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PubMed2000

Metastable Equilibrium Solubility Behavior of Carbonated Apatites in the Presence of Solution Fluoride.

The aims of the present investigation were to assess the applicability of the metastable equilibrium solubility (MES) concept for the carbonated apatites (CAPs) over a range of pH and a wide range of solution fluoride concentrations and to examine the hypothesis that, in the presence of solution fluoride, a surface complex with the stoichiometry of fluorapatite (FAP) governs the MES behavior. Two CAP samples were prepared by precipitation from reaction media containing calcium nitrate (Ca(NO(3))(2).4H(2)O) and sodium phosphate (NaH(2)PO(4).H(2)O) at two different levels of sodium bicarbonate. The MES distributions of the two CAP preparations were determined by equilibrating approximately 10 mg of CAP powder in 2 L of 0.1 M acetate buffers (ionic strength=0.50 M) at pH 4.5 and 5.5 and at various levels of calcium, phosphate, and fluoride. The fluoride concentrations ranged from 0.03 to 12 ppm. From the compositions of the equilibrating buffer solutions, ion activity products based upon the stoichiometries of hydroxyapatite (HAP) and FAP were calculated in an attempt to determine the correct function governing the dissolution of the CAP preparations. The results of this study demonstrated that both CAP preparations exhibit the MES distribution phenomenon in solution media of varying pH and fluoride concentrations. Furthermore, the experimental MES data obtained with both CAP preparations at the lower pH (4.5) and at higher solution fluoride levels (>/=0.1 ppm) were essentially superimposable when plotted against the ion activity product based upon the stoichiometry of FAP, suggesting that in the presence of solution fluoride the MES governing surface complex may be an entity possessing a stoichiometry approximated by that of FAP. When the HAP stoichiometry was assumed to represent the surface complex, good superposition of the data was not possible. Copyright 2000 Academic Press.

Journal Article↗

PubMed1982

Repair of experimental bone defect with a collagen block containing synthesized apatite.

Collagen solution extracted from the adult steer hide was mixed with the synthesized hydroxyapatite and after cross linking lyophilized. Small blocks of this sample were filled in bone defects of rabbit fibula. Two control groups were made, of which one was filled with the collagen block contained no apatite and the other group left as a sham operation. The experimental group showed more active bone formation than control groups.

Animals↗

PubMed1993

Anterior cervical discectomy and vertebral interbody fusion with hydroxy-apatite ceramic. Preliminary results.

Intervertebral plates of hydroxy apatite ceramic (HAC) have been used in three patients for cervical vertebral interbody fusion after anterior discectomy. In one case a pure HAC "Disc" was used, which proved to be too friable. Specially designed intervertebral plates, which were composed of an HAC-coated core of alumina ceramic, were used in the other two cases. Clinically and radiologically optimal results after 1-year- and 2-year-follow-up suggest that HAC-ceramic might be a very promising material for vertebral interbody fusion. Possible complications and pain due to bone removal from the iliac crest are avoided, and the operative procedure is simplified.

Adult↗

PubMed1995

Crowned dens syndrome: a manifestation of hydroxy-apatite rheumatism.

Crowned dens syndrome is defined as an association of acute cervical pain and calcifications in the peri-odontoid space. The authors report one case of this rare localization of hydroxy-apatite rheumatism and review 12 similar cases in the literature. This disease affects only adult females. Patients present with inflammatory signs, can be treated with non-steroid anti-inflammatory drugs and recover without sequela. Calcium pyrophosphate dihydrate deposition can also lead to this syndrome. Other perioodontoid calcifications and ossifications, usually asymptomatic, appear only as a radiologically crowned dens.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1990

Formation of carbonate-apatite crystals after implantation of calcium phosphate ceramics.

The aims of this study were (1) to determine at the crystal level, the nonspecific biological fate of different types of calcium phosphate (Ca-P) ceramics after implantation in various sites (osseous and nonosseous) in animals and (2) to investigate the crystallographic association of newly formed apatitic crystals with the Ca-P ceramics. Noncommercial Ca-P ceramics identified by X-ray diffraction as calcium hydroxylapatite (HA), beta-tricalcium phosphate (beta-TCP), and biphasic calcium phosphates (BCP) (consisting of beta-TCP/HA = 40/60) were implanted under the skin in connective tissue, in femoral lamellar cortical bone, articular spine bone, and cortical mandibular and mastoidal bones of animals (mice, rabbits, beagle dogs) for 3 weeks to 11 months. In humans, HA or beta-TCP granules were used to fill periodontal pockets, and biopsies of the implanted materials were recovered after 2 and 12 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Changes in apatite crystal size in bones of patients with osteogenesis imperfecta.

Apatite crystal size in compact bone of children (age less than 11 years) and adolescents (age greater than 12 years) with osteogenesis imperfecta (OI) was analyzed by X-ray diffraction. Eight type I, 4 type II, 11 type III, and 14 type IV OI patients were studied along with 9 controls. The crystal size was most significantly reduced in type II patients, all of whom had died at birth. Crystal size was also diminished in both children and adolescents with types III and IV, whereas with type I OI, crystal size was reduced in children only, returning to normal in adolescence. There was a trend toward increased bone crystal size with age in both OI patients and controls.

Adolescent↗

PubMed1997

X-ray pole figure analysis of apatite crystals and collagen molecules in bone.

X-ray pole figure analysis was performed on apatite (AP) crystals in bone mineral and collagen molecules in the bone matrix. For AP in bone mineral, the (0002) plane (c-axis) and {2130} plane were examined. The diffraction peaks from both planes were well isolated from other diffraction peaks in the bone. To investigate the orientation of collagen molecules in the bone matrix, demineralized bone by EDTA treatment was used. For collagen, the diffraction peak from about the 0.3 nm period along the helix axis of the collagen molecule was investigated. The c-axis of AP and the helical axis of the collagen molecule have strongly preferred orientations in a direction parallel to the bone axis. The c-axis of AP has an appreciable pole density peak in the radial and tangential direction of the bone, whereas collagen molecules were almost uniaxially oriented in the bone axis direction though having an appreciable distribution. This suggests that there are more than two types of morphology in the AP particle in bone mineral: one with the c-axis almost parallel to the bone axis and the other in which the c-axis is oriented almost perpendicular to the bone axis. The {2130} plane has isolated peaks of pole density in pole figures in both radial and tangential directions. On the basis of the classification of orientation for elongated polyethylene, the main portion of AP particles in bone is concluded to be biaxially oriented.

Animals↗

PubMed2001

Sexual dimorphism of porcine amelogenins: male-specific amelogenins have strong adsorption properties onto apatite crystals.

The present studies were undertaken to investigate the sexual dimorphism of porcine amelogenins and to gain information as to whether excesses of male amelogenins, if any, possess functional significance in protein-crystal interactions. Enamel proteins, including the intact full-length amelogenins and their degraded polypeptides, were isolated from the secretory enamel of male and female pigs. To identify the amelogenins among the separated pools of male- and female-matrix proteins, rabbit anti-C13 and C25 peptide sera were used, which reacted specifically with the conserved C-terminal domain. Immunoblotting showed that a few extra members of the amelogenins, sharing common epitopes at the C-terminus, were recognized in male products. The apparent yield of the male amelogenins was only marginal, on the basis of their stained intensities on the gel, but the secreted male amelogenins demonstrated selective (probably the strongest among the amelogenins) adsorption properties onto apatite crystals. Reflecting the general symmetric electrophoretic profiles of the male- and female-enamel proteins in toto, there were no sex-linked differences in the protein-crystal interaction and the resulting regulatory function of crystal precipitation.

Journal Article↗

PubMed1994

A histologic comparison of the functional loading capacity of an occluded dense apatite implant and the natural dentition.

A histologic comparison of the functional loading capacity of an occluded dense apatite implant and the natural dentition at a ratio of one implant to three natural teeth was carried out on six monkeys. Single implants were placed in the maxillary left second molar and mandibular right second molar of each monkey. Four months later, the vertical dimension of occlusion was raised at the contacting areas between the implant and the connected first, second, and third opposing molar teeth by placing metal crowns on them. The three connected molars gradually intruded over time, whereas the supporting bone of the mandibular and maxillary implants showed no abnormalities and was able to bear the load because of thickening and remodeling of the surrounding bone.

Alveolar Bone Loss↗

PubMed1990

Development of an automated experimental setup for the study of ionic-exchange kinetics. Application to the ionic adsorption, equilibrium attainment and dissolution of apatite compounds.

An ion-selective electrode and microcomputer-based experimental setup for the study of ionic-exchange kinetics between a powdered solid and the solution is described. The equipment is composed of easily available commercial devices and a data acquisition and regularization computer program is presented. The system, especially developed to investigate the ionic adsorption, equilibrium attainment and dissolution of hard mineralized tissues, provides good reliable results by taking into account the volume changes of the reacting solution and the electrode behaviour under different experimental conditions, and by avoiding carbonation of the solution. A second computer program, using the regularized data and the experimental parameters, calculates the quantities of protons consumed and calcium released in the case of equilibrium attainment and dissolution of apatite-like compounds. Finally, typical examples of ion-exchange and dissolution kinetics under constant pH of enamel and synthetic hydroxyapatite are examined.

Adsorption↗

PubMed1994

Compliance of an apatitic calcium phosphate cement with the short-term clinical requirements in bone surgery, orthopaedics and dentistry.

An apatitic calcium phosphate cement was developed containing a nucleator in its powder and an accelerator in the liquid and having an initial setting time of 7.5 min and a final setting time of 12.5 min according to testing with Gillmore needles at room temperature. At body temperature the initial setting time is 6 min, after which the wound can be closed. The dough time (during which it can be deformed without damaging its microstructure) is 4 min. Therefore, the time lost during an operation with this material is 2 min. The product does not shrink or expand during setting, neither is there a thermal effect; it does not swell or disintegrate upon exposure to aqueous fluids after initial setting. Upon soaking in Ringer's solution the product obtains a final compressive strength of 40 MPa and 65% of that strength is reached within 6 h at body temperature. Cytotoxicity is absent. Applications are envisaged in bone surgery, orthopaedics and dentistry, a.o. for acceleration of the osseointegration of metal endoprostheses.

Biocompatible Materials↗

PubMed1994

A procedure for the visualization of bone with hydroxyl-apatite coated implants.

A procedure for the histological visualization of the interface between implants coated with hydroxyl-apatite (HA) and bone, and the reaction of bones to the implants, has been developed. Thick sections of bones with HA-coated stainless-steel implants, were investigated with the implant still in situ with routine and (confocal) fluorescence microscopy. The prosthesis-HA-bone interface, bone cells, necrotic and vascularised bone, bone-ingrowth and bone remodelling could be visualised. After removal of the implant from the sections alternative sections were further processed for routine light microscopy, microradiography and detailed fluorescence studies. It appeared that the HA coating was still intact and the integrity of the HA-bone bond was very well preserved. The HA coating layer had the same appearance as after the first inspection with surface microscopy. However, more details were visible. Prosthesis-related and time-related changes in the appearance of the HA layer were detected. The advantage of the procedure is that observations can be made of bone reactions with the prosthesis still in situ, without previous embedding in plastics, and laborous sectioning and/or grinding procedures. Thereafter, sections can be processed for different histological techniques, e.g. immunocytochemistry, routine histology, microradiography, fluorescence microscopy, apparently without imparing the HA coating layer.

Animals↗

PubMed1995

EPR dating CO2- sites in tooth enamel apatites by ENDOR and triple resonance.

In this work we combine electron paramagnetic resonance (EPR), high-resolution electron nucleus double resonance (ENDOR) and general triple resonance (GTR) spectroscopies, to study the local environment of the CO2- groups created by ionizing radiation in fossil tooth enamel. We demonstrate that the CO2- groups occupy slightly modified phosphate sites in the hydroxyapatite lattice. In quaternary shark enamel we found these groups to be interacting with water molecules in the apatite channels. The absence of water molecules as first neighbors in mammalian samples indicate, however, that these molecules are not significantly responsible for the stabilization of CO2- dating centers in enamel.

Animals↗

PubMedDate not supplied

Effects of apatite cements on proliferation and differentiation of human osteoblasts in vitro.

Although apatite cement (AC) and sintered hydroxyapatite (s-HAP) are known to show good osteoconductivity, it is not clear whether or not the degree of their osteoconductivity is the same. In addition, it has not been clarified whether or not it is dependent on the type of AC; conventional AC (c-AC), fast-setting AC (fs-AC) or anti-washout AC (aw-AC). The aim of this study was to investigate the effects of ACs on cultured human osteoblasts, as they may provide a useful index of osteoconductivity. Human osteoblasts were cultured on the surfaces of ACs and s-HAP, and were evaluated with respect to cell attachment, proliferation, and differentiation. We found that ACs and s-HAP showed similar cell attachment. No significant difference between ACs and s-HAP was found with respect to the proliferation of osteoblasts. In contrast, we found that the differentiation of osteoblasts was enhanced on the surface of ACs compared with that of s-HAP. However, there was no difference among the types of AC. We therefore concluded that AC may show better osteoconductivity than s-HAP, and that osteoconductivity of AC may be similar, regardless of the type of AC.

Biocompatible Materials↗

PubMed2004

Apparent solubility distributions of hydroxyapatite and enamel apatite.

Samples of human dental enamel and hydroxyapatite were equilibrated at 5 mg/40 ml for 9 days at 37 degrees C with acetate buffers adjusted to a range of saturations with respect to hydroxyapatite. Sigmoidal apparent solubility distributions, in which the fraction dissolved was plotted against--log(ion activity product for hydroxyapatite) (pIHA), were constructed. About 10% of the hydroxyapatite and 14% of the enamel was very soluble, dissolving even at pIHA 55. The apparent solubility distributions for both solids were invariant with pH (4.5, 5.0, 5.5), within experimental error, showing that solubility was controlled by a phase with the stoichiometry of hydroxyapatite, probably in the form of a surface layer or complex on the crystals, in agreement with other studies on carbonate-apatites and bone mineral. The pIHA at 50% dissolution was employed as an average value. The pIHA (50%) values for pooled data (58.76 for enamel and 60.17 for hydroxyapatite) were lower than the respective pIHA previously measured by conventional equilibration techniques. However, the average pIHA measured for enamel was higher than that obtained by the same technique in another study, possibly because of differences in specimen preparation and equilibration time. The possible implications of the findings for understanding the process of dental caries are discussed.

Dental Enamel↗

PubMed1976

Apatite deposition disease. A new arthropathy.

A method for identifying particles of crystalline calcium hydroxyapatite in synovial fluids and biopsy material has been developed with high-resolution scanning electron microscopy and an energy-dispersive micro-analytical system. Particles of hydroxyapatite were identified in the joints of six patients diagnosed as having osteoarthritis, three of whom had acute inflammatory episodes with effusions into the joints. Apatite was not identified in joints affected by rheumatoid arthritis and other types of arthropathy. Animal studies showed that hydroxyapatic crystals can cause an acute inflammatory reaction, and this has been confirmed by experimental studies in man. It is suggested that a third type of crystal-deposition disease should be recognised--namely, calcium-hydroxyapatite crystal-deposition disease.

Aged↗

PubMed2002

Calcium phosphate apatites with variable Ca/P atomic ratio II. Calcination and sintering.

The calcination and natural sintering of calcium deficient hydroxyapatite powders Ca(10-x)(PO4)(6-x)(HPO4)x(OH)(2-x) (with 0 < or = x < or = 1) were studied. For temperature below 700 degrees C, particle coalescence occurs without densification. The particle coalescence is associated with a reduction of the specific surface area. This surface decreases all the more as the Ca/P molar ratio of the powder is small. The mechanism agrees with a transfer of matter occurring by superficial diffusion, which is enhanced by the augmentation of vacancies in the apatitic structure (i.e. by a decrease of the Ca/P ratio). The sintering of compacted powders begins at 700 degrees C. At the same temperature, the calcium deficient hydroxyapatites dissociate into biphasic mixtures of hydroxyapatite and tricalcium phosphate. The sintering is slowed down when the content of TCP in the biphasic mixture increases. In parallel, the grain size increases. This result relates to the augmentation of the coalescence of particles at low temperature.

Biocompatible Materials↗

PubMed2003

Synthesis and characterization of needlelike apatitic nanocomposite with controlled aspect ratios.

Calcium-deficient apatitic (cd-HA) crystals with core-shell nanostructure with needlelike shape, 5-10nm in diameter and 20-80nm in length, were prepared via an in situ formation in the presence of polyacrylic acid (PAA) under aqueous solution of different pH values, ranging from 9 to 11. Nanostructure of the resulting crystals showing a core-shell configuration with a thin layer of PAA shell of about 1nm thickness was investigated. Aspect ratio (AR) of the needlelike composite was found to depend on the concentration of the PAA and solution pH. At lower solution pH, crystal growth was inhibited, i.e., leading to a decreased AR, with increase of PAA concentration, while an increased AR was detected at higher solution pH, suggesting a preferential growth of the cd-HA nanocrystals. Mechanism of such preferential growth was tentatively proposed and is suggested to correct PAA adsorption along the long axis of the needlelike nanoparticles.

Acrylic Resins↗