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PubMedDate not supplied

The effect of NaF on the bacterial production of polysaccharide and subsequent adsorption on hydroxyapatite.

The affinity of some bacterial polysaccharides for hydroxyapatite was investigated. Water insoluble polysaccharide production by bacteria was inhibited by the presence of NaF in the growth medium, while the water soluble fraction was unaffected. The adsorption of the bacterial polysaccharide on hydroxyapatite decreased with decreasing levels of the water insoluble fraction. It is suggested that NaF can inhibit bacterial attachment and caries by interfering with bacterial attachment through reducing the production of water insoluble polysaccharide.

Adsorption↗
PubMed1981

Solubility and crystallinity in relation to fluoride content of fluoridated hydroxyapatites.

Fluoridated hydroxyapatites were synthesized at 80 degrees C (pH 7.4) to study their crystallinity and solubility in relation to fluoride content. The crystallinity of fluoridated hydroxyapatities increased initially, then decreased, and finally increased again with the degree of fluoridation, whereas the decrease in relative solubility of fluoridated hydroxyapatites at 25 degrees C (pH 4.0) was proportional to the logarithm of the fluoride content.

Crystallography↗
PubMed1982

Extraskeletal implantation of a porous hydroxyapatite ceramic.

Coralline replamineform hydroxyapatite implants were placed in canine subcutaneous tissues in an attempt to clarify whether the hydroxyapatite matrix acted as a passive matrix for osseous ingrowth when placed in some inherent bone induction capacity. The implants were well-tolerated and elicited no deleterious host response. Connective tissue rapidly infiltrated the pores, but no evidence of bone formation was noted in any of the specimens. It was concluded that this implant material does not act to induce bone formation.

Animals↗
PubMed1983

Mechanism of adhesion of polyelectrolyte cements to hydroxyapatite.

The interaction between polyacrylate ions and hydroxyapatite was examined using extraction techniques and infra-red spectroscopy. These studies have shown that polyacrylate ions become irreversibly attached to the surface of hydroxyapatite by displacing existing phosphate ions. The mechanism is not one of simple ion exchange, since calcium ions are displaced by the phosphate ions.

Acrylic Resins↗
PubMed1985

Adsorption of zirconyl salts and their acids on hydroxyapatite: use of the salts as coupling agents to dental polymer composites.

Zirconyl methacrylate (I) and zirconyl-2-ethylhexanoate (II) were synthesized, and their adsorption isotherms from solutions onto synthetic hydroxyapatite were studied. The isotherms of methacrylic and 2-ethylhexanoic acids were also determined from the same solvents. The adsorption of I was irreversible from methylene chloride, and that of II was irreversible from cyclohexane. The adsorption in both cases was constant from solutions above a certain concentration, and exhaustive below this threshold concentration. Both compounds rendered the dried apatite powder extremely hydrophobic; however, the adsorbate was slowly washed off by excess water. The configuration of the adsorbate molecules, deduced from the maximum adsorption and other adsorption characteristics of the two compounds, indicated that: (i) in both cases the adsorbate may be held to the surface by concerted hydrogen bonding of the carboxylate and zirconyl oxygen atoms; and (ii) the hydrocarbon moieties in both adsorbates expose themselves toward the solution, thereby making the dried surface hydrophobic. The adsorptive behavior of the respective acids was similar to that of the salts. Polymer, filled with synthetic hydroxyapatite covered with irreversibly adsorbed I, had a diametral tensile strength about 50% greater than that of the polymer filled with untreated apatite. The strength of the composite was not affected by treatment of the apatite with II or with the acids.

Acids↗
PubMed1986

Adsorption of benzoic acid on pure and cupric ion-modified hydroxyapatite: implications for design of a coupling agent to dental polymer composites.

The adsorption isotherms of benzoic acid on synthetic hydroxyapatite (containing about 1.5 monolayers of physisorbed water) were studied from ethanol, dimethylsulfoxide, p-dioxane, methylene chloride, and benzene to discern the role of solvent in the process. The adsorption is reversible from the first three solvents and follows the Langmuir plots. It is irreversible from the last two, and a constant amount of absorbent is removed from solutions above a certain concentration. The isotherms of potassium benzoate on the apatite from ethanol and dimethyl sulfoxide were reversible. The isotherms of the acid on cupric ion-modified apatite surfaces from ethanol and benzene were identical with those obtained on the pure hydroxyapatite. This may demonstrate that any "surface chelation" with the cation may not be a significant factor for adsorption to occur. The adsorptive behavior seems to depend upon the interplay of hydrogen-bonding among the solute, the solvent, and the hydrated apatite surface. The capability of a solvent to hydrogen-bond may determine whether adsorption from it will be reversible or irreversible. Based upon its compatibility with a solvent, the benzene ring is upright or lies flat on the surface. The adsorbed molecules rotate about the center of the carboxylate groups which are hydrogen-bonded to the surface. These factors should be considered in designing or selecting a suitable surface-active moiety for a coupling agent between tooth mineral and a restorative resin.

Adsorption↗
PubMed1987

Interference of IgA protease with the effect of secretory IgA on adherence of oral streptococci to saliva-coated hydroxyapatite.

It has previously been shown that secretory immunoglobulin A (S-IgA) influences the sorption of oral streptococci to hydroxyapatite as well as to cell surfaces. The present experiments demonstrate that bacterial IgA proteases, which cleave S-IgA in the hinge region, are capable of interfering with this mechanism. This result was obtained with an IgA1 specific protease from Haemophilus influenzae and with a protease from Clostridium ramosum that cleaves IgA1 as well as IgA2 of A2m(1) allotype. The modulation of S-IgA-mediated effects by IgA proteases were studied by means of an in vitro method which permits quantitative determination of the sorption of radiolabeled oral bacteria to hydroxyapatite beads. Other authors have suggested that IgA protease-mediated effects may be explained by a strongly reduced antigen-binding capacity of released Fab alpha fragments. Here we present evidence that streptococci, after exposure to specific S-IgA and IgA protease, are coated with Fab alpha fragments.

Adult↗
PubMed1988

Bone mineral content of the maxilla estimated by dual-photon absorptiometry after augmentation with bone or hydroxyapatite.

A new, precise, non-invasive method for measuring the bone mineral content (BMC) of the mandible in vivo by dual-photon absorptiometry has recently been introduced. The purpose of the present analysis was to examine the precision in vitro and in vivo and the accuracy in vivo for assessment of BMC in the maxilla. The precision was determined by repeated measurements in vitro on a cranium and in vivo on two test persons with and without a bone specimen fixed to a palatal plate. The accuracy in vivo was determined from the BMC measurements of the two test persons and of nine edentulous persons, scanned before and after augmentation of the maxillary alveolar ridge with hydroxyapatite. The analyses indicated that the precision for maxillary BMC assessments was high (0.9% in vitro and 2.0% in vivo) and the accuracy in vivo was 6.6%, corresponding to the accuracy in vitro for skeletal BMC measurements by dual-photon absorptiometry. The present method therefore seems to be well-suited for follow-up analyses of the BMC changes in the jaws after augmentation of the alveolar ridges with bone or hydroxyapatite.

Alveolar Ridge Augmentation↗
PubMed1990

Analysis of particle size distribution of hydroxyapatite crystallites in the presence of synthetic and natural polymers.

The particle size distribution (PSD) of suspended hydroxyapatite crystallites both at equilibrium and during crystal growth has been measured by a laser scattering technique. Addition of high-molecular-weight polyacrylate (PAA/C) resulted in appreciable crystallite aggregation, probably by polymer bridging of particles. In contrast, a lower-molecular-weight PAA was unable to bridge the hydrodynamic gap between particles and resulted in an overall dispersion. The addition of human serum albumin also markedly influenced the PSD and, with concomitant change in zeta potential to more negative values, resulted in dispersion due to steric interaction and electrostatic repulsion between the particles. The complex behavior of human saliva is illustrated by its tendency both to aggregate and to disperse hydroxyapatite crystallites, displaying the combined effects of different adsorbing macromolecules.

Acrylic Resins↗
PubMed1992

Examination by X-ray photoelectron spectroscopy of the adsorption of chlorhexidine on hydroxyapatite.

X-ray photoelectron spectroscopy (XPS) was used for determination of the effects of chlorhexidine (CHX) solutions (0.2% and 1% solutions of the digluconate salt) on the elemental composition of hydroxyapatite surfaces. So that the nature of the adsorbed species after they were washed with water could be identified, comparisons were made with reference spectra for CHX obtained from a CHX digluconate film and CHX dichloride powder. The XPS results clearly indicated the retention of CHX moieties, which could be ascertained from the spectra by the presence of N and Cl, features unique to CHX. The spectral envelopes were virtually identical to those obtained from the reference spectra. High-resolution C 1s spectra also gave support for the retention of CHX; however, the spectra differed from those of the CHX digluconate film in that no feature attributable to the C-OH of the gluconate anion was present, consistent with the view that the CHX cation remains behind to form an electrostatic bond with the phosphate groups of the hydroxyapatite. The N:Cl ratio for the washed samples was found to be higher than that for the reference samples and may be indicative of partial decomposition of the CHX. Decomposition was also seen to be induced by x-ray exposure. While the high-resolution spectra presented here do not directly address the controversy on the mechanism for the anti-plaque efficacy of CHX, they do provide the necessary basis for the application of XPS to future in vitro studies on the retention of CHX to dental surfaces.

Adsorption↗
PubMed1992

Adsorption of human salivary proteins to hydroxyapatite: a comparison between whole saliva and glandular salivary secretions.

The protein compositions of in vitro pellicles formed from whole saliva and parotid and submandibular secretions were determined by use of synthetic hydroxyapatite as a model for dental enamel. The adsorbed and unadsorbed protein fractions were analyzed by amino acid analysis and both anionic and cationic discontinuous polyacrylamide gel electrophoresis. For further characterization of the in vitro pellicle, the adsorbed fractions were subjected to gel filtration on Sephadex G-100 and reversed-phase chromatography on C18 columns. Amylase, acidic and glycosylated proline-rich proteins, statherins, and histatins were identified in the parotid-derived pellicle. Detailed analysis of the statherin-containing fractions resulted in the observation of several statherin-like proteins. The use of cationic gel electrophoresis allowed for the identification of histatin 3 and histatin 5, which have not been previously detected in pellicle formed in vitro. The protein composition of submandibular-derived pellicle was similar to that of parotid-derived pellicle except for the presence of cystatins and the absence of glycosylated proline-rich proteins. In contrast, in vitro pellicle derived from whole saliva exhibited a vastly different composition, consisting primarily of amylase, acidic proline-rich proteins, cystatins, and proteolytically-derived peptides. The results indicate that acidic phosphoproteins as well as neutral and basic histatins from pure secretions selectively adsorb to hydroxyapatite, whereas in whole saliva some of these proteins are proteolytically degraded, dramatically changing its adsorption pattern.

Adsorption↗
PubMed1994

The formation of hydroxyapatite-ionomer cements at 38 degrees C.

This study describes the formation of a calcium polyacrylate-hydroxyapatite cement. Our hypothesis was that calcium phosphates would rapidly hydrolyze in the presence of polyacrylic acid (PAA) to form a cement. PAA, tetracalcium phosphate (TetCP), and dicalcium phosphate (DCP) were reacted together and formed calcium polyacrylate (CPA) and hydroxyapatite(HAp) within 10 h at 38 degrees C, resulting in hardened masses. Reaction times increased with decreasing (HApreactants)/PAA ratios. In the first of three reaction stages, the pH increased while CPA and dicalcium phosphate dihydrate (DCPD) formed. Two steady-state pH conditions occurred during the second stage as TetCP reacted with DCPD and DCP. The first steady-state pH was the result of DCPD and TetCP reacting at near-equilibrium conditions. The second steady-state pH resulted as the reaction became limited by DCP dissolution. The third, diffusionally controlled, stage occurred as DCP and previously formed HA preacted to produce calcium-deficient HAp (Ca/P = 1.5). The emphasis of this investigation was to establish the mechanistic path involved and the rate-limiting steps of the reaction.

Acrylic Resins↗
PubMed1990

A novel skeletal drug delivery system for anti-bacterial drugs using self-setting hydroxyapatite cement.

To solve the problem of delivering drugs to skeletal tissue at high enough local concentrations for desirable therapeutic effects, we report a novel approach using a self-setting hydroxyapatite cement, with cephalexin and norfloxacin as model drugs. After setting, the cement was transformed into hydroxyapatite with affinity for hard bone tissue. Continuous in-vitro drug release profiles from loaded cement pellets (0.9-4.8% by weight) in phosphate buffer at pH 7.4 and 37 degrees C followed the Higuchi equation.

Anti-Infective Agents↗
PubMed1995

Reconstruction of suboccipital craniectomy defects with hydroxyapatite cement: a preliminary report.

Hydroxyapatite cement, a new biomaterial presently under clinical investigation, has been demonstrated to have potentially wide application in cranial reconstruction. We describe our experience with this biologic bone cement in the reconstruction of suboccipital craniectomy defects in seven patients after vestibular schwannoma removal. With up to 2-year follow-up, cranial bone integrity has been reestablished in five patients. Dissolution of cement has occurred in dependent areas and appears to be technique related. Cranial bone contour appears dependent on the amount of cement used. The frequency of debilitating postoperative headache was reduced in these patients when compared to patients who had no reconstruction of the craniectomy defect. Reconstruction of the bony defect after suboccipital craniectomy with hydroxyapatite cement is not only useful to restore cranial contour, but also appears to reduce some of the functional deficits attributed to this surgical approach.

Biocompatible Materials↗
PubMed1989

The effect of hydroxyapatite coating on bone growth into porous titanium alloy implants.

In rabbits and goats, test implants with a porous surface of two layers of Tl-6A;-4V beads were examined at intervals for bond strength with bone. Half of the implants were coated with hydroxyapatite by plasma spray. The bonding strength with bone in the coated specimens was about four times greater than that of the uncoated specimens at two weeks, and twice as strong at six weeks. Twelve weeks after implantation, the strengths were similar. The hydroxyapatite coating of the beads provided earlier and stronger fixation.

Alloys↗
PubMed1992

Hydroxyapatite coating of hip prostheses. Effect on migration into the femur.

We studied two groups of femoral hip prostheses: 43 TiAlV ridged press-fit stems, and 26 with similar stems coated with hydroxyapatite on the proximal half. At one year, radiological measurement showed a mean downward migration of 0.99 mm for the TialV prostheses and 0.12 mm for the HA-coated prostheses (p = 0.0002). Hydroxyapatite coating appeared to provide effective bio-active supplementary fixation.

Adult↗
PubMed1993

Hydroxyapatite coating converts fibrous tissue to bone around loaded implants.

In previous studies, we have demonstrated a fibrocartilaginous membrane around hydroxyapatite-coated implants subjected to micromovement in contrast to the fibrous connective tissue which predominates around similarly loaded titanium alloy implants. In the present study, in mature dogs, we investigated the effect of immobilising titanium (Ti)- or hydroxyapatite (HA)-coated implants already surrounded by a movement-induced fibrous membrane and compared the results with those of similar implants in which continuous micromovement was allowed to continue. The implants were inserted in the medial femoral condyles of 14 dogs and subjected to 150 microns movements during each gait cycle. After four weeks (when a fibrous membrane had developed), half the implants were immobilised to prevent further micromovement. The dogs were killed at 16 weeks and the results were evaluated by push-out tests and histological analysis. The continuously loaded Ti-coated implants were surrounded by a fibrous membrane, whereas bridges of new bone anchored the HA-coated implants. The immobilised implants were surrounded by bone irrespective of the type of coating. Push-out tests of the continuously loaded implants showed better fixation of those with HA coating (p < 0.001). The immobilised Ti-coated implants had four times stronger fixation than did continuously loaded Ti-coated implants (p < 0.01) but there was no equivalent difference between the two groups of HA-coated implants. The amount of bone ingrowth was greater into immobilised HA-coated implants than into immobilised Ti-coated implants (p < 0.01). Two-thirds of the HA coating had been resorbed after 16 weeks of implantation, but 25% of this resorbed HA had been replaced by bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

[Hydroxyapatite ceramic coatings for anchoring components of hip joint prostheses (technical aspects)].

Following the positive clinical results obtained with pure hydroxyapatite ceramic in the form of granules, the development of coatings of this material for anchoring components of artificial joints was initiated 6 years ago with the aim of improving implant bone bonding. Among the various coating procedures available, the plasma spraying process alone would appear capable of producing coatings which meet the requirements of a bioactive and osteotropic layer between bone and implant, in particular with respect to coating thickness and bond strength. However, the plasma spraying process at first seemed to be out of the question because of the high process temperature involved. After studying the factors affecting the transformation mechanism, it proved possible to suppress the phase transformation by a suitable preparation of the hydroxyapatite ceramic powder, and a combination of particular process parameters. The coating process and the quality checks are described in detail, and the properties of the coating compared with the requirements it has to fulfill.

Ceramics↗