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PubMed2005

Geometrical parameterization of the crystal chemistry of P6(3)/m apatites: comparison with experimental data and ab initio results.

Experimental structure refinements and ab initio simulation results for 18 published, fully ordered P6(3)/m (A;{\rm I}_4)(A;{\rm II}_6)(BO4)6X2 apatite end-member compositions have been analyzed in terms of a geometric crystal-chemical model that allows the prediction of unit-cell parameters (a and c) and all atom coordinates. To an accuracy of +/- 0.025 A, the magnitude of c was reproduced from crystal-chemical parameters characterizing chains of ...-A(II)-O3-B-O3-A(II)-... atoms, whereas that of a was determined from those describing (A(I)O6)-(BO4) polyhedral arrangements. The c/a ratio could be predicted to +/-0.2% using multi-variable functions based on geometric crystal-chemical model predictions, but could not be ascribed to the adjustment of a single crystal-chemical parameter. The correlations observed between algebraically independent crystal-chemical parameters representing the main observed polyhedral distortions reveal them as the minimum-energy solution to accommodate misfit components within this flexible structure type. For materials with given composition, good agreement (within +/- 0.5-2.0%) of ab initio crystal-chemical parameters was observed with only those from single-crystal refinements with R </= 4.0%. Agreement with single-crystal work with R > 4.0% was not as good, while the scatter with those from Rietveld refinements was considerable. Accordingly, ab initio cell data, atomic coordinates and crystal-chemical parameters were reported here for the following compositions awaiting experimental work: (Zn,Hg)10(PO4)6(Cl,F)2, (Ca,Cd)10(VO4)6Cl2 and (Ca,Pb,Cd)10(CrO4)6Cl2.

Apatites↗
PubMed1977

Apatite crystals in pseudoxanthoma elasticum: a combined study using electron microscopy and selected area diffraction analysis.

Calcium deposits in elastic fibers of involved skin of patients suffering from pseudoxanthoma elasticum have previously been reported. In the present work, the crystalline structure and composition were studied. Involved skin was obtained from 5 patients. Bright-field and dark-field electron microscopy and selected area electron diffraction of the calcium deposits were applied. The study demonstrates calcium apatite crystals.

Apatites↗
PubMed1980

Calcification of cultured urticaria pigmentosa skin. An electron optical study of the calcium-apatite deposition.

Mast cells participate in experimental calcinosis. Skin from patients with urticaria pigmentosa (cutaneous mastocytosis) calcifies in vitro. In the present report, the nature of the calcium deposit was studied by electron optical techniques. The cultured mast cells of urticaria pigmentosa skin were surrounded by a large number of round bodies with an average diameter of 200-300 nm. Most of the round bodies were membrane bounded, while a few contained lamellar structures. These bodies may represent matrix vesicles as seen in calcifying hard tissues and/or may be remnants of mast cell granules. The calcified deposits were located on the round bodies, collagen fibrils and elastic matrix. Electron diffraction and X-ray microanalysis demonstrated that the deposits consisted of crystalline calcium apatite.

Apatites↗
PubMed1990

Dental cutting behaviour of mica-based and apatite-based machinable glass-ceramics.

Some recently developed industrial ceramics have excellent machinability properties. The objective of this study was to evaluate the dental cutting behaviour of two machinable glass-ceramics, mica-containing Macor-M and apatite- and diopside-containing Bioram-M, and to compare them with the cutting behaviour of a composite resin typodont tooth enamel and bovine enamel. Weight-load cutting tests were conducted, using a diamond point driven by an air-turbine handpiece, While the transverse load applied on the point was varied, the handpiece speed during cutting and the volume of removal upon cutting were measured. In general, an increase in the applied load caused a decrease in cutting speed and an increase in cutting volume. However, the intensity of this trend was found to differ between four workpieces. Cutting Macor-M resulted in the second-most reduced cutting speed and the maximum cutting volume. Cutting Bioram-M gave the least reduced cutting speed and the minimum cutting volume. It was suggested that two machinable glass-ceramics could be employed as typodont teeth. This study may also contribute to the development of new restorative dental ceramic materials, prepared by machining.

Aluminum Silicates↗
PubMed1975

Degrees of saturation with respect to apatites in fruit juices and acidic drinks.

Some fruit juices and carbonated acidic drinks, recognized as agents causing dental erosions, were analyzed for calcium, phosphate, fluoride and pH. Ionic activity/concentration products for hydroxyapatite and fluorapatite were calculated. It was found that all liquids analyzed were unsaturated with respect to both apatites, which explains their erosive effect.

Apatites↗
PubMed2004

Morphological analysis of subgingival biofilm formation on synthetic carbonate apatite inserted into human periodontal pockets.

BACKGROUND: Details of the development of human subgingival biofilm are unknown due to the difficulties in conducting experiments and especially in obtaining undisturbed materials. METHODS: This study was performed using deposits on carbonate apatite that had been inserted into human periodontal pockets for up to three weeks. Scanning electron microscopy using the vertically sectioned method and transmission electron microscopy using the freeze-substitution method were adopted. RESULTS: The development of subgingival biofilm occurred in five sequential phases: pellicle formation, microbial adherence, initial colonization, microbial organization, and establishment. Certain species in each of the initial, secondary and tertiary colonizers were considered to have a predilection for biofilm formation. Gram-positive, bacillary initial colonizers and gram-negative, filamentous secondary colonizers organized one stable structure that served as the framework for biofilm formation, and gram-negative, rod-shaped tertiary colonizers with cell-surface vesicles showed multigeneric coaggregation. The microbiota in the tertiary colonizers underwent repeated microflora alteration. CONCLUSIONS: Subgingival biofilm is constituted by initial, secondary and tertiary colonizers. Microflora alteration which is suggested to be related to periodontal disease, frequently occurred in the tertiary colonizers.

Adult↗
PubMed1990

Septic arthritis complicating apatite associated destructive arthropathy.

Septic arthritis can complicate many forms of arthritis. Two cases of apatite associated destructive arthropathy (AADA) complicated by sepsis are described. Diagnosis of this complication in the setting of severe joint damage is difficult as AADA and sepsis share certain characteristics--an initial, rapidly progressive, severely painful course and radiographs which show rapidly destructive changes with marked cartilage loss, bone attrition, and virtual absence of osteophyte or cyst response.

Aged↗
PubMed1993

Defluoridation of drinking water by co-precipitation with apatite.

The two-step brushite saturation, apatite precipitation method which has previously been shown to be effective for the partial defluoridation of water containing 10 ppm F has now been tested at lower concentrations. The method also reduced F concentrations in the range 1-5 ppm, but was less efficient at lower F levels. Although co-precipitation as fluorapatite is the intended mechanism here, experiments indicated that F adsorption on the seed material added to the defluoridation effect. When the contribution of co-precipitation was isolated it was found that this mechanism could, on its own, account for a reduction of 2.2-2.6 ppm F in water initially containing 3-5 ppm F. A computer program which determines equilibrium F concentrations when supersaturated solutions are induced to precipitate fluorapatite was used to estimate the maximum possible F removal from water by co-precipitation. Using saturation with brushite as a starting point for precipitation, F reductions similar to those found experimentally were predicted. Computer simulations also suggest that any desired reduction in F concentration may be achieved by adding sufficient Ca and phosphate and/or by raising the initial pH.

Adsorption↗
PubMed2006

Apatite formation in composites of alpha-TCP and degradable polyesters.

The objective of this study was to investigate the conversion of alpha-Ca3(PO4)2 (alpha-TCP) in composite bone cements based on a water-degradable polyester matrix as a function of the polymer formulation and the alpha-TCP filler content. Cross-linkable dimethacrylates of epsilon-caprolactone/ D,L-lactide co-polymer or of epsilon-caprolactone/glycolide co-polymer were mixed with hydroxyethylmethacrylate, a photo-initiator and alpha-TCP to obtain composites with a filler content of 80 or 40 wt% alpha-TCP. The disk shaped composite samples were set by visible light irradiation and immersed in HEPES at 37 degrees C. At selected times the samples were removed from the solution and analysed with X-ray diffractometry and infrared spectroscopy. Conversion of alpha-TCP into calcium-deficient hydroxyapatite (CDHAp) was observed for all composites, but the reaction was not completed after 8 weeks immersion. The conversion rate of alpha-TCP and the crystallinity of the formed apatite apparently were not affected by the type of polyester used, but significantly depended on the alpha-TCP content of the composites. An increase of the amount of alpha-TCP in the composite resulted in a slower formation of CDHAp with a higher crystallinity.

Apatites↗
PubMed1979

Biological apatite crystal disolution.

The dissolution curves of human acid-treated enamel powder are characterized by a rapid initial step followed, after 10 or 15 minutes, by a second stage, with release of very small amounts of calcium. Increase in pH and addition of fluoride ions tend to diminish, for short intervals, the amount of dissolved apatites. For higher pH values the decrease is noted over a longer time. Study of the relative ionic variation of human enamel powder from young and adult patients subjected to acid requires infra-red vibration band analyses. Special attention was given to the absorptions at 610 cm-1 (phosphate groups), 880 cm-1 (CO32- in OH- sites and HPO42-), 1410 cm-1 (CO32- in phosphate sites) and 1550 cm-1 (CO32- in OH- position). All results were related to vibration band at 610 cm-1. A preferential loss of carbonates in the two possible sites was always observed for 10 or 15 minutes, followed by a high release of phosphate. The increase of pH or small amounts of fluoride displaced the preferential carbonate loss to longer times. In the presence of higher fluoride levels a disappearance of the preferential loss of carbonates was noted. A continuous increase of HPO42- in the absence of fluoride occurred; however a straight line with a smaller shape was present, with fluoride addition.

Apatites↗
PubMed1979

Differential adsorption and chemical affinities of proteins for apatitic surfaces.

Studies are reviewed which identify the interacting groups involved in protein adsorption onto hydroxyapatite. Thus, carboxyl and phosphoester groups bind to calcium sites in the adsorbent, and basic groups bind to phosphate sites. Detailed adsorption studies have been performed to quantitate some of these interactions. An adsorption model, based on the Langmuir adsorption isotherm, adequately fitted the data from experiments using selected amino acids, bovine albumin and two human salivary proteins. Adsorption parameters (affinities and maximum number of sites) were obtained for several apatitic adsorbents, with affinities increasing considerably in the series hydroxy- (HA), fluorhydroxy- (FHA) and fluorapatite (FA). A modest increase in the number of sites was also noted. The change in adsorption behavior, with increasing fluoride content, was attributed to a reduction in the surface free energy of the adsorbent, with a concomitant decrease in the interaction of the adsorbent with water, and a consequent enhancement of the adsorption bond. It is suggested that this effect may play a role in the cariostatic effect of fluoride. Unusual structural aspects of the salivary proteins are discussed in relation to their adsorption behavior, and the molecular segments responsible for binding to the adsorbent tentatively identified.

Adsorption↗
PubMed1981

Dissolution rate behavior of fluoridated apatite pellets.

The dissolution rate of synthetic fluoridated apatite pellets with various fluoride content was measured in acetate buffer solution at pH 4.0. The dissolution rate decreased with degree of fluoridation. The rate decreased greatly at low fluoride levels. The experimental data were analyzed by means of a diffusion-controlled model and compared with the solubility data. This model showed that the initial dissolution rate is greatly affected by both the solubility and the overall mass transfer resistance. Overall mass transfer resistance is affected by fluoride content.

Apatites↗
PubMed1984

Inhibition of seeded growth of enamel apatite crystals by amelogenin and enamelin proteins in vitro.

The effect of enamel matrix proteins on the seeded growth of enamel apatite crystals was studied in stable supersaturated solutions at pH 7.4 and 37 degrees C. Of the two major protein classes in the enamel matrix, the enamelins were considerably more effective than the amelogenins in retarding seeded growth. However, the amelogenin species that did show significant inhibitory activity are those known to be lost first from the enamel matrix during the rapid mineralization stage of enamel maturation.

Amelogenin↗
PubMed2000

Porous apatite-wollastonite glass-ceramic as an intramedullary plug.

We evaluated the efficacy and biocompatibility of porous apatite-wollastonite glass ceramic (AW-GC) as an intramedullary plug in total hip replacement (THR) for up to two years in 22 adult beagle dogs. Cylindrical porous AW-GC rods (70% porosity, mean pore size 200 microm) were prepared. Four dogs were killed at 1, 3, 6 and 12 months each and six at 24 months after implantation. Radiological evaluation confirmed the efficacy of porous AW-CG as an intramedullary plug. Histological evaluation showed osteoconduction at one month and resorption of the porous AW-GC, which was replaced by newly-formed bone, at 24 months. Our findings indicate that porous AW-GC can be used clinically as an intramedullary plug in THR.

Animals↗
PubMed1998

Apatite induction by insoluble dentin collagen.

Phosphoproteins are thought to play a role in mineral formation in dentin. A portion of this phosphoprotein is bound to collagen. We have investigated the requirement for bound phosphate in mineral induction by isolated dentin collagen. Insoluble bovine dentin collagen obtained by ethylene-diamino-tetra-acetic acid (EDTA) demineralization had 19.5 mol of P/mol of collagen that could not be extracted with 0.5 M EDTA in 4 M guanidine HCl. When this collagen was incubated in supersaturated solutions that did not spontaneously precipitate, apatite was induced. With progressive enzymatic dephosphorylation, induction times for mineral formation became progressively longer. The dentin did not induce mineral formation when 90% of the ester phosphate was removed. Insoluble bone collagen, which had even less phosphate, also did not induce mineral formation. Mineral induction times by dentin collagen increased with decreasing solution saturations. Using these data, the interfacial tension for mineral induction was determined to be 90 ergs/cm2. This value approximated that of phosphatidic acid liposomes and of phosvitin cross-linked to agarose beads, and it might reflect the energetics of heterogeneous nucleation on a highly phosphorylated surface. Sequestering of calcium-phosphate clusters on the phosphoprotein probably accounts for the observed calcium binding by dentin collagen in excess of that required to neutralize the phosphate esters of the collagen. Because the phosphoprotein is immobilized at a low density on the collagen, it cannot self-associate in calcium-phosphate solutions as it does when it is free in solution. This immobilized phosphoprotein allows the mineral clusters formed on its surface to grow into a crystalline order.

Animals↗
PubMed1989

[Self-setting apatite cement. 6. Possibility as bone substitute].

Self-setting apatite cement was investigated to evaluate its use as a possible bone substitute in the rat femur. The implant sites were recovered at intervals up 12 weeks postoperatively and investigated by the use of x-ray diffraction, contact microradiography, light and electron microscopy. By x-ray diffraction analysis, the cement placed for at least one day in the medullary canal of rats was found to be completely converted to a set phase of hydroxyapatite resembling the main inorganic phase of bone. In any specimens prepared at 1, 4, 12 weeks after implantation, no appreciable foreign body response was observed in the tissue around the set cement. At four weeks after implantation the set cement was in tight contact with the newly formed bone which appeared to involve osteocytes in lacunae and osteoblastic cells on its surface. At twelve weeks after implantation, the newly formed bone tended to grow into the interior of the set cement. With scanning electron microscopy, the newly formed bone was found to be directly deposited on the set cement. The newly formed bone consisted of fine needle-like crystals. These results strongly suggest that this cement is well tolerated by bone tissue and osteogenesis when used as a bone substitute. The advantage of the present material as a promising bone substitute is that it can be filled in surgical or traumatic bone defect as a slurry or paste.

Animals↗
PubMedDate not supplied

Apatite determination and distribution in an early stage of gallbladder calcification.

This study is concerned with the nature and distribution of mineral in the gallbladder of a patient with chronic cholecystitis. Light and electron microscopic imaging revealed the mineral to be in the epithelial cells of the mucosa and fibroblasts of the submucosa. In the epithelial cells at the early stages of deposition, mineral was located in the nuclei and throughout the cytoplasm in association with interdigitating cell processes and apical microvilli but was absent in mitochondria. Elemental and electron diffraction analyses indicated the mineral inclusions to be apatite in nature.

Adult↗