Inactivation of hydrofluoric acid by solutions intended for gastric lavage.
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Animals↗
Biomedical subjects
S J Jensen
Publications and source records attributed to S J Jensen.
The hydroxyapatite solubility product of human dental enamel as a function of pH in the range 4.6-7.6 at 20 degrees C.
Samples of 200 mg powdered enamel apatite were suspended in 10 ml of aqueous solutions made from phosphoric acid and calcium hydroxide for 60 days at 20 degrees C. Calcium and phosphate concentrations were determined by spectroscopy; pH and the concentrations of fluoride and carbonate by electrometry. The solubility product of hydroxyapatite varied linearly from 10-56.9 at pH 4.6 to 10-52.8 at pH 7.6. The carbonate concentration in the aqueous phase was too low to account for calcium carbonate complex formation of significance to the solubility product. After the equilibration, X-ray diffraction analysis of the powder showed that the salt was unchanged pure apatite with no trace of a transformation to brushite or any other calcium phosphate. A re-equilibration of some of the powder samples for another 60 days produced similar solubility products. Thus the change of the solubility product was most likely attributable to a pH-induced change of the ionic composition of the enamel crystal surface.
Calcium Carbonate↗
Stability and mutual conversion of enamel apatite and brushite at 20 degrees C as a function of pH of the aqueous phase.
By calculation, apatite is more soluble than brushite at low pH and less soluble at high pH. Apatite, therefore should be able to transform spontaneously to brushite at low pH and brushite to apatite at high pH. The aim was to describe this mutual conversion as related to the aqueous phase composition. Powdered enamel, brushite or 1:1 mixtures of the two salts were suspended in distilled water for up to 12 weeks at 20 degrees C, pH was adjusted to 4, 5, 6, 7, 8, 9 or 10 by drops of perchloric acid or potassium hydroxide. The calcium and the phosphate concentrations and pH were determined, and the nature of the calcium phosphate powder was examined by X-ray diffraction. At pH 8 and above, brushite was invariably converted to apatite, whilst it was transformed to octacalcium phosphate at pH 7. In the pH range 6-4 brushite was not converted to apatite and enamel apatite was not transformed to brushite spontaneously within 2 months. In the enamel apatite suspensions, the apatite ion product altered with pH, which explained why apatite did not transform to brushite at pH 5-4. At pH 3.7, however, the enamel apatite was converted to brushite. No transformation of apatite to brushite was identified in apatite-brushite mixtures at pH 6-4. Supplementary experiments showed that ethanol, used as an agent for removal of water, salted out the water-free dicalcium phosphate, monetite.
Apatites↗
Solubility, unit cell dimensions and crystallinity of fluoridated human dental enamel.
The aim was to describe the dimensions of the fluorhydroxyapatite unit cell and the solubility of fluorhydroxyapatite as a function of the fluoride concentration in the apatitic lattice. Various amounts of powdered human dental enamel were suspended in a pH 4.5 acetate buffer containing fluoride. The suspensions were equilibrated for 365 days at 20 degrees C. After equilibration the fluoride concentration in the apatite varied from 0.003 to 0.89 (mole fraction). X-ray diffraction showed that the length of the alpha-axis decreased with increasing fluoride concentration, whilst a broadening of the (300) reflection indicated the presence of mixtures of various fluorhydroxyapatites. The solubility of the apatite after the long equilibration decreased slightly with increasing fluoride concentration in the solid. In a few samples the fluoride concentration in the aqueous phase was still discernible, indicating that even after 365 days, equilibrium had not been attained. In these samples the amount of dissolved apatite was extraordinarily low.
Apatites↗
Decrease of gamma 1 lattice constant with time in dental silver amalgam.
As a measure of the mercury content of the gamma 1 phase in dental silver amalgam, the lattice constant of this phase in different amalgams was determined at various times after trituration. The lattice constants of amalgams prepared from alloys with a high silver content have lower values and show a steeper decline with time than amalgams with a low Ag-content. Therefore, since a higher lattice constant presumably is associated with increased mercury vapor, the mercury vapor emission from amalgams with a low Ag-content probably is greater than from amalgams with a high Ag-content, especially during the first weeks after trituration.
Chemical Phenomena↗
Solubility study of the initial formation of calcium orthophosphates from aqueous solutions at pH 5-10.
In unsaturated stock solutions with various concentrations of calcium and phosphate and pH of 4-5, supersaturation with respect to brushite, hydroxy- and fluorapatite, octacalcium phosphate and amorphous tricalcium phosphate was established at 20 degrees C by increasing pH in two series of portions, one containing low concentrations of fluoride, one fluoride-free. The precipitate as identified by X-ray diffraction was compared to the ion-activity products in the liquid. Brushite and amorphous tricalcium phosphate were formed at low supersaturation with respect to the salt in question; apatite formation required a high degree of supersaturation. Octacalcium phosphate was not observed presumably due to moderate supersaturations with respect to this salt. Fluoride had no effect on brushite and tricalcium-phosphate formation; only apatite was influenced slightly through a fluorapatite precipitation. The salts were often formed in mutual competition.
Apatites↗
On the properties of fluoride solutions used for topical treatment and mouth rinse.
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Calcium Fluoride↗
Ethanol-induced formation of solid calcium phosphates.
Conventional transmission electron microscopy requires an effective dehydration of the tissue specimens under investigation. This dehydration, for which ethanol most often is used, may influence the solubility of the slightly soluble calcium phosphates. To study the behavior of calcium phosphates in ethanol, stable neutral aqueous solutions containing the ions were mixed with ethanol in various ratios at 20 degrees C. After 24 hours, the precipitates formed wee identified by x-ray diffraction to be either apatite, brushite, or amorphous calcium phosphate. The results are discussed with reference to possible formation of calcium phosphate artifacts.
Calcium Phosphates↗
An X-ray diffraction and solubility study of equilibration of human enamel-powder suspensions in fluoride-containing buffer.
Various amounts of enamel-apatite powder were suspended in an acetate buffer (pH 4.5) containing sufficient fluoride to give molar ratios of fluoride/apatite from zero to unity. The suspensions were equilibrated at 20 degrees C for periods between 4h and 1 year, with continuous gentle stirring. Solubility studies showed dissolution of hydroxyapatite, formation and re-dissolution of calcium fluoride and formation of fluorapatite. The amount of mineral dissolved was low during the fluorapatite formation and increased by a factor of approx. 10 as equilibrium was approached. The fluoride content of the solid apatite, which ranged from 0.1 to 70 mol% fluorapatite, only influenced the solubility slightly, whereas the fluoride content of the bathing solution had a large effect. X-ray diffraction showed a linear correlation between the fluoride content and the a-axis of the apatite.
Apatites↗
Maximum contents of mercury in dental silver amalgams.
The maximum content of mercury forming intermetallic compounds has been determined in dental amalgams prepared from alloys with different copper contents. In amalgams made from alloys with silver contents less than about 42% there is a risk of occurrence of free mercury if an effective condensation technique has not been used.
Copper↗
Dimensional and phase changes of dental amalgams.
The relationship of long-term expansion to phase changes of dental amalgams was examined. Using multiple regression analysis, a predictive equation was found which showed that the linear dimensional change was dependent on the alterations in the content of gamma 2 and beta 1.
Chemical Phenomena↗
Creep and beta1 formation in dental amalgam.
Measurements of creep, beta1 phase content and gamma1 lattice parameter were performed on four conventional amalgams stored at 37 degrees C up to 2 years. The creep values and lattice parameters decreased and the beta1 content increased during this period; the most prominent alterations took place within the first 6 months.
Dental Amalgam↗
Influence of the heat treatment of commercial amalgam alloys on the phase composition of the alloys and the creep of the resulting amalgams.
The influence of heat treatment of dental alloys at several temperatures on the phases present in the alloy and the creep of the resulting amalgam as well as the correlation between phase changes and the creep was investigated. A dependence of the creep on the temperature of the heat treatment of the alloy was established. Substantial phase changes were observed after the different heat treatments. No correlation was detected between the creep rate and the changes in phases present in the dental alloys. A thermodynamically oriented explanation of the relation between the creep of the amalgam and the state of (non-) equilibrium of the corresponding amalgam alloy was proposed and discussed.
Dental Alloys↗
Phase content of a high copper dental silver amalgam.
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Chemical Fractionation↗
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↗
Chemical composition, particle form and annealing temperature of amalgam alloy versus creep of the resulting amalgam.
The influence of the chemical composition, particle form and annealing temperature of the amalgam alloy upon the creep of the resulting amalgam was investigated by means of a multiple regression model. Because no, or only little, information was available about the heat treatments of the different commercial alloys, the alloys were subjected to additional heat treatments at four different temperatures. The influence upon the creep of the amalgam of the Zn content, particle form and annealing temperature was found to be very significant. A higher Zn content as well as a spherical alloy resulted in less creep of the corresponding amalgam. The dependence of the creep upon the annealing temperature showed a minimum: more creep was obtained for amalgams prepared from the alloys heat treated at 150 degrees C and 435 degrees C than those from the alloys annealed at 315 degrees C and 319 degrees C, respectively.
Copper↗
Phases in preamalgamated silver amalgam alloy.
The phase content of six preamalgamated alloys available on the dental market has been determined by means of X-ray diffraction. The beta 1-phase was found in five alloys.
Dental Alloys↗
On the solubility of zinc in the gamma-phase of the silver-mercury system.
By measuring lattice constants of a number of Ag-Hg-Zn alloys with gamma-phase structure, it has been shown that apart from a possible two-phase field there exists a continuous solid solution between gamma (Ag-Hg) and gamma (Ag-Zn). A correlation between the Zn-content in the gamma 1 phase in set dental silver amalgam and the Zn-content in the corresponding alloy has been determined.
Alloys↗