Does xenogeneic demineralized bone matrix have clinical utility as a bone graft substitute?

Purified bone xenografts: A novel and efficient animal bone substitute derived from an optimized supercritical CO2 treatment

Bone xenografts represent a promising alternative to autologous or allograft transplants, yet antigenicity in animal-derived tissues remains a major limitation to their clinical use. To provide any risk of contamination or allogenic rejection, the Supercrit® process was developed to treat allogeneic human bone combining a supercritical CO2 treatment followed by a chemical treatment using high quantities of different solvents. The aim of this study was to produce a xenogeneic bone substitute thanks to the development of a new one-step supercritical process, 'Goxcrit', and to test it in vivo. This new process reduces the use of solvents by injecting them under pressure into the supercritical CO2 flow, while maintaining the cleaning quality of the bone matrix and better preserving its inner structure, essential for its future bone integration. Porcine derived bone samples were treated using Goxcrit or Supercrit®, and compared with human bone treated with Supercrit®, the commercialized bone allograft. In vitro analyses demonstrated the absence of cytotoxicity and of the alpha-gal epitope mainly responsible for cross-species immunogenicity. Additionally, in vivo experiments revealed improved bone formation in rats critical calvarial defects (BV/TV and von Kossa analyses) implanted with Goxcrit samples, with bone remodeling (TRAP/ALP stains), compared to those treated with Supercrit®. These results can be attributed to the less aggressive chemical process of the Goxcrit, which preserves the bone's inner structure critical for remodeling. Our study highlighted the interest of using a porcine bone source treated with the Goxcrit process to meet the growing demand for reliable and effective bone substitutes.

Histologic and Histomorphometric Analysis of Bone Regeneration with Bovine Grafting Material after 24 Months of Healing. A Case Report

Anorganic bovine bone mineral matrix (ABBMM) has been reported to have osteoconductive properties and no inflammatory or adverse responses when used as grafting material in sinus augmentation procedures. However, controversy remains in regard to degradation rate of ABBMM. The aim of this study was to histologically and histomorphometrically evaluate the degradation of ABBMM in human bone samples obtained in one patient 24 months after sinus augmentation. Materials and Methods: The histologic and histomorphometric analysis was performed by means of light microscopy in three specimens harvested from the same patient, Results: After 24 months the tissue pattern appeared to be composed of residual particles, some in close contact with the newly formed bone, others separated by translucent areas and osteoid tissues. Newly-formed bone presented different levels of maturation and numerous osteocytes, with greater numbers in bone closer to the grafted particles (27.3% vs. 11.2%, p < 0.05). The histomorphometric analysis showed mean values of 40.84% newly-formed bone, 33.58% residual graft material, 23.84% marrow spaces, and 1.69% osteoid tissue, Conclusions: Even though ABBMM underwent considerable resorption, a great amount of residual grafting material was still present after two years of healing following sinus augmentation. This study confirms that the bovine grafts can be classified as long-term degradation materials.

Clinical, Radiographic, and Histologic Evaluation of Maxillary Sinus Lift Procedure Using a Highly Purified Xenogenic Graft (Laddec(®))

OBJECTIVES

The aim of this study was to evaluate the clinical, radiographic and histologic results when a highly purified xenogenic bone (Laddec(®)) was used as grafting material in maxillary sinuses.

MATERIAL AND METHODS

In fifteen patients requiring unilateral maxillary sinus augmentation, the grafting procedure was performed with Laddec(®). Forty-two implants were installed after a 6 month healing period. The height of the augmented sinus was measured radiographically immediately after augmentation and postoperatively up to 36 months. At the time of implant placement, a bone core was harvested in each patient for histological examination.

RESULTS

The cumulative implant survival rate was 97.6%. The original height was 3.65 (SD 0.7) mm and the augmented sinus height was 13.8 (SD 1.4) mm after the surgery. The reduced height of grafted xenogenic material (RDL) at the implant insertion was 0.83 (SD 0.38) mm, and at the final postoperative visit was 0.91 (SD 0.25) mm, showing no significant correlation with the follow-up periods by Spearman's test (P = 0.118). In addition, no significant difference in the RDL was observed according to the site of implantation (P = 0.682). The mean implant marginal bone loss was 0.38 (SD 0.24) mm. Histological analysis showed the bone cores were composed of 64.72 (SD 3.44)% newly formed bone, 17.41 (SD 2.02)% connective tissue, 16.93 (SD 2.83)% residual graft particles, and 0.94 (SD 0.11)% inflammatory cells.

CONCLUSIONS

According to our data, the highly purified xenogenic bone (Laddec(®)), used as graft material in the sinus lift procedure, may create adequate bone volume, and appropriate osseointegration of dental implants.

[Osteostimulating effect of bone xenograft on bone tissue regeneration]

The aim of experimental case-control study performed in 28 dogs divided in 2 groups was to assess local tissue reactions on bone xenograft transplantation; dynamics of bone remodeling and formation at the site of bone defect wall contacting with bone xenograft; dynamics and mechanisms of xenograft remodeling. Transplantation of xenograft in conventional bone defects did not cause inflammatory of destructive reactions because of high biocompatibility of the material. At transplantation site active fibrous bone trabeculae formation filling the spaces between xenograft participles was observed. On the 90th day newly formed bone showed lammelar structure. Simultaneously from the 42d day the invasion of cell elements from recipient bed into the material was seen leading to xenograft resorption. The observed dynamics may be assessed as gradual substitution of xenograft with newly formed host bone structures.

A novel controlled-release system for antibacterial enzyme lysostaphin delivery using hydroxyapatite/chitosan composite bone cement

In this work, a lysostaphin-loaded, control-released, self-setting and injectable porous bone cement with efficient protein delivery was prepared by a novel setting method using hydroxyapatite/chitosan (HA/CS) composite scaffold. The cement samples were made through cementitious reactions by mixing solid powder, a mixture of HA/CS composite particles, lysostaphin, Ca(OH)2, CaCO3 and NaHCO3, with setting liquid containing citric acid, acetic acid, NaH2PO4, CaCl2 and poloxamer. The setting parameters of the cement samples were determined. The results showed that the final setting time was 96.6±5.2 min and the pH value increased from approximately 6.2 to nearly 10 during the setting process and the porosity was 34% at the end. And the microstructure and composition were detected by scanning electron microscopy (SEM), x-ray diffraction and Fourier transform-infrared spectroscopy. For the release behavior of lysostaphin loaded in the cement sample, the in vitro cement extract experiment indicated that about 94.2±10.9% of the loaded protein was released before day 8 and the in vivo Qdot 625 fluorescence tracking experiment showed that the loaded protein released slower than the free one. Then the biocompatibility of the cement samples was evaluated using the methylthiazol tetrazolium assay, SEM and hematoxylin-eosin staining, which suggested good biocompatibility of cement samples with MC 3T3-E1 cells and subcutaneous tissues of mice. Finally the antibacterial activity assay indicated that the loaded lysostaphin had good release ability and strong antibacterial enzymatic activity against methicillin-resistant Staphylococcus aureus. Collectively, all the results suggested that the lysostaphin-loaded self-setting injectable porous bone cement released the protein in a controlled and effective way and the protein activity was well retained during the setting and releasing process. Thus this bone cement can be potentially applied as a combination of artificial bone substitute and controlled-release system for delivery of lysostaphin to treat bone defects and infections.

Effect of Synthesis Temperature on the Crystallization and Growth of In Situ Prepared Nanohydroxyapatite in Chitosan Matrix

Hydroxyapatite nanoparticles (nHA) have been used in different biomedical applications where certain particle size distribution and morphology are required. Chitosan/hydroxyapatite (CS/HA) nanocomposites were prepared using in situ coprecipitation technique and the effect of the reaction temperature on the crystallization and particle growth of the prepared nanohydroxyapatite particles was investigated. The composites were prepared at different synthesis temperatures (−10, 37, and 60°C). XRD, FTIR, thermal analysis, TEM and SEM techniques were used to characterize the prepared specimens. It was found that the increase in processing temperature had a great affect on particle size and crystal structure of nHA. The low temperature (−10°C) showed inhabitation of the HA growth in c-direction and low crystallinity which was confirmed using XRD and electron diffraction pattern of TEM. Molar ratio of the bone-like apatite layer (Ca/P) for the nanocomposite prepared at 60°C was higher was higher than the composites prepared at lower temperatures (37 and −10°C).

Inactivation of enveloped and non-enveloped viruses in the process of chemical treatment and gamma irradiation of bovine-derived grafting materials

BACKGROUND

Xenografts, unlike other grafting products, cannot be commercialized unless they conform to stringent safety regulations. Particularly with bovine-derived materials, it is essential to remove viruses and inactivate infectious factors because of the possibility that raw materials are imbrued with infectious viruses. The removal of the characteristics of infectious viruses from the bovine bone grafting materials need to be proved and inactivation process should satisfy the management provision of the Food and Drug Administration (FDA). To date, while most virus inactivation studies were performed in human allograft tissues, there have been almost no studies on bovine bone.

METHODS

To evaluate the efficacy of virus inactivation after treatment of bovine bone with 70% ethanol, 4% sodium hydroxide, and gamma irradiation, we selected a variety of experimental model viruses that are known to be associated with bone pathogenesis, including bovine parvovirus (BPV), bovine herpes virus (BHV), bovine viral diarrhea virus (BVDV), and bovine parainfluenza-3 virus (BPIV-3). The cumulative virus log clearance factor or cumulative virus log reduction factor for the manufacturing process was obtained by calculating the sum of the individual virus log clearance factors or log reduction factors determined for individual process steps with different physicochemical methods.

RESULTS

The cumulative log clearance factors achieved by three different virus inactivation processes were as follows: BPV ≥ 17.73, BHV ≥ 20.53, BVDV ≥ 19.00, and BPIV-3 ≥ 16.27. On the other hand, the cumulative log reduction factors achieved were as follows: BPV ≥ 16.95, BHV ≥ 20.22, BVDV ≥ 19.27, and BPIV-3 ≥ 15.58.

CONCLUSIONS

Treatment with 70% ethanol, 4% sodium hydroxide, or gamma irradiation was found to be very effective in virus inactivation, since all viruses were at undetectable levels during each process. We have no doubt that application of this established process to bovine bone graft manufacture will be effective and essential.

Clinical evaluation of demineralized bone allograft for sinus lifts in humans: a clinical and histologic study

PURPOSE

Severe alveolar bony resorption in the edentulous posterior maxilla and pneumatization of the maxillary sinus wall make traditional implant placement impossible in the posterior maxilla. To reconstruct the severely resorbed maxilla for dental implant placement, 1 successful technique is to elevate the maxillary sinus floor using demineralized bone matrix (DBM) grafts. The purpose of this study was to evaluate a histologic and histomorphometric evaluation of DBM grafts in the human maxilla.

PATIENTS AND METHODS

Nine months after grafting, at the time of dental implantation, biopsy samples were taken from the grafted areas of 8 patients and were analyzed histologically.

RESULTS

All the sinus lifts were successful in the clinical study conducted after implantation. Resorption of the graft materials and new bone formation were observed, and there was direct deposition of bone on the surface of the graft particles.

CONCLUSION

The results of this study indicate that limited maxillary sinus lift with DBM graft material is a clinically reliable preimplant procedure.

Preparation and characterization of homogeneous chitosan-polylactic acid/hydroxyapatite nanocomposite for bone tissue engineering and evaluation of its mechanical properties

Homogeneous nanocomposites composed of hydroxyapatite and chitosan in the presence of polylactic acid were synthesized by a novel in situ precipitation method. The morphological and compositional properties of composites were investigated. Hydroxyapatite nanoparticles in a special rod-like shape with a diameter of about 50nm and a length of about 300nm were distributed homogeneously within the chitosan-polylactic acid matrix. The interaction between the organic matrix and the inorganic crystallite and the formation mechanism of the rod-like nanoparticles were also studied. The results suggested that the formation of the special rod-like nanoparticles could be controlled by a multiple-order template effect. High-resolution images showed that the rod-like inorganic particles were composed of randomly orientated subparticles about 10nm in diameter. The mechanical properties of the composites were evaluated by measuring their compressive strength and elastic modulus. The data indicated that the addition of polylactic acid can make homogeneous composites scaffold resist significantly higher stress. The elastic modulus of the composites was also improved by the addition of polylactic acid, which can make them more beneficial for surgical applications.

In vitro and in vivo behaviour of biodegradable and injectable PLA/PGA copolymers related to different matrices

This study comparatively investigates the in vitro and in vivo behavior of injectable polymeric materials for the treatment of bone defects. The tested materials were three injectable and biodegradable PLA/PGA 50/50 copolymers dispersed in different matrices: Fisograft-gel (GEL) was dispersed in an aqueous matrix of poly-ethyl-glycole (PEG); Slurry2 (SL2) was dispersed in an aqueous matrix of PEG and dextran; and Slurry6 (SL6) was dispersed in a 3% agarose matrix. The biological characterization of these materials was studied by in vitro and in vivo tests: the in vitro test assessed the cellular response in terms of viability, differentiation and synthetic activity, while the in vivo test evaluated the healing capacity of bone defects treated with these biomaterials. GEL and SL2 induced a similar response for viability and differentiation of MG63 osteoblast-like cells after a 7-day culture, while SL6 caused a higher production of both interleukin-6 and type I collagen. Since the results showed that the materials were biocompatible and not cytotoxic in vitro, the in vivo study was carried out: materials were implanted, under general anesthesia, in critical size defects of rabbit femoral condyles; after 4 and 12 weeks, the healing rates and the quality of the regenerated bone were histomorphometrically calculated. The SL2-treated defects healed better at 12 weeks with a more similar microarchitecture of the newly formed bone to normal bone in comparison with other materials, as demonstrated by bone volume fraction and trabecular thickness values.

Xenogenic bone matrix extracts induce osteoblastic differentiation of human bone marrow-derived mesenchymal stem cells

Colloss® and Colloss-E® are sterile acellular lyophilizates extracted from bovine and equine bone matrix, respectively. Animal and clinical studies have shown that these xenogenic bone matrix extracts (BMEs) are effective as bone graft substitutes. In this report, we investigated the effect of Colloss and Colloss-E on human adult in vitro-expanded bone marrow-derived mesenchymal stem cells (BMMSCs). Specifically, we assessed whether these xenogenic BMEs induced osteoblastic differentiation of cultured BMMSC. We show that BMMSCs treated with either Colloss or Colloss-E exhibited characteristic osteoblastic morphological changes accompanied by the expression of osteoblast-specific markers, such as alkaline phosphatase activity, osteopontin secretion and calcium deposits, explicitly demonstrating that these bone matrix extracts induce osteoblastic differentiation of BMMSCs in vitro. Hence, xenogenic BMEs induce bone-specific differentiation of BMMSCs, presumably through providing stem cells with structural and soluble mediators that mimic the in vivo microenvironment. These results may explain the in vivo mode of action of these medical devices, and potentially provide a novel tissue engineering-based treatment of bone defect, using autologous BMMSCs pretreated with BMEs.

Osteoinductivity of demineralized bone matrix in immunocompromised mice and rats is decreased by ovariectomy and restored by estrogen replacement

The osteoinduction potential of human demineralized bone matrix (DBM) in females with low estrogen (E2) is unknown. Moreover, the osteoinductivity of commercial human DBM is tested in male athymic rats and mice, but DBM performance in these animals may not reflect performance in female animals or provide information on E2's role in the process. To gain insight, human DBM was implanted bilaterally in the gastrocnemius of twenty-four athymic female mice (10 mg/implant) and twenty-four athymic female rats (15 mg/implant). Eight animals in each group were sham-operated (SHAM), ovariectomized (OVX), or ovariectomized with E2-replacement (OVX+E2) via subcutaneous slow release capsules of 17beta-estradiol. OVX and OVX+E2 animals were pair-fed to SHAM animals. Four animals from each group were euthanized at 35 days and four at 56 days. Animal weight, uterine weight, and blood estrogen levels confirmed that pair feeding, ovariectomy, and E2 replacement were successful. Histological sections of implanted tissues were evaluated qualitatively for absence or presence of DBM, ossicle formation, and new bone or cartilage using a previously developed qualitative scoring system (QS) and by histomorphometry to obtain a quantitative assessment of osteoinduction. OVX mice had a small but significant QS decrease at 35 days compared to SHAM mice, confirmed by quantitative measurement of ossicle, marrow space, and new bone areas. The QS in rats was not affected by OVX but histomorphometry showed decreased new bone in OVX rats, which was restored by E2. The QS indicated that the number of new bone sites was not reduced by OVX in rats or mice at 56 days, but the relative amount of new bone v. marrow space was affected and differed with animal species. Residual DBM was less in OVX animals, indicating that DBM resorption was affected. Cartilage was present in rats but not in mice, suggesting that endochondral ossification was slower and indicating that bone graft studies in these species are not necessarily comparable. These results show the importance of E2 in human DBM-induced bone formation and suggest that E2 may be needed for clinical effectiveness in post-menopausal women.

Antigenicity and immunogenicity of collagen

Pertinent issues of collagen antigenicity and immunogenicity are concisely reviewed as they relate to the design and application of biomedical devices. A brief discussion of the fundamental concepts of collagen immunochemistry is presented, with a subsequent review of documented clinical responses to devices containing reconstituted soluble or solubilized collagen. The significance of atelocollagen, concerns regarding collagen-induced autoimmunity, and other relevant topics are also addressed in the context of current understanding of the human immune response to collagen.

Preparation and characterization of nano-hydroxyapatite/chitosan composite scaffolds

A novel nano-hydroxyapatite (HA)/chitosan composite scaffold with high porosity was developed. The nano-HA particles were made in situ through a chemical method and dispersed well on the porous scaffold. They bound to the chitosan scaffolds very well. This method prevents the migration of nano-HA particles into surrounding tissues to a certain extent. The morphologies, components, and biocompatibility of the composite scaffolds were investigated. Scanning electron microscopy, porosity measurement, thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transformed infrared spectroscopy were used to analyze the physical and chemical properties of the composite scaffolds. The biocompatibility was assessed by examining the proliferation and morphology of MC 3T3-E1 cells seeded on the scaffolds. The composite scaffolds showed better biocompatibility than pure chitosan scaffolds. The results suggest that the newly developed nano-HA/chitosan composite scaffolds may serve as a good three-dimensional substrate for cell attachment and migration in bone tissue engineering.

Reconstruction of cartilage, bone, and hematopoietic microenvironment with demineralized bone matrix and bone marrow cells

Highly specialized hard tissues, such as cartilage, bone, and stromal microenvironment supporting hematopoiesis, originate from a common type of mesenchymal progenitor cell (MPC). We hypothesized that MPCs present in bone marrow cell suspension and demineralized bone matrix (DBM) that possess natural conductive and inductive features might constitute a unit containing all the essential elements for purposive bone and cartilage induction. Using a rodent preclinical model, we found that implantation of a composite comprising DBM and MPCs into A) a damaged area of a joint; B) an ablated bone marrow cavity, and C) a calvarial defect resulted in the generation of A) a new osteochondral complex comprising articular cartilage and subchondral bone; B) trabecular bone and stromal microenvironment supporting hematopoiesis, and C) flat bone, respectively. The new tissue formation followed differentiation pathways controlled by site-specific physiological conditions, thus developing tissues that precisely met local demands.

Quantitative microcomputed tomography analysis of mineralization within three-dimensional scaffoldsin vitro

Synthetic and naturally derived scaffold biomaterials in combination with osteogenic cells or bioactive factors have the potential to serve as bone graft substitutes. Porous poly(l-lactide-co-dl-lactide) (PLDL) scaffolds with mechanical properties comparable to trabecular bone and an oriented, interconnected porosity designed to enhance internal mass transport were recently developed. In this study, PLDL scaffolds were seeded with rat calvarial or rat stromal cells and cultured up to 8 weeks in media containing osteogenic supplements. Cell-seeded human demineralized trabecular bone matrix (DTBM) scaffolds were included for comparison. All constructs were imaged weekly from 4 to 8 weeks using microcomputed tomography (micro-CT) to nondestructively quantify the amount and distribution of mineralized matrix formation. The total mineralized matrix volume increased with time in culture for all construct groups. DTBM constructs contained significantly more mineralized matrix than PLDL constructs. However, an analysis of the acellular DTBM scaffolds exposed to osteogenic media revealed partial remineralization of the demineralized matrix whereas no mineralization was detected in acellular PLDL scaffolds. Differences in mineral distribution were also evident with cell-mediated mineralization found throughout the PLDL constructs but localized to the periphery of the DTBM constructs for both cell types. Expression of bone marker genes indicating osteoblast differentiation was demonstrated in all groups at 8 weeks using a quantitative reverse transcription polymerase chain reaction. Osteocalcin expression was significantly higher for calvarial cell constructs compared to stromal cell constructs, regardless of the type of scaffold. This study demonstrated that micro-CT imaging may be used to nondestructively and quantitatively monitor mineralization within three-dimensional scaffolds in vitro. PLDL scaffolds with an oriented microarchitecture were shown to support cell attachment, differentiation, and cell-mediated mineralization comparable to natural DTBM scaffolds.

Effects of Low-Dose Cyclosporin on Osteogenesis of Human Demineralized Bone Grafts in a Surgically Created Mandibular Defect in Rats

BACKGROUND

Demineralized freeze-dried bone matrix (DFDBM) stimulates new bone formation; however, immune reactions from the residual antigens of prepared grafts might play a role in inducing osteogenesis. This study examined whether cyclosporine-A (CsA), an immunosuppressant, enhanced the DFDBM-induced new bone formation.

METHODS

After creating a bony defect in the posterior mandible, 40 male Sprague-Dawley rats were divided into four groups of 10 each: no graft with mineral oil (control); no graft with CsA in mineral oil; DFDBM with mineral oil; and DFDBM with CsA in mineral oil (combined therapy). CsA was administered at 2 mg/kg body weight. Five rats in each group were sacrificed at days 10 and 28 and tissue samples were taken for histological examination.

RESULTS

Soft tissue was observed in the defects of all animals without grafts, whereas the repaired hard tissue formed in the defects of animals with grafts. Histometery, which was performed only at day 10, revealed both DFDBM and CsA therapies produced a significant increase in the total area of repaired hard tissue. Only CsA therapy significantly increased the new bone area. Compared with the DFDBM group, the composition of the repaired hard tissue in the combined therapy group shifted; i.e., the new bone area increased but the residual particle area decreased. The cartilage formation was greater in the combined therapy group than the DFDBM group.

CONCLUSION

Within the limitations of this study, we suggest that the DFDBM grafts play a major role, which could be enhanced by CsA, in the induction of new bone formation, especially at an early phase.

Chemical, structural properties, and osteoconductive effectiveness of bone block derived from porcine cancellous bone

The purpose of this study is to determine the efficacy of bioactive calcium phosphate obtained from porcine cancellous bone for the treatment of bone defects and nonunion. Porcine cancellous bone blocks were heat treated at 1300 degrees C for 2 h. The chemical composition, calcium-to-phosphate ratio, and microstructure of the porcine bone blocks were examined. For in vivo implantation, bone defects were created on the anteromedial aspect of the proximal tibia in seven beagle dogs and the xenograft bone blocks were placed into these defects. Plain radiographs were taken at 2-week intervals for roentgenographic evaluation. At 12 weeks, the specimens were stained with hematoxylin and eosin (H&E). The composition and morphology of heat-treated porcine cancellous bone were found to be similar to heat-treated human cancellous bone. Radiographs showed union between the host bone/bone-block interfaces. At 12 weeks, uniform and substantial new bone formation was observed. It is concluded that heat-treated porcine cancellous bone demonstrated effective osteoconductivity. This high-temperature heat-treatment technique has several advantages, including decreased risk of disease transmission and immunoreactivity, while also offering excellent biocompatibility.

Characterization of bone defect repair in young and aged rat femur induced by xenogenic demineralized bone matrix

BACKGROUND

The osteoinductive effect of some biomaterials could be affected by those systemic conditions typical of old age. The aim of the present paper was to assess the effects of age on the healing of bone defects treated with demineralized bone matrix (DBM).

METHODS

The study was conducted in young (3 month old) and aged (18 month old) rats to assess the efficacy of DBM in the treatment of osseous defects in bone with limited repair capacities. A standard bone defect was created in the distal femoral condyles of male Wistar rats: the left condyle was filled with rabbit DBM granules, while the right condyle was left empty (control). Histological and microhardness analyses were performed at 30 and 45 days after implant surgery.

RESULTS

After implantation of xenogenic DBM, bone healing areas of the aged and young groups showed a significant increase in the formation of newly mineralized bone relative to controls. Measurements of trabecular thickness on day 45 revealed no differences between newly formed and preexisting bone in the young group, while control values were lower. Microhardness measurements demonstrated that newly mineralized bone, either induced by DBM or not, and preexisting bone were comparable in terms of trabecular hardness after 45 days.

CONCLUSIONS

In conclusion, xenogenic DBM seems to be effective in bone defect healing, since it increases mineralized tissue volume. In both DBM-filled and empty sites, age seems to have a detrimental effect on the volume of new bone formation but no influence on bone maturation.

The effects of varying degrees of allograft decalcification on cultured porcine osteoclast cells

BACKGROUND

Demineralized freeze-dried bone allograft (DFDBA) is widely used in periodontal therapy as a scaffold for new bone formation in periodontal defects. It is demineralized, theoretically, to expose osteoinductive or osteoconductive bone matrix proteins that should facilitate osteogenesis. The degree of DFDBA demineralization varies between tissue banks and may affect clinical regeneration. A 2% residual calcium level in DFDBA has been shown to result in the highest alkaline phosphatase activity levels in cultured human periosteal cells and is optimally osteoinductive or osteoconductive for new bone formation. The purpose of this study was to evaluate the effect of 4 different residual calcium levels in commercially available DFDBA samples on porcine osteoclast activity as measured by resorption on calcium phosphate-coated disks.

METHODS

Bone marrow was harvested from the femurs of 3-week-old farm pigs and cultured for 3 weeks. Hematopoietic stem cells were allowed to differentiate into mature active polykaryons displaying genuine osteoclast characteristics. The osteoclast cells displayed a dense actin band inside the margins of the cytoplasm under light microscopy. Culture media was decanted and collagenase added to free the attached cells. Equal cell samples were pipetted onto calcium phosphate-coated disks in 24-well plates. DFDBA samples with 1.44%, 2.41%, and 5.29% residual calcium; FDBA (30% residual calcium); and control cultures without allograft samples were prepared and all samples incubated for 1 week. Cells were fixed and stained for tartrate-resistant acid phosphatase (TRAP), Oregon Green 488-phalloidin, a stain for cytoskeletal proteins, and counterstained with propidium iodide. Specimens were examined by light and fluorescence microscopy using epi-illumination. Calcium phosphate disks were then rinsed in 5% sodium hypochlorite to remove adherent osteoclasts, and substrate surface changes were measured by white light interferometry and image analysis.

RESULTS

A higher yield of TRAP-positive cells was produced without DFDBA; however, resorptive activity appears to be significantly increased in the presence of 2.41% residual calcium as compared to all other experimental groups (P<0.0065).

CONCLUSION

In this in vitro model, porcine osteoclasts show significantly more resorptive activity as measured on calcium phosphate-coated disks in the presence of 2.41% residual calcium in DFDBA than in other DFDBA residual calcium levels.

O uso da matriz óssea desmineralizada na reparação de lesões osteocondrais: estudo experimental em coelhos

Este estudo teve como finalidade a avaliação do uso de matriz óssea desmineralizada na reparação de lesões osteocondrais. A cartilagem articular tem pequena capacidade regenerativa devido a suas características histológicas e à ausência de vasos sanguíneos. Implantes teciduais e cultura de células condrogênicas foram utilizadas para o tratamento de lesões osteocondrais, porém trazem dificuldades técnicas na fixação e suporte mecânico da região subcondral. A matriz óssea desmineralizada pode facilitar tecnicamente a fixação destes implantes em razão de ser um material firme, porém com características elásticas. Além de ter capacidade osteogênica e produzir osso subcondral, assim funcionando como suporte mecânico, também tem fatores indutores de condrogênese. Lesões osteocondrais foram produzidas em joelhos de 15 coelhos. Os joelhos esquerdos foram tratados com matriz óssea desmineralizada, e os direitos usados como controle comparativo. Realizaram-se avaliações macroscópicas e histológicas nas semanas 02, 04 e 06. Nas lesões tratadas com matriz óssea desmineralizada foi obtido 100% de viabilidade do enxerto e formação de tecido normal de reparação, o qual preencheu a lesão completamente com matriz óssea desmineralizada. A análise histológica demonstrou neoformação óssea e integração do enxerto com o tecido ósseo da região subcondral, e na região superficial da lesão ocorrera a indução de formação de tecido condrogênico. A conclusão deste estudo é que a matriz óssea desmineralizada é útil na reparação de lesões osteocondrais devido a sua capacidade de indução óssea e indução de formação de tecido condrogênico. Pode ser usada no tratamento de lesões osteocondrais como componente de um enxerto composto com tecido condrogênico ou cultura de células condrogênicas. Pode também diminuir as dificuldades técnicas de fixação e suporte estes implantes.

Mineralization processes in demineralized bone matrix grafts in human maxillary sinus floor elevations

For reconstruction of the severely resorbed lateral maxilla for dental implant placement, one of the successful procedures is to elevate the maxillary sinus floor by implanting demineralized bone matrix (DBM). We studied bone formation in DBM grafts in the lateral maxilla in humans by means of histology and histomorphometry. Six months after grafting, at the time of dental implantation biopsies were taken from the grafted areas of seven patients. All biopsies contained mineralized matrix (MM) in the grafted area. At close inspection, three types of mineralization were found. First, lamellar biomineralization was seen in and near the maxillary host bone. Second, remineralization was observed in some particles that probably had not been completely demineralized. In the area connecting the graft and host bone, where woven bone was formed against DBM particles, a third mechanism was detected. In this case many dotlike foci of remineralization appeared close to the bone-DBM interface. The remineralized DBM and woven bone were both subsequently remodeled. Bone formation was most active in the area adjoining the maxillary host bone. We conclude that in human sinus floor elevation, allogenic DBM increases mineralized tissue volume by osteoconduction that is supported by the remineralization processes. Osteoinduction by this material seems questionable.

Evaluation of 2 novel approaches for assessing the ability of demineralized freeze-dried bone allograft to induce new bone formation

BACKGROUND

Because of the wide variation in the ability of human demineralized freeze-dried bone allograft (DFDBA) to reproducibly induce new bone formation, there is a need for a reliable measure of bone induction activity. In this study we examined an immature osteoprogenitor cell line for its potential utility in measuring the activity of DFDBA in vitro.

METHODS

We characterized the response of 2T9 cells, an immature osteoprogenitor cell line derived from the calvariae of transgenic mice containing the SV40 T-antigen driven by the mouse bone morphogenetic protein (BMP)-2 promoter, to recombinant human BMP-2 by measuring alkaline phosphatase specific activity, osteocalcin production, and matrix mineralization. Responses were compared to those obtained with 1,25-(OH)2D3. In addition, 2T9 cells were cultured with active or inactive human DFDBA in the presence or absence of BMP-2. We also tested the hypothesis that radio-opacity of tissue following implantation of DFDBA in vivo correlates with the ability of human DFDBA to induce new bone. DFDBA from 9 different donors, stratified by age, were implanted subcutaneously in the thorax of 18 nude (nu/nu) mice. Tissue was harvested at 36 days postoperatively and examined histologically and biochemically for calcium and phosphorus uptake.

RESULTS

2T9 cells exhibited a dose- and time-dependent response to soluble BMP-2. Proliferation was decreased and alkaline phosphatase activity, osteocalcin production, and mineralized nodule formation were increased. The effects were dose- and time-dependent. Peak effects on alkaline phosphatase and osteocalcin were noted on day 8, whereas mineral deposition did not begin to occur until day 12. 1,25-(OH)2D3 did not regulate these effects unless used with BMP-2. When the cells were exposed to active or inactive DFDBA in the presence or absence of BMP-2, no effect on 2T9 cell differentiation was observed. This indicated that DFDBA released no soluble factors with bone inductive ability and that if any active factors were adsorbed to the DFDBA, they were inactivated. When DFDBA was implanted subcutaneously in the thorax of nude mice, there was no histologic evidence of new bone formation. However, there was a donor age-dependent decrease in Ca and P uptake of the implanted tissue, reflecting a donor age-dependent decrease in remineralization of DFDBA.

CONCLUSIONS

These data indicate that cell culture assays like the one used in this study may not be appropriate indicators of bone induction ability by DFDBA since soluble factors may not be responsible for bone induction in vivo. Nonetheless, in vitro assays are still needed. While Ca and P uptake by DFDBA-implanted tissue in the present study correlated with the age-dependent decrease in bone induction at intramuscular sites in a previously reported study, these data show that early x-rays may actually detect remineralization and not new bone formation. Thus, assessment of bone induction ability may still depend on histologic analysis of animal models.

In vitro osteoinduction of demineralized bone

Among numerous available materials for osseous repair and reconstruction, those presenting osteoinductive characteristics and promoting bone regeneration are preferable. Fresh autologous bone is one of the most effective, but it has some disadvantages and risks. Demineralized bone matrix (DBM) is considered to be a valid alternative, because it seems to show osteogenic potential, ascribed to the presence of bone morphogenetic proteins. In addition it can be prepared without difficulty and preserved without losing osteoinductive properties. The aim of the study was to evaluate the osteoinductive ability of xenogenic DBM, by testing DBM powder obtained from rabbit long bones, in cell culture of murine fibroblasts, alone or associated with electromagnetic field (EMF), that are known to exhibit biologic effects on cells: in particular they are used in orthopedics to improve bone formation. At the end of experiment, alkaline phosphatase (ALP) activity, calcium levels and cell proliferation and morphology were evaluated. A statistically significant stimulation of ALP activity and cell proliferation and a morphological change of fibroblasts were found. The results obtained show how DBM and EMF have different effects on cells, and that together they have synergic action toward bone induction.