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PubMed2001

Coating of hydroxyapatite on various substrates via hydrothermal reactions of Ca(edta)2- and phosphate.

Hydroxyapatite was coated on various substrates such as 12 mol % ceria-doped tetragonal zirconia (12Ce-TZP), 3 mol % yttria-doped tetragonal zirconia (3Y-TZP), alumina, monetite coated titanium (Ti/CaHPO4) and calcium titanate coated titanium (Ti/CaTiO3) via hydrothermal reactions of Ca(edta)2- and 0.05 M NaH2PO4 at initial pH 6 and 160-200 degrees C for 0.5-6 h. Rod-like particles of hydroxyapatite precipitated to form film on the substrates above 160 degrees C. The morphology of the film changed significantly depending on the characteristics of substrate, i.e. hydroxyapatite entirely coated the surfaces of 12Ce-TZP, Ti/CaHPO4 and Ti/CaTiO3 plates, but sparsely deposited on 3Y-TZP and Al2O3 plates. Film thickness increased with time (ca. 20 and 90 microm on 12Ce-TZP plates for 0.5 and 6 h, respectively, at pH 6 and 200 degrees C). The adhesive strength of the film for the substrate was in the order, 12Ce-TZP/hydroxyapatite(28 MPa) > Ti/CaTiO3/hydroxyapatite (22 MPa) > Ti/CaHPO4/hydroxyapatite (9 MPa).

Journal Article↗
PubMed1997

The dependence of osteoblastic response on variations in the chemical composition and physical properties of hydroxyapatite.

Two synthetic hydroxyapatite powders (A and B), supplied by different manufacturers, were physically and chemically characterized before being die pressed and sintered at 1250 degrees C. The powders were characterized using X-ray diffraction (XRD), infrared spectroscopy (IRS), X-ray fluorescence, surface area analysis (BET), particle size analysis and scanning electron microscopy (SEM). The materials were then pressed and sintered to produce hydroxyapatite discs of similar densities and grain sizes for in vitro evaluation. The ceramics were seeded with osteoblastic cells and after 15 days in culture the cell morphology was assessed using scanning electron microscopy (SEM), the ultrastructure of the cells was studied using transmission electron microscopy (TEM) with EDAX, and the rate of cell growth was assessed using biochemical techniques. The results clearly showed that the rate of cell proliferation but not the rate of alkaline phosphatase production, was highly dependent on the composition of the hydroxyapatite powders that were used to make the ceramic discs. The ultrastructural studies confirmed the relative viabilities of the cells and the nature of the ceramic interface indicating visually the marked differences in the performance of the two materials.

Journal Article↗
PubMed1997

Hydroxyapatite-zirconia composites prepared by precipitation method.

Chemical routes to prepare ceramic precursor powders are frequently envisaged, especially when the aspects related to the microstructure are important and need to be controlled. An understanding of which parameters of synthesis and thermal treatment can influence the mechanical properties of hydroxyapatite compounds is essential for the production of such materials. Hydroxyapatite-zirconia composites have been prepared, in this study, by a precipitation method. This led to the formation of homogeneous powders with a very defined particle-size distribution. Ceramic pellets prepared from these powders were easily compacted and sintered without cracking. As expected, the presence of the zirconia phase improved composite densities and appeared to have an important role in thermal stabilization of the hydroxyapatite phase.

Journal Article↗
PubMed1997

Characterization of hydroxyapatite and carbonated apatite by photo acoustic FTIR spectroscopy.

An understanding of the interfacial relationship between a bioceramic implant and the adjacent bone tissue is facilitated by precise characterization of the associated structures. The structure of different commercial synthetic hydroxyapatite powders and a novel carbonated apatite have been studied with photo-acoustic (PAS) Fourier transform infrared (FTIR) spectroscopy. The PAS technique is an ideal method for analysing biomaterials, as materials can be analysed without the need to reduce the particle size or to dilute with KBr. Spectra from carbonated apatite appear to be different from those of commercial hydroxyapatite powders, with the main difference lying in the carbonate and phosphate ratio. Commercial hydroxyapatite powders from different sources have also been analysed and compared.

Journal Article↗
PubMed2004

Influence of fluorapatite minor additions on behavior of hydroxyapatite ceramics.

Fluorinated hydroxyapatite is known to be less soluble by body fluids, resulting in enhanced resistance to biodegradation in vivo conditions, as compared to the pure hydroxyapatite ceramics. The present work was aimed at the investigation of the effect of minor additions of ultrafine fluorapatite (up to 10 wt%) on the sintering behavior and mechanical properties of hydroxyapatite ceramics. In vitro testing for the osteoblast-like cells viability and proliferation was performed with the samples of varying fluorapatite content. It was found that the fluorapatite addition hinders the sintering shrinkage and lowers the strength, but does not generally affect negatively the viability of the cells.

Apatites↗
PubMed2004

The effect of hot pressing on the physical properties of glass reinforced hydroxyapatite.

Hydroxyapatite (HA), being of physiological importance, can be developed synthetically for implant application. A number of avenues have been explored in order to improve the physical and biological properties of a variety of hydroxyapatite composites. However, the fact remains, hydroxyapatite lacks the mechanical properties needed to sustain high loads. This study investigates the advantages of hot pressing on the physical properties of HA and glass reinforced HA (GR-HA). The results show a significant enhancement in the mechanical properties of GR-HA composites compared to HA e.g. flexural bending strength values were given at 91.75 and 88.87 M Nm(-2) for GR-HA (CP15F) and GR-HA (CP20F) respectively, compared to 78.9 M Nm(-2) for HA. The results for other properties such as elastic modulus, fracture toughness, Vicker's hardness, density and porosity also demonstrate the benefit of adding phosphate based glasses as a sintering aid. This is supported by XRD analysis, highlighting the presence of a secondary phase (beta-TCP) in GR-HA systems and the positive effect it has on the physical properties. It must be brought to attention that densification of hot pressed HA and GR-HA composites is reached at a lower temperature compared to a previous study on the same materials that have undergone pressureless sintering.

Biocompatible Materials↗
PubMed1998

Bovine hydroxyapatite for maxillary sinus augmentation: analysis of interfacial bond strength of dental implants using pull-out tests.

This study examines the effect of sinus lift surgery using bovine hydroxyapatite on the bone anchorage of titanium plasma flame-spray-coated cylindrical implants. A total of 54 implants were placed in the lateral bony antral walls of 27 mountain sheep. Host site augmentation was done simultaneously using bovine hydroxyapatite and autogenous cancellous bone from the iliac crest in 18 sinuses each. The bone walls of the remaining 18 sinuses received no augmentation. Pull-out tests were carried out at 12, 16, and 26 weeks, revealing a significant influence of the implants' residence time on pull-out strength (P = 0.004). The implants of the non-augmented group and those of the group augmented using cancellous bone showed a linear increase in pull-out strength to 169.8 N and 523.7 N, respectively, until the 26th week. The implants of the group augmented with bovine hydroxyapatite exhibited the highest initial pull-out strength (325.1 N) that further increased to 521.8 N until the 26th week. All in all, this group showed a significantly greater pull-out strength tan did the negative control group (P = 0.03).

Analysis of Variance↗
PubMed2002

Evaluation of stability of titanium and hydroxyapatite-coated osseointegrated dental implants: a pilot study.

An endosseous implant is described as osseointegrated when it is immobile in function. Objective measures of stability testing have been described. The Periotest is a commercially available device that is used for this purpose. This study was designed to measure stability of endosseous implants placed in the mandible. Implants were placed in the mandibular canine or first premolar area to support an overdenture prosthesis. Stability was evaluated through the use of a Periotest device at the time of implant placement and following one year of functional loading. Implant designs were either a screw-shaped titanium alloy or a hydroxyapatite-coated cylinder. A total of 54 implants were placed, 37 were titanium screw-shaped implants, while the remaining 17 were hydroxyapatite cylinders. Initial measurements of stability showed no difference due to implant type. Following one year of functional loading, titanium screw-shaped implants were more stable than hydroxyapatite implants (P < 0.05). The difference in implant rigidity following a period of functional loading may be an indication of a difference in osseointegration between the two implants used in this study.

Aged↗
PubMed2003

Effects of hydroxyapatite-coated and commercially pure titanium oral implant surfaces on compound nerve action potentials.

The aim of this study was to investigate the effects of hydroxyapatite-coated and commercially pure titanium oral implants on nerve conduction. Isolated rat sciatic nerves were placed between two suction electrodes in a bath containing a tyrode solution. The implants were brought into intimate contact with the nerves and evoked compound action potentials (cAPs) were recorded before and after contact with the implants. The commercially pure titanium implants did not cause any change in cAPs. A gradual reduction in cAPs was observed for hydroxyapatite-coated implants. However, this reduction was < 50% after an application time of 120 min. Recovery of the cAPs in this group was recorded after approximately 60 min. We conclude that, although intimate contact with hydroxyapatite-coated implants leads to a reduction in cAPs in nerves in vitro, neither this surface nor a commercially pure titanium surface leads to irreversible neurotoxic effects.

Action Potentials↗
PubMed1998

The hydroxyapatite orbital implant: post-operative pain.

PURPOSE: To compare and quantify the degree of post-operative pain experienced by patients undergoing primary and secondary hydroxyapatite orbital implantation. METHODS: A prospective survey design was employed to monitor patients' pain pre-operatively and up to 7 days post-operatively. Fifty-five consecutive patients undergoing primary and secondary hydroxyapatite orbital implantation were recruited over a period of 1 year. Standardised anaesthetic, operative and post-operative protocols were followed. During the patients' in-patient stay nurses completed a data proforma that required them to record patients' pain using an 11-item numerical rating scale. A self-completion proforma was given to patients to score their pain at home until the first post-operative out-patient appointment. RESULTS: Patients undergoing primary implant surgery tend to experience more post-operative pain than those undergoing secondary implant surgery. A small proportion of patients experience severe post-operative pain. CONCLUSION: Post-operative pain experienced by patients undergoing primary and secondary hydroxyapatite implantation has been underestimated. This study has provided the necessary data to enable such patients to be effectively counselled pre-operatively and to plan a rational discharge policy.

Adult↗
PubMed1998

A study of the hydroxyapatite orbital implant drilling procedure.

PURPOSE: The hydroxyapatite orbital implant has been introduced as a buried, integrated implant for use in the anophthalmic patient. The second stage of the procedure involves drilling the implant and inserting a motility peg that allows direct coupling of the artificial eye to the implant. Other authors have advocated an assessment of implant vascularity by imaging prior to drilling. We aimed to see whether our practice of drilling after a predetermined time interval without assessment of implant vascularity would result in a higher complication rate. We also aimed to determine how successful the drilling procedure was in improving both the motility and the stability of the artificial eye. METHODS: The notes of 41 consecutive patients who underwent drilling were studied to determine the time interval between implantation with a hydroxyapatite sphere and drilling, the nature of any complications and any further surgical procedures undertaken. A postal questionnaire was sent to all patients asking them to grade the motility of their implant before and after drilling, and to state whether or not there had been any improvement in the stability of their artificial eye. RESULTS: The most frequent complication encountered was extrusion of the motility peg, which occurred in 3 patients. A total of 5 patients required redrilling. There was an 80% response rate to the questionnaire. Ninety-one per cent of patients felt that there had been an improvement in the motility of their artificial eye and 76% felt that the stability of their artificial eye had been improved. CONCLUSION: Pegging of the hydroxyapatite implant improves both the motility and the stability of the artificial eye in the majority of cases. Complications are infrequent and minor. If sufficient time is allowed after implantation for full implant vascularity to occur, it is not necessary to perform imaging studies. This practice does not result in an increase in complications, and significantly reduces the expense of the procedure.

Adolescent↗
PubMed2005

Primary placement of a titanium sleeve in hydroxyapatite orbital implants.

BACKGROUND: To study a new surgical option of primary placement of a titanium sleeve into hydroxyapatite implants during enucleation or evisceration. METHODS: A standard enucleation or cornea preserved evisceration was performed, followed by preplacement of a titanium sleeve into the hydroxyapatite implant by a hand drill sleeve driver. Care must be taken to ensure that the titanium sleeve is positioned centrally when the implant is put inside the orbital socket or eviscerated shell. The Tenon capsule and conjunctiva were meticulously closed with minimal tension. Complications such as sleeve exposure, coralline exposure, and infection of the titanium sleeve were closely observed. RESULTS: In all, 30 patients were treated in the above fashion with 10 enucleation and 20 evisceration procedures. The follow-up period ranged from 9 to 24 months. Three of the sleeves were found to have exposed spontaneously at 5 and 7 weeks following original surgery. They had no further complication except one sleeve loosening. The remaining 27 sleeves that did not spontaneously expose pursued secondary exposure of the titanium sleeve and peg insertion by conjunctival cutdown procedure 3 months after original surgery. Two sleeves were found to be oblique positioned after the conjunctival cutdown procedure. Fortunately, all the 30 patients were successfully fit with a peg-coupled prosthesis with good motility. CONCLUSION: Primary placement of a titanium sleeve into hydroxyapatite implants has several advantages, including high patient acceptance, technical simplicity, and office-based conjunctival cutdown pegging procedure. By avoiding the expense of postoperative imaging study and additional prosthetic modification, a more rapid and efficient rehabilitation is possible.

Adult↗
PubMed2006

Bovine pericardium (Tutopatch) wrap for hydroxyapatite implants.

PURPOSE: To evaluate bovine pericardium (Tutopatch) as a wrapping material for hydroxyapatite implants in patients undergoing enucleation for uveal melanoma. METHOD: Prospective cohort study of patients who had enucleation for uveal melanoma between January 2003 and August 2003 were included in the study. Any patient with less than 3 months follow-up was excluded. Enucleation was performed under general anaesthesia followed by insertion of hydroxyapatite implants wrapped in bovine pericardium (Tutopatch). The recti muscles were sutured directly to the wrap. The tenon's capsule and conjunctiva were closed in two layers. A conformer was inserted at 1 week and artificial eye at 2-3 months. The patients were followed up regularly and were assessed for cosmetic result, exposure of implant, and the need for any further surgical procedures. RESULTS: A total of 19 patients (seven male and 12 female) were included in the study. Median age at diagnosis was 63 years (range 38-80 years). Median follow-up was 26 months (range 22-30 months). No patient developed postoperative complications of wound dehiscence. The overall cosmetic result was excellent in all the patients. The rate of postoperative complications compared favourably with published data using other wrapping materials/implants. CONCLUSION: Tutopatch is a safe wrapping material for hydroxyapatite orbital implants in patients undergoing enucleation for uveal melanoma.

Adult↗
PubMed1994

Modulation of crystal formation by bone phosphoproteins: role of glutamic acid-rich sequences in the nucleation of hydroxyapatite by bone sialoprotein.

Bone sialoprotein (BSP) is a bone-specific glycoprotein containing phosphoserine and sulphotyrosine residues and regions of contiguous glutamic acid residues. Recent studies in this laboratory have shown that BSP is capable of nucleating the bone mineral hydroxyapatite in a steady-state agarose gel system. We show here that chemical modification of carboxylate groups abolishes the nucleation activity of BSP, but enzymic dephosphorylation has no effect. Formation of hydroxyapatite is also induced by poly(L-glutamic acid) and poly(D-glutamic acid), but not by poly(L-aspartic acid) or poly(L-lysine). Calreticulin, a muscle protein with short sequences of contiguous glutamic acid residues, also lacks nucleation activity. These findings suggest that the nucleation of hydroxyapatite by BSP involves one or both of the glutamic acid-rich sequences. Based on these findings and others, we propose that polycarboxylate sequences represent a general site for growth-modulating interactions between proteins and biological crystals.

Amino Acid Sequence↗
PubMed1995

Substitutions of aspartic acid for glycine-220 and of arginine for glycine-664 in the triple helix of the pro alpha 1(I) chain of type I procollagen produce lethal osteogenesis imperfecta and disrupt the ability of collagen fibrils to incorporate crystalline hydroxyapatite.

We identified two infants with lethal (type II) osteogenesis imperfecta (OI) who were heterozygous for mutations in the COL1A1 gene that resulted in substitutions of aspartic acid for glycine at position 220 and arginine for glycine at position 664 in the product of one COL1A1 allele in each individual. In normal age- and site-matched bone, approximately 70% (by number) of the collagen fibrils were encrusted with plate-like crystallites of hydroxyapatite. In contrast, approximately 5% (by number) of the collagen fibrils in the probands' bone contained crystallites. In contrast with normal bone, the c-axes of hydroxyapatite crystallites were sometimes poorly aligned with the long axis of fibrils obtained from OI bone. Chemical analysis showed that the OI samples contained normal amounts of calcium. The probands' bone samples contained type I collagen, overmodified type I collagen and elevated levels of type III and V collagens. On the basis of biochemical and morphological data, the fibrils in the OI samples were co-polymers of normal and mutant collagen. The results are consistent with a model of fibril mineralization in which the presence of abnormal type I collagen prevents normal collagen in the same fibril from incorporating hydroxyapatite crystallites.

Adult↗
PubMed2000

Successful surgical treatment of haemophilic pseudotumour, filling the defect with hydroxyapatite.

A preliminary report is made on the use of hydroxyapatite for surgical procedure of pseudotumour, a rare but serious complication of the bleeding diathesis in patients with inherited bleeding disorders. Surgical or percutaneous treatment and refilling with fibrin sealant is shown to be a successful therapy in a 19-year-old male with severe haemophilia B. The pseudotumour, in the upper pad of the left leg, was filled with hydroxyapatite after surgery. We suggest that the use of hydroxyapatite is a new and useful option in the surgical treatment of haemophilic pseudotumour.

Adult↗
PubMed2003

Collagen-hydroxyapatite/tricalcium phosphate microspheres as a delivery system for recombinant human transforming growth factor-beta 1.

The purpose of this study is to evaluate the carrier capability of collagen-hydroxyapatite/tricalcium phosphate (Col-HA/TCP) microspheres to the rhTGF-beta 1 (recombinant human transforming growth factor-beta 1). After anesthesia, a bone defect (7.0 mm in diameter and 10.0 mm in depth) was created at the distal femoral condyles of New Zealand white rabbits. These defects were then completely filled with the implant materials. After 5, 7, 9, 11, 13, and 15 weeks, the animals were sacrificed and histological evaluations were performed. The results showed that when the defects were treated with Col-HA/TCP microspheres without rhTGF-beta 1, there was only spotty new bone formation during the 15 week experimental period and most of the defect was filled with fibrous tissue and inflammatory cells, whereas active bone formation with mature marrow tissue formation was evident in the defect treated with Col-HA/TCP microspheres containing rhTGF-beta 1. Collagen-hydroxyapatite/tricalcium phosphate microspheres were expected to be replaced by the regenerated bone structure as the bone reconstruction and bone-remodeling process occurred. It was apparent that bone regeneration was influenced by the addition of rhTGF-beta 1. Collagen-hydroxyapatite/tricalcium phosphate microspheres were a good carrier for rhTGF-beta 1.

Animals↗
PubMedDate not supplied

Ossicular reconstruction using hydroxyapatite prostheses with interposed cartilage.

PURPOSE: Despite the excellent biocompatibility of hydroxyapatite ossicular prostheses, extrusion of the prosthesis may be found during long-term follow-up, mainly due to the retraction of the eardrum. Although interposition of autologous cartilage between the eardrum and the prosthesis is empirically used to prevent extrusion, the clinical effect of this procedure has not been confirmed. The purpose of this study was to evaluate the effect of interposing a cartilage on the extrusion rate and hearing outcome. MATERIALS AND METHODS: Fifty-four ears in which cartilage was interposed with a hydroxyapatite prosthesis were compared with 53 ears without interposition. Three years after surgery, the otoscopic findings and hearing outcome were evaluated. RESULTS: The extrusion rate was 1.9% in the group with interposition and 13.2% in the group without interposition. The difference between the two groups was statistically different (chi(2) = 4.986; P =.03). There was no significant difference between the two groups in the postoperative air-bone gap. CONCLUSION: This procedure is an effective method for reducing the extrusion rate of hydroxyapatite prostheses without reducing the hearing gain resulting from ossiculoplasty.

Adolescent↗