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PubMed1998

Bilateral total hip arthroplasty comparing hydroxyapatite coating to porous-coated fixation.

Fifteen patients had bilateral hip replacement with a porous-coated hip replacement in one hip and in the contralateral hip the same design, which had adjunctive hydroxyapatite coating on the porous coating. These patients were followed for an average of 6.5 years (range, 5-7.9 years). There was no difference in the clinical Harris Hip Scores between the two hips in these patients. The radiographic measurements did show improved bone remodeling in hips with adjunctive hydroxyapatite coating as measured by proximal cancellous hypertrophy and evidence of a buttress sign. The fixation of stems with hydroxyapatite coating showed fewer radiolucent lines (P = .013). The improved bone remodeling, which we had previously reported, has been maintained in these hips at intermediate-term follow-up and the fixation of the hydroxyapatite-coated stems is also now better. The results in these patients with bilateral hips, which allows complete control of the bone type, immunology, weight, activity, and age of the patient, suggests that the use of hydroxyapatite coating does provide improved fixation and the possibility of improved durability.

Adult↗
PubMed1994

Bone healing after implantation of hydroxyapatite granules and blocks (Interpore 200) combined with autolyzed antigen-extracted allogeneic bone and fibrin glue. Experimental studies on adult rabbits.

Bone healing around hydroxyapatite granules and blocks (Interpore 200), implanted in mandibular and tibial bone cavities with or without autolyzed, antigen-extracted, allogeneic (AAA) bone, was studied in young adult rabbits. The study was done in two series. In series I, standardized bone cavities were filled with implants in granular form mixed with a fibrin glue, Tisseel, for half of the cavities. The animals were followed for 5 and 8 weeks. In all cavities implanted with AAA bone, regardless of the combination with hydroxyapatite or the fibrin glue, bone had formed in excess of the cavities, resembling exostosis formation. AAA bone significantly increased (P < 0.005 or 0.01) bone formation. In series II, a 6 x 3-mm cavity was created in the medial aspect of the proximal part of each tibia. This was filled with a hydroxyapatite block--its cross section measuring 6 x 3 mm--such that 2 mm of the block extended outside the bone surface. In alternation between left and right sides, half of the blocks were covered with a paste of AAA bone and Tisseel, and half with Tisseel with the fibrin glue alone. The observation time was 8 weeks. The area of newly formed bone within and around the hydroxyapatite blocks was significantly increased (P < 0.001) when AAA bone was used. Thus, hydroxyapatite, both as granules and blocks for supporting structures, can be successfully combined with AAA bone, the bone-inductive capacity of AAA bone being utilized.

Animals↗
PubMed2001

About the use of stoichiometric hydroxyapatite in compression - incidence of manufacturing process on compressibility.

Literature concerning calcium phosphates in pharmacy exhibits the chemical diversity of the compounds available. Some excipient manufacturers offer hydroxyapatite as a direct compression excipient, but the chemical analysis of this compound usually shows a variability of the composition: the so-called materials can be hydroxyapatite or other calcium phosphates, uncalcined (i.e. with a low crystallinity) or calcined and well-crystallized hydroxyapatite. This study points out the incidence of the crystallinity of one compound (i.e. hydroxyapatite) on the mechanical properties. Stoichiometric hydroxyapatite is synthesized and compounds differing in their crystallinity, manufacturing process and particle size are manufactured. X-Ray diffraction analysis is used to investigate the chemical nature of the compounds. The mechanical study (study of the compression, diametral compressive strength, Heckel plots) highlights the negative effect of calcination on the mechanical properties. Porosity and specific surface area measurements show the effect of calcination on compaction. Uncalcined materials show bulk and mechanical properties in accordance with their use as direct compression excipients.

Calcium↗
PubMed1997

Attachment of osteoblastic cells to hydroxyapatite crystals by a synthetic peptide (Glu7-Pro-Arg-Gly-Asp-Thr) containing two functional sequences of bone sialoprotein.

We investigated activity of bone sialoprotein (BSP) to mediate attachment of cells to hydroxyapatite using a model peptide, Glu7-Pro-Arg-Gly-Asp-Thr, which contains a putative hydroxyapatite-binding site (poly-Glu) and a cell-attachment site. The peptide has affinity to hydroxyapatite with a dissociation constant of 13.5 microM. The peptide affected in vitro mineralization in a gel system, indicating interaction between this peptide and calcium phosphate. The osteoblastic cell line MC3T3-E1 was incubated with hydroxyapatite powder coated with the peptide or proteins. Attachment of the cells was observed on the powder coated with BSP, but not on the powder coated with serum albumin. The cells were attached to the powder coated with the peptide. The cells were flattened on the powder, and pseudopods developed. The attachment of the cells was inhibited by an excessive amount of Gly-Arg-Gly-Asp-Ser peptide. In conclusion, BSP mediated attachment of osteoblastic cells to hydroxyapatite, and this activity could be accomplished only by the poly-Glu sequence and the Arg-Gly-Asp sequence.

Amino Acid Sequence↗
PubMed1997

Clinical evaluation of hydroxyapatite-coated titanium plasma-sprayed and titanium plasma-sprayed cylinder dental implants: a preliminary report.

OBJECTIVE: The purpose of this article was to present the preliminary results of a prospective clinical trial comparing titanium plasma-sprayed versus hydroxyapatite-coated titanium plasma-sprayed cylinder (press fit) implants in different regions of the mouth. STUDY DESIGN: Sixty-five subjects met the inclusion requirements. Surgery was done in two phases by four experienced surgeons. Implant placement and abutment connection were separated by 3 to 4 months in the mandible, 6 to 7 months in the maxilla. Patients were assigned to either titanium plasma-sprayed or hydroxyapatite-coated implants on the day of surgery. Implant placement was not stratified for the region of the jaws. Outcome assessment was failure (loss) of an implant before or within 3 months of second phase surgery. RESULTS: Three hundred fifty-two implants equally distributed between titanium plasma-sprayed and hydroxyapatite-coated titanium plasma-sprayed implants were placed in four different sites; anterior maxilla, posterior maxilla, anterior mandible, and posterior mandible. There were a total of 15 failures (4.26%). Overall, titanium plasma-sprayed implants showed a higher but not significant failure rate compared with hydroxyapatite-coated implants (p = 0.06). Although not statistically significant, we believe that a smoking history played an important role in the failure of implants. CONCLUSION: This study suggests that an hydroxyapatite-coating of an implant allows superior initial integration when compared with a titanium plasma-sprayed surface.

Adult↗
PubMedDate not supplied

Quantification of bone ingrowth within bone-derived porous hydroxyapatite implants of varying density.

Hydroxyapatite has been investigated for use in the osseous environment for over 20 years and the biocompatibility of the ceramic and its osseoconductive behavior is well established. Therefore, the use of porous hydroxyapatite for the repair of osseous defects seems promising with potential for complete penetration of osseous tissue and restoration of vascularity throughout the repair site. However, there have been few systematic studies of the effects of physical properties such as macropore size and pore connectivity on the rate and quality of bone integration within porous hydroxyapatite implants. This paper quantifies the early biological response to a well-characterized series of implants with uniform microstructure and phase composition, but differing macrostructures and demonstrates the dependence of the rate of osseointegration on the apparent density of porous hydroxyapatite as a function of pore connectivity. Furthermore, compression testing established that bony ingrowth has a strong reinforcing effect on porous hydroxyapatite implants, which is more pronounced in the lower density implants, as a result of a greater relative volume of bone ingrowth.

Journal Article↗
PubMed2001

Polishing and whitening properties of toothpaste containing hydroxyapatite.

Toothpastes containing hydroxyapatite (HA-toothpaste) have demonstrated efficacy in preventing caries, treating hypersensitivity and curing periodontal diseases, however, their effects on whitening teeth have not been investigated. In this study, the polishing and whitening properties of hydroxyapatite contained toothpastes were evaluated in a combined experimental and clinical study. The polishing properties were evaluated in artificial teeth by polishing with different toothpastes, while the brightening and whitening properties were examined in volunteers using two colorimeters with two specially made fiberscopes. The results revealed that the addition of hydroxyapatite to toothpaste did not alter its polishing properties, while it did result in a marked increase in tooth-whiting. It was also found that the brightening and whitening properties increased as the amount of hydroxyapatite in the toothpaste increased. It is concluded that toothpaste containing hydroxyapatite are effective at whitening tooth and that whitening was not due to their polishing effect on tooth surface.

Journal Article↗
PubMed1999

Bioactive nanocrystalline sol-gel hydroxyapatite coatings.

Sol-gel technology offers an alternative technique for producing bioactive surfaces for improved bone attachment. Previous work indicated that monophasic hydroxyapatite coatings were difficult to produce. In the present work hydroxyapatite was synthesized using the sol-gel technique with alkoxide precursors and the solution was allowed to age up to seven days prior to coating. It was found that, similar to the wet-chemical method of hydroxyapatite powder synthesis, an aging time is required to produce a pure hydroxyapatite phase. A methodology that has been successfully used to produce nanocrystalline hydroxyapatite thin film coatings via the sol-gel route on various substrates including alumina, Vycor glass, partially stabilized zirconia, Ti-6Al-4V alloy and single crystal MgO is described. Coatings produced on MgO substrates were characterized by X-ray diffraction and atomic force microscopy, while the analogous gels were examined with thermogravimetric and differential thermal analyses. The coatings were crack free and the surface was covered with small grains, of approximately 200 nm in size for samples fired to 1000 degrees C. Coating thickness varied between 70 and 1000 nm depending on the number of applied layers.

Journal Article↗
PubMed1998

Bovine hydroxyapatite for maxillary sinus grafting: comparative histomorphometric findings in sheep.

This experimental study in animals examines the value of bovine hydroxyapatite as grafting material in one-stage sinus lift procedure. The Schneiderian membrane was elevated from extraorally in 54 sinuses of 27 adult female mountain sheep. Two titanium plasma-flame-spray coated cylindrical implants were placed in each sinus in the same session. In 2 groups of 18 sinuses each, the subantral hollow space was filled with bovine hydroxyapatite and autogenous cancellous bone from the iliac crest, respectively. Eighteen sinuses that were left empty served as a control group. Polyfluorochrome sequential labelling (tetracycline, calcein green, alizarin complexon) was carried out 4 weeks postoperatively, 2 weeks before the animals were sacrificed, and halfway through the observation period to assess new bone formation. The selected observation periods were 12 weeks, 16 weeks, and 26 weeks. Six sinuses per observation period and test group were available for histologic evaluation. All implants showed favourable osseointegration into local bone. New bone formation was observed in a triangular area bound by the implant surface, the local buccal antral wall, and submucous connective tissue in all implants. Bovine hydroxyapatite adjacent to local bone was mainly surrounded by bone tissue. There was a great variation in the extent of bony sheathing of the hydroxyapatite particles, irrespective of the animals' survival time. Macrophages were found around HA particles that were not surrounded by bone as well as on free implant surfaces. The mean length of the bone-implant bond was 3.86 mm in the group of empty sinuses, 4.87 mm in the group augmented with hydroxyapatite, and 5.66 mm in the group augmented with autogenous cancellous bone. During the observation period, the relative length of bone in direct contact with the implant surface increased from 20.0% to 25.1% in the control group, from 30.4% to 35.5% in the group treated with autogenous cancellous bone, and from 27.4% to 34.7% in the HA group. Autogenous cancellous bone showed a significantly greater bone-implant contact than did the control group (P = 0.0004) and the HA group (P = 0.0499). When the apical implant portions were examined separately, both HA (P = 0.006) and autogenous cancellous bone (P = 0.005) showed a significantly better bone-implant bond than did the control group.

Animals↗
PubMed2003

Collagen-hydroxyapatite microspheres as carriers for bone morphogenic protein-4.

The purpose of the current study is to evaluate the carrier capability of collagen-hydroxyapatite microspheres to the bone morphogenic proteins (BMP). After anesthesia, a bone defect (6.0 mm in diameter and 10.0 mm in depth) was created at the distal femoral condyles of New Zealand white rabbits. These 10.0 mm3 defects were then completely filled with the implant materials. After 2, 4, 6, and 8 weeks, the animals were sacrificed and histological evaluations were performed. The results showed that when the defects were left untreated, there was no evidence of bone formation during the eight-week experimental period. In the group treated with collagen-hydroxyapatite microspheres without BMP-4, the defect was filled with fibrous tissue and inflammatory cells, while active bone formation with mature marrow tissue formation was evident in the defect treated with collagen-hydroxyapatite microspheres containing BMP-4. Collagen-hydroxyapatite microspheres were expected to be replaced by the regenerated bone structure as the bone reconstruction and bone remodelling process occurred. It was apparent that bone regeneration was influenced by the addition of BMP-4. Collagen-hydroxyapatite microspheres were good carriers for bone morphogenic proteins.

Animals↗
PubMed1993

Variability of mineral density in coralline hydroxyapatite spheres: study by quantitative computed tomography.

Quantitative computed tomography (qCT) can be employed to determine the mineral density (MD) of bone or similar mineralized alloplastic materials with high precision. Porous spheres made from coralline hydroxyapatite are currently used for reconstruction after enucleation procedures. The long-term fate of these implants is unknown. Using qCT, MD was determined in hydroxyapatite spheres prior to implantation. Intersphere MD varied up to 200% with a near Gaussian distribution. Intrasphere MD did not vary significantly when comparing central to peripheral sites. The density of coralline hydroxyapatite spheres was approximately 400% greater than the density of newly formed endochondral bone. This study demonstrates that qCT data were an invaluable tool for MD determination, detecting a marked variability in hydroxyapatite MDs. Because the long-term fate of these implants is unknown and fibrovascular ingrowth is an important event in the integration of these implants, monitoring of MDs of coralline hydroxyapatite implants is of interest.

Densitometry↗
PubMed1998

Rate of vascularization of coralline hydroxyapatite spherical implants pretreated with saline/gentamicin, rTGF-beta 2, and autogenous plasma.

Several authors have reported significant exposure rates using the hydroxyapatite orbital implant in the treatment of the anophthalmic socket. Histologic studies by ourselves and others have suggested that lack of fibrovascular ingrowth into the implants may contribute to conjunctival breakdown and exposure. Recently, much attention has been given to angiogenic factors, such as rTGF-beta 2 and those found in plasma, in accelerating wound healing and fibrovascular ingrowth. This pilot study compares the rate of vascularization of hydroxyapatite orbital implants pretreated with plasma, rTGF-beta 2, and a saline/gentamicin solution with that in untreated controls ina population of New Zealand albino rabbits. Hydroxyapatite orbital spheres were implanted subcutaneously and in enucleated orbits. Untreated implants were used as a control. Implants pretreated with plasma, rTGF-beta 2, and a saline/gentamicin solution were removed and examined histologically at weekly intervals for the first 3 weeks after implantation. Histologic studies demonstrated that the rate of vascularization significantly increased between 2 and 3 weeks postoperatively in all study groups. Pretreating the implants with rTGF-beta 2 in phosphate buffered solution (PBS) or autogenous plasma did not significantly increase the rate of vascularization in comparison with controls at weeks 1 and 2. However, pretreating the implants with a saline/gentamicin solution or PBS alone was associated with an increased rate of vascularization at weeks 2 and 3. No statistically significant difference in vascularization was noted between the subcutaneous and orbital implants at any week. Hydroxyapatite implants pretreated with saline/gentamicin or phosphate buffered solutions underwent more rapid vascularization at weeks 2 and 3 in comparison with controls. Additionally, all groups were noted to have a more rapid rate of ingrowth between weeks 2 and 3 than between weeks 1 and 2. Plasma and rTGF-beta 2 (at the dose used) did not significantly alter the rate of vascularization of hydroxyapatite implants during the first 2 to 3 weeks. The significance of these findings is discussed.

Animals↗
PubMed1998

A synthetic hydroxyapatite implant: the so-called counterfeit implant.

This article evaluates three generations of synthetic hydroxyapatite implants in a rabbit model. Fourteen New Zealand white rabbits received synthetic hydroxyapatite orbital implants (first, second, and third generation). The rabbits underwent enucleation of one eye and then received a 12-mm synthetic hydroxyapatite implant wrapped in Vicryl (polygalactin 910; Ethicon, Inc.) mesh or sclera. Magnetic resonance imaging was conducted to assess host fibrovascularization of the implant 4 and 12 weeks after implantation. Animals were killed at each of these times and the implant was removed for histopathologic examination. Enhancement on magnetic resonance imaging and extent of fibrovascularization by histopathologic examination were assessed. The first-generation synthetic hydroxyapatite (FCI, Issy-Les-Moulineaux, France) was not 100% hydroxyapatite as is the Bio Eye (Integrated Orbital Implants, Inc., San Diego, CA, U.S.A.). It contained 3.2% calcium oxide. The implant was heavier and much less porous than the original Bio Eye implant. Central vascularization eventually occurred but was not extensive. The second-generation implant was more porous than the first, with rapid central vascularization to the center of the implant by 4 weeks. However, the second-generation implant was very fragile and crumbled easily. The second-generation synthetic implant was chemically identical to the original Bio Eye implant with no calcium oxide. The third-generation implant was more porous than its predecessors. When compared side by side with the Bio Eye, a difference in pore uniformity and interconnectivity seems apparent. However, an early extensive vascularization pattern to the center of the implant is seen histopathologically, similar to that with the Bio Eye. Magnetic resonance imaging also shows extensive enhancement as is the case with the Bio Eye. The third-generation synthetic implant is not fragile as was the second-generation implant, and chemically it is identical to the Bio Eye with no calcium oxide present. The third-generation implant is approximately half the price of the original Bio Eye implant.

Animals↗
PubMed1994

Accuracy of quantifying coronary hydroxyapatite with electron beam tomography.

RATIONALE AND OBJECTIVES: The electron beam tomography coronary calcium score continues to be used without experimental validation. To determine its accuracy, a series of experiments was performed. METHODS: A chest phantom model was constructed with coronary arteries represented by cylindrical holes containing hydroxyapatite granules embedded in a gelatin matrix to simulate coronary arteries. Experiments were performed to determine the relationship between the mass of hydroxyapatite in each of these arteries, the coronary calcium score currently used in coronary screening, and an alternative method of estimating mass from the images. The model was scanned with equal amounts of hydroxyapatite in each artery: 1) when the cylindrical heart was rotated 36 degrees 10 times between scans, and 2) when the particle diameters varied from 0.1 mm to 4 mm. The scores were calculated, and a subtraction algorithm was applied to estimate the exact mass of hydroxyapatite in each artery. RESULTS: The hydroxyapatite scores varied by 42% with position and by 1.54 x 10(6)% with particle diameter. The estimated masses from the subtraction algorithm were more stable with position and particle size, with maximum percent errors of 10% and 14% for position and particle size, respectively. CONCLUSIONS: These results suggest that the coronary calcium score is invalid, and that more precise and clinically relevant methods, such as the arterial summation method, should be rigorously tested in clinical studies.

Algorithms↗
PubMed1996

Improvement of the bone-pin interface with hydroxyapatite coating: an in vivo long-term experimental study.

The present study was designed to comparatively evaluate the bone-pin interface in a long-term unloaded experimental study in two groups of pins, uncoated and coated with hydroxyapatite. Forty pins made of stainless steel were used. Half of the pins were plasma-sprayed with hydroxyapatite, and the other half remained uncoated. Four adult sheep were selected. Each sheep tibia was implanted with five pins. Two sheep were euthanized 4 months after surgery and the remaining two 12 months after surgery. Extraction torque was higher in the hydroxyapatite-coated pins compared with the uncoated ones at both 4 (p < or = 0.0005) and 12 months (p < or = 0.0005) after implantation. The histological patterns observed in the sheep euthanized 4 and 12 months after implantation were very similar. An extensive bony coverage of the hydroxyapatite-coated pins without any coating resorption and delamination from the metallic substrate was observed. Fibrous tissue encapsulation was found in the uncoated pins. These results demonstrate that the hydroxyapatite coating significantly improved the bone-pin interface. A similar improvement of bone-pin interface rigidity in many clinical situations is likewise possible.

Animals↗
PubMed2004

Mastoid obliteration with hydroxyapatite cement: the Ipswich experience.

OBJECTIVE: This article reports the outcomes of a series of patients who underwent obliteration of the mastoid cavity using hydroxyapatite cement. A comparison is made with a group of patients who underwent similar surgery in the same period using hydroxyapatite granules. STUDY DESIGN: Nonrandomized observational analysis. SETTING: Tertiary otology unit. PATIENTS AND INTERVENTIONS: All patients requiring mastoid surgery and primary obliteration or revision mastoid surgery and obliteration. MAIN OUTCOME MEASURES: Dry cavity with full epithelialization and good tolerance to swimming at 1 year postoperatively. RESULTS: In four of eight patients who had obliteration using hydroxyapatite cement, there was infection of the obliteration site, requiring revision. All of the patients who had obliteration with hydroxyapatite granules had dry and well-epithelialized mastoid cavities at 1-year follow-up, with ears that tolerated swimming. CONCLUSION: The use of hydroxyapatite cement is not recommended in mastoid obliteration surgery.

Adolescent↗
PubMed2004

The efficacy of a hydroxyapatite composite as a biodegradable antibiotic delivery system.

Local biodegradable carriers have been studied for use as a skeletal drug delivery system. This study investigated the efficacy of a local biodegradable composite composed of hydroxyapatite, plaster of Paris, and chitosan impregnated with antibiotics to treat methicillin-resistant Staphylococcus aureus. The composite, impregnated with vancomycin, fosfomycin, or sodium fusidate was tested for its sustained elution characteristics during 3 months and compared with similarly impregnated polymethylmethacrylate using the modified disc diffusion technique. Physicochemical properties using scanning electron microscopy and xray diffraction analysis of each preparation also were analyzed. Vancomycin and fosfomycin incorporated into the hydroxyapatite composite inhibited the organism for 3 months, whereas sodium fusidate was effective only for 3 weeks. Vancomycin and fosfomycin loaded into the hydroxyapatite composite had a significantly better inhibitive effect than when loaded in polymethylmethacrylate, whereas sodium fusidate loaded in polymethylmethacrylate showed a significantly better inhibitive effect than when loaded in the hydroxyapatite composite. Scanning electron microscopy and xray diffraction analysis elucidated the patterns of each drug release profile. The local hydroxyapatite composite is a promising local biodegradable delivery system for vancomycin and fosfomycin, whereas PMMA is a better carrier for sodium fusidate in treating methicillin-resistant staphylococcus aureus osteomyelitis.

Anti-Bacterial Agents↗
PubMedDate not supplied

Pyogenic granuloma as a presenting sign of hydroxyapatite orbital implant exposure: a clinicopathologic study.

PURPOSE: We report 5 unusual cases of exposed hydroxyapatite orbital implants that presented as pyogenic granulomas. We propose pathogenesis and histopathologic correlations. METHODS: A clinicopathologic study of 5 patients with hydroxyapatite implants who presented with pyogenic granuloma. RESULTS: Pyogenic granulomas were detected 1.5 to 30 months after implantation in 5 patients. The lesions were multiple but were not related to the wound margin at the exposed area and were not covered by the surface epithelium in most instances. Exposure defects were detected in all patients at the time of lesion excision. The mean exposure size in the greatest dimension was 16 mm (range, 9-20 mm). Three patients were treated successfully with simple excision of the granulomas, burring down of the anterior surface of the implants, and direct repair of the exposure defects. Explantation of the implant was performed in 2 cases. Histopathologic examination revealed chronic inflammation and microabscess formation in the explanted implants. CONCLUSIONS: Five patients with pyogenic granulomas were found to have hydroxyapatite exposure. Pyogenic granuloma should not be considered a benign lesion on a hydroxyapatite orbital implant, especially in recurrent cases. Ophthalmologists must be aware of the possibility of conjunctival dehiscence with hydroxyapatite-implant exposure beneath the lesion.

Adolescent↗