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At least 451 records · Page 25Linked to original sources
PubMed2005

Amelogenin control over apatite crystal growth is affected by the pH and degree of ionic saturation.

OBJECTIVE: To study the mechanisms which promote the interactions of amelogenin proteins with the forming mineral to establish suitable conditions for the biomimetic synthesis of enamel in vitro. DESIGN: Saturated calcium phosphate solutions were used in conjunction with recombinant amelogenin proteins to induce mineral formation on glass-ceramics substrates containing oriented fluoroapatite crystals (FAP). The height of mineral layers formed on these substrates within 24 h was measured by atomic force microscopy (AFM). EXPERIMENTAL VARIABLES: The effect of protein concentration, pH and degree of saturation (DS) on the growth of apatite mineral was evaluated. Mineralization experiments were performed at 0, 0.4 and 1.6 mg/ml amelogenin concentrations. Mineralization solutions were used at pH values of 6.5, 7.4, 8.0 and 8.8 and DS of calcium and phosphate between 9 and 13. OUTCOME MEASURE: Height and morphology of mineralized layer formed on glass-ceramic substrates as determined from AFM measurements. RESULTS: Homogeneous nucleation and crystal growth of thin layers on the FAP were observed, when calcium and phosphate ions were added. The height of these layers grown on (001) planes of FAP was strongly dependent on the protein concentration and pH. At concentrations of 0 and 0.4 mg/ml crystal grew 5-15 nm on the FAP, while they grew approximately to 200 nm at 1.6 mg/ml. The enhanced crystal growth was observed only at pH 6.5, 7.4 and 8.0, while layers only 20 nm thick were obtained at pH 8.8. An increase in DS resulted in uncontrolled growth of calcium phosphate mineral covering large areas of the substrate. CONCLUSIONS: Protein concentration, pH and the saturation of the mineralizing solution need to be considered carefully to provide suitable conditions for amelogenin-guided growth of apatite crystals.

Amelogenesis↗
PubMed1962

Carbonic anhydrase and the precipitation of apatite.

On theoretical grounds it is unlikely that the catalytic action of the enzyme carbonic anhydrase would be required for the precipitation of apatite in vitro. The presence of carbonic anhydrase in either active or inactivate form did not initiate precipitation in a metastable calcifying solution. It is unlikely that carbonate (or bicarbonate) ions are essential for the precipitation of apatite in vitro or in vivo.

Apatites↗
PubMed1967

Lepidocrocite, an apatite mineral, and magnetic in teeth of chitons (Polyplacophora).

X-ray diffraction patterns show that the mature denticles of three extant chiton species are composed of the mineral lepidocrocite and an apatite mineral, probably francolite, in addition to magnetite. Each of the three minerals forms a discrete microarchitectural unit of the chiton denticles. This is the first indication that lepidocrocite is precipitated by marine organisms and an apatite mineral by chitons.

Animals↗
PubMed1976

Characterization and modification of permselective properties of apatite membranes.

Compressed apatite disks were used as models for tooth enamel. Their permselective properties were studied as functions of the pH of the gradient solutions, the composition of the apatites, and the pretreatments with anionic phosphate compounds and cationic proteins. The results are discussed in relation to the caries mechanisms.

Apatites↗
PubMed1980

The influence of fluoride on the seeded growth of apatite from stable supersaturated solutions at pH 7.4.

Previous studies have shown that fluoride affected the formation of apatite in spontaneous precipitations from unstable calcium phosphate solutions partly through its effect on the stability of such nonapatitic precursors as octacalcium phosphate, Ca8H2(PO4)6.5 H2O. The present study shows that fluoride had a comparable effect on the seeded growth of apatite from stable solutions when the degree of solution supersaturation favored the transient development of octacalcium phosphate precursors on the seed surface.

Apatites↗
PubMed1983

Acid reactivity of carbonated apatites with strontium and fluoride substitutions.

Carbonated apatites containing approximately 3.0 or 6.5% CO3 were precipitated in the presence of sodium, strontium, and/or fluoride at various concentrations. Almost all the available strontium and fluoride was incorporated into the crystals, whereas only a portion of the carbonate and sodium present was taken up. When incorporated together, Sr and F improved the crystallinity of carbonated apatites and markedly reduced their acid reactivity. This phenomenon may partially explain the observed reduction in caries for populations whose drinking water contains optimum levels of Sr at 5-10 mg/l and F at 1-2 mg/l.

Apatites↗
PubMed1997

The effect of fluoride on apatite structure and growth.

Fluoride participates in many aspects of calcium phosphate formation in vivo and has enormous effects on the process and on the nature and properties of formed mineral. The most well-documented effect of fluoride is that this ion substitutes for a column hydroxyl in the apatite structure, giving rise to a reduction of crystal volume and a concomitant increase in structural stability. In the process of enamel mineralization during amelogenesis (a unique model for the cell-mediated formation of well-crystallized carbonatoapatite), free fluoride ions in the fluid phase are supposed to accelerate the hydrolysis of acidic precursor(s) and increase the driving force for the growth of apatitic mineral. Once fluoride is incorporated into the enamel mineral, the ion likely affects the subsequent mineralization process by reducing the solubility of the mineral and thereby modulating the ionic composition in the fluid surrounding the mineral, and enhancing the matrix protein-mineral interaction. But excess fluoride leads to anomalous enamel formation by retarding tissue maturation. It is worth noting that enameloid/enamel minerals found in vertebrate teeth have a wide range of CO3 and fluoride substitutions. In the evolutionary process from elasmobranch through enameloid to mammalian enamel, the biosystems appear to develop regulatory functions for limiting the fluoridation of the formed mineral, but this development is accompanied by an increase of carbonate substitution or defects in the mineral. In research on the cariostatic effect of fluoride, considerable emphasis is placed on the roles of free fluoride ions (i.e., preventing the dissolution and accelerating the kinetics of remineralization) in the oral fluid bathing tooth mineral. Fluoride also has been used for the treatment of osteoporosis, but much still remains to be learned about maximizing the benefit and minimizing the risk of fluoride when used as a public health measure.

Amelogenesis↗
PubMed2006

Indirect selective laser sintering of an apatite-mullite glass-ceramic for potential use in bone replacement applications.

The feasibility of using indirect selective laser sintering (SLS) to produce parts from glass-ceramic materials for bone replacement applications has been investigated. A castable glass based on the system SiO2 x Al2O3 x P2O5 x CaO x CaF2 that crystallizes to a glass-ceramic with apatite and mullite phases was produced, blended with an acrylic binder, and processed by SLS. Green parts with good structural integrity were produced using a wide range of processing conditions, allowing both monolayer and multilayer components to be constructed. Following SLS the parts were post-processed to remove the binder and to crystallize fully the material, evolving the apatite and mullite phases. The parts were heated to 1200 degrees C using a number of different time-temperature profiles, following which the processed material was analysed by differential thermal analysis, X-ray diffraction, and scanning electron microscopy, and tested for flexural strength. An increase in strength was achieved by infiltrating the brown parts with a resorbable phosphate glass, although this altered the crystal phases present in the material.

Aluminum Silicates↗
PubMed2003

Cell-mediated bioresorption of sintered carbonate apatite in rabbits.

Bone apatite contains carbonate and is therefore not pure hydroxyapatite. We have successfully developed sintered carbonate apatite (CA) with a concentration of carbonate of 6 weight% and have evaluated its osteoconductive and bioresorption characteristics. Cylindrical porous sintered CA and sintered hydroxyapatite (HA) measuring 4 x 4 mm with a porosity of 20% were implanted into surgically-created bone defects in the knees of rabbits. The animals were killed after 1, 3, 6 and 12 months. The defects were evaluated by microfocus CT and histology. Bone growth into and around both materials increased. Newly-formed bone was placed in direct contact with both. Osteoclast-like cells resorbed only CA, and were coupled with osteoblasts. The porosity of sintered CA increased, indicating bioresorption, whereas that of sintered HA did not increase. Our findings indicate that sintered CA may be useful as a bioresorbable bone substitute.

Animals↗
PubMed1988

The reaction of peri-implant tissues to titanium alloy and apatite-coated implants during the healing phase.

Oral implantation has been a controversial dental therapeutic procedure. Many implant materials and designs are presently in progress of study to evaluate the long term response of peri-implant tissues, together with anticipated loading considerations. The purpose of this examination was to make clear whether a fibrous layer would form between bone and Titanium alloy and apatite-coated Titanium implants under stressed and unstressed conditions, during the healing phase after implantation. The in vivo evaluation of 10 implants were made on two dogs. The upper 2nd and 3rd and lower 3rd and 4th premolar teeth were extracted and the sockets allowed to heal for 3 months. The implants in the unstressed condition were completely submerged, and in the stressed condition they were left with their top 2 mm above the surface of the bone, so that after suturing the top of the implant was exposed to the oral environment. After the postoperative healing phase of 3 months, the animals were killed and the specimens were prepared for histological, SEM examinations and EDX analysis of the interface zone between bone and the implants. Histological examination showed a direct contact between the apatite-coated implant and new bone, so that the implant became anchored to bone without an intervening soft tissue layer and a similar result was obtained between the Titanium implant and bone in the unstressed condition. However the high magnification electron micrographs showed a thin connective tissue between the bead-blasted surface of the Titanium implant and bone, and this peri-implant tissue could be detached from the implant. In the stressed condition, a thin layer of fibrous tissue was interposed between the Titanium implant and bone. The high magnification electromicroscopical views of the interface zone between the bone and these implants showed coarse fiber bundles developed perpendicular to the Titanium surface and their terminal ends were confluent with the rugged Titanium surface presumably as a result of micro-movement during the 3 months healing phase. In this study, an adequate space for a development of fibro-anchorage was about 20-200 microns in width. If occlusal stresses were within permissible range in healing period, the relative motion of the implant and bone was then optimal for the formation of a fibro-anchorage. It could be suggested that an ideal stress transfer from the Titanium implant to bone might be achieved by this fibro-anchorage.

Animals↗
PubMed1989

[A study on the formation of apatite crystallized with gel method].

About apatite produced with a silicahydro gel method using calcium nitrate (group I) or calcium chloride (group II) and a gelatin gel method by use of calcium nitrate (group III) or calcium chloride (group IV), the formative volume as well as the formative condition of a periodic-layered precipitate (Liesegang ring), the pH measurement, calculation of Ca/P ratio, an estimation of the chlorine ion, morphological observation with a scanning electron microscope, qualitative analyses by X-ray diffraction (identification, crystallite size, lattice imperfections, lattice constants) and the composition analysis by infrared absorption spectroscopy were carried out to elucidate the formation of apatite using the gel method. The result showed that there were no distinct differences between group I-II and group III-IV, and it is suggested that it is possible to form satisfact fluorapatite with a gel method using calcium chloride as well as calcium nitrate.

Apatites↗
PubMed2002

Calcium-ion incorporation into titanium surfaces accompanied by electrochemical apatite-deposition.

The depths of calcium-ion incorporation into a commercially pure titanium and an experimental beta-type titanium alloy were determined using Auger electron spectroscopy. After the electrochemical deposition of apatite, new compositional gradients appeared in the profiles in which the Ca and P concentrations gradually decreased as a function of the depth up to 6-8 nm. The relative concentration of Ca in the outermost layer was higher than that of P. On the other hand, after the soaking in a simulated body fluid, the relative concentration of P was higher than that of Ca in the outermost layer. These results suggested that Ca ions were well incorporated into the outermost oxide layer of titanium accompanied by the electrochemical apatite-deposition on its surface.

Apatites↗
PubMed2003

Real-time monitoring of apatite deposition using electrochemical quartz crystal microbalance.

The electrochemical deposition process of apatite was monitored in real-time using an electrochemical quartz crystal microbalance (EQCM). A piezoelectric quartz oscillator with titanium was fixed to a cell and connected to a frequency counter. The electrolyte temperature was maintained at 20, 37, and 60 degrees C and the direct current density was constant at 0.2, 0.5, 1.0, and 2.0 mA/cm2. The deposited amount derived from the frequency change increased as electrolyte temperature and current density increased. The critical times, which are the starting times of quick increases of deposition, decreased with them. The critical times observed in the present study, namely in situ, were much shorter than those obtained from real weight change reported in our previous report. The apparent activation energies of the electrochemical deposition of apatite under 1.0 and 2.0 mA/cm2 were about 36.1 and 31.9 kJ/mol, respectively. These results indicate that electro current loading may reduce the activation energy required for the deposition of calcium phosphates.

Adsorption↗
PubMed2006

Comparison of carbonate apatite and beta-tricalcium phosphate (resorbable calcium phosphates) implanted subcutaneously into the back of rats.

Bioresorption and biocompatibility of carbonate apatites, both sintered and non-sintered (S-CAP and N-CAP), and of sintered beta-tricalcium phosphate (beta-TCP) were compared by implanting particles of these materials into the back of adult rats. Bioresorption--when evaluated non-destructively with non-decalcified tissues using microfocus X-ray tomography--was essentially the same for N-CAP and beta-TCP, while S-CAP exhibited statistically lower bioresorption at 2, 4, and 12 weeks postoperatively. Biocompatibility--when evaluated by ED1 immunostaining--was in the order of beta-TCP > N-CAP > S-CAP. The intensity of ED1 immunostaining decreased with time, but persisted longer in beta-TCP than in S-CAP and N-CAP, indicating that beta-TCP produced the strongest and most enduring stimulation of macrophages. Although no statistical differences were found in tartrate-resistant acid phosphatase (TRAP) staining among the materials at each implantation period, the degree of TRAP staining for S-CAP was statistically greater at 12 weeks than at 2 and 4 weeks, indicating that osteoclast-like cells were in part responsible for the resorption of the carbonate apatite.

Absorbable Implants↗
PubMed1977

Arthritis associated with apatite crystals.

Needle-shaped crystals of 75 to 250 A diameter have been identified by transmission electron microscopy in clumps within synovial fluid mononuclear cell vacuoles in a variety of joint diseases. These crystals, similar to those previously associated with calcific periarthritis, were seen in acute undiagnosed arthritis and in exacerbations of osteoarthritis where they may be inducing a synovitis similar to that seen with urate and pyrophosphate crystals in gout and pseudogout. By light microscopy purple staining cytoplasmic inclusions or extracellular globules can suggest the presence of clumps of these crystals. Apatite clumps can also occasionally appear as small birefringent chunks or rods and thus might mimic urate or calcium pyrophosphate. Ultrastructural appearance, electron probe analysis, and X-ray diffraction pattern were those of apatite. Experimental injection of hydroxyapatite crystals into dog knee joints produces inflammation supporting the potential role for these crystals in joint disease.

Acute Disease↗
PubMed2000

[Physical properties of apatite bone cement].

Some properties of the apatite bone cement which is composed of alpha-tricalcium phosphate and hydroxyapatite for use as a biomaterial were investigated. The powder of cement was synthesized from calcium phosphate, calcium carbonate and dicalcium phosphate by solid reaction. Several kinds of citric acid solutions were used for hardening. When the liquid for hardening was 30% (w/w) citric acid solution, the setting time was about six minutes, the compressive strength of hardened bodies was 24.96 MPa, and the solubility was about 1.4 wt%. The compressive strength was increased by the addition of Na or K salt. Especially, when copolymer of acrylic acid/itaconic acid was added to the liquied, the strength was increased about three times, but the setting time was significantly shortened. The results of this study indicate that the apatite bone cement is a potentially highly useful biomaterial for dental and medical applications.

Apatites↗
PubMed1997

[The study on apatite castable glass-ceramics in composition and physicochemical properties].

The authors reported the result of the study of the glass formation range and physicochemical characteristics of apatite (APA) castable ceramics in the CaO-MgO-Al2O3-SiO2-P2O5 system. The relationship between its component and casting properties, the mechanical property and chemical stability was mainly discussed. The result showed that homogeneous glass could be formed in the experimental scope. This glass crystallized enamel-analogous apatite phase. It has improved mechanical property of parent glass, the bending strength was up to 165 MPa and possessed a fine chemical stability. This investigation could provide a new castable ceramics material for dental restoration.

Apatites↗