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Results for “Calcium Phosphates”

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At least 19 recordsLinked to original sources
PubMed1977

Direct complexometric titration of calcium phosphates.

Calcium was determined in calcium phosphate samples by dissolving the sample in hydrochloric acid, adding hydroxynaphthol blue indicator and triethanolamine, adjusting the pH to 12.3--12.5 with potassium hydroxide solution, and titrating with standard disodium ethylenediaminetetraacetate solution. Time can be saved and the formation of a precipitate (which dissolves readily during the titration) can be avoided by adding at least 85% of the amount of complexing agent required for titration before adjusting the pH.

Calcium↗
PubMed1991

Glycochenodeoxycholic acid inhibits calcium phosphate precipitation in vitro by preventing the transformation of amorphous calcium phosphate to calcium hydroxyapatite.

Calcium hydroxyapatite can be a significant component of black pigment gallstones. Diverse molecules that bind calcium phosphate inhibit hydroxyapatite precipitation. Because glycine-conjugated bile acids, but not their taurine counterparts, bind calcium phosphate, we studied whether glycochenodeoxycholic acid inhibits calcium hydroxyapatite formation. Glycochenodeoxycholic acid (2 mM) totally inhibited transformation of amorphous calcium phosphate microprecipitates to macroscopic crystalline calcium hydroxyapatite. This inhibition was not mediated by decreased Ca2+ activity. Taurocholic acid (2-12 mM) did not affect hydroxyapatite formation, but antagonized glycochenodeoxycholic acid. Both amorphous and crystalline precipitates contained a surface fraction relatively rich in phosphate. The surface phosphate content was diminish by increasing glycochenodeoxycholic acid concentrations, and this relationship was interpreted as competition between bile acid and HPO4(-4) for binding sites on the calcium phosphate surface. A phosphate-rich crystal surface was associated with rapid transition from amorphous to crystalline states. These results indicate that glycochenodeoxycholic acid prevents transformation of amorphous calcium phosphate to crystalline hydroxyapatite by competitively inhibiting the accumulation of phosphate on the crystal embryo surface.

Calcium↗
PubMedDate not supplied

Seeded growth of calcium phosphates: effect of different calcium phosphate seed material.

Seed crystals of OCP, TCP, and HAP are effective nucleators of DCPD in stable supersaturated solutions under conditions in which DCPD is the predominant phase. The crystals will grow with the second-order kinetics (TCa = 5.0 X 10(-3)M, Tp = 1.0 X 10(-2)M [pH, 5.60]) characteristic of DCPD. TCP is the least efficient, DCPD growth taking place only after an initial induction period. In all instances, the rate of DCPD crystallization is proportional to the square of the supersaturation with respect to DCPD, and the reaction is surface controlled. Scanning electron micrographs show an amorphous or microcrystalline precursor to the development of the characteristic platelets of DCPD. In stable supersaturated calcium phosphate solutions at a physiologic pH (TCa = 1.4 X 10(-3)M, Tp = 8.0 X 10(-4)M [pH, 7.40]), only OCP and HAP seed crystals are effective nucleators. The efficiency of OCP as a nucleator adds further evidence for its participation as a precursor in the precipitation of HAP under these conditions.

Calcium Phosphates↗
PubMed1991

[Evaluation of the effect of ligation of the inferior thyroid arteries during non-radical thyroidectomy in simple goiter on selected parameters of calcium-phosphate metabolism in the body].

The aim of the paper was to evaluate the effect of inferior thyroid arteries ligation during the incomplete excision of the thyroid gland in patients with simple goitre, exerted on selected parameters of phosphate-calcium balance in the organism as compared with a group of patients, in whom no inferior thyroid arteries were ligated. The study material comprised 84 patients with simple goitre, free of other diseases. The evaluation covered the following parameters of the phosphate-calcium balance in the organism, namely: the concentration of total calcium, protein, dialyzing calcium, inorganic phosphate as well as immunoreactive parathyroid hormone. The study was performed three times: prior to operative procedure, directly after the operative procedure, and three months after the procedure. It has been shown that there are slight, but statistically significant, differences in the behaviour involving the concentration of total and dialyzing calcium as well as IRPTH in serum, depending on the applied operative technique. Directly after the procedure the changes affecting the studied parameters were more pronounced in patients with ligated inferior thyroid arteries. Three months after the operative procedure the mean concentration of IRPTH, total and dialyzing calcium was somewhat higher in patients, whose inferior thyroid arteries were ligated, than in patients, in whom the arteries were not ligated. The described changes were of subclinical character.

Adolescent↗
PubMed1978

Aluminium phosphate but not calcium phosphate stimulates the specific IgE response in guinea pigs to tetanus toxoid.

The ability of aluminium phosphate and calcium phosphate to stimulate the synthesis of tetanus toxoid-specific anaphilactic and antitoxic antibodies is compared. The observed differences in the kinetics of IgG1a, IgG1b and antitoxines are quantitative--titres after application of aluminium phosphate are higher. Booster immunization with aluminium but not calcium phosphate-adsorbed toxoid leads to a prolonged synthesis of specific IgE. It is hypothesized that the regular application of aluminium compound-containing vaccines on the entire population could be one of the factors leading to the observed increase of allergic diseases.

Aluminum↗
PubMedDate not supplied

[Calcium phosphates in otological surgery. II. The bony integration of calcium phosphates. An experimental study].

Calcium phosphates have been proposed for obliteration of the mastoid cavity as well as TORP and PORP. Their use is based on a very good biocompatibility and host acceptance. The osseous integration of a dense and a porous hydroxyapatite is studied experimentally in artificially created epitympanic holes of rabbits. Osteoneogenesis was observed from the third week after surgery starting from the walls od the defects themselves. This had been evidenced using intravital fluorescent dyes. Porous granules showed more "osteoconductivity" in the beginning, probably due to their greater surface area. Bonding osteogenesis with both materials did not show differences after six months. No resorption was observed, excepting remodelation processes.

Animals↗
PubMed1992

Histopathological reactions of calcium phosphate cement.

Calcium phosphate cement (CPC) consisting of Ca4 (PO4)2O and CaHPO4 (2H2O) was recently developed. This study evaluated in vivo aspects of CPC and CPC mixtures compared to those of commercial hydroxyapatite (HP) and several endodontic materials: Grossman's cement (GC), calcium hydroxide-iodine paste (CHP) and gutta-percha plate (GP). Biocompatibility of subcutaneous implants in Donryu rats was evaluated after one month. Results showed very slight inflammatory reactions from CPC, CPC mixtures and HP. The materials were surrounded by thin fibrous connective tissues with a small number of lymphocytes and plasma cells. Severe inflammatory reactions were provoked by GC. Granulation tissues induced by CHP resembled those of pseudoxanthomatous granuloma. The GP material was encapsulated by relatively thick fibrous connective tissues with little inflammatory reactions.

Animals↗
PubMedDate not supplied

[Calcium phosphate materials].

Calcium phosphate materials are being studied from the beginning of this century in its several dental and medical applications. There are different types depending on the origin, production procedure and its numerous commercial brandts. They have some features in common: non toxic, biocompatibility, biodegradation, bioresorption and strong bond to the bone and to the soft tissues. The differences between the materials developed so far can be found in other characteristics like density, porosoity, resistance, strength and osteogenic potential.

Animals↗
PubMedDate not supplied

[Calcium phosphates in otologic surgery. III. The role of fibrin glue in the integration of calcium phosphate implants. Experimental study].

Obliteration of the mastoid cavity has been realized with calcium phosphates associated to heterologous fibrin glue in otologic surgery. 22 artificially created epitympanic and 65 femoral defects in 22 rabbits were closed by means of dense or porous granulates of hydroxyapatite with homologous fibrin glue. Follow-up was for three weeks to 6 months. Osteo-integration of the implants was significantly delayed in the first weeks, comparing the integration of the same phosphates without fibrin glue.

Animals↗
PubMed1978

Biological calcium phosphates and their role in the physiology of bone and dental tissues I. Composition and solubility of calcium phosphates.

Variations in the composition of bone and tooth mineral are consistent with the model that the constituents are a mixed microcrystalline apatite (AP)-octocalcium phosphate (OCP) like phase and an amorphous or submicrocrystalline calcium phosphate (ACP) like phase whereby these phases can occur in different proportions. An appropriate model for a description of the variable composition and the solubility behavior of the apatite phase is given by the formula (formula: see text) in which the compositional parameters x, y, z, and u each account for one type of defect mechanism. Other point defects are formed as well by incorporation of minority amounts of ions such as Cl-, K+, and F-; a number of trace elements can substitute for Ca2+ ions under in vivo conditions. It is suggested that the incorporation of ions in or loss from the crystals in contact with aqueous solutions is reversible. Literature data are used to show the direction in which the solubility product of the apatite phase shifts by incorporation of the different physiologically relevant ions. A quantitative evaluation of the available literature data revealed that Na+ and CO3= incorporation is the main cause for shifts in the solubility product of biological apatites.

Apatites↗
PubMed1975

Precipitation of calcium phosphates from electrolyte solutions. III. Radiometric studies of the kinetics of precipitation and aging of calcium phosphates.

Precipitation and precipitate transformation in the system sodium phosphate (pre-adjusted to pH 7.4)--calcium chloride (25 degrees) was studied by means of radiometric analysis using 45Ca and 32P as tracers. Changes in the pH and the total concentrations of calcium and phosphate were followed during solid phase formation and the data were used to calculate composition changes of the precipitates and their supernatants. In all investigated systems two-step precipitation was observed, the precursor being more basic than the secondary precipitate. The composition of the latter was mostly within the range of the composition of octacalcium phosphate. The course of further chemical changes was dependent on the pH established during secondary precipitation. The heterogeneous exchange of the radionuclides between the solid phase and their supernatant solutions was also followed as a function of time. The results indicate that recrystallization through the mother liquid accompanied by composition changes is the dominant mechanism of equilibrium of the solid phases.

Apatites↗
PubMed1979

Effect of human salivary proteins on the precipitation kinetics of calcium phosphate.

Inhibition of calcium phosphate precipitation in saliva, and prevention of the formation of mineral accretions on tooth surfaces, has been ascribed to the existence of inhibiting salivary macromolecules. Marked reductions in the crystal growth rate of hydroxyapatite (HA) seeds were measured in supersaturated solutions containing either of two proline-rich proteins, PRP1 or PRP3, or statherin; the three macromolecules were isolated from human parotid saliva. The reductions were also observed when the HA seeds were pretreated with solutions of the macromolecules before adding them to the supersaturated calcium phosphate solution. This effect was very similar in the case of the two PRPs and it was directly related to the extent of adsorption site coverage of these proteins on the HA seeds. The effect of statherin was larger than anticipated from its adsorption behavior. However, comparison on the basis of number of moles adsorbed per unit area of HA shows that the PRP are more effective inhibitors than statherin. The macromolecule concentrations used were considerably lower than those in the salivary secretions, therefore these macromolecules could readily prevent mineral accretion on tooth surfaces through their adsorption onto the enamel surface.

Adsorption↗
PubMed1992

Arthropathies associated with basic calcium phosphate crystals.

Basic calcium phosphate (BCP) crystals refer to a family of crystals including partially carbonate substituted hydroxyapatite, octacalcium phosphate, and tricalcium phosphate. These crystals have been found in and around joints and have been associated with several forms of arthritis and periarthritis. Identification of BCP crystals remains problematic because of the lack of a simple, reliable analytic procedure. Methods currently in use include alizarin red S staining, labelled diphosphonate binding, scanning and transmission electron microscopy with energy dispersive X-ray microanalysis, X-ray diffraction, and atomic force microscopy. Periarthropathies associated with BCP crystals include calcific tendinitis and bursitis. Intra-articular BCP crystal deposition is common in osteoarthritis, often found together with calcium pyrophosphate dihydrate crystals. Uncommon conditions in which BCP crystals are found include destructive shoulder arthropathies, acute inflammatory attacks of arthritis, and erosive arthritis. Secondary deposition of BCP crystals has been observed in chronic renal failure, in patients with "collagen vascular" diseases, following neurologic injury and after local corticosteroid injection.

Arthritis↗
PubMed1991

Calcium phosphate, bile acids and colorectal cancer.

The biochemical and nutritional studies discussed here are consistent with the model presented in Figure 1. As shown in vitro, bile acids are precipitated by insoluble calcium phosphate. This calcium phosphate dependent precipitation drastically inhibits their cytotoxicity. A diet-induced increase in luminal surfactant concentration stimulates lytic activity of faecal water and intestinal cell damage resulting in an increased proliferation. The increase in luminal surfactant concentration and lytic activity of faecal water can be counteracted by supplemental dietary calcium phosphate. Supplemental calcium in humans increases the formation of insoluble calcium-phosphate-bile acid complexes in faeces, decreases the soluble fatty acid concentration and decreases lytic activity of faecal water. This sequence of effects offers a molecular explanation of the protective effects of supplemental calcium on proliferation as frequently observed (see studies cited above). It should be realised that this chain of evidence still lacks final proof of a preventive effect of dietary calcium on colorectal cancer. Until now, only protective effects on the first stage of development of colorectal cancer (hyperproliferation) have been observed. More well-designed studies in patients and healthy volunteers are needed using a combined biochemical, nutritional and clinical approach to elucidate the complex mechanism of the protective effect of calcium on colon cancer.

Animals↗