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Biomedical subjects

S J Jensen

Publications and source records attributed to S J Jensen.

At least 37 records · Page 2Linked to original sources
PubMed1985

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↗
PubMed1985

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↗
PubMed1985

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↗
PubMed1985

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↗
PubMed1983

Corrosion of zinc-containing dental amalgam.

The gamma 1 lattice constant of amalgams with and without zinc kept under corrosive and non-corrosive conditions was determined at different times after trituration. Zinc disappeared during 1 d from the gamma 1 phase of an amalgam made from 0.9% Zn alloy and during 30 d from an amalgam made from 4% Zn alloy, when powdered amalgam was in contact with a 1% NaCl solution.

Corrosion↗
PubMed1981

Stoichiometric and X-ray diffraction analysis on the gamma 2 leads to eta' transformation in a dispersant phase silver amalgam.

Phase composition of an amalgam prepared form a two-particle alloy was determined over a 2-year period by X-ray diffraction. The gamma 2-content decreased from 3.6% to 0.3% and eta' increased from 3.9% to 10.0%. These alterations in phase content agreed with stoichiometric calculations performed on the basis of the solid state reaction: gamma 2 + Ag/Cu leads to eta' + gamma 1.

Copper↗
PubMed1980

Effects of fluoride, calcium, and phosphate administration on mineralization in rats.

Seven days before a fluoride injection of 20 mg sodium fluoride per kg body weight, 3-month-old rats grown on a standard pellet diet containing 0.8% calcium and 1.4% phosphate were given a diet of rice with only 0.025% calcium and 0.1% phosphate. Microradiographs of the continuously growing incisors showed a hypermineralized and subsequent hypomineralized zone. Blood analysis demonstrated a decrease and a subsequent reestablishment of plasma calcium concentration. In some experiments calcium and phosphate were administered to compensate the hypocalcemia which prevented the hypomineralized zone from arising. A delay of calcium and phosphate administration led to formation of a mineralized band within the hypomineralized zone. The results are discussed with reference to calcium homeostasis.

Administration, Oral↗
PubMed1978

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↗
PubMed1977

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↗
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↗
PubMed1977

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↗
PubMed1976

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↗