It was found that the calcium fluoride ion product after suspension for 1-3 h in distilled water ranged closely around 10(-10.7) for all salts. In the phosphate solution, the commercial product dissolved slowly, the ratio between dissolved fluoride and calcium ranged from 4 to 7, in buffered solutions approaching 2. The supernatant was not saturated by the salt. Our two calcium fluoride salts dissolved quickly and made the phosphate-containing solutions supersaturated with respect to fluorapatite, leading to fluorapatite formation, and because of compensating calcium fluoride dissolution, this led to increasing fluoride concentrations in saliva of up to around 85-95 ppm. The results of this study indicate that calcium fluoride of less than Suprapur standard may dissolve quickly in saliva, unless the dissolution is retarded by a physical barrier, like a forming pellicle.

Apatites↗
PubMed1988

Alkali solubility of calcium fluoride pre-exposed to inorganic orthophosphate at pH 6.8.

The dissolution behavior in 1 M KOH solution of calcium fluoride which had been pre-exposed to inorganic orthophosphate at pH 6.8 was investigated. Chemically pure calcium fluoride (50 mg) was incubated in 5 ml of 2 mmol/l sodium phosphate buffer, pH 6.8, for 24 h or 120 h and subsequently incubated in 5 ml 1 M KOH for 24h. Control samples were incubated in distilled water before KOH exposure. Pre-treatment with phosphate caused a significantly reduced dissolution rate of calcium fluoride in alkali. Longer exposure to phosphate resulted in further reduction of the dissolution rate in alkali. Calcium fluoride formed on teeth in vitro and in vivo will always be exposed to phosphate. The alkali method thus has limitations because calcium fluoride that has been exposed to phosphate will be underestimated.

Alkalies↗
PubMed2004

The microwave characterization of single crystal lithium and calcium fluoride at cryogenic temperatures.

The whispering-gallery mode method is used for very accurate permittivity and dielectric loss measurements of single crystal lithium fluoride (LiF) and calcium fluoride (CaF2) over the temperature range of 4.5 K to 300 K. The absolute uncertainty in the real part of permittivity was estimated to be less than 0.1%, and it was limited principally by uncertainty in dimensions of the samples. Dielectric losses were measured with uncertainties of about 10% limited by the accuracy of Q-factor measurements. The measured materials exhibited dielectric losses between 2-4 x 10(-7) near 5 K. The relative permittivity was evaluated as 6.502 (4.9 K) to 6.844 (296 K) at 17.5 GHz for CaF2 and 8.534 (4.6 K) to 9.063 (300 K) at 13.5 GHz for LiF.

Journal Article↗
PubMed1991

Determination of citric acid based on inhibition of the crystal growth of calcium fluoride.

Inhibition of the growth of calcium fluoride crystals in the presence of citrate was followed using a kinetic-potentiometric technique and a calcium ion-selective electrode, and as a consequence, a method for the determination of citrate in the range 0.5-2.4 micrograms ml-1 has been developed. The method was successfully applied to the determination of citrate contained in pharmaceutical products and urine. Urine analysis requires prior separation of phosphate, sulphate and magnesium(II). Elimination of these interferences was studied and accomplished using precipitation processes. Magnesium and phosphate were jointly eliminated in basic media by the addition of ammonium ions. Phosphate and sulphate were eliminated with barium(II). Phosphate was also eliminated as a lithium salt.

Calcium Fluoride↗
PubMed1988

On the role of calcium fluoride in the cariostatic mechanism of fluoride.

The literature concerning the formation and stability of CaF2 in the oral environment is reviewed. In early work the CaF2 formed during topical application with fluoride was assumed to be beneficial. It was suggested that it could protect the enamel surface directly or provide free fluoride ions for subsequent incorporation into the hydroxyapatite lattice. However, McCann claimed, in 1968, that CaF2 is soluble in saliva (12-15 mg/l), that it would be rapidly lost in the oral cavity, and that the clinical effect of fluoride was related to formation of firmly bound fluoride only. In this period many authors reported total loss of CaF2 during 24 h after a topical application of fluoride. It has now been shown in several laboratories that calcium fluoride is stable in saliva at neutral pH owing to surface adsorption of HPO2-4 to the crystal surface and formation of a solubility-limiting phase. Extended exposure of saliva can cause formation of a fluorapatite layer on the CaF2 crystals, restricting their dissolution further. Low pH (pH less than 5) causes loss of the solubility-limiting adsorbed HPO2-4 and a slow dissolution of CaF2. The CaF2 crystals may thus serve as pH-controlled reservoirs of fluoride ions on the enamel or in plaque and release fluoride during caries challenges. It is suggested that calcium fluoride is an essential phase explaining important aspects of the mechanism of topically applied fluoride, contrary to what was assumed in the past.

Calcium Fluoride↗
PubMed1991

[Calcium fluoride or not? That is the question!].

The relative cariostatic effect of fluoride as fluorapatite, calcium fluoride-like material, loosely bound fluoride or KOH-soluble fluoride is debated. The present study was carried out to investigate this further in an intraoral caries model. Pair of premolars extracted for orthodontic reasons were used. Enamel from one tooth of each pair was used as controls (untreated). Two slabs were cut from the enamel of the other contralateral premolar. These slabs were treated with 2% NaF for 24 h. One slab was then treated with 1 mol/L KOH for 24 h to remove all loosely bound fluoride. The slabs treated with 2% NaF and then 1 mol/L KOH would contain the KOH-insoluble fluoride. Those treated with only 2% NaF would, in addition, contain KOH-soluble fluoride. Each slab, control, KOH-insoluble F and KOH-soluble and insoluble F, was mounted on different upper removable appliances. The slabs were covered with orthodontic banding material, allowing space for plaque accumulation. Five individuals wore the appliances in 3 separate 4-week periods. The slabs were analyzed by quantitative microradiography. The average mineral loss (delta Z) was 1680 +/- 1000 vol% z microns in the control teeth, 620 +/- 76 vol% . microns in the KOH-soluble and insoluble F teeth and 2167 +/- 1278 vol% . microns in the KOH-insoluble F teeth. The average lesion depths were 90 +/- 41 microns in the control teeth, 35.3 +/- 5.5 microns in the KOH-soluble F teeth and 88 +/- 35 microns in the KOH-insoluble F teeth. It was concluded that only KOH-soluble fluoride reduced mineral loss and lesion depths significantly compared with the untreated teeth.

Calcium Fluoride↗
PubMed1993

Detection and quantification of calcium fluoride using micro-Raman spectroscopy.

Investigations on the caries-preventive effect of calcium fluoride have been seriously hampered by the lack of adequate detection techniques. In this paper, the micro-Raman technique is introduced as a suitable method for CaF2 quantification with a spot size typically 5 microns. Advantages of this measuring technique and associated problems are described for CaF2 determination in the presence of large amounts of hydroxyapatite. The data show that a comparative analysis of Raman intensities of calcium fluoride and phosphate ions of hydroxyapatite can be used for quantification of CaF2 concentrations. The intensity behaviour of the CaF2 and hydroxyapatite Raman lines is explained considering the absorption-scattering cross-sections of the two components. The ratio of the Raman intensity (322 cm-1) of CaF2 to the phosphate Raman intensity (432/447 cm-1) of hydroxyapatite was found to be related linearly to the ratio of the concentration of CaF2 to that of hydroxyapatite. At present, the lower limit of CaF2 quantification is approximately 3 wt%. The technique has already been applied on fluoridated bovine enamel, and Raman emissions due to CaF2 or CaF2-like material formed on/in enamel have been detected for the first time.

Animals↗
PubMed1997

A method for determining the distribution of fluoride, calcium and phosphorus in human dental plaque and the effect of a single in vivo fluoride rinse.

A new sampling method, capable of sampling plaque from its surface to its interior for quantitative studies, was modified to meet some of the requirements for the determination of the fluoride and mineral (Ca and P) profiles within dental plaque formed in vivo. Plaque samples were repeatedly collected from the same individual, using special devices, before a single fluoride rinse (900 parts/10(6) fluoride) and 10 min and 24 hr after rinse. The method allowed examination of fluoride, calcium and phosphorus distribution along the entire thickness of plaque. Fluoride content significantly increased throughout the sample 10 min after rinsing, indicating the fluoride had rapidly penetrated into the plaque. Although the elevated fluoride concentrations diminished almost to baseline with 24 hr, a high correlation was found between fluoride and minerals in each plaque fraction. It is concluded that this technique will be useful for evaluating the fluoride and mineral behaviour in the saliva/plaque and plaque/enamel interfaces, and the anti caries efficacy of fluoride applications.

Calcium↗
PubMed2006

Study on the influence of additives in an industrial calcium fluoride and waterworks sludge co-melting system.

This work explores the effect of additives on the pouring temperature in a waterworks and industrial calcium fluoride sludge co-melting system. Two kinds of sludge were mixed in various ratios to find a mixing ratio at which the operating temperature for subsequent additive tests was relatively low. Various proportions of either sodium carbonate (Na2CO3) or potassium carbonate (K2CO3) reagent were added to the mixed-sludge samples to elucidate the consequent changes in pouring temperature. The experimental results revealed that the pouring temperature was lowest when calcium fluoride was mixed with waterworks sludge in a ratio of 4:6 (w/w). Adding sodium carbonate or potassium carbonate reagent to the mixed-sludge samples further reduced the pouring temperature. Increasing the amount of sodium carbonate did not significantly reduce the pouring temperature beyond that observed when 2% was added, suggesting that 2% was the optimal additional percentage of sodium carbonate. In contrast, the pouring temperature was increased when over 2% potassium carbonate was added to the mixed-sludge samples, revealing that the optimal additional percentage of potassium carbonate was also 2%. These findings indicate that both sodium carbonate and potassium carbonate can be used as additives to increase the energy efficiency of the melting process, but sodium carbonate is more operationally convenient.

Calcium Fluoride↗
PubMed1982

Transformation of calcium fluoride for caries prevention.

Oral application of fluoride for caries prevention may tend to form calcium fluoride (CaF 2) instead of the desired fluorapatite. In view of this, the transformability of CaF2 to fluorapatite has been studied. This investigation shows that CaF2 can be converted to fluorapatite in phosphate solutions ar various temperatures ranging between 25 and 75 degrees C in the pH range of 6.5 to 8.5. In the initial stage, phosphate ions, believed to be HPO4= adsorb on the particle surface. A dissolution/precipitation mechanism is proposed for the growth of fluorapatite.

Apatites↗
PubMed2005

Calcium fluoride micro cells for synchrotron radiation circular dichroism spectroscopy.

De-mountable calcium fluoride micro cells have been developed for use in synchrotron radiation circular dichroism (SRCD) spectroscopy. They have the advantages that they require only very small sample volumes (as low as 1 microliter) and have short path lengths (as small as 2 micrometers). Highly reproducible spectra can be obtained in consecutive loadings with these spacer-free, fixed path length cells, which enable low wavelength data collection.

Calcium Fluoride↗
PubMed1986

Effects of calcium, fluoride and magnesium supplementations on tissue mineralization in calcium- and magnesium-deficient rats.

There is considerable uncertainty about the interrelated effects of calcium (Ca), magnesium (Mg) and fluoride (F) on hypocalcification of the skeleton and Ca accumulation in vital soft tissues. This paper describes experiments with rats fed a diet deficient in Ca and Mg, the latter deficiency being accentuated by a low potassium content. For different groups the drinking water was supplemented with Ca, Mg, F, Ca + F or Mg + F; Ca and F were supplied as chemically compatible compounds. At the end of the 54-d experiment, plasma Ca was strongly reduced in the Ca-deficient groups. Plasma Mg was reduced particularly in the test groups supplied with Ca, without any influence of F supply or varying plasma F. Ca accumulation was much more pronounced in the kidneys than in the heart or aorta, but was mitigated by both Mg and F supplementation. Bone mineralization disturbance due to the dietary imbalance was preventable only by Ca or Ca + F supplementation, and was less in alveolar bone than in femur. However, the Ca supplement was associated with the highest aorta and heart Ca contents, and Ca + F was associated with marked renal Ca accumulation; adequate Mg supply may be essential with Ca + F administration against osteoporosis.

Animals↗