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PubMed1995

Intrinsic factors of apatite influencing its amorphization during plasma-spray coating.

Hydroxyapatite coatings were prepared from differently treated starting powders to investigate the intrinsic factors of apatite influencing its amorphization during plasma-spray coating. The joint analyses of X-ray diffraction and infrared spectra show that the vacancies located on missing hydroxyl sites retard the amorphous/crystalline conversion and enforce retention of the amorphous component; the absorbed water molecules that pre-exist in the starting powder can be incorporated into the vacancies in the hydroxyapatite lattice during plasma-spray coating and compensate for the missing hydroxyls so as to promote the transformation of amorphous into crystalline apatite in the coating process. The more vacancies there are in the apatite structure due to missing hydroxyl sites, the more amorphous the component in the resultant coatings. Moreover, the amorphous phase formed in this way is stable in room conditions.

Biodegradation, Environmental↗

PubMed2005

A computer modelling study of the uptake, structure and distribution of carbonate defects in hydroxy-apatite.

Computer modelling techniques have been employed to qualitatively and quantitatively investigate the uptake and distribution of carbonate groups in the hydroxyapatite lattice. Two substitutional defects are considered: the type-A defect, where the carbonate group is located in the hydroxy channel, and the type-B defect, where the carbonate group is located at the position of a phosphate group. A combined type A-B defect is also considered and different charge compensations have been taken into account. The lowest energy configuration of the A-type carbonate has the O-C-O axis aligned with the channel in the c-direction of the apatite lattice and the third oxygen atom lying in the a/b plane. The orientation of the carbonate of the B-type defect is strongly affected by the composition of the apatite material, varying from a position (almost) flat in the a/b plane to being orientated with its plane in the b/c plane. However, Ca-O interactions are always maximised and charge compensating ions are located near the carbonate ion. When we make a direct comparison of the energies per substitutional carbonate group, the results of the different defect simulations show that the type-A defect where two hydroxy groups are replaced by one carbonate group is energetically preferred (DeltaH = -404 kJ mol(-1)), followed by the combined A-B defect, where both a phosphate and a hydroxy group are replaced by two carbonate groups (DeltaH = -259 kJ mol(-1)). The type-B defect, where we have replaced a phosphate group by both a carbonate group and another hydroxy group in the same location is energetically neutral (DeltaH = -1 kJ mol(-1)), but when the replacement of the phosphate group by a carbonate is charge compensated by the substitution of a sodium or potassium ion for a calcium ion, the resulting type-B defect is energetically favourable (DeltaH(Na) = -71 kJ mol(-1),DeltaH(K) = -6 kJ mol(-1)) and its formation is also promoted by A-type defects present in the lattice. Our simulations suggest that it is energetically possible for all substitutions to occur, which are calculated as ion-exchange reactions from aqueous solution. Carbonate defects are widely found in biological hydroxy-apatite and our simulations, showing that incorporation of carbonate from solution into the hydroxyapatite lattice is thermodynamically feasible, hence agree with experiment.

Bone Substitutes↗

PubMed2001

Effect of polyacrylic acid on the apatite formation of a bioactive ceramic in a simulated body fluid: fundamental examination of the possibility of obtaining bioactive glass-ionomer cements for orthopaedic use.

Glass-ionomer cements, which consist of CaO-Al2O3-SiO2-CaF2 glass powders and a polyalkenoic acid solution, such as polyacrylic acid (PAA), have been widely used in dentistry. They set rapidly without any shrinkage, the lack of temperature increase on reaction, and develop high mechanical strength. Therefore, if bioactive glass-ionomer cements can be obtained, such cements are expected to be useful as cements for fixing orthopaedic implants to the surrounding bone. In the present study, to examine the possibility of obtaining bioactive glass-ionomer cements, the effect of PAA on the apatite formation on bioactive ceramics in a simulated body fluid was investigated. It was revealed that presence of even a small quantity of PAA inhibits the apatite formation in the body environment. It is speculated that when glass-ionomer cements are implanted into the body, PAA can be released from the glass-ionomer cements and inhibits the apatite formation on their surfaces. It is reasonable to suppose that this will occur with any glass-ionomer cement that contains PAA. Therefore, it might be considered difficult to obtain bioactive glass-ionomer cements.

Acrylic Resins↗

PubMed2004

Apatite-forming ability and mechanical properties of PTMO-modified CaO-SiO2-TiO2 hybrids derived from sol-gel processing.

Hydrolysis and polycondensation of triethoxysilane end-capped Poly (tetramethylene oxide) (Si-PTMO), tetraethoxysilane (TEOS), tetraisopropyltitanate (TiPT) and calcium nitrate (Ca(NO(3))(2)) gave transparent monolithics of PTMO-modified CaO-SiO(2)-TiO(2) hybrids. The samples with (TiPT)/(TEOS+TiPT) molar ratios from 0 to 0.20 under constant ratio of (Si-PTMO)/(TEOS+TiPT) of 2/3 in weight were prepared. It was found that the incorporation of TiO(2) component into a PTMO-CaO-SiO(2) hybrid results in an increase in the apatite-forming ability in a simulated body fluid: the hybrids with (TiPT)/(TEOS+TiPT) of 0.10 and 0.20 in mol formed an apatite on their surfaces within only 0.5 day. It seemed that, within the range of compositions studied, the TiO(2) content little affects the overall mechanical properties: Young's modulus were 52-55MPa, tensile strength, 7-9MPa, and strain at failure, about 30%. Thus, the organic-inorganic hybrids exhibiting both fairly high apatite-forming ability and high capability for deformation were obtained. These hybrid materials may be useful as new kind of bioactive bone-repairing materials.

Body Fluids↗

PubMed1999

Feasibility of using natural fishbone apatite as a substitute for hydroxyapatite in remediating aqueous heavy metals.

Fishbone, a natural, apatite rich substance, was examined for suitability as a substitute for hydroxyapatite in the sequestering of aqueous divalent heavy metal ions. The fishbone exhibited lower metal removal capacity than pure hydroxyapatite, due primarily to its purity ( approximately 70% apatite equivalent). In other ways the fishbone behaves in a similar manner as pure hydroxyapatite in the sequestration process. It was observed that it can remove all Pb(2+), Cu(2+), Cd(2+) and Ni(2+) to below detectable levels as measured by inductively coupled plasma atomic absorption, and the rate of reaction with either Zn(2+), Ni(2+), or Pb(2+) was also found to be similar to hydroxyapatite. Also, a two level, three variable full factorial design was performed for the Pb/apatite reaction and both apatites performed similarly. The main difference, besides capacity, was on exposure to high (2.4 mM) Pb concentrations. The fishbone removed less of the Pb(2+) than capacity correction predicted.

Animals↗

PubMed2001

The influence of calcium to phosphate ratio on the nucleation and crystallization of apatite glass-ceramics.

The nucleation and crystallization behavior of a series of glasses based on 4.5SiO2-3Al2O3-YP2O5-3CaO-1.51CaF2 was studied. The parameter Y was varied to give calcium to phosphate ratios between one and two. All of the glasses studied crystallized firstly to fluorapatite (Ca5PO4)3F). The glass with a calcium to phosphate ratio of 1.67, corresponding to apatite, bulk nucleated to give fluorapatite (FAP). The glasses with calcium : phosphate ratios either less than that of apatite, or greater than that of apatite all exhibited surface nucleation of FAP. However, following a nucleation hold of one hour at approximately 50 K above the glass transition temperature these glasses exhibited bulk nucleation of FAP.

Journal Article↗

PubMed1997

In-vitro apatite formation on phosphorylated bamboo.

Natural self-reinforced composite, bamboo, was surface modified by phosphorylation with urea-H3PO4 and NaOH-H3PO4 methods; then precalcification was performed by immersing samples in saturated Ca(OH)2 solution. After that, calcium phosphate can be formed on the surface of bamboo samples in calcification media: simulated body fluid (1.5 SBF) and accelerated calcification solution (ACS). Experimental results reveal that pre-calcification is an inevitable step for the formation of calcium phosphate. The calcium phosphate formed in 1.5 SBF was identified by thin-film X-ray diffraction as apatite which was not well crystallized. Compared with the urea-H3PO4 method, the NaOH-H3PO4 method has the advantages of quicker and continuous apatite formation and stronger adhesive between apatite and bamboo.

Journal Article↗

PubMed1999

Effects of apatite, transforming growth factor beta-1, bone morphogenetic protein-2 and interleukin-7 on ameloblast differentiation in vitro.

Preameloblasts overtly differentiate in vitro when recombined with cell-free predentin-dentin. The predentin-dentin components able to trigger ameloblast terminal differentiation have not been identified, but some growth factors (members of the TGFbeta superfamily) have been demonstrated to be associated with this matrix, and in situ hybridization has demonstrated the presence of transcripts for TGFbetas and BMP-2 in odontoblasts facing differentiating ameloblasts. Moreover, intense expression of receptors for the cytokine interleukin-7 (IL-7) in polarizing ameloblasts has been reported. In this study, isolated E-18 and E-19 mouse molar enamel organs were cultured in vitro in presence of BMP-2, TGFbeta-1, IL-7 or synthetic apatite. TGFbeta-1 and BMP-2 combined with heparin induced cytodifferentiation of ameloblasts. IL-7 maintained the polarized state of ameloblasts. BMP-2-soaked apatite induced functional differentiation of ameloblasts (secretion of amelogenin). Integrating these data with previous work, a working hypothesis concerning the control of ameloblast terminal differentiation is presented: members of the TGFbeta superfamily secreted by odontoblasts might be trapped by predentin components first and then by dentin apatites, and these growth factors might trigger the cytological-functional sequence of ameloblast terminal differentiation.

Ameloblasts↗

PubMed2004

Calcium-lead fluoro-vanadinite apatites. I. Disequilibrium structures.

The synthetic vanadinites (Pb(x)Ca(10-x))(VO4)6F2delta, 1 < x < 9, adopt a P6(3)/m apatite structure with 9.7590 (1) < or = a < or = 10.1179 (1) A and 7.0434 (3) < or = c < or = 7.4021 (1) A. The partitioning of calcium and lead over the AI(4f) and AII(6h) positions is nonstoichiometric with lead preferentially entering the larger AII site. High-resolution electron microscopy showed that samples annealed for 10 h at 1073 K are in disequilibrium with calcium- and lead-rich microdomains co-existing at unit-cell scales. For (Pb5Ca5)(VO4)6F2delta, sintering in excess of 2 weeks is required for the metals to order macroscopically. As annealing progresses, c/a, the partitioning coefficient kPb(AI/AII) and the AIO6 metaprism twist angle (phi) adjust cooperatively to enlarge the apatite channel, and thereby accommodate higher lead content. These results demonstrate that phi is a sensitive measure of disequilibrium and a useful device for monitoring changes in apatite topology as a function of composition.

Journal Article↗

PubMed1988

Bonding of bone to apatite-coated implants.

Implants of solid sintered hydroxyapatite form very tight bonds with living bone, but are susceptible to fatigue failure. This problem can be overcome by using plasma-sprayed apatite coatings on titanium implants. A very strong bond is formed between bone and this composite material; this was studied in canine bone with plug implants, avoiding any mechanical retention. Mechanical testing showed an interface shear strength at six weeks of 49 MPa with a maximum of 64 MPa after six months. There was histological evidence of direct bonding between the apatite coating and living bone while uncoated control plugs were easily extracted. The results indicate that apatite-coated implants can form a chemical fixation with a strength comparable to that of cortical bone itself. This fixation is far stronger than that provided by current cemented or uncemented fixation techniques.

Adhesiveness↗

PubMed1989

[Studies on physico-chemical properties of self-setting apatite cement].

A new dental cement was developed by use of tetracalcium phosphate monoxide (Te-CP) and dicalcium phosphate dihydrate (DCPD). When an equimolar mixture of the two calcium phosphates was mixed with diluted phosphoric acid, it hardened into a phase of hydroxyapatite (HAp) resembling the main inorganic phase of hard tissues. The present study was undertaken to investigate physico-chemical properties of this newly developed apatite cement and to evaluate its potential as dental cement to clinical application. The setting time was reduced in the presence of synthetic HAp, indicating added HAp to be an accelerator in the setting reaction. The pH of paste rapidly increased to a neutral range from initial solution acidity of about 2.0 and the subsequent setting reaction proceeded in a neutral and weak alkaline pH range. The hardened solid 4 hours after saturation was identified as single phase of apatite by X-ray diffraction. The HAp crystallinity of the set cement varied with the crystallinity of HAp added as setting accelerator. The wet compressive strength of the cement stored for one day in synthetic saliva at 37 degrees C increased to 400 kg/cm2 as added HAp crystallinity decreased. Moreover no disintegration took place when the cement was stored at 37 degrees C in synthetic saliva, which was undersaturated with respect to DCPD but well supersaturated for HAp. In clinical application to animals, no significant cleavage was observed between the hard tissues and the cement by SEM even three months after the cement paste was filled in the tooth cavity of monkeys. In the specimen prepared one week after implantation in the medullary canal of rats, no inflammatory cell appeared. The specimen prepared one month after implantation showed that the set cement was tightly contacted with newly formed bone. These findings strongly suggest that the newly developed self-setting apatite cement is useful as a pulp capping agents, root canal fillings and bone substitute.

Animals↗

PubMed1982

ESR on the hydroxyl ion vacancies in the apatites.

Heating biological apatites and synthetic apatites in the stream of inert gas saturated with heavy water vapor, introduces OD ions which substitute for the hydroxyl (OH) ions and partially for the OH vacancies, depending on the heating time and the gas flow rate. This has been verified by ESR and partially by IR. Deuteration gives no serious alterations of the a-axis dimension or of the PO4 bands in the IR spectra. These findings have been interpreted as suggesting that the OH ions diffuse out and the OD ions diffuse in through specific pathways, and the diffusing ions interact permanently with none of the other ions in the apatite structure. Heating in dry inert gas results in the formation of hydroxyl ion vacancies. The ESR spectra of these samples in the g = 2.06 region have been interpreted in terms of O-2 and O-. The shortening of the a-axis dimension in this case has been accounted for based on the loss of structurally incorporated H2O and the loss of the OH ions on the hexad axis.

Bone and Bones↗

PubMedDate not supplied

Carbonated apatite and hydroxyapatite in craniofacial reconstruction.

Alloplastic biomaterials have revolutionalized craniofacial reconstruction. Commercially available bone substitute cements allow easy contouring and application, as well as avoidance of postoperative donor site complications. Hydroxyapatite and carbonated apatite are commercially available biomaterials currently being used as moldable bone substitutes in craniofacial reconstruction. This study presents 35 patients with 46 sites of reconstruction using hydroxyapatite or carbonated apatite. The characteristics, effectiveness, advantages, and limitations of each biomaterial are discussed.

Adolescent↗

PubMed1997

Ectopic bone induction in porous apatite-wollastonite-containing glass ceramic combined with bone morphogenetic protein.

To accelerate the integration of ceramic implants with the surrounding bone and to search for a suitable carrier for bone morphogenetic protein (BMP), we studied ectopic bone induction in porous apatite-wollastonite-containing glass ceramic (A-W GC) combined with partially purified bovine BMP (bBMP) and recombinant Xenopus BMP-4/7 (rxBMP-4/7). Porous A-W GC rods [4 mm in diameter, 5 mm in height, 70% porosity, 200 microns mean pore size, 17.54 +/- 3.82 MPa (mean +/- SD) compressive strength] were used. An apatite coating formed on the surface of porous A-W GC that had been immersed in simulated body fluid at 36.5 degrees C for 7 days. In experiment 1, porous A-W GC rods were combined with either bBMP, collagen, or with both bBMP and collagen. The rods were implanted into subcutaneous pouches in rats and were harvested 4 weeks after implantation. Low-energy radiographic, scanning electron microscopic (SEM), and histological examinations showed ectopic bone formation and within the rods only in the porous A-W GC combined with the bBMP and collagen group. Quantitative analysis also revealed that this group alone showed a significant increase in bone formation. In experiment 2, porous A-W GC rods were combined with rxBMP and collagen, implanted into rats, and harvested as described above. SEM and histological examination showed ectopic bone formation around and within the rods. Because of its relatively high mechanical strength, ease of handling, and good osteoinductivity, porous A-W GC combined with BMP and collagen may be clinically useful in patients with large cancellous bone defects or craniomaxillofacial lesions.

Animals↗

PubMed1998

Preparation of a chitin-apatite composite by in situ precipitation onto porous chitin scaffolds.

Composites of chitin with calcium phosphate were obtained by in situ precipitation of the mineral from a supersaturated solution onto chitin scaffolds. The chitin scaffolds were obtained by freeze drying to give a highly porous structure possessing a polar surface favorable for apatite nucleation and growth. THe extent and arrangement of calcium phosphate deposits on the chitin and substituted chitin scaffolds were explored. Up to 55% by mass of calcium phosphate could be incorporated into chitin scaffolds. Deposits on the chitin surface were a continuous apatite carpet nature while deposits on carboxymethylated chitin surfaces displayed a spherical morphology. Carboxymethylation of chitin exerts an overall inhibitory effect towards calcium phosphate deposition, but it provides for site-specific nucleation of the mineral phase. In situ precipitation can be an important route in the future production of various polymer-calcium phosphate composites.

Apatites↗

PubMed1998

Bioactive bone cement: comparison of apatite and wollastonite containing glass-ceramic, hydroxyapatite, and beta-tricalcium phosphate fillers on bone-bonding strength.

A study was conducted to compare the bone-bonding strengths of three types of bioactive bone cement, consisting of either apatite- and wollastonite-containing glass-ceramic (AW-GC) powder, hydroxyapatite (HA) powder, or beta-tricalcium phosphate (beta-TCP) powder as an inorganic filler and bisphenol-a-glycidyl methacrylate (Bis-GMA) based resin as an organic matrix. Seventy percent (w/w) filler was added to the cement. Rectangular plates (10 x 15 x 2 mm) of each cement were made and abraded with #2000 alumina powder. After soaking in simulated body fluid for 2 days, the AW cement (AWC) and HA cement (HAC) formed bonelike apatite over their entire surfaces, but the TCP cement (TCPC) did not. Plates of each type of cement were implanted into the tibial metaphyses of male Japanese white rabbits, and the failure loads were measured by a detaching test at 10 and 25 weeks after implantation. The failure loads of AWC, HAC, and TCPC were 3.95, 2.04, and 2.03 kgf at 10 weeks and 4.36, 3.45, and 3.10 kgf at 25 weeks, respectively. The failure loads of the AWC were significantly higher than those of the HAC and TCPC at 10 and 25 weeks. Histological examination by contact microradiogram and Giemsa surface staining of the bone-cement interface revealed that all the bioactive bone cements were in direct contact with bone. However, scanning electron microscopy and energy-dispersive X-ray microanalysis showed that only AWC had contacted to the bone via a Ca-P rich layer formed at the interface between the AW-GC powder and the bone, which might explain its high bone-bonding strength. Neither the HAC nor the TCPC contacted the bone through such a layer between each powder and the bone, although the HAC and TCPC directly contacted with bone. Our results indicate that all three types of abraded and prefabricated cement have bonding strength to bone, but AWC has superior bone-bonding strength compared to HAC and TCPC.

Animals↗

PubMed1999

Precipitation of carbonated apatite in the cement system alpha-Ca(3)(PO(4))(2)-Ca(H(2)PO(4))(2)-CaCO(3).

Powder mixtures of alpha-Ca(3)(PO(4))(2), Ca(H(2)PO(4))(2), and CaCO(3) were investigated to assess their potential for the precipitation of a carbonated apatite suitable for cement applications from a supersaturated solution. Of particular interest was the requirement of carbon dioxide release during the setting reaction to obtain Ca(9-x)(HPO(4))(1-1.5x) (PO(4))(5-2.5x)(CO(3))(3.5x)(OH)(1 + 1.5x) with a fixed carbonate content. Results indicated that a compromise is necessary with respect to the maximum permissible level of CaCO(3) addition to the powder mixture as against appropriate setting and hardening properties. Cementlike materials with good setting and hardening properties were obtained when alpha-Ca(3)(PO(4))(2) was the main reactant using Ca(H(2)PO(4))(2) and CaCO(3) as additives in relative proportions of <10 wt % corresponding, approximately, to the stability field area (x,lambda) contained within the lines lambda = -1.5x, x = 0.3, and lambda = -1. Desirable workability and setting properties were lost as the parameters x and -lambda increased. Finally, it was also found to be virtually impossible to obtain a predetermined chemical composition for the setting apatite precipitate, since to increase the amount of carbon dioxide released from the initial powder mixture during setting, the solution pH would need to be decreased, and in doing so the nature of the precipitate could be altered to fulfil the thermodynamic conditions of the solubility diagrams of calcium phosphates.

Apatites↗

PubMed2000

High-resolution electron microscopy study of synthetic carbonate and aluminum containing apatites.

Aluminum (Al)-containing calcium-deficient carbonated hydroxyapatites were produced by a precipitation method from aqueous solution with carbonate (0-6.1%) and aluminum (0.1-0.5%) concentrations close to those found in biological materials. Two series of apatites were prepared: one at pH 7.0 and another at pH 9. 0. High-resolution electron microscopy has shown that many of them possess structural defects such as screw dislocations, grain boundaries, and central defects. Samples with high carbonate content and high water and high Al(3+) content had a high amount of structural defects. Accordingly, a sample (7Al1) with a relatively high carbonate content (6.1%) and a sample (7Al6) without carbonate but with a relatively high water (2.0 mol) and Al(3+) content (0. 39%) presented the highest amount of structural defects, 54% and 47%, respectively. A sample (7Al13) with a low level of crystalline water (1 mol) and low carbonate (2.5%) showed a small amount of defects. The presence of water associated with Al(3+) induced a high number of crystals having a central defect with a great similarity to the so-called water layer of octacalcium phosphate (OCP). Observed images of all these crystals have shown good correspondence with the computer-simulated image based on the crystal structure of hydroxyapatite, indicating that the addition of Al(3+) and carbonate does not perturb the apatitic structure.

Aluminum↗