PubMed Health⌕ Search

Biomedical subjects

N Eidelman

Publications and source records attributed to N Eidelman.

9 recordsLinked to original sources
PubMed2001

Graded microstructure and mechanical properties of human crown dentin.

The mineralized tissue of intertubular dentin is a collagen-mineral composite with considerable local variations of mechanical properties. Area scans of human coronal dentin were made by complementary methods to investigate correlations between local mechanical properties and the density, size, and crystallinity of the mineral particles. Scanning images from the same specimen were collected with Fourier-transform infrared microspectroscopy in reflectance mode (FTIR-RM), small angle X-ray scattering (SAXS), quantitative backscattered electron imaging (qBEI), and Nanoindentation in an atomic force microscope. The mineral content of dentin was found to decrease and the thickness of mineral crystals to increase towards the dentin-enamel junction (DEJ). Hardness and elastic modulus both decreased towards the DEJ. In a correlation analysis, the mineral content and, even more, the thickness of mineral crystals were found as the best predictors of hardness. The dentin layer close to the DEJ corresponds to a local minimum in hardness and elastic modulus, a configuration known to be an effective obstacle for crack propagation. Hence, the observed variations of mechanical and structural properties in an area between 0 and 1.5 mm below the DEJ define crown dentin as a gradient material optimized for its mechanical function.

Crystallization↗
PubMed1998

Bisphosphonates and tetracycline: experimental models for their evaluation in calcium-related disorders.

PURPOSE: This work was aimed at synthesizing novel bisphosphonates (BPs) and examining them in comparison to clinically used BPs such as pamidronate and alendronate, and to tetracycline, in order to evaluate their potential as anticalcification and antiresorption agents. The correlation between the various models was examined in order to establish facile experimental models for pre-screening of potential compounds. METHODS: Nitrogen-containing heterocyclic, novel BPs such as 2-(3-methylimidazolio) ethylidene-1,1-bisphosphonic acid betaine (VS-5b), 2-(2-dimethylamino-4-pyrazinio)ethylidene-1,1-bisphosphonic acid betaine (VS-6b), and 2-(2-alpha-pyridylethylthio) ethylidene-1,1-bisphosphonic acid (ISA-225), were synthesized and evaluated in comparison to clinically used BPs, in various experimental models of resorption and calcification. RESULTS: The physicochemical properties of the novel compounds are slightly different than the BPs in clinical use: the pKa values are lower, the affinity for hydroxyapatite is lower and the solubilities of the calcium salts are higher. The anticalcification potencies of the novel compounds were high and ranked as follows: alendronate = pamidronate > VS-6b = VS-5b = ISA-225 > tetracycline. The in vivo antiresorption activity of VS-5b and VS-6b in comparison to that of the clinically employed, pamidronate, was shown to be similar and higher, respectively. CONCLUSIONS: The anticalcification activity of the novel compounds as well as that of tetracycline was lower than that of alendronate. The antiresorption activity of VS-6b was similar to that of pamidronate. A good correlation between the different models was found, enabling the facile screening of novel compounds. The activities of tetracycline and EDTA highlight the distinct behavior of BPs as "crystal poison." In addition, tetracycline was found to be a potent anticalcification agent in the ectopic calcification model.

Alendronate↗
PubMed1996

In vitro inhibition of membrane-mediated calcification by novel phosphonates.

The effects of a series of novel phosphonates on the kinetics of mineral development in an ionophore-primed 7:2:1 phosphatidylcholine (PC): dicetylphosphate (DCP): cholesterol (Chol) liposomal model system are reported. When present at 2.5 micromol/liter or 25 micromol/liter concentrations in the solution surrounding the liposomes, the investigated phosphonates did not significantly delay the initial formation of hydroxyapatite-like calcium phosphate salts (HAP) within the liposomes or the penetration of HAP crystals through the enclosing membranes. However, the phosphonates variably retarded the subsequent growth and proliferation of the HAP crystals once they became directly exposed to the phosphonate-containing solution. The effectiveness of phosphonates in inhibiting extraliposomal precipitation strongly depended on their structure. The inhibitory action on active surface growth sites of released intraliposomal crystals was found to be the most effective if the phosphonate molecule contained two phosphonic groups linked to the same C atom. At a phosphonate concentration of 25 micromol/liter, the following general order of effectiveness was established: geminal bisphosphonate >/= geminal tetrakisphosphonate > bisacylphosphonates > monoacylphosphonate > bisalkylphosphonate. Within the bisacylphosphonate family, the highest inhibitory action was observed when four or five -CH2- groups separated the ketophosphonic groups.

Apatites↗
PubMed1991

Effects of pH and calcium on hydrolysis of Na2SiF6 and Na2SnF6. A quasi-constant composition titration study.

In the present work, hydrolysis reactions of sodium hexafluorosilicate (Na2SiF6) and sodium hexafluorostannate (Na2SnF6) were studied at various combinations of pH and calcium ion (Ca2+) concentrations using a quasi-constant composition titration method. Under high concentrations of hydrogen ion (H+) and Ca2+, the promoting effect of Ca2+ on the hydrolysis of Na2SiF6 was stronger than the inhibition effect of H+. However, the inhibition effect of H+ on the hydrolysis of Na2SnF6 was stronger than the promoting effect of Ca2+. Na2SiF6 and Na2SnF6 were found to have hydrolysis properties that may make them suitable for use with an acidic calcium phosphate solution in a topical fluoride treatment which forms dicalcium phosphate dihydrate as an intermediate.

Calcium↗
PubMed1987

Calcium phosphate phase transformations in serum.

A better knowledge of the pathological calcification mechanisms should provide a rational basis for their control. In the present study, dicalcium phosphate dihydrate (DCPD, CaHPO4 X 2H2O) was used as a source of calcium and phosphate ions to investigate the mechanism of formation of more basic and more insoluble calcium phosphates in ultrafiltered serum (u.f.s.). DCPD crystals were suspended in u.f.s. at 37 degrees C by constant stirring; samples were removed periodically for calcium and phosphate analysis and pH measurement. Occasionally, samples of solids were removed for X-ray diffraction. The experiments were carried out both with and without a 5.5% CO2 atmosphere. After initially becoming saturated with DCPD, the u.f.s. composition changed and became saturated with respect to octacalcium phosphate (OCP, Ca8H2(PO4)6 X 5H2O). At this point OCP crystals were detected in the solid phase by X-ray diffraction. Further stirring changed the composition so that it became undersaturated with both DCPD and OCP and shifted toward, but did not reach, a value so low as to be saturated with hydroxyapatite (OHAp, (Ca5(PO4)3OH). The presence of CO2 in the atmosphere slowed down, but did not prevent, the above sequence of events. The above results strongly suggest that calcifications, beneficial and pathological, that take place in serum may involve OCP as a precursor, which hydrolyzes in situ to a more basic apatitic product. The results also indicate that direct formation of OHAp in u.f.s. is a very slow process and may occur only rarely. The process appears to be similar in whole serum.

Calcium↗
PubMed1987

Calcium phosphate saturation levels in ultrafiltered serum.

Calcifications occurring in arteriosclerotic plaque and other pathological deposits are important health concerns, and the nature of these deposits and their mechanisms of formation warrant investigation. Crystals of the relevant calcium phosphates were equilibrated with the undiluted ultrafiltered human serum (u.f.s.) at 37 degrees C by constant stirring and periodically removing samples for calcium and phosphate analysis and for pH measurement. The solubility measurements were carried out both with and without a 5.5% CO2 atmosphere, the physiological partial pressure of CO2. The apparent ion activity products of well-crystallized dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP), and hydroxyapatite (OHAp) equilibrated in u.f.s. were calculated from the calcium and phosphate concentrations and pH in each case for comparison with their known solubility products. In this way the well-crystallized calcium phosphates serve as fiducial solubility standards, thereby minimizing errors due to complexing of calcium and phosphate ions by u.f.s. constituents. Under 5.5%, CO2 native u.f.s. was found to be substantially undersaturated with respect to DCPD, slightly supersaturated with respect to OCP, and highly supersaturated with respect to OHAp. The ion activity product of DCPD in DCPD-saturated u.f.s. was 2.4 X 10(-7), and the ion activity product of OCP in OCP-saturated u.f.s. was 4 X 10(-49), slightly above their solubility products (Ksp(DCPD) = 2.3 X 10(-7), Ksp(OCP) = 2.5 X 10(-49). The ion activity products of DCPD and OCP in u.f.s. under CO2 indicate that the concentrations of calcium and phosphate complexing agents (except bicarbonate) are quite low. The u.f.s. remained supersaturated with respect to OHAp even after 2 months of equilibration.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMedDate not supplied

Dental composites based on hybrid and surface-modified amorphous calcium phosphates.

The objectives of this study were to prepare hybrid and surface-modified amorphous calcium phosphates (ACPs) as fillers for mineral-releasing dental composites, and determine whether the mechanical strength of the composites could be improved without decreasing their remineralization potential. ACP was hybridized with tetraethoxysilane or zirconyl chloride and surface-treated with 3-methacryloxypropoxytrimethoxy silane (MPTMS) or zirconyl dimethacrylate (ZrDMA). Composites fabricated with unmodified ACP (u-ACP), hybrid or surface-modified ACP filler and photo-activated Bis-GMA, TEGDMA and 2-hydroxyethyl methacrylate (HEMA) (BTH resin), Bis-GMA, TEGDMA, HEMA and MPTMS (BTHS resin) or Bis-GMA, TEGDMA, HEMA and ZrDMA (BTHZ resin) were tested for their remineralizing potential and biaxial flexure strength (BFS). Ion releases from all composites were significantly above the minimum necessary for reprecipitation of apatite. The BFS of unfilled polymers was not adversely affected by immersion in saline solutions. The BFS of BTH and BTHS composites deteriorated upon soaking. However, BTHZ composites were practically unaffected by exposure to saline solutions. Filler hybridization resulted in a modest, but significant, improvement in the BFS (up to 24%) of BTHZ composites. Heterogeneous distribution of the ACP on disk surfaces was detected by the FTIR microspectroscopy analyses. This might have been caused by uncontrolled aggregation of ACP particles that appeared to hinder interfacial filler/resin interactions and diminish the mechanical strength of composites.

Animals↗