Porous hydroxyapatite as a bone graft substitute in maxillary augmentation. An histometric study

Postoperative lumbar spinal stenosis after intertransverse fusion with granules of hydroxyapatite: a case report

In the present case of postoperative lumbar spinal stenosis after non-instrumented intertransverse fusion with granules of hydroxyapatite (HA), bone union was not completed and the patient felt the recurrence of his symptoms within two years. We performed re-decompression with fusion, and in hematoxylin and eosin staining of HA granulation harvested during revision surgery, fibrous tissue with hyaline degeneration surrounded the cavity where the HA had existed. Multinuclear giant cells and lymphocytes infiltrated some parts of the marginal layer of the cavity, and no obvious bony bridge had regenerated from autologous bone. No tartrate-resistant acid phosphate (TRAP) -positive osteoclasts could be seen in the new bone, suggesting that the activity of osteoclasts in the new bone decreased during the seven years after the primary surgery.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/3483360258050263

Quantitative analysis of the resorption and osteoconduction of a macroporous calcium phosphate bone cement for the repair of a critical size defect in the femoral condyle

Clinical orthopaedic use of calcium phosphate cement has been limited due to its slow resorption rate, but a new macroporous alpha-tricalcium phosphate (alpha-TCP) bone cement has been designed to accelerate resorption and to increase bone ingrowth. To assess its clinical potential, the in vivo behaviour of alpha-TCP was evaluated in a critical-size defect drilled in the femoral condyles of 36 adult female New Zealand rabbits. Macroporous or standard cement was injected immediately after preparation of the defect. The foaming agent was albumen, which gave up to 75% porosity. The rabbits were divided into three groups and the lesions examined histopathologically at 1, 4 and 12 weeks. No inflammatory reaction was detected at any time period following implantation with either macroporous or standard cement. At 12 weeks, the area of the implanted macroporous cement was approximately 35% of the initial lesion size. Bone growth and revascularisation was observed inside the central pores of the macroporous cement, not only at the margins, as was found with standard calcium phosphate cement. The results indicated that both cements were osteoconductive, biocompatible and biodegradable but their different physicochemical and biological properties had a marked influence on their post-implant behaviour.

In vivo evaluation of an injectable Macroporous Calcium Phosphate Cement

Although Calcium Phosphate Cements (CPC) are highly biocompatible and osteconductive materials, its resorption rate still remains too slow for some applications. In this work the introduction of Macroporosity in an injectable CPC is evaluated as a way to accelerate resorption and to increase bone ingrowth. A Macroporous and a standard CPC were injected just after preparation in a defect drilled in rabbit femur for their in vivo evaluation. The foaming agent used was Albumen, which gave up to a 75% porosity. Sodium Alginate was added to promote the cohesion of the foamed paste after implantation. In the case of the Macroporous Cement, bone growth and neovascularisation was observed inside the pores of the material, not only at the margins of the cement but also in some central pores. After 12 weeks of implantation, the residual material volume of the Macroporous Cement was approximately 35% of the initial value, whereas only the outer layers of non-Macroporous CPC were resorbed, being the residual material volume close to 100%. The higher resorption rate was due to the higher surface contact with body fluids which increased the dissolution rate, and to the enhancement of the cellular activity.

Building bone tissue: matrices and scaffolds in physiology and biotechnology

Deposition of bone in physiology involves timed secretion, deposition and removal of a complex array of extracellular matrix proteins which appear in a defined temporal and spatial sequence. Mineralization itself plays a role in dictating and spatially orienting the deposition of matrix. Many aspects of the physiological process are recapitulated in systems of autologous or xenogeneic transplantation of osteogenic precursor cells developed for tissue engineering or modeling. For example, deposition of bone sialoprotein, a member of the small integrin-binding ligand, N-linked glycoprotein family, represents the first step of bone formation in ectopic transplantation systems in vivo. The use of mineralized scaffolds for guiding bone tissue engineering has revealed unexpected manners in which the scaffold and cells interact with each other, so that a complex interplay of integration and disintegration of the scaffold ultimately results in efficient and desirable, although unpredictable, effects. Likewise, the manner in which biomaterial scaffolds are "resorbed" by osteoclasts in vitro and in vivo highlights more complex scenarios than predicted from knowledge of physiological bone resorption per se. Investigation of novel biomaterials for bone engineering represents an essential area for the design of tissue engineering strategies.

The role of the osteoconductive scaffold in synthetic bone graft

Autogenous bone is regarded as the gold standard for bone graft materials as it provides 3 elements necessary to generate and maintain bone: scaffolding for osteoconduction, growth factors for osteoinduction, and progenitor cells for osteogenesis. Allograft is more limited than autograft in these essential elements and yields more variable clinical results. Composite synthetic grafts offer an alternative that can potentially unite the 3 salient bone-forming properties in more controlled and effective combinations than can be obtained in many clinical situations, without the disadvantages found with autograft. This article examines the underemphasized but crucial role of the osteoconductive scaffold in the composite synthetic bone graft.

Effects of calcium phosphate ceramic bone graft materials on permanent teeth eruption in beagles

OBJECTIVE

The aim of this study was to evaluate the use of calcium phosphate ceramic (CPC) materials as a potential alternative to autogenous secondary alveolar bone grafting in cleft lip and palate patients who are in mixed dentition.

SAMPLE

Four 12-week-old beagles and one 15-week-old beagle were used as subjects.

INTERVENTIONS

In each experimental beagle, the third and fourth deciduous premolars were extracted. The sockets were filled with four different CPC materials and sutured. MAIN OUTCOME MEASURES The beagles were fed a soft diet for the following 8 weeks and then sacrificed for clinical, radiological, histological, transmission electron microscope (TEM), and infrared (IR) absorption analysis.

RESULTS

All four experimental graft materials allowed normal development and eruption of permanent premolars. In histological sections, small particles of biphasic calcium phosphate (BCP) and carbonate apatite (CO(3)-AP) were resorbed, and large particulate forms served as bone frames in cortical bones. Polymer coated with carbonate apatite (Poly/CO(3)-AP) did not cause inflammation but was pushed away to the soft tissue by erupting teeth. Alginate coated with carbonate apatite (alginate/CO(3)-AP) caused a severe inflammatory reaction to the point of destroying a part of the dental follicle and cortical bone. In TEM, resorption activity by phagocytic cells was observed only in CO(3)-AP. Direct bonding of CO(3)-AP to the bone was observed as the electron-dense interface between bone and CO(3)-AP.

CONCLUSION

BCP and CO(3)-AP proved to be suitable as alveolar bone graft materials in areas where tooth eruption occurs. Of the four materials tested, CO(3)-AP produced the best results.

Deproteinized bovine bone used as an adjunct to guided bone augmentation: an experimental study in the rat

BACKGROUND

Promising results have been reported following treatment of periodontal and peri-implant bone defects with deproteinized bovine bone grafts, but their influence on bone formation has not been clarified.

PURPOSE

The goal of this study was to examine whether implantation of deproteinized bovine bone (Bio-Oss, Geistlich AG, Wolhusen, Switzerland) influences bone formation when used as an adjunct to guided bone augmentation (GBA).

MATERIALS AND METHODS

A rigid, hemispherical, Teflon capsule was loosely packed with a standardized quantity of Bio-Oss and placed with its open part facing the lateral surface of the mandibular ramus (test) in 30 rats. At the contralateral side of the jaw, an empty capsule was placed (control). Groups of 10 animals were sacrificed after 1, 2, and 4 months. The volumes of the space created by the capsule and of the (1) newly formed bone, (2) remaining Bio-Oss particles, (3) soft connective tissue, and (4) acellular space in the capsule were estimated by a point-counting technique in three or four histologic sections, taken by uniformly random sampling.

RESULTS

Bone formation at 1 month was limited in both tests and controls. After 2 months, the mean volume of the newly formed bone occupied 9.0% of the space created by the capsule in the test specimens compared with 23.8% in the control specimens (p < .01). After 4 months, the respective figures were 11.6% (tests) versus 38.7% (controls) (p < .01).

CONCLUSION

It can be concluded that Bio-Oss, used as an adjunct to GBA, interferes with bone formation.

Dissolution of dense carbonate apatite subcutaneously implanted in Wistar rats

Hydroxyapatite (HA) is used as a biomaterial in orthopedic applications because it is similar in composition to bone mineral; however, carbonate apatite (CHA) is closer in chemical composition to bone mineral because bone mineral contains significant amounts of carbonate, yet there have been few reports comparing biological responses to HA and CHA. It is generally agreed that bone forms a bond of some kind to HA, and there is conflicting evidence as to whether HA is resorbed in vivo or not. However, comparative reports generally agree that beta-tricalcium phosphate (beta-TCP) is removed faster than HA from an implant site by an undetermined combination of resorption and/or dissolution. The work reported here attempts to provide the first directly comparable subcutaneous dissolution data for dense sintered HA, beta-TCP, and CHA in rats. The weight losses of HA, beta-TCP, and 3.2 wt % CHA were approximately 60, 520, and 320 mg m(-2) day(-1), respectively. Histological sections did not show any evidence of giant cells, and all of the samples were encapsulated with fibrous tissue. beta-TCP and (to a lesser degree) CHA were found to be resistant to dissolution around the edges of the sample. An X-ray analysis did not indicate that any phase transformation had occurred in the dissolution resistant region.

Calcium sulfate- and calcium phosphate-based bone substitutes. Mimicry of the mineral phase of bone

Calcium sulfate and calcium phosphate have provided the orthopedic surgeon a viable alternative to autogenous bone grafting as either an osteoconductive bone void filler or a bone graft extender. These materials mimic the mineral phase of bone and are resorbed at a rate similar to the rate of bone formation. Thus, they are able to provide some structural support and prevent ingrowth of fibrous tissue while facilitating creeping substitution by the host bone.

Migration of hydroxyapatite onlays into the mandible and nasal bone and local bone turnover in growing rabbits

To determine the effects of local bone turnover on the migration of macroporous hydroxyapatite onlays in the nasal bone and mandibular ramus, we performed histomorphometric analyses of the underlying bone area in 41 New Zealand White rabbits from the age of 4 weeks. The hydroxyapatite implants were placed under the periosteum of the right nasal bone (a depository bone onto its periosteal surface and endosteal resorptive) and the mandibular ramus (resorptive onto its outer surface). The corresponding left sides were sham operated. Following fluorescence bone labeling, composite specimens of the hydroxyapatite block including both sides of the nasal bone and mandible were removed at 0 (n = 1), 3, 6, 9, 12, and 16 weeks postoperatively (n = 8, respectively) and processed to yield undecalcified sections. Bone-bone marrow interfaces in the entire area within 200 microns beneath the base of the hydroxyapatite and in the counter-area on the sham-operated side were measured under a light microscope. In all grafted specimens, the hydroxyapatite matrix was directly united with the underlying tissue by bone ingrowth. However, the sinking of the hydroxyapatite graft in the nasal bone was significant at 3 weeks postoperatively and gradually increased thereafter. In the mandible, the sinking became significant at 6 weeks. In the nasal bone, the bone area density beneath the graft showed a time-dependent decrease during the experimental period, but in the mandibular bone, the value was initially decreased at 3 weeks and then recovered to baseline level. In both bones, parameters of bone resorption, such as osteoclast number and osteoclast surface, were significantly increased from 3 weeks. While the parameters of bone formation, such as osteoblast surface and mineralizing surface, were significantly decreased from 3 weeks in the nasal bone, they were significantly increased in the mandible. Mineral apposition rate showed a significant decrease in both bones. Our data indicate that while the bone area density beneath the hydroxyapatite seemed to depend on bone formation, increased bone resorption would be more critical for the remodeling of underlying bony architecture in the migration of the hydroxyapatite graft.

Augmentation of the atrophic maxillary alveolar ridge with hydroxyapatite granules in a Vicryl (polyglactin 910) knitted tube and simultaneous open vestibuloplasty

A modified technique for augmentation of the severely atrophic edentulous maxillary alveolar ridge is described. The augmentation was carried out using a knitted polyglactin 910 mesh tube filled with porous hydroxyapatite granules, the tube being inserted through the access achieved by an open vestibuloplasty. The results of an in-vivo animal study showed that the absorption of the mesh was complete between 49 and 70 days. The clinical study included 11 patients in all of whom there was severe maxillary ridge atrophy and major prosthetic problems; follow-up was for a mean of 25 months. The procedure was without significant complication and produced a mean immediate absolute augmentation of 5.5 mm and substantially increased vestibular depth. A gradual reduction of ridge height was found over time. Nevertheless all patients showed significantly increased ability to wear their dentures. The technique is presented as a safe and predictable alternative to the use of bone grafts and titanium implants in these severely atrophic cases.

The 'sandwich' zygomatic osteotomy: technique, indications and clinical results

The classical approach to lateral midface hypoplasia is reconstruction with onlays. Dislocation and asymmetry, early and late infection, and extrusion are possible complications with alloplastic implant materials. Unpredictable resorption, irregular contours and asymmetry are problems that can arise with autogenous, homogenous and hetergenous onlay grafts. We describe a technique by which the zygomatic body is luxated laterally and ventrally after a combined oblique-horizontal and vertical osteotomy. The resultant greenstick fracture at the temporo-zygomatic suture together with minimal lateral degloving causes the malar body to return to its former position. An interpositional porous hydroxyapatite block acts as a space maintainer until the osteotomy sites are ossified. The restoration of contour is performed by the zygomatic body itself, not by the implants. The indications are discussed and the results of three year follow-up are illustrated.

Experimental transplantation of hydroxylapatite-bone composite grafts

PURPOSE

This study was undertaken to determine if autogenous bone can be cultivated in vivo in a porous hydroxylapatite (HA) matrix by ingrowth from underlying bone and if this autogenous HA-bone composite graft can then be transplanted.

PATIENTS AND METHODS

Five Göttingen minipigs received subperiosteal implantation of one HA block each (40 x 10 x 10 mm), covered by a polylactic membrane, on the ascending ramus of the mandible. After 5 months, half of each implant was harvested and transplanted as an onlay graft to the horizontal ramus of the mandible with simultaneous insertion of a titanium implant. Polychrome fluorescence labeling was done 1, 2, 4, and 8 weeks postoperatively. After 3 months, the vascular system of the animals was filled with BaSO4 for microangiographic examination, and all blocks were retrieved.

RESULTS

Fluorescence microscopy showed that there was a significant decrease in deposition of the label in the grafted blocks at 1 week when compared with later labels. After the second week, there were no significant changes. A 20% to 30% decrease in the frequency of fluorochrome staining was noted in the upper third of each block. In this region, microangiography demonstrated highly vascularized tissue and limited bone resorption.

CONCLUSION

It was concluded that cultivation of mandibular bone in a porous matrix under guided bone regeneration is possible and that this autogenous HA-bone composite graft can be transplanted at a later date.

Experimental study by fluorescence microscopy and microangiography of remodeling and regeneration of bone inside alloplastic contour augmentations

Five female Göttingen minipigs received unilateral subperiosteal implantation of a block of porous hydroxyapatite covered by a polylactic membrane. Five months later, biopsies were taken from the blocks, which were left in place for another 3 months. The biopsies showed bone formation in all pores, indicating complete penetration of the blocks after 5 months. Highly vascular tissue with radiographic signs of bone resorption was found in the upper third of the augmentation 3 months later. Fluorescence microscopy showed that all sequential labels were present throughout the whole block. However, a significant decrease in the frequency of the 1-week label was recorded, showing that elevation of the overlying soft tissue may lead to temporary impairment of vascular supply.

The role of the periosteum in osteointegration of hydroxyapatite granules

The role of the periosteum in the osteointegration of hydroxyapatite (HA) granules was studied in the skull and tibial bone of eight adult Göttingen minipigs. Calcein and tetracycline were used as labeling stains to determine new bone formation. Depending on the condition of the periosteum, three different patterns of osteointegration of HA were found.

Creation of new bone by an osteopromotive membrane technique: an experimental study in rats

Domes, 5 and 8 mm in diameter, were made of expanded polytetrafluorethylene membrane with different degrees of stiffness and internodal distance. The domes were placed on denuded calvarial bones of rats and covered by the skin and periosteal flaps. Histologic evaluation 9 to 16 weeks after surgery showed the formation of various amounts of new bone on the calvarial bone surface inside the domes. The amount of bone neogenesis was dependent on membrane qualities, such as stiffness and porosity, and the length of the healing period. In the most successful experiments, about 80% of the dome volume was filled with newly formed bone, whereas in other experiments considerable amounts of connective tissue were present. Using bioabsorbable membrane domes proved less successful in that they did not maintain their shape and thus did not provide space for bone formation. This study showed that it is possible to obtain bone neogenesis by an osteopromotive membrane technique. This possibility may eventually be of great significance for reconstructive surgery.

Maxillary sinus augmentation: histomorphometric analysis of graft materials for maxillary sinus floor augmentation

This study used histomorphometric analysis to quantitate the bone composition of four different sinus grafting materials biopsied at the time of implant installation. The study consisted of five patients in whom eight bone biopsies were obtained from seven grafted sites. The grafting materials consisted of hydroxylapatite (HA) granules mixed with cortical chin bone, HA mixed with demineralized bone powder, HA alone, and cortical chin bone alone. Histomorphometry was performed using backscattered scanning electron microscopy images and a computerized image analysis system. The biopsy cores yielded 46 sections from which a total of 255 fields, measuring 2.0 mm x 2.0 mm each, were imaged and analyzed. The biopsy cores contained 44.4% bone after grafting with HA granules and chin bone, 59.4% bone after grafting with chin bone alone, 20.3% bone after grafting with HA granules alone, and 4.6% bone after grafting with HA granules and demineralized bone powder. The small number of biopsies did not permit analysis of statistical significance. However, this study demonstrated the feasibility of correlating mineralized tissue composition of different sinus grafting materials with clinical outcome after dental implant installation.

The use of particulate hydroxyapatite and plaster of Paris in aesthetic and reconstructive surgery

The authors describe their early investigative results of using a mixture of hydroxyapatite (HA) and plaster of Paris (PP) in skull and frontal sinus defects in a large series of cats. Histologically, bone was found to form and infiltrate the HA-PP implant over a period of months, with gradual resorption of the plaster in 6-8 weeks. Clinically, the HA-PP combination has been used in 24 patients over the past seven years for various skull, zygomatic, and mandibular defects.

Bone ingrowth and mechanical properties of coralline hydroxyapatite 1 yr after implantation

A previous study of coralline hydroxyapatite as a bone-graft substitute was extended from 4 to 12 months to determine better the relationships between implantation time, bone ingrowth and mechanical properties. The model consisted of a 10 x 30 mm window defect in the shaft of the canine radius (a cortical site), and a 10 mm diameter cylindrical defect in the head of the humerus (a cancellous site). In the new study, these two defects were made bilaterally in eight dogs, and filled with block-form coralline hydroxyapatite. The radius defects were supported by a metal fixation plate which was removed after 9 months. After 12 months, the dogs were killed and the left-side implants were analyzed histomorphometrically and mechanically. The right-side radius and humerus were reserved for structural analysis. The results were combined with those previously measured after 4, 8, 12 and 16 wk of implantation. In the cortical site, bone ingrowth increased from 52% at 16 wk to 74% at 1 yr. In the cancellous site, bone ingrowth was 38% after 4 wk, then fell monotonically, reaching 17% at 1 yr. Bending and compressive strength and stiffness of the radius implants increased throughout the post-implantation year, but compressive strength and stiffness of the humerus implants did not change after the first 2-4 months. Mechanical properties were strongly correlated to bone ingrowth in the cortical, but not the cancellous, site. The volume fraction of the coralline hydroxyapatite material diminished significantly with time in the cortical, but not the cancellous, site.

Osseous response to implanted natural bone mineral and synthetic hydroxylapatite ceramic in the repair of experimental skull bone defects

The purpose of this study was to assess and compare the osseous responses to implanted particles of resorbable anorganic xenograft bone mineral and non-resorbable dense synthetic hydroxylapatite of two different granule sizes. Four trephine calvarial defects were produced in each of 13 adult rabbits. The experimental materials were subsequently implanted in three defects, leaving the fourth defect for control purposes. Six animals were killed 4 weeks after surgery and seven at 14 weeks. The tissue responses were assessed by contact radiography, light microscopy, and histometry. The biocompatibility of the implants was confirmed. All defects healed uneventfully, although the resorbable hydroxylapatite seemed to promote initial bone regeneration. The importance to orthognathic surgery of early and effective healing of bone gaps, as well as of the advantage of implant resorbability to bone remodeling, are discussed.