Ultrastructural identification of cells involved in the healing of intramembranous and endochondral bones

Repair processes of flat bones formed via intramembranous versus endochondral ossification

OBJECTIVES

Although fractures occur in various bones, including long, short, and flat bones, fracture repair investigations focus on the diaphysis of the long bone. The cell composition, osteogenic capacity, and bone matrix differ among osteogenesis patterns. However, the differences in the bone repair process have not been studied. Here, we compared the bone repair processes in the parietal bone and scapula of adolescent mice.

METHODS

Bone apertures were created in the parietal bone and scapula. Samples were collected at indicated times after surgery, and the repair process was analyzed using micro-computed tomography, histological, immunohistochemical, and mRNA expression analyses.

RESULTS

In both repair processes, cartilage formation was not detected on the periosteum side. The parietal bone aperture was gradually filled with newly formed bone produced from the edge of the aperture by day 14 but was not completely repaired even by day 49. In the scapula, a bony callus was detected on the periosteum at day 7, and the aperture was bridged by day 14. Subsequently, the bony callus was remodeled to the original bone architecture. Alkaline phosphatase activity and osteocalcin synthesis occurred earlier in the repair region of the scapular periosteum, compared with that in the parietal periosteum. The mRNA expression of osteogenic markers in the periosteum was markedly upregulated in the scapula versus the parietal bone.

CONCLUSION

Our study findings clarify the differences between parietal bone and scapula repair and suggest that the bone repair process differs among ossification patterns.

Inter-trabecular bone formation: a specific mechanism for healing of cancellous bone

Background and purpose - Studies of fracture healing have mainly dealt with shaft fractures, both experimentally and clinically. In contrast, most patients have metaphyseal fractures. There is an increasing awareness that metaphyseal fractures heal partly through mechanisms specific to cancellous bone. Several new models for the study of cancellous bone healing have recently been presented. This review summarizes our current knowledge of cancellous fracture healing. Methods - We performed a review of the literature after doing a systematic literature search. Results - Cancellous bone appears to heal mainly via direct, membranous bone formation that occurs freely in the marrow, probably mostly arising from local stem cells. This mechanism appears to be specific for cancellous bone, and could be named inter-trabecular bone formation. This kind of bone formation is spatially restricted and does not extend more than a few mm outside the injured region. Usually no cartilage is seen, although external callus and cartilage formation can be induced in meta-physeal fractures by mechanical instability. Inter-trabecular bone formation seems to be less sensitive to anti-inflammatory treatment than shaft fractures. Interpretation - The unique characteristics of inter-trabecular bone formation in metaphyseal fractures can lead to differences from shaft healing regarding the effects of age, loading, or drug treatment. This casts doubt on generalizations about fracture healing based solely on shaft fracture models.

Combined orthodontic-periodontal treatment in periodontal patients with anteriorly displaced incisors

INTRODUCTION

Flared and elongated incisors are associated with different types of periodontal bone defects, usually horizontal. Combined orthodontic-periodontal treatment is being used in periodontal patients with anterior displacement of the incisors. The purpose of this study was to investigate the changes in periodontal health and the shape of bone defects in the incisors after such combined treatment.

METHODS

Fourteen adults were included in the study. In total, 56 elongated maxillary incisors with horizontal bone defects received orthodontic-periodontal treatment with circumferential supracrestal fibrotomy. To improve bone morphology, periodontal regenerative surgery and guided tissue regeneration were performed on the anterior teeth with angular bone defects after orthodontic treatment. Cone-beam computed tomography scans were taken before treatment (T0), at the end of the orthodontic intrusion (T1), and 6 months after the guided tissue regeneration surgery (T2). Probing pocket depth and clinical attachment loss were examined at T0, T1, and T2. The data were analyzed using paired t tests.

RESULTS

From T0 to T1, clinical attachment loss decreased significantly by 0.29 mm (P <0.05). The distance from the cementoenamel junction to the marginal bone crest decreased by 0.66 mm (P <0.05). The labial side of alveolar bone thickness increased by 0.54 mm (P <0.05), and the lingual side of alveolar bone thickness decreased by 0.46 mm (P <0.05). The shape of the bone defect was changed from horizontal to vertical on some teeth. From T1 to T2, both probing pocket depth and clinical attachment loss improved significantly, and the radiographic examinations showed bone redepositions of 2.15 ± 0.68 mm (P <0.05) vertically and 1.44 ± 0.92 mm (P <0.05) horizontally. The distance from the most apical point of the bone defect to the cementoenamel junction after combined treatment decreased by 2.11 ± 1.30 mm (P <0.05).

CONCLUSIONS

Combined orthodontic-periodontal treatment improved the periodontal conditions of the defective bone sites. Bone morphology, altered by orthodontic intrusion with fibrotomy, can improve the results of subsequent guided tissue regeneration.

A special healing pattern in stable metaphyseal fractures

BACKGROUND AND PURPOSE

Metaphyseal fractures heal in a rapid fashion that is different from the bone shaft healing process. Animal studies have focused on diaphyseal fractures. We investigated the metaphyseal fracture-healing process in rabbits.

ANIMALS AND METHODS

60 rabbits (divided into 12 groups) underwent proximal tibial osteotomy, anatomical reduction, and fixation with screws. After surgery, the proximal tibiae were harvested at different time points for histology.

RESULTS

No obvious osteonecrosis or bone resorption were found 2 weeks after surgery. From day 5 to week 5, woven bone or new trabeculae formed. From week 2, remodeling into lamellar bone started and reached a peak at week 6. These 3 stages overlapped. Histomorphometry showed that the structure changed as a unimodal curve.

INTERPRETATION

The healing process of metaphyseal fractures appears to differ from the commonly studied healing process in diaphyseal fractures. It is rapid, and can be divided into 4 histological stages: cellular activation and differentiation, formation of woven bone, transformation of woven bone into lamellar bone, and further remodeling.

Endochondral ossification for enhancing bone regeneration: converging native extracellular matrix biomaterials and developmental engineering in vivo

Autologous bone grafting (ABG) remains entrenched as the gold standard of treatment in bone regenerative surgery. Consequently, many marginally successful bone tissue engineering strategies have focused on mimicking portions of ABG's "ideal" osteoconductive, osteoinductive, and osteogenic composition resembling the late reparative stage extracellular matrix (ECM) in bone fracture repair, also known as the "hard" or "bony" callus. An alternative, less common approach that has emerged in the last decade harnesses endochondral (EC) ossification through developmental engineering principles, which acknowledges that the molecular and cellular mechanisms involved in developmental skeletogenesis, specifically EC ossification, are closely paralleled during native bone healing. EC ossification naturally occurs during the majority of bone fractures and, thus, can potentially be utilized to enhance bone regeneration for nearly any orthopedic indication, especially in avascular critical-sized defects where hypoxic conditions favor initial chondrogenesis instead of direct intramembranous ossification. The body's native EC ossification response, however, is not capable of regenerating critical-sized defects without intervention. We propose that an underexplored potential exists to regenerate bone through the native EC ossification response by utilizing strategies which mimic the initial inflammatory or fibrocartilaginous ECM (i.e., "pro-" or "soft" callus) observed in the early reparative stage of bone fracture repair. To date, the majority of strategies utilizing this approach rely on clinically burdensome in vitro cell expansion protocols. This review will focus on the confluence of two evolving areas, (1) native ECM biomaterials and (2) developmental engineering, which will attempt to overcome the technical, business, and regulatory challenges that persist in the area of bone regeneration. Significant attention will be given to native "raw" materials and ECM-based designs that provide necessary osteo- and chondro-conductive and inductive features for enhancing EC ossification. In addition, critical perspectives on existing stem cell-based therapeutic strategies will be discussed with a focus on their use as an extension of the acellular ECM-based designs for specific clinical indications. Within this framework, a novel realm of unexplored design strategies for bone tissue engineering will be introduced into the collective consciousness of the regenerative medicine field.

Regulation of the osteoblastic and chondrocytic differentiation of stem cells by the extracellular matrix and subsequent bone formation modes

While various factors have been reported to direct stem cell differentiation lineage, little is known about how nature orchestrates the mesenchymal stem cell (MSC) differentiation and bone morphogenesis during skeleton development and bone regeneration. The present study reports that the matrix has a critical regulating effect on MSC differentiation and the subsequent bone formation modes. A simply combined hydroxyapatite (HA)-collagen matrix stimulates the MSC differentiation into the osteoblastic lineage and leads to a straightforward intramembranous bone formation mode, in contrast to the chondrocytic differentiation and endochondral mode observed on HA-synthetic hydrogel matrix. The accelerated MSC condensation and robust MSC-matrix and MSC-MSC interactions on collagen-based matrix might be the critical factors contributing to such events, likely through the orchestrated signal cascades and cellular events modulated by the extracellular matrix. The results demonstrate that matrix plays critical role in modulating the stem cell differentiation lineage and bone formation mode, which has been largely overlooked.

Bone regenerative properties of rat, goat and human platelet-rich plasma

To explore the reported contradictory osteogenic capacity of platelet-rich plasma (PRP), the aim of the study was to examine and compare the bone regenerative effect of: PRPs of different species (rat, goat, human); human bone graft (HB) vs. HB combined with human PRP (HB+hPRP); and HB+hPRP vs. synthetic hydroxyapatite-tricalcium phosphate bone substitute combined with hPRP (HA/TCP+hPRP). For this purpose, 72 implants, divided into 6 groups (n=6) were inserted in critical-sized defects of immunodeficient rats. After 2 and 4 weeks, descriptive and quantitative histological, and micro-CT analyses were performed on the specimens. Rat and goat PRP combined with HA/TCP did not enhance bone regeneration compared with HA/TCP. In contrast, human PRP combined with HA/TCP resulted in significantly increased bone fill compared to HA/TCP. The addition of human PRP to human bone graft increased significantly the amount of newly formed bone after 2 weeks. HB+hPRP demonstrated enhanced bone healing compared to HA/TCP+hPRP. In conclusion, rat and goat PRP had no effect on bone formation. Human PRP improved the initial osteogenic response of human bone graft. Human PRP combined with human bone graft had better osteogenic capacity than human PRP combined with synthetic bone substitute.

Particulate inlay nasal graft with immediate dental implant placement in a patient with repaired alveolar cleft: case report

Primary bone grafts in congenital cleft alveolus do not always provide sufficient bulk or height of bone for ideal placement of endosseous implants. Thus, maxillary sinus or nasal floor elevation and inlay bone grafts in previously grafted areas are not exceptions in the daily routine. This case report stresses the need of a detailed treatment plan and careful surgical management of nasal floor elevation with particulate autogenous bone graft to successfully provide the patient with osseointegrated prostheses.

Differences in matrix composition between calvaria and long bone in mice suggest differences in biomechanical properties and resorption: Special emphasis on collagen

The mammalian skeleton consists of bones that are formed in two different ways: long bones via endochondral ossification and flat bones via intramembranous ossification. These different formation modes may result in differences in the composition of the two bone types. Using the 2D-difference in gel electrophoresis technique and mass spectrometry, we analyzed the composition of murine mineral-associated proteins of calvaria and long bone. Considerable differences in protein composition were observed. Flat bones (calvariae) contained more soluble collagen (8x), pigment epithelium derived factor (3x) and osteoglycin (4x); whereas long bones expressed more chondrocalcin (3x), thrombospondin- 1 (4x), fetuin (4x), secreted phosphoprotein 24 (3x), and thrombin (7x). Although cystatin motifs containing proteins, such as secreted phosphoprotein 24 and fetuin are highly expressed in long bone, they did not inhibit the activity of the cysteine proteinases cathepsin B and K. The solubility of collagen differed which coincided with differences in collagen crosslinking, long bone containing 3x more (hydroxylysine)-pyridinoline. The degradation of long bone collagen by MMP2 (but not by cathepsin K) was impaired. These differences in collagen crosslinking may explain the differences in the proteolytic pathways osteoclasts use to degrade bone. Our data demonstrate considerable differences in protein composition of flat and long bones and strongly suggest functional differences in formation, resorption, and mechanical properties of these bone types.

Proteínas morfogenéticas ósseas associadas a osso esponjoso autógeno na reparação de falhas experimentais na calota craniana de coelhos (Oryctolagus cuniculus)

Foi avaliada a reparação óssea após implantação de proteínas morfogenéticas ósseas (BMP) em diferentes concentrações e períodos de observação, carreadas por auto-enxerto ósseo esponjoso (EOE), em falhas ósseas, produzidas na região fronto-parietal do crânio de 20 coelhas. A falha I não foi preenchida, a II foi completamente preenchida com 3mg de EOE e as falhas III, IV, V e VI foram preenchidas com EOE associado a 0,5; 1; 2 e 5mg de BMP, respectivamente. Nas avaliações mesoscópicas, post mortem, verificou-se que, independentemente do período de tratamento, o preenchimento ósseo iniciou-se a partir das bordas para o centro e do fundo para a superfície das falhas. Na falha I manifestou-se o menor preenchimento ósseo quando comparada com as demais falhas, em todos os períodos, e nas que receberam 2mg de BMP exibiu-se a melhor cobertura óssea. Microscopicamente, verificou-se que, aos sete dias, o preenchimento ósseo iniciou-se a partir das bordas e do fundo da lesão, com mobilização e diferenciação de células provenientes do periósteo e das meninges, respectivamente e, nas avaliações subseqüentes, a atividade osteoblástica originou-se, também, de "ilhas de ossificação" semelhantes a centros de ossificação, localizadas no centro da falha. A formação trabecular aumentou, proporcionalmente, com a concentração utilizada de BMP, e a aposição e organização óssea aumentaram com o tempo de observação. Verificou-se também a presença de tecido cartilaginoso. A BMP associada ao EOE contribuiu para a formação de novo tecido ósseo, promovendo maior mobilização, diferenciação e organização celular, e abreviou o tempo de formação óssea, sugerindo processo de ossificação endocondral. Os melhores resultados foram observados com a associação de 2mg de BMP a 3mg de enxerto, e a adição de BMP, mesmo em menor quantidade, determinou precocidade de formação óssea. A maior quantidade de BMP não determinou maior preenchimento ósseo.

Clinical results of localized alveolar ridge augmentation with bone grafts harvested from symphysis in comparison with ramus

Background and aims

Autogenous onlay bone grafting is a common procedure for alveolar ridge augmentation. It has been suggested that the amount of healed bone after this technique would be significantly less than the initial quantity. The aim of this study was to determine the relationship between the various parameters influencing the outcome of ridge augmentation procedures.

Materials and methods

Thirty-two patients, 17 males and 15 females (mean age 40 ± 8.66), requiring lateral ridge augmentation in the anterior maxilla were recruited. Bone grafts obtained from either the mandibular ramus or symphysis were grafted on the recipient site and the buccolingual dimensions of the edentulous ridge before and six months after the procedure were measured and the difference between them was considered as ridge augmentation (RA). Parameters including graft thickness (GT), graft area (GA) and donor site (DS) were also recorded.

Results

Onlay bone grafts, taken from mandibular and symphysis areas, significantly increased the buccolingual dimension of the alveolar ridge (mean 1.98 ± 1.22 mm, p< 0.001). However, the mean RA by symphysis grafts was significantly greater than ramus grafts (2.49 mm vs. 1.48 mm). There was also a significant correlation between graft thickness, surface area and the amount of bone augmentation.

Conclusion

Symphysis area provides thicker and larger grafts, which may result in a better clinical outcome in alveolar ridge augmentation.

Interdisciplinary treatment of localized juvenile periodontitis: A new perspective to an old problem

What can be done for a 17-year-old girl with localized juvenile periodontitis, a Class II malocclusion, and flared teeth? Is it possible to regain epithelial attachment and rebuild the bone architecture? Is it possible to achieve good esthetics and occlusion with conventional orthodontic treatment, or is an interdisciplinary approach needed? What sequence should be followed? What is the prognosis for the affected teeth in the long term? Our aim in this article was to review the literature and present a clinical case to shed more light on the subject.

Expression of bone morphogenetic proteins in normal human intramembranous and endochondral bones

Bone morphogenetic proteins (BMPs) are growth and differentiation factors that have been purified and widely accepted to be the most important regulators in the processes of bone formation. The aim of this study was to identify the BMPs that are expressed in normal human bone, and to investigate the specific pattern of BMP2-BMP9 expression in normal human intramembranous and endochondral bone to maintain homeostasis, as well as in ex vivo primary cell culture of human osteoblasts from intramembranous and endochondral bone. Semi-quantitative RT-PCR indicated that 2 types of bone of different embryological origin have distinct patterns of BMP expression. BMP3, 4, 7 and 8 were strongly expressed in normal intramembranous bone compared to endochondral bone, whereas BMP2 and 5 were highly expressed in endochondral bone. The expression of BMP9 and BMP15 in human bone was identified for the first time. From the very similar expression patterns of BMPs in fresh normal bone and ex vivo osteoblastic cell culture, it can be proposed that the different proportions of BMPs in normal human intramembranous and endochondral bone needed to maintain normal homeostasis.

Histologic and Ultrastructural Study on Statin Graft in Rabbit Skulls

PURPOSE

To study the early healing pattern of statin-induced osteogenesis, we examined the early histologic and ultrastructural pictures of bone defect healing with and without statin.

MATERIALS AND METHODS

Twenty-eight bone defects were created in the parietal bone of 14 New Zealand White rabbits. In the Statin Group of 7 rabbits, the defects were grafted with collagen matrix carriers mixed with statin solution. In the Collagen Matrix Group of 7 rabbits, the defects were grafted with collagen matrix carriers mixed with water for injection. The Statin Group and the Collagen Matrix Group were killed on day 1, 2, 3, 4, 5, 6, or 14 after surgery. Bone defects with surrounding tissues were prepared for histologic assessment. Bone defects of day 14 were also prepared for ultrastructural assessment.

RESULTS

New bone was formed on day 5 in the defects grafted with statin. No cartilage intermediate stage was detected. This occurred 1 day earlier than for those grafted with the carrier alone. The bone defects of day 14 showed that an abundance of bone was formed in the Statin Group and osteocytes were identified ultrastructurally.

CONCLUSIONS

This study supported statin-induced and accelerated bone formation locally.

VEGF-Activated Angiogenesis During Bone Regeneration

PURPOSE

The aim of this study was to investigate the influence of controlled release of recombinant human vascular endothelial growth factor (rhVEGF(165)) on angiogenesis and osteogenesis in a mandibular defect model.

MATERIAL AND METHODS

A total of 56 rabbits were operated and bicortical holes were placed at the lower border of the mandible. The defects were filled with type-I collagen, with collagen complexed with 0.8 mug rhVEGF(165), or left without any filling. After 3, 7, 14, and 28 days, specimens were taken and histologic, histomorphometric, and immunohistologic analyses were carried out concerning number of vessels, cross-sectional area of vessels, and area and density of regenerated bone.

RESULTS

Bone formation occurred in a typical centripetal direction and showed all stages of bone regeneration and maturation. New vessel formation took place in front of the osteogenic regeneration front. The number of vessels increased in all groups until day 14, followed by physiologic regression in the control groups as opposed to persisting high numbers in the study group. The area of newly formed bone showed no difference to the control group but the density of regenerated bone was significantly higher in the study group.

CONCLUSION

Blood vessels are an important component of bone formation and maintenance and the bone tissue differentiation is related to the local presence of blood vessels. The activation of angiogenesis using rhVEGF(165) leads to more intensive angiogenesis and bone regeneration.

Microarchitecture of rabbit mandibular defects grafted with intramembranous or endochondral bone shown by micro-computed tomography

The aim of this study was to assess the integration of intramembranous and endochondral autogeneous bone grafts into membranous bony defects, by analysing the microarchitectural changes of the grafted bone 3 months after grafting. Twelve critical size defects (15 x 10mm) were created in rabbit mandibles bilaterally. Six defects on the right side of the mandible were grafted with autogenous endochondral bone, and six on the left were grafted with intramembranous bone. Three months later, the defects were retrieved for imaging with micro-computed tomography (Micro-CT) and for radiographic and histological evaluation. Micro-CT showed that intramembranous bone gave more bone volume a larger, trabecular number and trabecular thickness (P<0.001), and that endochondral bone had more trabecular separation (P<0.001). These findings indicate that intramembranous bone grafts integrate better than endochondral bone grafts in three-dimensions when they are grafted into membranous bony defects.

Composite autogenous bone and demineralized bone matrices used to repair defects in the parietal bone of rabbits

We compared the amount of new bone produced by endochondral and intramembranous autogenous bone grafts in the presence of demineralized bone matrices (DBMs) prepared from intramembranous bone (DBM(IM)) or endochondral bone (DBM(EC)). Thirty-five bone defects were created in the parietal bone of 20 New Zealand White rabbits. In the experimental groups, 5 defects were grafted with endochondral bone, 5 with endochondral bone mixed with DBM(IM)) (EC-DBM(IM)), 5 with intramembranous bone mixed with DBM(IM)(IM-DBM(IM)) and 6 with endochondral bone mixed with DBM(EC)(EC-DBM(EC)). In the control groups, 10 defects were left alone (passive control) and 4 were grafted with rabbit skin collagen (active control). They were all killed on day 14 and the defects were prepared for histological study. Serial sections were cut across the whole defect. Quantitative analyses were made on 202 sections of the experimental groups by image analysis. A total of 414%, 708%, and 85% more new bone was formed in defects grafted with composite EC-DBM(IM), IM-DBM(IM)and EC-DBM(EC), respectively, than those grafted with endochondral bone alone (P<0.001). No bone was formed in either passive or active controls. In conclusion, demineralized bone matrices, particularly those derived from intramembranous bone, have extremely high osteoinductive properties and greatly improve the integration of autogenous bone grafts in the skull.

Does fetal antigen 1 (FA1) identify cells with regenerative, endocrine and neuroendocrine potentials? A study of FA1 in embryonic, fetal, and placental tissue and in maternal circulation

Fetal antigen 1 (FA1) is a circulating EGF multidomain glycoprotein. FA1 and its membrane-associated precursor is defined by the mRNAs referred to as delta-like (dlk), preadipocyte factor 1 (pref-1) or zona glomerulosa-specific factor (ZOG). Using a polyclonal antibody recognising both forms, the localisation of FA1/dlk was analysed in embryonic and fetal tissues between week 5 to 25 of gestation and related to germinal origin and development. FA1 was observed in endodermally derived hepatocytes, glandular cells of the pancreas anlage, and in respiratory epithelial cells. FA1 was also present in mesodermally derived cells of the renal proximal tubules, adrenal cortex, Leydig and Hilus cells of the testes and ovaries, fetal chondroblasts, and skeletal myotubes. Ectodermally derived neuro- and adenohypophysial cells, cells in the floor of the 3rd ventricle and plexus choroideus were also FA1 positive. The number of cells expressing FA1 decreased during fetal development where the expression became restricted to specific functional cells. Epidermis, gut epithelium, gall bladder, blood cells, spleen, thyroid gland, salivary glands, and smooth muscle cells were FA1 negative. Analysis of extra-embryonic tissues from normal and pathological pregnancies revealed FA1 in stromal cells surrounding the blood islands of the yolk sac as well as in placental fibroblasts where the expression was most pronounced in diploid, androgenic complete hydatidiform moles. However, as measured by ELISA, the circulating maternal FA1 levels in complete moles were not different from normal pregnancies. The results presented suggest that FA1 is a growth and/or differentiation factor extensively expressed in immature cells and down-regulated during fetal development. FA1 down-regulation was associated with a shift in the subcellular localisation indicating differential post-translational/post-transcriptional modifications during fetal development. FA1 may be a new marker of cellular subtypes with a regenerative potential and of specific cells with endocrine or neuroendocrine functions.

Clinical applications of composite intramembranous bone grafts

The aim of this article is to introduce the composite intramembranous bone graft mixed with demineralized bone matrix to the clinician and to demonstrate its various clinical applications in the field of clinical orthodontics in the form of case reports. Understanding the mechanism of healing of this composite bone graft provides sound experimental precedent that allows this graft material to become a predictable part of our future orthodontic management. The cases highlighted here took advantage of the several properties of the composite intramembranous demineralized bone matrix graft. An accidental loss of the buccal plate of bone occurred during extraction of a buccally placed premolar for orthodontic purposes. The defect was repaired using chin bone mixed with demineralized bone matrix, and the teeth were successfully moved into the grafted area. A 5-year follow-up showed a stable gingival condition at the grafted area. In this report, ridge augmentation with intramembranous demineralized bone matrix as an adjunct to orthodontic treatment allowed successful placement of endosseous implants. In conclusion, the same graft material was successfully used in the repair of a massive alveolar cleft. Long-term follow-up of these cases showed that this graft is a promising graft material that could be integrated into our orthodontic practice.

Healing of autogenous intramembranous bone in the presence and absence of homologous demineralized intramembranous bone

This study was designed to examine the osteogenecity of demineralized bone matrix (DBM) prepared from intramembranous (IM) bone and to quantitatively assess the amount of new bone formed by IM autogenous bone grafts with or without DBM(IM). Forty-two defects were created in 42 New Zealand White rabbits. Twenty-one defects were grafted with IM bone alone, and the other 21 defects were grafted with composite IM-DBM(IM). Eleven rabbits, 22 defects were used as controls, where 11 defects were left empty (passive control) and the other 11 defects were filled with rabbit skin collagen (active control). Tissues were retrieved on days 1, 2, 3, 4, 5, 6, 7, and 14 for qualitative and quantitative analysis. Cells involved in the healing of composite IM and IM-DBM(IM) bone grafts were identified. No cartilage cells were detected during the healing of either grafts. Appearance of small blood vessels into the newly formed matrix was seen on day 5 in IM bone grafts and on day 4 in composite IM-DBM(IM) bone graft. Quantitative analysis was performed by means of image analysis on 100 sections of tissues retrieved after 14 days. Approximately 204% more new bone was formed in defects grafted with composite IM-DBM(IM) than in those grafted with IM bone alone (P <.0001). No bone was formed across the defects in either active or passive controls. In conclusion, DBM(IM) significantly increases the osteogenicity of IM bone grafts.

Vascular endothelial growth pattern during demineralized bone matrix induced osteogenesis

The purpose of the current study was to determine the timely ingrowth of blood vessels associated with demineralized bone matrix (DMB) induced osteogenesis. Critical-size (10 x 5mm), full thickness bony defects in rabbit parietal bone were implanted with DBM. Histological and ultrastructural changes were examined 1, 2, 3, 4, 5, 6, 7 and 14 days later. Neovascularization was assessed by immunohistochemical staining for factor VIII antigen (marker for vascular endothelium) and also confirmed by staining using pan-endothelial antibody (CD31) (a marker for endothelium). Immunohistochemical evaluation revealed a positive staining for CD31 and Factor VIII expressed by endothelial cells by day 3 post grafting. By day 4, small blood vessels were first seen budding from host bed towards the grafted DBM. Ultrastructural identification of cells in the early stages of healing revealed the presence of macrophages. The monocyte-derived macrophage appears to play a central role in the repair process using DBM. Results of this study demonstrated a rapid vascularization during the DBM induced osteogenesis. This rapid vascularization is vital to the healing and bone induction ability of the DBM.