Induced osteogenesis--the biological principle and clinical applications

The Role of Research Experiences in the Training of Oral and Maxillofacial Surgeons

The importance of active adult learning methods and critical thinking skills is appreciated in dental and OMFS residency training. Known barriers to research are finding time in the curriculum and funding needed for research experiences. These barriers have inspired many institutions to design programs to provide research opportunities, but they can be expensive and of minimal interest to those not planning academic careers. During OMFS residency training, the primary emphasis is on mastery of all aspects of surgical care. Strong partnerships between PhD researchers and OMFS clinical investigators, formed to advance the field, can also have an impact on trainees' involvement in research and their understanding of rigorous evidence-based principles of clinical care.

In vitro analysis of the influence of mineralized and EDTA-demineralized allogenous bone on the viability and differentiation of osteoblasts and dental pulp stem cells

Grafting based on both autogenous and allogenous human bone is widely used to replace areas of critical loss to induce bone regeneration. Allogenous bones have the advantage of unlimited availability from tissue banks. However, their integration into the remaining bone is limited because they lack osteoinduction and osteogenic properties. Here, we propose to induce the demineralization of the allografts to improve these properties by exposing the organic components. Allografts fragments were demineralized in 10% EDTA at pH 7.2 solution. The influence of the EDTA-DAB and MAB fragments was evaluated with respect to the adhesion, growth and differentiation of MC3'T3-E1 osteoblasts, primary osteoblasts and dental pulp stem cells (DPSC). Histomorphological analyses showed that EDTA-demineralized fragments (EDTA-DAB) maintained a bone architecture and porosity similar to those of the mineralized (MAB) samples. BMP4, osteopontin, and collagen III were also preserved. All the cell types adhered, grew and colonized both the MAB and EDTA-DAB biomaterials after 7, 14 and 21 days. However, the osteoblastic cell lines showed higher viability indexes when they were cultivated on the EDTA-DAB fragments, while the MAB fragments induced higher DPSC viability. The improved osteoinductive potential of the EDTA-DAB bone was confirmed by alkaline phosphatase activity and calcium deposition analyses. This work provides guidance for the choice of the most appropriate allograft to be used in tissue bioengineering and for the transport of specific cell lineages to the surgical site.

Craniofacial Tissue Engineering

The craniofacial complex is composed of fundamental components such as blood vessels and nerves, and also a variety of specialized tissues such as craniofacial bones, cartilages, muscles, ligaments, and the highly specialized and unique organs, the teeth. Together, these structures provide many functions including speech, mastication, and aesthetics of the craniofacial complex. Craniofacial defects not only influence the structure and function of the jaws and face, but may also result in deleterious psychosocial issues, emphasizing the need for rapid and effective, precise, and aesthetic reconstruction of craniofacial tissues. In a broad sense, craniofacial tissue reconstructions share many of the same issues as noncraniofacial tissue reconstructions. Therefore, many concepts and therapies for general tissue engineering can and have been used for craniofacial tissue regeneration. Still, repair of craniofacial defects presents unique challenges, mainly because of their complex and unique 3D geometry.

Physical characteristics and biocompatibility of the polycaprolactone-biphasic calcium phosphate scaffolds fabricated using the modified melt stretching and multilayer deposition

Physical properties and biocompatibility of polycaprolactone (PCL)-biphasic calcium phosphate (BCP) scaffolds fabricated by the modified melt stretching and multilayer deposition (mMSMD) technique were evaluated in vitro. The PCL-BCP scaffold specimens included group A; PCL: BCP (wt%) = 80:20 and group B; 70:30. Mechanical properties of the scaffolds were assessed using a universal testing machine. Degradation behaviors of the scaffolds were assessed over 60 days. The amount of calcium and phosphate ions released from the scaffolds was detected over 30 days. Attachment and growth of osteoblasts on the scaffolds and indirect cytocompatibility to those cells were evaluated. The results showed that the scaffolds of both groups could withstand compressive forces on their superior aspect very well; however, their lateral aspect could only withstand light forces. Degradation of the scaffolds over 2 months was low (group A = 1.92 ± 0.47% and group B = 2.9 ± 1.3%,p > 0.05). The concentrations of calcium and phosphate ions released from the scaffolds of both groups significantly increased on day 7 (p < 0.05). Growth of the cells seemed to relate to accumulative increase in those ions. All results between the two ratios of the scaffolds were not statistically different.

The dynamics of adult haematopoiesis in the bone and bone marrow environment

This review explores the dynamic relationship between bone and bone marrow in the genesis and regulation of adult haematopoiesis and will provide an overview of the haematopoietic hierarchical system. This will include the haematopoietic stem cell (HSC) and its niches, as well as discuss emerging evidence of the reciprocal interplay between bone and bone marrow, and support of the pleiotropic role played by bone cells in the regulation of HSC proliferation, differentiation and function. In addition, this review will present demineralized bone matrix as a unique acellular matrix platform that permits the generation of ectopic de novo bone and bone marrow and provides a means of investigating the temporal sequence of bone and bone marrow regeneration. It is anticipated that the utilization of this matrix-based approach will help researchers in gaining deeper insights into the major events leading to adult haematopoiesis in the bone marrow. Furthermore, this model may potentially offer new avenues to manipulate the HSC niche and hence influence the functional output of the haematopoietic system.

Surgical techniques for maxillary bone grafting - literature review

For oral rehabilitation with implant-supported prostheses, there are required procedures to create the bone volume needed for installation of the implants. Thus, bone grafts from intraoral or extraoral donor sites represent a very favorable opportunity. This study aimed to review the literature on the subject, seeking to discuss parameters for the indications, advantages and complications of techniques for autogenous bone grafts.

Influence of select extracellular matrix proteins on mesenchymal stem cell osteogenic commitment in three-dimensional contexts

Growth factors have been shown to be powerful mediators of mesenchymal stem cell (MSC) osteogenic differentiation. However, their use in tissue engineered scaffolds not only can be costly but also can induce undesired responses in surrounding tissues. Thus, the ability to specifically promote MSC osteogenic differentiation in the absence of exogenous growth factors via the manipulation of scaffold material properties would be beneficial. The current work examines the influence of select extracellular matrix (ECM) proteins on MSC osteogenesis toward the goal of developing scaffolds with intrinsically osteoinductive properties. Fibrinogen (FG), fibronectin (FN) and laminin-1 (LN) were chosen for evaluation due to their known roles in bone morphogenesis or bone fracture healing. These proteins were conjugated into poly(ethylene glycol) diacrylate (PEGDA) hydrogels and their effects on encapsulated 10T½ MSCs were evaluated. Specifically, following 1week of culture, mid-term markers of various MSC lineages were examined in order to assess the strength and specificity of the observed osteogenic responses. PEG-LN gels demonstrated increased levels of the osteogenic transcription factor osterix relative to day 0 levels. In addition, PEG-FG and PEG-LN gels were associated with increased deposition of bone ECM protein osteocalcin relative to PEG-FN gels and day 0. Importantly, the osteogenic response associated with FG and LN appeared to be specific in that markers for chondrocytic, smooth muscle cell and adipocytic lineages were not similarly elevated relative to day 0 in these gels. To gain insight into the integrin dynamics underlying the observed differentiation results, initial integrin adhesion and temporal alterations in cell integrin profiles were evaluated. The associated results suggest that α(2), α(v) and α(6) integrin subunits may play key roles in integrin-mediated osteogenesis.

Current views on calcium phosphate osteogenicity and the translation into effective bone regeneration strategies

Calcium phosphate (CaP) has traditionally been used for the repair of bone defects because of its strong resemblance to the inorganic phase of bone matrix. Nowadays, a variety of natural or synthetic CaP-based biomaterials are produced and have been extensively used for dental and orthopaedic applications. This is justified by their biocompatibility, osteoconductivity and osteoinductivity (i.e. the intrinsic material property that initiates de novo bone formation), which are attributed to the chemical composition, surface topography, macro/microporosity and the dissolution kinetics. However, the exact molecular mechanism of action is unknown. This review paper first summarizes the most important aspects of bone biology in relation to CaP and the mechanisms of bone matrix mineralization. This is followed by the research findings on the effects of calcium (Ca²⁺) and phosphate (PO₄³⁻) ions on the migration, proliferation and differentiation of osteoblasts during in vivo bone formation and in vitro culture conditions. Further, the rationale of using CaP for bone regeneration is explained, focusing thereby specifically on the material's osteoinductive properties. Examples of different material forms and production techniques are given, with the emphasis on the state-of-the art in fine-tuning the physicochemical properties of CaP-based biomaterials for improved bone induction and the use of CaP as a delivery system for bone morphogenetic proteins. The use of computational models to simulate the CaP-driven osteogenesis is introduced as part of a bone tissue engineering strategy in order to facilitate the understanding of cell-material interactions and to gain further insight into the design and optimization of CaP-based bone reparative units. Finally, limitations and possible solutions related to current experimental and computational techniques are discussed.

Severe maxillary atrophy treatment with Le Fort I, allografts, and implant-supported prosthetic rehabilitation

PURPOSE

Recently, several authors have described that autologous and fresh-frozen bones are effective materials to correct jaw bone defects before endosseous implant positioning. The aim of this study was to report a multistep oral rehabilitation of severe atrophic maxilla by means of Le Fort I osteotomy for maxillary downward and forward repositioning, allografts, implant insertion, and prosthetic loading.

METHODS

Patients with severe maxillary atrophy underwent Le Fort I osteotomy associated to fresh-frozen interpositional bone allografts. At 7 months after reconstructive procedure, 2 biopsies for each patient have been taken, and in the same surgical procedure, endosseous implants were placed. Five months afterward, abutments were connected for the final prosthodontic restauration. Each patient was evaluated at 1-year follow-up after prosthetic loading.

RESULTS

At 1-year follow-up after functional prosthetic loading, no infection of the allografts or implant failure has been reported. Clinical and radiologic follow-up showed no sign of bone resorption in all the osteotomic sites and in the grafted areas. Histological analysis showed evidence of allograft osteointegration and healing.

CONCLUSIONS

Multistep oral rehabilitation of severe atrophic maxilla with Le Fort and interpositional bone allografts represents a reliable surgical technique. According to this clinical, radiologic, and histologic reports, interpositional fresh-frozen bone allograft seems to be a valuable material for grafting jaw as it is cheaper than other materials and is safe, and it avoids donor site, decreasing the morbidity of the treatment

Osteoconductivity and osteoinductivity of NanoFUSE(®) DBM

Bone graft substitutes have become an essential component in a number of orthopedic applications. Autologous bone has long been the gold standard for bone void fillers. However, the limited supply and morbidity associated with using autologous graft material has led to the development of many different bone graft substitutes. Allogeneic demineralized bone matrix (DBM) has been used extensively to supplement autograft bone because of its inherent osteoconductive and osteoinductive properties. Synthetic and natural bone graft substitutes that do not contain growth factors are considered to be osteoconductive only. Bioactive glass has been shown to facilitate graft containment at the operative site as well as activate cellular osteogenesis. In the present study, we present the results of a comprehensive in vitro and in vivo characterization of a combination of allogeneic human bone and bioactive glass bone void filler, NanoFUSE(®) DBM. NanoFUSE(®) DBM is shown to be biocompatible in a number of different assays and has been cleared by the FDA for use in bone filling indications. Data are presented showing the ability of the material to support cell attachment and proliferation on the material thereby demonstrating the osteoconductive nature of the material. NanoFUSE(®) DBM was also shown to be osteoinductive in the mouse thigh muscle model. These data demonstrate that the DBM and bioactive glass combination, NanoFUSE(®) DBM, could be an effective bone graft substitute.

Craniofacial Bone Grafting: Wolff's Law Revisited

Bone grafts are used for the reconstruction of congenital and acquired deformities of the facial skeleton and, as such, comprise a vital component of the craniofacial surgeon's armamentarium. A thorough understanding of bone graft physiology and the factors that affect graft behavior is therefore essential in developing a more intelligent use of bone grafts in clinical practice. This article presents a review of the basic physiology of bone grafting along with a survey of pertinent concepts and current research. The factors responsible for bone graft survival are emphasized.

The efficacy of periosteal cells compared to chondrocytes in the tissue engineered repair of bone defects

We studied the efficacy of tissue generated from polymers seeded with periosteal cells and compared it to that of polymers seeded with chondrocytes, for its ability to repair surgically created cranial bone defects in rats. Large (approximately 40 mm2) bilateral defects were created in the parietal and temporal bones of 20 nude rats. One defect in each mouse was filled with synthetic biocompatible and biodegradable polymer templates seeded in vitro with either bovine periosteal cells (experimental group I) or chondrocytes (experimental group II). Contralateral defects were filled with either polymer not seeded with cells (control group I), or nothing at all (control group II). There was gross evidence of new bone formation repairing the defect in 7 of the 10 defects filled with polymers seeded with periosteal cells, while 8 of the 10 defects filled with polymers containing chondrocytes showed gross evidence of new cartilage formation covering the defect. Control defects showed no gross evidence of repair with either bone or cartilage.

A comparison of bone generation capability in rabbits using tooth ash and plaster of Paris with platelet-rich plasma or fibrin sealant

OBJECTIVES

Increased attention has been focused on determining the most efficacious materials for generalized bone grafts. This article presents the results of a histomorphometric analysis of bone healing in the calvaria of rabbits. The study compared the use of a tooth ash and plaster of Paris mixture alone, in association with platelet-rich plasma (PRP), and in association with fibrin sealant.

STUDY DESIGN

Twelve rabbits were divided into control (group 1) and experimental groups (groups 2, 3, and 4). Group 1 was maintained as an unfilled control, and tooth ash and plaster of Paris were used in group 2, tooth ash and plaster of Paris with PRP were used in group 3, and tooth ash and plaster of Paris with fibrin sealant (Tissucol Duo Quick) were used in group 4. One-half of the animals were killed after 4 weeks, and the rest were killed after 8 weeks. Bone samples were taken from the defect areas, and newly formed bone was analyzed histomorphometrically.

RESULTS

The rate of new bone formation in groups 2, 3, and 4 was significantly higher than the rate in the control group. The rate of new bone formation in groups 3 and 4 was higher than the rate in group 2, but the difference was not statistically significant.

CONCLUSION

The concomitant use of PRP or fibrin sealant with tooth ash and plaster of Paris graft materials may have a positive effect on bone healing.

Osteoconductivity and Osteoinductivity of Puros® DBM Putty

Bone graft substitutes have been developed due to the limited supply and morbidity associated with using autogenous graft material. Allogeneic demineralized bone matrix (DBM) has been used extensively as a clinical graft material because of its inherent osteoinductive and osteoconductive properties. Differential enhancement of these properties may optimize the performance of these products for various orthopedic and craniofacial applications. Commercially available bone paste products consist of formulations that combine DBM with a carrier to facilitate handling and containment. In the present study, we present results of a comprehensive in vitro and in vivo characterization of a 100% human DBM putty product, Puros DBM Putty. Results indicate the DBM particles are completely dispersed in the putty. Data are presented showing the porosity of and cell attachment to Puros DBM Putty, thereby demonstrating the osteoconductive properties of this DBM. Puros DBM Putty was also shown to be osteoinductive in the rat ectopic pouch model. We demonstrate here for the first time that Puros DBM Putty maintains its activity to markedly stimulate or induce bone formation over the entire period of its shelf life. Taken together, these data demonstrate that the 100% human allograft derived Puros DBM Putty could be an effective bone graft substitute.

Histological differences in iliac and tibial bone graft

BACKGROUND

Cancellous bone graft is frequently used during orthopedic procedures. While the iliac crest has traditionally been the most common donor site, the proximal tibia is an alternative donor site, especially for foot and ankle procedures. This study tested the null hypothesis that the histologic composition of iliac and tibial bone grafts is similar.

MATERIALS AND METHODS

Specimens from the iliac crest (n = 10) and tibia (n = 10) in excess of that needed for patients undergoing foot or ankle fusion were examined histologically. Iliac samples were taken from the anterior iliac crest. Tibial samples were harvested from the region of Gerdy's tubercle. Specimens were graded based on the percent of bone surfaces that opposed active hematopoietic marrow, with Grade I at 0%, through Grade VI at 81% to 100%. Differences between iliac and tibial grafts were evaluated with Fisher's Exact Test.

RESULTS

Iliac crest and tibial bone grafts both showed trabecular fragments with abundant osteocytes. All iliac grafts contained active hematopoietic marrow. In contrast, the medullary space of tibial grafts contained fat and little hematopoietic marrow. Nine iliac grafts were graded V or VI; whereas the ten tibial bone grafts were all graded I or II (p = 0.0001). The difference in the numbers of samples in each group ranked as grade VI was also statistically significant (p = 0.005).

CONCLUSION

Iliac bone grafts contained active hematopoietic marrow, whereas quiescent medullary fat predominated in tibial grafts.

CLINICAL RELEVANCE

These findings raise questions about the cellular contributions of different sources of bone graft to bone healing.

Effect of Tisseel on bone healing with particulate dentin and plaster of Paris mixture

OBJECTIVES

The purpose of this study was to evaluate the effect of Tisseel on the early healing of bone defects in the skulls of rats.

STUDY DESIGN

Forty-eight rats were randomly assigned to 4 groups, and each group was further divided into 3 subgroups which were examined at 4 and 8 weeks after the defects were filled. The 4 different groups were animals containing: no graft (group 1); particulate dentin and plaster of Paris mixture graft (group 2); Tisseel and particulate dentin and plaster of Paris mixture graft (group 3); and Tisseel graft (group 4). After killing the animals at 4 and 8 weeks after surgery, all implant blocks were prepared for histologic sections and histomorphometric analysis.

RESULTS

The overall new bone formation was significantly different between the 4-week samples and the 8-week samples. Significant differences between groups 1 and 2, groups 1 and 3, groups 1 and 4, groups 2 and 4, and groups 3 and 4 were observed at 4 weeks after surgery. At 8 weeks after surgery, significant differences between groups 1 and 2, groups 1 and 3, groups 1 and 4, and groups 2 and 4 were observed. As expected, effective bone formation was observed when the defects were filled with either particulate dentin, Tisseel, or particulate dentin-Tisseel combination. It was also observed from this study that particulate dentin is especially effective, followed by the particulate dentin-Tisseel combination and Tisseel.

CONCLUSION

It was concluded that the use of Tisseel may be an alternative therapy for regenerating bone in defects when used in combination with particulate dentin.

A novel poly(ethylene glycol)–fibrinogen hydrogel for tibial segmental defect repair in a rat model

The aim of this study is to investigate regeneration in a segmental bone defect using a novel fibrinogen-based hydrogel material. The use of hydrogels made from poly(ethylene glycol) (PEG) conjugated to fibrinogen for this purpose may be better to conventional fibrin-based materials as it offers an additional degree of control over the structural characteristics and biodegradation of the material. At the same time, it maintains some of the inherent biofunctionality of the fibrinogen molecule. PEGylated fibrinogen hydrogels with various degrees of proteolytic resistance based on PEG and fibrinogen composition were designed for slow, intermediate, and fast biodegradation. The hydrogels were implanted into 7-mm segmental rat tibial defects without additional osteoinductive factors with the rationale that the ingrowth matrix will displace the normal fibrin clot while sustaining a similar healing effect for a longer duration. Histological and X-ray results confirmed that the extent and distribution of newly formed bone in the defect after 5 weeks strongly parallels the biodegradation pattern of the implanted material. When compared to nonunions in animals treated with the fast-degrading implants and untreated control animals, the rats implanted with the intermediate-degrading material exhibited osteoneogenesis. This data supports the hypothesis that the perseverance of the PEGylated fibrinogen material can be synchronized with the optimal healing characteristics of a segmental osseous defect and that the consequent sustained release of fibrinogen fragments facilitates the osteogenic response at the injury site. The PEGylated fibrinogen material may, therefore, be a highly efficacious material for promoting the healing of bone defects and especially nonunion fractures.

Biological and biophysical principles in extracorporal bone tissue engineering. Part III

Over the last decade extracorporal bone tissue engineering has moved from laboratory to clinical application. The restoration of maxillofacial bones from cell harvesting through product manufacture and end-use has benefited from innovations in the fields of biomechanical engineering, product marketing and transplant research. Cell/scaffold bone substitutes face a variety of unique clinical challenges which must be addressed. This overview summarises the recent state of the art and future anticipations in the transplantation of extracorporally fabricated bone tissues.

Osteoclastogenesis on Tissue-Engineered Bone

Bone remodeling plays an important role in bone function. To date, bone tissue-engineering research has focused primarily on bone formation from osteoblasts. This study demonstrates that osteoclastogenesis can occur on a mineralized polymer scaffold. Porcine bone marrow-derived mesenchymal stem cells (pMSCs) and hematopoietic cells were isolated from the bone marrow of Yucatan minipigs (n = 3) and cultured separately. pMSCs were differentiated into osteoblasts, seeded on porous poly(D,L-lactic-co-glycolic acid) foams, and cultured in a rotating oxygen-permeable bioreactor system. Once the cell-polymer constructs had started to mineralize, the hematopoietic cells were added and cocultured to include osteoclastogenesis. The cultured constructs were evaluated by histochemical and microscopic examination. Our results show that osteoblasts and osteoclasts were successfully differentiated from bone marrow on the scaffolds. This is the first demonstration of osteoclast formation on mineralized polymer surfaces.

Induction of osteogenesis by demineralized homologous and xenograft bone matrix

The osteogenesis induction by demineralized bone matrix grafts remains as a challenge in the reconstructions of the mandible through homologous and xenografts or in implants in abdominal muscle. PURPOSE: Observed the behaviour of implants of demineralized bone matrix at the mandible (right side with homologous graft and left side with xenograft of pig). METHODS: Experimental study with homologous and heterologous implants of demineralized bone matrix at the mandible and in ectopic muscle at the Center of Experimental Surgery of Heliopolis Hospital, Hosphel, São Paulo, Brazil. In 6 white New Zeland rabbits, 46 grafts were performed being 23 with homologous (rabbit) and 23 with xenograft (pig). 12 homologous implants (6 at the right side of the mandible and 6 at abdominal muscle of the rabbit) and 12 heterologous implants of pigs (6 at the left side of the mandible and 6 at abdominal muscle rabbit) were performed with demineralized bone matrix. RESULTS: Osteogenesis was assessed through histologic features after 30 and 60 days. After 1 rabbit dead, osteogenesis (mandible) were detected in 9 of 11 (82%) rabbits that received homologous matrix, in spite of heterologous implants showed osteogenesis in 6 out of 11 (54%) (p=0,18). The abdominal muscle showed induced osteogenesis in 3 out of 11(27%) animals with homologous and 0% with heterologous implants (p=0,10). CONCLUSIONS: Osteogenesis induction through homologous grafts in rabbit mandible and abdominal muscle were more effective than xenografts.

Restoration of large bone defects using a hard-setting, injectable putty containing demineralized bone particles compared to cancellous autograft bone

An injectable, hard-setting, calcium sulfate-based putty containing demineralized bone matrix particles (AlloMatrix II, Wright Medical Technology, Inc, Arlington, Tenn) was compared to autogenous cancellous bone graft to evaluate healing in a canine model. Area fraction of new bone, modulus of elasticity, and compressive strength of new bone were evaluated, as was radiographic and histologic healing. Bilateral defects were created in the proximal humeri, and each defect was implanted with either the putty or autogenous bone according to a randomized schedule. Dogs were euthanized at 6, 13, and 26 weeks. The area fraction, modulus of elasticity, and compressive strength of newly formed bone was not significantly different between the putty and autogenous bone at 6, 13, or 26 weeks. The putty had excellent handling characteristics, was biocompatible, and was as effective as autograft bone in achieving near complete bony restoration of a large, critical-sized defect.

Cranioplasty using allogeneic perforated demineralized bone matrix with autogenous bone paste

The efficacy of allogeneic perforated demineralized bone matrix with autogenous bone paste in the treatment of full-thickness cranial defects was evaluated in 10 consecutive patients between June 1998 and December 1998. The skull defects resulted from trauma in 9 patients and removal of a cranial tumor in 1 patient. The size of the skull defects ranged from 8 x 6 cm to 11 x 12.5 cm. Follow-up averaged 33 months for all patients. Postimplantation evaluations included serial photographs, repeated physical examination, and three-dimensional computed tomography for all patients. Visual inspection of the implanted biomaterial 6 months later was possible in 1 patient. The contour of the reconstructed skull was acceptable aesthetically without any secondary depression noted during the follow-up period. Three-dimensional computed tomographic scans taken 2 years after implantation indicated that the allogeneic perforated demineralized bone matrix provided a matrix for new bone formation with remarkable osteoinductive potential for new bone formation. The autogenous bone paste was able to caulk the demineralized bone matrix and fill the contour irregularities and gaps of the reconstructed cranium. The results from this clinical study indicated that allogeneic perforated demineralized bone matrix with autogenous bone paste is a promising alternative to an autogenous bone graft and or alloplastic material for cranioplasty.

Fibrin glue as an osteoinductive protein in a mouse model

Fibrin sealant or fibrin glue (FG) has been found to be effective as a wound-healing substance in surgery. However, its role in bone fracture healing and osseous tissue response is not fully understood. This ambiguity questions the potential of FG as an inductive protein. The present study was undertaken to evaluate the osteoinductive property of FG when coated with calcium phosphate and glass ceramics and implanted in the extraskeletal site of male Swiss albino mice. Implant materials used for this study were hydroxyapatite (HA) porous granules (300-350 microm), bioactive glass system (BGS)-AW type and calcium phosphate calcium silicate system (HABGS) non-porous granules (300-350 microm). Uncoated granules (control) and coated granules with 2.5 mg FG and 5 mg FG were implanted in the quadriceps muscle of mice and sacrificed after 28 days. Histologically, HA, BGS and HABGS implanted animal groups showed good healing response. However, neo-osteogenesis was observed only in the BGS and HABGS granules impregnated with FG. Furthermore, bone formation was observed to be more conspicuous in 5 mg FG coated BGS and HABGS granules when compared with 2.5 mg FG coated BGS and HABGS granules. Fluorochrome labeling proved that mineralization had already started by day 15 with FG preadsorbed BGS and HABGS granules. On the contrary, the uncoated granules did not show any de novo bone formation. This experimental study provides an evidence of the positive role of FG as a potential osteoinductive biologic tissue adhesive.

The science of tissue engineering

This article reviews the development of tissue engineering during the last decade. The science began to fully develop in association with efforts to combine viable cells with biocompatible material. The history and scope of this new field are presented. Basic principles of cell biology, materials, and technologies are discussed. Future challenges in the field are presented.

An overview of tissue engineered bone

Numerous important developments in tissue engineering of new bone during the last 10 years are reviewed. Early efforts to combine cells with biocompatible materials are described and applications of this technology are presented with particular focus on uses in orthopaedics and maxillofacial surgery. Basic principles of tissue engineering focusing on cell biology and materials science as used currently in the field are presented. Finally, future challenges are outlined from the perspective of integrating technologies from medicine, biology, and engineering in hopes of translating tissue engineering to clinical applications.

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.

Fixation of the craniofacial skeleton with butyl-2-cyanoacrylate and its effects on histotoxicity and healing

Butyl-2-cyanoacrylate is an easily applied, biocompatible, bioresorbable polymer glue that provides an alternative to conventional rigid fixation techniques. Our aim was to determine if cyanoacrylate fixation of the bone flap in a rabbit craniotomy model provides the healing and strength afforded by plate and screw fixation. We also investigated the inflammatory responses of adjacent tissues including the scalp, cranium, and brain. A unilateral parietal bone flap was elevated in 33 adult New Zealand rabbits. The bone was fixed in position with cyanoacrylate (n = 13), fixed with a microplate and screws (n = 14), or was replaced without fixation (sham-control, n = 6). Normal scar formation and no residual polymer were found in scalp specimens. Neuropathologic analysis identified the presence of residual polymer on the surface of 2 of the 13 rabbit brains. Histopathologic analysis of the bone flap-to-skull interface revealed no difference in the degree but rather in the quality of inflammation and healing between the plate and screw and polymer fixation groups. Microdensitometric analysis of the bone gap revealed nearly equivalent bone density in the cyanoacrylate and plated groups, tending to less density in the sham group (p = 0.11 and 0.09, respectively). An additional study focusing on neurotoxicity was performed in 20 adult rabbits with 3-week and 11-week recovery periods and similarly found the absence of a marked inflammatory response to the polymer. In conclusion, bone healing and soft-tissue inflammation were comparable between cyanoacrylate and plate and screw fixation groups. Although butyl-2-cyanoacrylate glue fixation may provide a reasonable alternative to hardware fixation, further investigations are necessary to identify its ideal utilization.

Bone induction using demineralized bone in the rabbit femur: a long-term study

While traditional bone grafting is the standard for replacement of segmental bony defects, alternative options (avoiding morbidity of autologous grafts) are attractive and continue to be sought. This study attempted to determine whether demineralized bone powder could be used reliably to replace a significant bony deficit at a weight-bearing site. The long-term functional characteristics of this induced bone were analyzed to determine whether it maintained its strength and shape and reacted normally to physiologic stress over an extended period of time (12 months). In 55 New Zealand White rabbits, a 1-cm length of femur was removed (approximately 20 percent of the total length of the rabbit femur). The femur was then reconstructed with a titanium mandibular plate, leaving the gap intact. In 38 of the animals, this gap was filled with demineralized bone powder in an attempt to induce bone to form across the defect. In group 1 (n = 23), the mandibular plate remained in place for the duration of the study (12 months). In group 2 (n = 15), the plate was removed 8 weeks after placement of the demineralized bone powder, and the animals were followed for an additional 12 months. In group 3 (n = 10), nothing was placed within the bony gap. In group 4 (n = 7), the gap was repaired with autologous bone graft. All the animals that received demineralized bone powder completely filled the osteotomy gap with new bone within 6 to 8 weeks after implantation. None of control group 3 formed bone across the gap (p < 0.001). Eighty-six percent of control group 4 (autologous bone graft) successfully formed bone across the osteotomy gap. In addition, 90 percent of control group 3 had hardware failure within 8 weeks after surgery compared with 0 percent (0 of 38) of the group that received demineralized bone powder (p < 0.001). In group 1, analysis after 12 months revealed that the bone formed ultimately became thin and easily fractured, most likely because of shielding from stress loading by the mandibular plate. In contrast, in group 2 (in which the plate was removed after 8 weeks), the bone remodeled and hypertrophied in response to the physiologic stress of weight bearing and at the end of the 12-month period was essentially identical to normal femur. In certain circumstances, reconstruction of bony defects using bone-induction techniques may be as good as autologous bone grafting, with the advantage of limiting the donor-site morbidity for the patient.

Integration of endochondral bone grafts in the presence of demineralized bone matrix

The use of endochondral bone grafts (EC) and demineralized bone matrix (DBM), which contains a potent osteoinductive matrix, may promote the repair of nonregenerative defects. The purpose of the current work is to assess qualitatively and quantitatively the effect of DBM on the healing of EC bone grafts and to compare it to the healing of EC bone grafts alone. Twenty-four defects in rabbit skulls were filled with EC bone grafts alone, DBM alone, or combined EC and DBM. Histologic and immunohistologic changes were examined in 2 weeks. The amount of new bone formation was quantified by image analysis. Healing of all the groups was characterized by the presence of a cartilage intermediate stage. In the EC bone grafts alone, healing was localized to the host bone/graft interface. In the composite group, amalgamation of the new bone, DBM, and bone graft progressed throughout the whole width and depth of the defect, uniting the graft to the recipient bed. The amount of new bone formed was significantly greater (47%) in the composite group than the EC group. In conclusion, DBM powder augments the bone-induction capacity of the recipient bed as well as the bone graft. The composite EC bone grafts and added DBM possess properties required for an effective graft material and merit further clinical evaluation.

Effect of Er:YAG laser holes on osteoinduction in demineralized rat calvarial allografts

Massive cortical autografts and allografts have been found to incorporate into host bone very slowly and thus are subject to complications such as fatigue fracture and infection. In order to understand and improve the process of osteogenesis in these types of bone grafts, a new experimental model was developed using bone discs from rat calvaria prepared by demineralization and drilling of 0.5 mm diameter holes with a pulsed, 2.94 microns wavelength Erbium:Yttrium-Aluminum-Garnet laser. Four types of bone discs were analyzed: untreated (Type I), demineralized (Type II), laser-ablated (Type III), and laser-ablated then demineralized (Type IV). The discs were transplanted into a subcutaneous site in adult Sprague-Dawley rats and followed for as long as 6 weeks. Histologic analysis of the discs at weekly intervals with use of hematoxylin and eosin staining confirmed the presence of new bone growth in Type-II and Type-IV discs. The amount of new bone growth in each disc was estimated by determining the mineral x-ray attenuation coefficient, which is proportional to mineral density, from digitized radiographs of the discs. The results showed that the processes of demineralization (P < 0.001) and laser ablation with demineralization (p < 0.05) were both significant in enhancing new bone growth in this model. This study demonstrated that osteoinduction can be fostered in cortical bone through the processes of demineralization and laser ablation. To the extent that laser ablation may allow maintenance of structural integrity while altering the surface geometry in such a way as to promote ingrowth of new bone, this experimental model represents an advance in understanding how osteogenesis in cortical bone grafts might be improved.

Application of purified bone morphogenetic protein (BMP) in cranio-maxillo-facial surgery. BMP in compromised surgical reconstructions using titanium implants

After a review of the clinically relevant literature on early modified whole bone products (demineralized bone; AAA bone (Urist et al., 1975))--predecessors of purified bone morphogenetic protein (BMP)--and a summary of the only published clinical experience with purified human BMP (in orthopedic surgery; from the group of Urist; Johnson et al., 1988-1992), an introductory overview of our experience with our own preparations of BMP from bovine bone in 271 procedures on the face and cranium in 145 patients is presented. In this first article of a series of three, major preprosthetic reconstructions using iliac bone grafts and titanium screw implants are described. All patients are examples of compromised bone and/or soft tissue conditions and cannot be considered routine indications for the operations performed. The most endangered implants became osseointegrated after 6 to 8 1/2 months as judged from clinical examination and CT imaging. These results demonstrate the efficacy of purified, concentrated BMP preparations, able unequivocally to induce bone even in areas with seemingly lost implants.

Biodegradation and bioresorption of calcium phosphate ceramics

The use of several calcium phosphate (Ca-P) materials for bone repair, augmentation, substitution and as coatings on metal implants has gained clinical acceptance in many dental and medical applications. These Ca-P materials may be of synthetic or natural origin, available in different physical forms (dense or macroporous, particles or blocks) and are used in bulk as coatings for metallic and non-metallic substrates or as components in composites, cements and bioactive glasses. Biodegradation or bioresorption of calcium phosphate materials implies cell-mediated degradation in vitro or in vivo. Cellular activity during biodegradation or bioresorption occurs in acid media; thus the factors affecting the solubility or the extent of dissolution (which in turn depends on the physico-chemical properties) of the Ca-P materials are important. Enrichment of the microenvironment due to the release of calcium and phosphate ions from the dissolving Ca-P materials affects the proliferation and activities of the cells. The increase in the concentrations of the calcium and phosphate ions promotes the formation of carbonate apatite which are similar to the bone apatite. The purpose of this invited paper is to discuss the processes of biodegradation or bioresorption of Ca-P materials in terms of the physico-chemical properties of these materials and the phenomena involved including the formation of carbonate apatite on the surfaces and in the vicinity of these materials. This phenomenon appears to be related to the bioactivity of the material and the ability of such materials to directly attach to bone and to form a uniquely strong material-bone interface.

The use of fresh frozen allogeneic bone for maxillary and mandibular reconstruction

The use of fresh frozen bone (FFB) alone, or in combination with autogenous bone (AB), for bony augmentation of the maxilla and mandible in preparation for dental reconstruction with endosseous implants has been studied. Ten patients received FFB +/- AB for augmentation of a severely atrophic mandible (n = 6) or for reconstruction of a jaw defect secondary to trauma or tumor resection (n = 4). Average follow-up was 26.3 +/- 5.4 months. At the time of implant placement, the bone grafts were found to be firm in consistency, well incorporated, and well vascularized in all 10 patients. Twenty-nine endosseous implants were placed an average of 8.3 +/- 3.1 months following bone grafting. One implant failed and was replaced, and one implant remains buried as a nonfunctional unit. All patients have been restored prosthetically by means of 28 of the 29 implants. This preliminary study indicates that FFB may be used alone or in combination with autogenous bone for augmentation or reconstruction of the atrophic maxilla and mandible. The resultant ridge is adequate to support loaded endosseous implants. A potential disadvantage is the minimal risk of disease transmission.

Bone-inducing agent (BIA) from cultured human Saos-2 osteosarcoma cells

The Saos-2 line of human osteosarcoma cells was established in culture in 1975. These cells produce a large amount of alkaline phosphatase but little or no matrix in vitro, and are unable to grow when transplanted into athymic mice. We decided to test our local strain of Saos-2 cells for bone-inducing ability in the skeletal muscle of athymic mice by implanting freeze-dried, acetone-defatted cells, with and without a collagen carrier. A bone-inducing activity (BIA) thus was demonstrated in 88% of 90 implants of devitalized Saos-2 cells. In further studies, we have used guanidinium hydrochloride (Gu-HCl) to extract, solubilize, and remove the Saos bone-inducing agent(s) in an active state which when reprecipitated by aqueous dialysis was able to induce ultrastructurally typical endochondrial bone formation in nude mouse muscle in 92% of 48 implants. This preliminary report is offered to alert investigators to the presence of an extractable BIA in Saos-2 cells.

Bone-particle-impregnated bone cement: an in vivo weight-bearing study

To evaluate an experimental inorganic-bone-particle-impregnated bone cement, canine hip prostheses were implanted in dogs using a regular bone cement on one side and the experimental bone cement on the other. In a preliminary feasibility study, bone ingrowth into the resorbed bone-particle spaces was established 3 months after implantation in three dogs. In a more detailed study, twenty-eight (28) dogs were divided in four groups to delineate the effects of time on the phenomena of bony ingrowth. One month after implantation, active bone ingrowth into the bone cement was obvious. By 3 months postimplantation, the ingrowth appeared to have traversed the thickness of the bone-particle-impregnated cement. By the fifth month, most of the interconnected inorganic bone particles were replaced by new bone. At the end of a year, the ingrown bone was mature and negligible new bone activity was present. Biomechanical pushout tests closely corroborated the histologic observations. The maximum shear strength of the cement/bone interface of the experimental side reached 3.6 times that of the control side at 5 months postimplantation. No further improvements were seen at 12 months postimplantation. A viable bone/cement interface may result in a better orthopedic implant fixation system by combining the advantages of both cement for immediate rigidity and biological ingrowth for longterm stability.

Monkey bone matrix induces bone formation in the athymic rat, but not in adult monkeys

Demineralized bone matrix from young and adult monkeys was implanted intramuscularly for 6 weeks in athymic rats and adult monkeys. Cartilage and bone induction was evaluated by histology and calcium content. In the athymic rat, most implants induced cartilage or bone. In the monkeys, cartilage was formed only on rare occasions and there was no sign of bone formation. We conclude that (a) adult monkey bone matrix contains bone inductive properties; (b) these properties are not sufficient to induce bone formation in adult monkey muscle sites.

Chondroclasts in osteoneogenesis

Allogenic, demineralized bone powder (DBP) was implanted into rat rectus abdominis muscle to induce osteoneogenesis. The main induction steps are invasion of the implant by host mesenchyme cells, differentiation of cartilage, invasion by blood capillaries or angiogenesis, differentiation of osteoblasts and bone marrow. The result is the formation of a cancellous ossicle. Giant polykarions appear in the implant after calcification of the cartilage matrix. As the DBP particles are not resorbed in the implant, these polykarions could either be foreign body giant cells brought about in reaction to foreign matrix or chondroclasts which resorb the cartilage. The results obtained by histological and histochemical methods (McNeals-von Kossa stain, tartrate resistant acid phosphatase reaction), as well as ultrastructural studies, lead to the conclusion that these large polynucleated cells are chondroclasts.

Calvarial bone regeneration using osteogenin

This experimental study reports on the application of a partially purified noncollagenous protein extracted from cortical bone to restore craniotomy defects in Papio species (baboon). The partially purified protein (osteogenin) produced significantly more bone formation in calvarial wounds than was found in the untreated controls. There were no adverse tissue reactions from the implanted xenogeneic osteogenin.

Cranial bone grafts for post-traumatic facial defects

Recent interest in onlay cranial bone grafts has shown it to be a preferred technique in the reconstruction of facial defects. This paper reports seven patients in whom outer table cranial bone grafts were used to reconstruct post-traumatic facial deformities. These included orbital and zygomatic deformities (2 patients), maxillary defects (2 patients), mandibular defects (2 patients), and nasal deformity (1 patient). A brief review of the development of membranous bone grafting for maxillofacial reconstruction is given. Good cosmetic results were obtained in six of seven patients with no evidence of graft resorption. One patient required removal of the graft because of inadequate soft tissue coverage. No patient suffered any significant donor site morbidity. In summary, this technique is extremely useful in treating post-traumatic bony deformities of the facial skeleton. The excellent graft survival and ease in harvesting the graft make this technique preferable to traditional endochondral grafts taken from the iliac crest and rib.