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Results for “Calcium Fluoride”

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At least 235 records · Page 13Linked to original sources
PubMed1987

Comparison of sample preparation methods for the high-performance liquid chromatographic analysis of cell culture extracts for triphosphate ribonucleosides and deoxyribonucleosides.

We compared four different procedures for the purification and concentration of nucleoside triphosphates in cell extracts prior to HPLC analysis. Two methods involved precipitation, with either acetonitrile or calcium fluoride. The acetonitrile procedure yielded reasonable recovery and sufficient purity for the subsequent HPLC analysis. The calcium fluoride coprecipitation procedure gave both good recovery and purity; but the recovery was shown to be dependent on the concentration of the nucleoside triphosphates. The other two methods involved small Sep-Pak cartridges. The silica cartridge procedure yielded unfavorable recoveries in periodate-treated cell extracts, apparently due to poor solubility of nucleoside triphosphates in the requisite solvents. The strong anion exchange cartridge procedure yielded both good recovery and purity. This procedure was found to be fast, efficient, and reliable for purifying and concentrating nucleotides in cell extracts.

Acetonitriles↗
PubMed1977

Fluoride release and physical properties of a fluoride-containing amalgam.

1. The amount and percentage of fluoride released from amalgam were less for the 1:1.6 alloy/mercury ratio than for the 1:1 ratio. 2. Higher fluoride concentrations resulted in a greater quantity but lower percentage of fluoride released from the amalgam. 3. Longer immersion times resulted in a greater amounts and percentages of released fluoride. However, the fluoride released per hour decreased with immersion time. 4. Immersion of the amalgam in lactic acid caused a greater release of fluoride than immersion in distilled water. 5. Disintegration of the amalgam was greater in lactic acid than in distilled water. The contribution of calcium fluoride to weight loss was greater in water than in lactic acid, indicating a corrosive effect for lactic acid. 6. The higher calcium fluoride content (2 per cent) decreased the compressive strength of the amalgam but did not alter the dimensional change.

Calcium Fluoride↗
PubMedDate not supplied

Kinetics of crystal growth and dissolution of calcium and magnesium fluorides.

Kinetic results of the crystal growth and dissolution of seed crystals of calcium fluoride and magnesium fluoride, obtained conductimetrically and potentiometrically, indicate that both processes are controlled by a surface reaction mechanism. An initial reaction surge in the case of magnesium fluoride is consistent with a concomitant secondary nucleation process. The activation energies for the growth and dissolution of calcium fluoride, 14.5 and 1.4 kcal mole-1, also point to surface reaction control. The heat of solution of this salt, obtained calorimetrically, was 2.9 +/- 0.1 kcal mole-1.

Calcium Fluoride↗
PubMed1979

The interaction of dietary vitamin C, protein, and calcium with fluoride: effects in guinea pigs in relation to breaking strength and radiodensity of bone.

Guinea pigs were maintained on semisynthetic diets with or without the adequate amounts of dietary vitamin C, protein, and calcium, and were exposed to 25 ppm of fluoride in drinking water. Bone radiodensity was increased in the guinea pig humerus and tibia by fluoride supplementation, while femur and pelvic bones showed no density increases. Fluoride administration did not affect the torsion or bending strength of the bones of guinea pigs fed normal diets but increased the tensile strength. These physical properties of bones were not altered by low vitamin C or low protein diets. Low calcium diet significantly reduced the tensile strength of guinea pig humeri while the simultaneous administration of fluoride counteracted this effect.

Animals↗
PubMedDate not supplied

Plaque fluoride concentrations in a community without water fluoridation: effects of calcium and use of a fluoride or placebo dentifrice.

The results of a recent study by Whitford et al. [Caries Res 2002;36:256-265] with subjects whose drinking water was fluoridated led to two major conclusions: (1) Compared to the use of a placebo dentifrice, plaque fluoride concentrations ([F]) throughout much of the day are not significantly increased by the use of an F dentifrice but (2) they are positively related to plaque [Ca] (p = 0.0001). The present double-blind, double-crossover study with 16 subjects used the same protocol and was done to: (1) determine the effects of the use of an F dentifrice on salivary and plaque [F] in a community without water fluoridation and (2) further examine the relationship between plaque [Ca] and [F]. Following the use of an F dentifrice or placebo for one week, whole saliva and plaque were collected 1.0 and 12 h after the last use of the products. The study was repeated to include rinsing with a 20 mmol/l CaCl(2) solution immediately before the use of the dentifrices. The CaCl(2) rinse had only minor effects on salivary [Ca] and [F] and none on the plaque concentrations. Unlike the results found in the fluoridated community, all salivary and plaque [F] associated with the use of the F dentifrice were significantly higher than those associated with the use of the placebo. The results suggest that the cariostatic effectiveness of an F dentifrice should be greater in areas without water fluoridation. As noted previously, plaque [F] were positively related to plaque [Ca] (p = 0.0001).

Adolescent↗
PubMed1980

Effect of aluminum hydroxide on fluoride metabolism.

Aluminum inhibits intestinal absorption of fluoride in animals but little information is available about man. To determine whether and to what extent aluminum affects fluoride absorption in man, effects of aluminum hydroxide on fluoride metabolism were studied under controlled dietary conditions. Relatively small amounts of aluminum hydroxide were used (30 ml three times daily, containing a total of 1.8 gm aluminum, were given for several weeks). Fluoride balances were determined in control studies and during the intake of aluminum hydroxide. The fluoride intake was the fluoride content of the diet and the drinking water. Two studies were also carried out on a high-fluoride intake. The use of aluminum hydroxide was associated with an increase in fecal fluoride excretion and a decrease in net absorption of fluoride regardless of the intake fluoride, calcium, phosphorus, or magnesium. Urinary fluoride decreased during aluminum hydroxide ingestion. Our studies show that relatively small amounts of aluminum hydroxide inhibit intestinal absorption of fluoride in man.

Aged↗
PubMed2005

New device and method for flux-proportional sampling of mobile solutes in soil and groundwater.

The importance of monitoring the transport of organic contaminants in soil and groundwater, and the pros and cons of existing sampling methods, are outlined. A new, alternative sampling method is proposed, using a passive sampler that functions as a water-permeable, semi-infinite sink for passing solutes of interest. Tracers integrated in the device store information on the volume of water passing through the sampler during the installation period. The conceptual basis of the sampling method is described. This device enables flux-proportional monitoring of the concentrations of mobile contaminants in the soil and groundwater. 14C-labeled phenanthrene (PHEN) and glyphosate (GLY) are used as case study compounds in laboratory experiments. The sorption capacities and uptake kinetics of 13 adsorbents are screened and compared, as well as the dissolution kinetics of three tracer salts: calcium citrate, calcium fluoride (CaF2), and calcium hydrogen phosphate (CaHPO4). The application of the passive sampler is then demonstrated in long-term laboratory experiments, using large soil columns under steady-state hydraulic conditions. The accumulated flux of PHEN was sampled with an accuracy of 3.6%-17.8%, using graphitized carbon, hexagonal mesoporous silica, and cross-linked polymers as adsorbents. The accumulated flux of GLY was sampled with an accuracy of 12.4%, using gamma-alumina as an adsorbent. The advantages and limitations of this new environmental monitoring method are discussed.

Adsorption↗
PubMed1991

Fluoride mobilizes intracellular calcium and promotes Ca2+ influx in rat proximal tubules.

In the renal proximal tubule, external Ca2+ ([Ca2+]o) is required for parathyroid hormone to elevate cytosolic Ca2+ ([Ca2+]i). However, other hormones increase [Ca2+]i in the absence of [Ca2+]o. These differences may arise from a diversity of signal transduction pathways acting on external and internal Ca2+ pools. However, Ca2+ influx may be necessary to expedite and maintain the rise of [Ca2+]i for a period after the initial surge. In this study, F- was used to probe the roles of intracellular Ca2+ mobilization, Ca2+ influx, and phosphoinositide (PI) hydrolysis on the surge of [Ca2+]i in rat proximal tubules. In the presence of external Ca2+; 1-20 mM F- evoked incremental rises of [Ca2+]i in tubules loaded with aequorin. Whereas 10 mM F- increased [Ca2+]i in the absence of [Ca2+]o, the time constant for the [Ca2+]i surge was increased. These findings are consistent with a role of Ca2+ influx on the effect of F- on [Ca2+]i. Indeed, 10 mM F- also enhanced the uptake of 45Ca2+, and promoted Ca2+ influx in aequorin- and fura-2-loaded, Ca(2+)-deprived tubules. In tubules, F- also activated PI hydrolysis with a time course that paralleled Ca2+ mobilization. The effect of F- on [Ca2+]i was not altered when the 39-kDa pertussis toxin substrate was inactivated with the toxin. This G protein was most likely Gi, because prostaglandin E2, an activator of Gi in tubules, dissociated the pertussis toxin-sensitive protein. The results support the notion that activation of a signal-transduction complex, the F- substrate, causes Ca2+ influx, mobilizes internal Ca2+, and activates PI hydrolysis in rat proximal tubules.(ABSTRACT TRUNCATED AT 250 WORDS)

Aequorin↗
PubMed1994

Dental tissue effects of fluoride.

It is now well-established that a linear relationship exists between fluoride dose and enamel fluorosis in human populations. With increasing severity, the subsurface enamel all along the tooth becomes increasingly porous (hypomineralized), and the lesion extends toward the inner enamel. In dentin, hypomineralization results in an enhancement of the incremental lines. After eruption, the more severe forms are subject to extensive mechanical breakdown of the surface. The continuum of fluoride-induced changes can best be classified by the TF index, which reflects, on an ordinal scale, the histopathological features and increases in enamel fluoride concentrations. Human and animal studies have shown that it is possible to develop dental fluorosis by exposure during enamel maturation alone. It is less apparent whether an effect of fluoride on the stage of enamel matrix secretion, alone, is able to produce changes in enamel similar to those described as dental fluorosis in man. The clinical concept of post-eruptive maturation of erupting sound human enamel, resulting in fluoride uptake, most likely reflects subclinical caries. Incorporation of fluoride into enamel is principally possible only as a result of concomitant enamel dissolution (caries lesion development). At higher fluoride concentrations, calcium-fluoride-like material may form, although the formation, identification, and dissolution of this compound are far from resolved. It is concluded that dental fluorosis is a sensitive way of recording past fluoride exposure because, so far, no other agent or condition in man is known to create changes within the dentition similar to those induced by fluoride. Since the predominant cariostatic effect of fluoride is not due to its uptake by the enamel during tooth development, it is possible to obtain extensive caries reductions without a concomitant risk of dental fluorosis.

Amelogenesis↗