Early healing pattern of autogenous bone grafts with and without e-PTFE membranes: A histomorphometric study in rats

Beyond Bone Volume: Understanding Tissue-Level Quality in Healing of Maxillary vs. Femoral Defects

Currently, principles of tissue engineering and implantology are uniformly applied to all bone sites, disregarding inherent differences in collagen, mineral composition, and healing rates between craniofacial and long bones. These differences could potentially influence bone quality during the healing process. Evaluating bone quality during healing is crucial for understanding local mechanical properties in regeneration and implant osseointegration. However, site-specific changes in bone quality during healing remain poorly understood. In this study, we assessed newly formed bone quality in sub-critical defects in the maxilla and femur, while impairing collagen cross-linking using β-aminopropionitrile (BAPN). Our findings revealed that femoral healing bone exhibited a 73% increase in bone volume but showed significantly greater viscoelastic and collagen changes compared to surrounding bone, leading to increased deformation during long-term loading and poorer bone quality in early healing. In contrast, the healing maxilla maintained equivalent hardness and viscoelastic constants compared to surrounding bone, with minimal new bone formation and consistent bone quality. However, BAPN-impaired collagen cross-linking induced viscoelastic changes in the healing maxilla, with no further changes observed in the femur. These results challenge the conventional belief that increased bone volume correlates with enhanced tissue-level bone quality, providing crucial insights for tissue engineering and site-specific implant strategies. The observed differences in bone quality between sites underscore the need for a nuanced approach in assessing the success of regeneration and implant designs and emphasize the importance of exploring site-specific tissue engineering interventions. STATEMENT OF SIGNIFICANCE: Accurate measurement of bone quality is crucial for tissue engineering and implant therapies. Bone quality varies between craniofacial and long bones, yet it's often overlooked in the healing process. Our study is the first to comprehensively analyze bone quality during healing in both the maxilla and femur. Surprisingly, despite significant volume increase, femur healing bone had poorer quality compared to the surrounding bone. Conversely, maxilla healing bone maintained consistent quality despite minimal bone formation. Impaired collagen diminished maxillary healing bone quality, but had no further effect on femur bone quality. These findings challenge the notion that more bone volume equals better quality, offering insights for improving tissue engineering and implant strategies for different bone sites.

Unveiling the consequences of early human saliva contamination on membranes for guided bone regeneration

AIMS

GBR membranes have various surface properties designed to elicit positive responses in regenerative clinical procedures; dental clinicians attempt to employ techniques to prevent the direct interaction of contaminated oral fluids with these biomaterials. However, saliva is uninterruptedly exhibited in oral surgical procedures applying GBR membranes, suggesting a persistent interaction with biomaterials and the surrounding oral tissues. This fundamental study aimed to investigate potential alterations in the physical, chemical, and key biological properties of membranes for guided bone regeneration (GBR) caused by isolated early interaction with human saliva.

METHODS

A reproducible step-by-step protocol for collecting and interacting human saliva with membranes was developed. Subsequently, membranes were evaluated for their physicochemical properties, protein quantification, DNA, and 16S rRNA levels viability of two different cell lines at 1 and 7 days, and ALP activity. Non-interacted membranes and pure saliva of donors were applied as controls.

RESULTS

Qualitative morphological alterations were noticed; DNA extraction and 16S quantification revealed significantly higher values. Furthermore, the viability of HGF-1 and MC3T3-E1 cells was significantly (p < .05) reduced following saliva interaction with biodegradable membranes. Saliva contamination did not prejudice PTFE membranes significantly in any biological assay.

CONCLUSIONS

These outcomes demonstrated a susceptible response of biodegradable membranes to isolated early human saliva interaction, suggesting impairment of structural morphology, reduced viability to HGF-1 and MC3T3-E1, and higher absorption/adherence of DNA/16S rRNA. As a result, clinical oral procedures may need corresponding refinements.

The Effect of Different Types of Collagen Membranes on Peri-Implant Dehiscence Defects

AIM

This experimental study aimed to compare the bone-implant contact (BIC) following guided bone regeneration with 3 bioabsorbable collagen membranes on peri-implant dehiscence defects.

METHODS

Forty-eight standard dehiscence defects were created in the sheep iliac bone crest, and dental implants were placed into the defects. With the guided bone regeneration technique, the autogenous graft was placed into the defect and covered with different types of membranes: Geistlich Bio-Gide, Ossix Plus, and Symbios Prehydrated were covered. One group was left without a membrane as the control group (C) by applying only an autogenous graft. After recovery periods of 3 and 6 weeks, the experimental animals were sacrificed. Histologic sections were prepared by a nondecalcified method, and BIC was examined.

RESULTS

There was no statistically important difference between groups in the third week ( P >0.05). A statistically significant difference between groups was found in the sixth week ( P <0.01). Bone-implant contact values of the C group were significantly lower than those of the Geistlich Bio-Gide and Ossix Plus groups ( P <0.05). There was no statistically significant difference between control and Symbios Prehydrated groups ( P >0.05). In all sections, osseointegration was observed, with no signs of inflammation, necrosis, or foreign body reaction.

CONCLUSION

In our study, it has been concluded that the resorbable collagen membranes used in treating peri-implant dehiscence defects might affect the BIC, and the success varies according to the type of membrane used.

Viable cryopreserved human bone graft exhibit superior osteogenic properties in mandibular lateral augmentation

Lack of bone volume to place dental implants is frequently a problem in the reconstruction of edentulous patients. Even though autografts are the gold standard for jaw regeneration, morbidity associated with the harvesting site stimulates the demand for other substitutes. The aim of this study is to characterize the incorporation and the osteogenic ability of a viable cryopreserved human bone graft (VC-HBG) in the mandibular augmentation in rats. Bone chips from fresh human vertebrae cadaveric donors were processed, cryoprotected and deep-frozen at - 80 °C maintaining its cell viability. A jaw augmentation model was used in 20 athymic nude rats allocated into 2 groups to either receive the VC-HBG or an acellular graft as control (A-HBG). The assessment of the grafts' incorporation was performed at 4 and 8 weeks by micro-CT, histomorphometry and immunohistochemistry. Bone volume gain was significantly higher for the VC-HBG group at both time points. At 4 weeks, the A-HBG group presented significantly higher mineral density, but at 8 weeks, the VC-HBG group showed significantly higher values than the A-HBG. There was no statistical difference between VC-HBG and A-HBG groups at 4-weeks for remaining graft particles, while at 8 weeks, the VC-HBG group showed significantly less graft remnants. Collagen I, osteopontin and tartrate-resistant acid phosphatase expression were significantly higher in the VC-HBG group at both time points, while osteocalcin expression was significantly higher in the VC-HBG group at 8-weeks compared to the A-HBG group. This experimental research demonstrated that the VC-HBG shows positive osteogenic properties, greater bone formation, higher rate of bone remodeling and a better overall incorporation in rats' mandibles compared to the A-HBG.

Barrier membranes: More than the barrier effect?

AIM

To review the knowledge on the mechanisms controlling membrane-host interactions in guided bone regeneration (GBR) and investigate the possible role of GBR membranes as bioactive compartments in addition to their established role as barriers.

MATERIALS AND METHODS

A narrative review was utilized based on in vitro, in vivo and available clinical studies on the cellular and molecular mechanisms underlying GBR and the possible bioactive role of membranes.

RESULTS

Emerging data demonstrate that the membrane contributes bioactively to the regeneration of underlying defects. The cellular and molecular activities in the membrane are intimately linked to the promoted bone regeneration in the underlying defect. Along with the native bioactivity of GBR membranes, incorporating growth factors and cells in membranes or with graft materials may augment the regenerative processes in underlying defects.

CONCLUSION

In parallel with its barrier function, the membrane plays an active role in hosting and modulating the molecular activities of the membrane-associated cells during GBR. The biological events in the membrane are linked to the bone regenerative and remodelling processes in the underlying defect. Furthermore, the bone-promoting environments in the two compartments can likely be boosted by strategies targeting both material aspects of the membrane and host tissue responses.

Influence of Cigarette Smoke Inhalation on an Autogenous Onlay Bone Graft Area in Rats with Estrogen Deficiency: A Histomorphometric and Immunohistochemistry Study

PURPOSE

The present study aimed to evaluate the influence of cigarette smoke inhalation on an autogenous onlay bone graft area, either covered with a collagen membrane or not, in healthy and estrogen-deficient rats through histomorphometry and immunohistochemistry.

MATERIALS AND METHODS

Sixty female rats (Wistar), weighing 250-300 g, were randomly divided and allocated into groups (either exposed to cigarette smoke inhalation or not, ovariectomized and SHAM). After 15 days, the test group underwent cigarette smoke inhalation. Sixty days after exposition, autogenous bone grafting was only performed on all right hemimandibles, and the left ones underwent autogenous onlay bone grafting with the collagen membrane (BioGide^®). The graft was harvested from the parietal bone and attached to the animals' jaws (right and left). They were euthanized at 21, 45, and 60 days after grafting. Histological measurements and immunohistochemical analyses were performed, and results were submitted to a statistical analysis.

RESULTS

The addition of a collagen membrane to the bone graft proved more efficient in preserving graft area if compared to the graft area without a collagen membrane and the one associated with cigarette smoke inhalation at 21 (p = 0.0381) and 60 days (p = 0.0192), respectively. Cigarette smoke inhalation combined with ovariectomy promoted a significant reduction of the autogenous graft area at 21 and 60 days. At 45 days, no statistically significant results were observed. In the immunohistochemical analysis, the ovariectomized and smoking subgroups, combined or not with collagen membrane, received moderate and intense immunolabeling at 21 days for Receptor Activator of Nuclear Factor Kappa-B Ligand (RANKL) (p = 0.0017 and p = 0.0381, respectively). For Osteoprotegerin (OPG), intense immunolabeling was observed in most subgroups under analysis at 60 days.

CONCLUSION

Smoking inhalation promoted resorption on the autogenous onlay bone graft, mainly when associated with ovariectomy. Furthermore, when associated with the collagen membrane, a lower resorption rate was observed if compared to the absence of the membrane.

Influence of Chromium-Cobalt-Molybdenum Alloy (ASTM F75) on Bone Ingrowth in an Experimental Animal Model

Cr-Co-Mo (ASTM F75) alloy has been used in the medical environment, but its use as a rigid barrier membrane for supporting bone augmentation therapies has not been extensively investigated. In the present study, Cr-Co-Mo membranes of different heights were placed in New Zealand white, male rabbit tibiae to assess the quality and volume of new bone formation, without the use of additional factors. Animals were euthanized at 20, 30, 40, and 60 days. Bone formation was observed in all of the cases, although the tibiae implanted with the standard membranes reached an augmentation of bone volume that agreed with the density values over the timecourse. In all cases, plasmatic exudate was found under the membrane and in contact with the new bone. Histological analysis indicated the presence of a large number of chondroblasts adjacent to the inner membrane surface in the first stages, and osteoblasts and osteocytes were observed under them. The bone formation was appositional. The Cr-Co-Mo alloy provides a scaffold with an adequate microenvironment for vertical bone volume augmentation, and the physical dimensions and disposition of the membrane itself influence the new bone formation.

Premaxillary Osteotomy and Guided Tissue Regeneration in Secondary Bone Grafting in Children with Bilateral Cleft Lip and Palate

Objective:

To introduce a surgical technique for secondary alveolar bone grafting performed in conjunction with premaxillary osteotomy and guided tissue regeneration in children with bilateral clefts. This paper also looks at the outcomes of this surgery in a series of 15 consecutive patients.

Methods:

Secondary alveolar bone grafting (with a premaxillary osteotomy and guided tissue regeneration with a collagen membrane) is usually carried out in the mixed dentition stage. This retrospective study used patients’ medical records, radiographs, and clinical examination to assess the outcome of the surgery. Patients were followed up for an average of 3 years.

Results:

Bone grafting was successful in all cases. No premaxillae were lost and there was no long-term morbidity of the donor site. Radiographic assessment of the bone heights showed an average of 94% retention, 3 months postoperatively. Preliminary assessment of maxillary canine eruption is encouraging, with 79% being fully erupted in those patients who are at least 3 years post–bone grafting.

Conclusion:

Premaxillary osteotomy allows repositioning of the premaxilla to its optimal preplanned position and successful closure of all fistulae. We have found that use of a collagen membrane is a useful adjunct.

A description of the sequence of long-term behavior of autogenous boneblock in maxillary sinus augmentation in sheep: Additional morphologic and histomorphometric evidence

OBJECTIVE

To document the behavior of autogenous bone block in sinus lift and surgical consequences.

STUDY DESIGN

Twelve sinus lifts with autogenous hip bone blocks and simultaneous insertion of two implants in 6 adult female sheep. Polychrome sequential labelling and histologic and histomorphometric evaluation after 6, 16, and 26 weeks.

RESULTS

Augmentation material in the apical third was almost fully resorbed after 26 weeks (P = .00388). Percentage of bone tissue increased 0.5-1.0 mm from the implant in crestal region (15.3 ± 7.5% to 16.2 ± 10.1%), whereas it vanished in the apical region from 16 to 26 weeks (4.2 ± 10.4% to 0%) (P = .363).

CONCLUSIONS

Autogenous bone block leaves an apical thin but functionally crucial layer covering implants in a form follows function way. Denial of animal-originated biomaterials and prion diseases remain a rarely discussed issue. The use of an implant length-adapted autogenous transplant with osseoinductive advantages should be taken into consideration.

Guided bone regeneration: materials and biological mechanisms revisited

Guided bone regeneration (GBR) is commonly used in combination with the installment of titanium implants. The application of a membrane to exclude non‐osteogenic tissues from interfering with bone regeneration is a key principle of GBR. Membrane materials possess a number of properties which are amenable to modification. A large number of membranes have been introduced for experimental and clinical verification. This prompts the need for an update on membrane properties and the biological outcomes, as well as a critical assessment of the biological mechanisms governing bone regeneration in defects covered by membranes. The relevant literature for this narrative review was assessed after a MEDLINE/PubMed database search. Experimental data suggest that different modifications of the physicochemical and mechanical properties of membranes may promote bone regeneration. Nevertheless, the precise role of membrane porosities for the barrier function of GBR membranes still awaits elucidation. Novel experimental findings also suggest an active role of the membrane compartment per se in promoting the regenerative processes in the underlying defect during GBR, instead of being purely a passive barrier. The optimization of membrane materials by systematically addressing both the barrier and the bioactive properties is an important strategy in this field of research.

Immunolocalization of markers for bone formation during guided bone regeneration in osteopenic rats

Objective

The aim of this paper was to evaluate the repair of onlay autogenous bone grafts covered or not covered by an expanded polytetrafluoroethylene (e-PTFE) membrane using immunohistochemistry in rats with induced estrogen deficiency.

Material and Methods

Eighty female rats were randomly divided into two groups: ovariectomized (OVX) and with a simulation of the surgical procedure (SHAM). Each of these groups was again divided into groups with either placement of an autogenous bone graft alone (BG) or an autogenous bone graft associated with an e-PTFE membrane (BGM). Animals were euthanized on days 0, 7, 21, 45, and 60. The specimens were subjected to immunohistochemistry for bone sialoprotein (BSP), osteonectin (ONC), and osteocalcin (OCC).

Results

All groups (OVX+BG, OVX+BMG, SHAM+BG, and SHAM+BMG) showed greater bone formation, observed between 7 and 21 days, when BSP and ONC staining were more intense. At the 45-day, the bone graft showed direct bonding to the recipient bed in all specimens. The ONC and OCC showed more expressed in granulation tissue, in the membrane groups, independently of estrogen deficiency.

Conclusions

The expression of bone forming markers was not negatively influenced by estrogen deficiency. However, the markers could be influenced by the presence of the e-PTFE membrane.

Bone Augmentation in Rabbit Tibia Using Microfixed Cobalt-Chromium Membranes with Whole Blood and Platelet-Rich Plasma

Background: Bone augmentation is a subject of intensive investigation in regenerative bone medicine and constitutes a clinical situation in which autogenous bone grafts or synthetic materials are used to aid new bone formation. Method: Based on a non-critical defect, Co-Cr barrier membranes were placed on six adult Fauve de Bourgogne rabbits, divided into two groups: whole blood and PRP. Three densitometric controls were performed during the experiment. The animals were euthanized at 30, 45, 60, and 110 days. The presence of newly formed bone was observed. Samples for histological studies were taken from the augmentation center. Results: External and internal bone tissue augmentation was observed in almost all cases. Significant differences between PRP- and whole blood–stimulated bone augmentation were not observed. At 60 days, bones with PRP presented higher angiogenesis, which may indicate more proliferation and cellular activity. Conclusion: PRP activates the bone regeneration process under optimized conditions by stimulation of osteoblast proliferation after six weeks, when a significant difference in cellular activity was observed. Membranes could stimulate bone augmentation at the site of placement and in the surrounding areas.

Bone Replacement Materials and Techniques Used for Achieving Vertical Alveolar Bone Augmentation

Alveolar bone augmentation in vertical dimension remains the holy grail of periodontal tissue engineering. Successful dental implant placement for restoration of edentulous sites depends on the quality and quantity of alveolar bone available in all spatial dimensions. There are several surgical techniques used alone or in combination with natural or synthetic graft materials to achieve vertical alveolar bone augmentation. While continuously improving surgical techniques combined with the use of auto- or allografts provide the most predictable clinical outcomes, their success often depends on the status of recipient tissues. The morbidity associated with donor sites for auto-grafts makes these techniques less appealing to both patients and clinicians. New developments in material sciences offer a range of synthetic replacements for natural grafts to address the shortcoming of a second surgical site and relatively high resorption rates. This narrative review focuses on existing techniques, natural tissues and synthetic biomaterials commonly used to achieve vertical bone height gain in order to successfully restore edentulous ridges with implant-supported prostheses.

Effect of periosteum attached to autogenous iliac block bone graft on bone resorption in rabbits

The purpose of this study was to evaluate the effect of the periosteum attached to an iliac block bone graft on resorption of the grafted bone. Twenty-one rabbits were used. Iliac bone was harvested with (experimental group) or without a periosteum (control group) and grafted on the rabbit calvarium and fixed with miniscrews. The animals were killed, and specimens were harvested at 1, 4, and 8 weeks after the surgery. Histologic examination and histomorphometry were done. Grafted bones were severely resorbed, and the overall shapes were changed in the control group. On the contrary, the overall shape of the grafted bone was maintained, although the grafted bone was resorbed in the experimental group. Moreover, there were no osteoclasts adjacent to the periosteum of the graft. These results suggest that the periosteum attached to grafted bone can help establish early revascularization and prevent the resorption of grafted bone.

A comparison study between periosteum and resorbable collagen membrane on iliac block bone graft resorption in the rabbit calvarium

BACKGROUND

To compare the different resorption patterns between resorbable membrane barrier and periosteum after iliac block bone grafting radiographically and histologically.

METHODS

Eighteen mature male rabbits weighing from 2.0 to 2.5 kg were used. The recipient site was the rabbit skull, and autogenous iliac bone was used as the grafting material. The harvested iliac block bones were divided in the following groups: autogenous iliac block bone with preservation of the periosteum (the periosteum group), autogenous iliac block bone covered with a resorbable collagen membrane (Biomesh®, Samyang Co, Korea) after removing the periosteum (the collagen membrane group), and autogenous iliac block bones with removal of the periosteum (the control group). In each experimental group, periosteum or resorbable collagen membrane of the donor site was fixed directed to the periosteum of the recipient site. The specimens were examined macroscopically, radiographically, histologically, and histomorphometrically at every 2, 4, and 8 weeks.

RESULTS

All groups presented excellent bone graft healing state without inflammation, dehiscence, or displacement. The radiolucency increased from mild to moderate in all groups over the experiment. The mean thickness of the upper end of the cortical iliac bone graft was statistically significantly different between the control group and the periosteum group, between the four-week and eight-week control group, and between the four- week and eight-week periosteum group (p & 0.05).

CONCLUSION

This study suggests that both the periosteum and the resorbable collagen membrane may help to prevent soft tissue infiltration into the bone graft and to reduce bone graft resorption compared to block graft alone.

Immunohistochemial study on the expression of von Willebrand factor (vWF) after onlay autogenous iliac grafts for lateral alveolar ridge augmentation

INTRODUCTION

The main problems of autogenous bone transplants are their unpredictable atrophy and their loss of structure. One key factor lies in the poor revascularization of simple onlay grafts. The the aim of this study was to evaluate the revascularization processes in autogenous bone grafts from the iliac crest to the alveolar ridge.

METHODS

In a sheep model, autogenous bone grafts were harvested from the iliac crest. A combination of a resorbable collagen membrane (CM) and deproteinized bovine bone material (DBBM) was used to modify the bone graft (experiment 2). This was compared with a simple onlay bone graft (control group, experiment 1). The amount of vessels in bone and connective tissue (CT), and the amount of CT were analyzed. The expression of von Willebrand factor (vWF) was compared between the two experimental groups using immunohistochemical analysis.

RESULTS

The ratio of the amount of vessels in bone and CT changed over time, and more vessels could be detected in bone at 12-16 weeks of graft healing. The number of vessels were significantly higher in experiment 2 than in experiment 1. More CT was found in experiment 1, whereas the amount of CT in both experiments decreased over time.

CONCLUSION

This study shows a more intensive and extensive revascularization in experiment 2, as significantly more vessels were detected. The decreased amount of CT in experiment 2 clarifies its clinical superiority.

Demineralization of the contacting surfaces in autologous onlay bone grafts improves bone formation and bone consolidation

BACKGROUND

Autologous bone grafts are usually well consolidated after 4 to 5 months but can be incompletely interlocked with the native bone. This study investigated the effect of acid demineralization of the graft-bed interface on graft consolidation.

METHODS

Onlay bone grafts were performed on the calvaria of 36 guinea pigs. Half of the animals had the graft-bed contacting surfaces demineralized with 50% citric acid (pH 1.0) for 3 minutes (test group). The other half received no demineralization (control group). The bone grafts were immobilized by a resorbable membrane glued to the recipient bed with cyanoacrylate. After 7, 30, and 90 days, specimens (n = 6) were obtained for light microscopy. Data from qualitative analysis and computerized histomorphometry were statistically processed at a significance level of 5%.

RESULTS

Osteogenesis was not seen at the interface after 7 days. After 30 days, the test group showed 34.39% ± 13.4% of the interface area filled with mineralized tissue, compared to 17.14% ± 8.6% in the control group (P = 0.026). After 90 days, the mean percentages of mineralized tissue at the interface in the test and control specimens were 54.00% ± 11.23% and 38.65% ± 7.76% (P = 0.041), respectively. Within groups, a higher percentage of the area filled with mineralized tissue was seen at 90 days compared to 30 days (P = 0.004 for control and 0.041 for test).

CONCLUSIONS

Demineralization of the contacting surfaces between autologous bone graft and bone bed improved new bone formation and bone consolidation. These data need to be confirmed in humans.

Role of oxidative and nitrosative stress in autogenous bone grafts to the mandible using guided bone regeneration and a deproteinized bovine bone material

The aim of this study was to evaluate the role of oxidative and nitrosative stress in autogenous bone grafts to the mandible based on immunohistochemical analysis.

MATERIAL AND METHODS

Using a well-established sheep model autogenous bone grafts were harvested form the iliac bone. A combination of a Collagen Membrane (CM) and Deproteinized Bovine Bone Material (DBBM) was used to cover the bone graft (Experiment 2). This modification was compared with simple onlay bone grafts (Experiment 1). Immunohistochemically, the expression of specific stable degradation products of oxidative and nitrosative stress was compared between the two experimental groups.

RESULTS

Specific markers for oxidative and nitrosative stress showed statistically significant differences in expression in the different experimental groups. The influence of oxidative and nitrosative stress on osteoblasts (OB), osteoclasts (OC), and osteocytes (OCy) was analysed. Experiment 2 showed increased expression of markers in OB and decreased expression in OC.

CONCLUSIONS

Taking the result of this study and reports from the literature into consideration grafts in Experiment 2 showed less resorption and atrophy, higher activity of OB and inhibition of OC, and less expression of Reactive Oxygen and Nitrogen Species (RONS) as markers of oxidative stress within the graft. These data illustrate the improved remodelling processes in grafts using CM and DBBM.

Immunolocalization of bone morphogenetic protein 2 during the early healing events after guided bone regeneration

OBJECTIVE

The objective of this study was to evaluate the immunolocalization of bone morphogenetic protein 2 (BMP-2) after autogenous block grafting covered or not with an e-PTFE membrane.

STUDY DESIGN

Forty-eight rats were divided into 2 groups, autogenous block graft (B) and autogenous block graft + e-PTFE membrane (MB), and were evaluated by immunohistochemistry at baseline and 3, 7, 14, 21, and 45 days.

RESULTS

The largest number of positive cells in the recipient bed was observed after 3 days in both groups. At the graft border, the largest number of positive cells was seen after 7 days in group B and after 14 days in group MB. The highest proportion of staining in the graft was observed after 3 days in group B and after 21 days in group MB.

CONCLUSIONS

High proportions of stain were related to intense revascularization and osteogenesis. Except for the interface, BMP-2 staining occurred later in group MB than in group B in all structures analyzed.

Events of wound healing/regeneration in the canine supraalveolar periodontal defect model

AIM

The objective of this research was to elucidate early events in periodontal wound healing/regeneration using histological and immunohistochemical techniques.

METHODS

Routine critical-size, supraalveolar, periodontal defects including a space-providing titanium mesh device were created in 12 dogs. Six animals received additional autologous blood into the defect prior to wound closure. One animal from each group was killed for analysis at 2, 5, 9, 14 days, and at 4 and 8 weeks.

RESULTS

Both groups behaved similarly. Periodontal wound healing/regeneration progressed through three temporal phases. Early phase (2-5 days): heterogeneous clot consolidation and cell activation in the periodontal ligament (PDL) and trabecular bone was associated with PDL regeneration and formation of a pre-osteoblast population. Intermediate phase (9-14 days): cell proliferation (shown by PCNA immunostaining)/migration led to osteoid/bone, PDL and cementum formation. Late phase (4-8 weeks): primarily characterized by tissue remodelling/maturation. Fibrous connective tissue from the gingival mucosa entered the wound early, competing with regeneration. By day 14, the wound space was largely filled with regenerative and reparative tissues.

CONCLUSION

Activation of cellular regenerative events in periodontal wound healing/regeneration is rapid; the general framework for tissue formation is broadly outlined within 14 days. Most bone formation apparently originates from endosteally derived pre-osteoblasts; the PDL possibly acting as a supplementary source, with a primary function likely being regulatory/homeostatic. Blood accumulation at the surgical site warrants exploration; supplementation may be beneficial.

Expression of growth factors during the healing process of alveolar ridge augmentation procedures using autogenous bone grafts in combination with GTR and an anorganic bovine bone substitute: an immunohistochemical study in the sheep

OBJECTIVES

This study aims to evaluate the expression of various immunohistochemical growth factors and vascularization markers in augmentation on the mandible comparing onlay bone grafts and Guided Bone Regeneration (GBR).

MATERIALS AND METHODS

Using a sheep in vivo model, autogenous bone grafts were harvested from the iliac crest. A combination of a resorbable collagen membrane (CM) and a Deproteinized Bovine Bone Material (DBBM) was performed. This modification of the host side was compared with an onlay bone graft control group. Expression of different vascularization markers was compared between these groups.

RESULTS

The expression of revascularization markers was significantly higher within the modification of the host side using GBR and DBBM. Regarding different graft regions, a significantly higher expression within the bone graft using GBR and DBBM could be observed in staining on bone morphogenetic protein-2 (BMP-2) (5.75 vs. 3.55), vascular endothelial growth factor (VEGF) (3.08 vs. 1.64), VEGF Receptor 1 (VEGFR-1) and VEGF Receptor 2 (VEGFR-2) (4.88 vs. 2.24 and 5.06 vs. 2.74), and endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) (5.29 vs. 3.28 and 5.22 vs. 3.09; p = 0.000, all others p < 0.05), whereas the control group showed a higher rate of resorption during the surveillance period until euthanasia of sheep after 16 weeks.

CONCLUSION

The use of GBR and DBBM in the transplantation process of autogenous bone grafts compared with the therapeutical use of certain growth factors may enhance vascularization and lower atrophy and resorption.

CLINICAL RELEVANCE

The use of a combination of GBR and DBBM in augmentation procedures on the mandible shows less resorption than simple onlay bone grafts and seems to be superior in a clinical use.

Evaluation of early healing events around mesenchymal stem cell-seeded collagen-glycosaminoglycan scaffold. An experimental study in Wistar rats

PURPOSE

Tissue engineering using cell-seeded biodegradable scaffolds offers a new bone regenerative approach that might circumvent many of the limitations of current therapeutic modalities. The aim of this experiment was to study the early healing events around mesenchymal stem cell-seeded collagen-glycosaminoglycan scaffolds.

METHODS

The 5-mm critical size defects were created in the calvarial bones of 41 Wistar rats. The defects were either left empty to serve as controls (n = 11), filled with cell-free scaffolds (n = 12), cell-seeded scaffolds that were maintained in standard culture medium (n = 9), or cell-seeded scaffolds that were maintained in osteoinductive factor-supplemented medium (n = 9). The animals were sacrificed at 7 days after surgery, and specimens were prepared for histological analysis. Early healing events such as host cell penetration, blood vessel in-growth, and scaffold integration were observed. The degree of inflammatory cell infiltrate was assessed.

RESULTS

While defects in the control group healed with a thin fibrous tissue, the collagen-glycosaminoglycan scaffold in the test groups preserved the three-dimensional form of the defects. After 7 days in vivo, the scaffold maintained its integrity and appeared populated with host cells. The cell-seeded scaffold induced more inflammatory response compared to the cell-free scaffolds. New blood vessels and areas of early bone formation were also evident in the cell-seeded scaffolds.

CONCLUSIONS

In conclusion, the findings show that mesenchymal stem cell-seeded collagen-glycosaminoglycan scaffolds have good tissue tolerance and exhibit an osteoinductive effect as indicated by early stage healing.

Influence of host periosteum and recipient bed perforation on the healing of onlay mandibular bone graft: an experimental pilot study in the sheep

PURPOSE

The aim of this study was to evaluate the role of host periosteum and recipient bed perforation on the healing of an onlay graft to the mandible based on histologic and immunohistochemical analysis.

MATERIALS AND METHODS

Each of the 12 adult sheep used in the study received four iliac corticocancellous onlay bone grafts on the lateral surface of the mandible. In experiment 1, the block graft was placed in direct contact with the recipient bed and fixed with micro-screws, and in experiment 2, the recipient cortical bed was perforated before graft placement. The host periosteum around the graft was excised before flap replacement in experiment 3, and in experiment 4, a sheet of silicone membrane was placed between the graft and the recipient bed. The animals were euthanised at 4, 8, 12 and 16 weeks after surgery and the findings were analysed by routine microscopy (haematoxylin and eosin and tartrate-resistant acid phosphatase [TRAP] stains) and immunohistochemistry for proliferation and apoptotic markers (Ki67, caspase-3 and TUNEL stains).

RESULTS

After 8 weeks, full graft-host integration was seen in all the experimental groups except experiment 4. After 16 weeks, pronounced graft resorption and volume reduction was observed in experiments 1 and 2, whilst experiment 3 was characterised with extensive connective tissue infiltration and severe resorption of the graft. The number of osteoclasts expressed peaked at 4 weeks in experiments 1 and 2 and at 16 weeks in experiment 3. Immunoreactivity for Ki67 by osteoblasts lining the trabecular bone of the graft's spongiosa expressed moderate level of Ki67 at 8 weeks, and thereafter declined markedly. The strongest expression of caspase-3 on the bone surface was observed after 16 weeks.

DISCUSSION AND CONCLUSION

Recipient cortical bed perforation offered no advantage over non-perforated bed regarding healing and integration of a bone graft. Excision of the host overlying the periosteum was accompanied with rapid absorption of the grafts and partial or complete replacement with fibrous connective tissue. This study also demonstrated that cell death by apoptosis is a fundamental component of osteoblastic phenotypic differentiation during healing of corticocancellous bone graft.

Healing of onlay mandibular bone grafts covered with collagen membrane or bovine bone substitutes: a microscopical and immunohistochemical study in the sheep

The objective of this study was to evaluate the role of collagen membrane and Bio-Oss coverage in healing of an onlay graft to the mandible. Twelve adult sheep each received an onlay bone graft (experiment 1), bone graft+Bio-Gide (experiment 2), and bone graft+Bio-Oss/Bio-Gide (experiment 3) on the lateral surface of the mandible. The animals were euthanized at 4, 8, 12 or 16 weeks after surgery, and findings were analysed by routine microscopy and immunohistochemistry for proliferation (Ki67) and apoptotic (Caspase-3) markers. Grafts were fully incorporated in all specimens. Pronounced resorption was observed in experiment 1. Minimal loss of graft volume was seen in experiment 2 specimens without membrane displacement. A remarkable increase in the augmented region of the mandible was observed in experiment 3. A high number of osteoclasts were expressed within the grafts during the early healing period, and thereafter declined markedly. Osteoblasts within the grafts expressed a moderate level of Ki67 at 8 weeks, which thereafter declined markedly. The strongest expression of Caspase-3 on the bone surface was observed after 16 weeks. In conclusion, the effect of collagen membrane coverage on bone graft volume maintenance was dependent on membrane stability during healing. An autogenous bone graft covered with Bio-Oss particles resulted in a remarkable increase in augmented lateral surface of the mandible. The late stage of bone graft healing was associated with a high apoptotic induction pathway of osteoblasts lining the surfaces of the new bone, demonstrated by strong positive Caspase-3 immunoreactivity.

A histologic and histomorphometric evaluation of anorganic bovine bone retrieved 9 years after a sinus augmentation procedure

BACKGROUND

Anorganic bovine bone (ABB) has been shown to have osteoconductive properties and no inflammatory or adverse responses as grafting materials used in sinus augmentation procedures. Despite these successful results, histologic data in humans over the long-term period are scarce. The purpose of this study was to analyze the histomorphometric data 9 years after surgery in a case of maxillary sinus augmentation using ABB.

METHODS

The histologic evaluation was performed in five different thin sections of the specimen, comparing histomorphometric measures for newly formed bone, marrow spaces, biomaterial particles remnants, and number of osteocytes embedded in both trabecular bone and bone tissue near the ABB. The investigation was carried out by means of scanning electron microscopy and brightfield and circularly polarized light microscopy.

RESULTS

We observed a mean amount of newly formed bone of 46.0% +/- 4.67%, ABB remnants of 16.0% +/- 5.89%, and marrow spaces of 38.0% +/- 8.93%. The osteocyte index was 4.43 for bone around ABB and 3.27 in the trabecular bone at a distance from the particles.

CONCLUSIONS

After 9 years, the tissue pattern appeared composed by residual ABB particles in close contact to the newly formed bone. The bone mineralized matrix around the ABB had collagen fibers randomly oriented and more osteocytes embedded. The results demonstrate both a high level of osteoconductivity and a "biomimetic" behavior over the long term.

Bone Augmentation Techniques

BACKGROUND

The advent of osseointegration and advances in biomaterials and techniques have contributed to increased application of dental implants in the restoration of partial and completely edentulous patients. Often, in these patients, soft and hard tissue defects result from a variety of causes, such as infection, trauma, and tooth loss. These create an anatomically less favorable foundation for ideal implant placement. For prosthetic-driven dental implant therapy, reconstruction of the alveolar bone through a variety of regenerative surgical procedures has become predictable; it may be necessary prior to implant placement or simultaneously at the time of implant surgery to provide a restoration with a good long-term prognosis. Regenerative procedures are used for socket preservation, sinus augmentation, and horizontal and vertical ridge augmentation.

METHODS

A broad overview of the published findings in the English literature related to various bone augmentation techniques is outlined. A comprehensive computer-based search was performed using various databases that include Medline and PubMed. A total of 267 papers were considered, with non-peer-reviewed articles eliminated as much as possible.

RESULTS

The techniques for reconstruction of bony defects that are reviewed in this paper include the use of particulate bone grafts and bone graft substitutes, barrier membranes for guided bone regeneration, autogenous and allogenic block grafts, and the application of distraction osteogenesis.

CONCLUSIONS

Many different techniques exist for effective bone augmentation. The approach is largely dependent on the extent of the defect and specific procedures to be performed for the implant reconstruction. It is most appropriate to use an evidenced-based approach when a treatment plan is being developed for bone augmentation cases.

Effect of calcitonin on bone regeneration in male rats: a histomorphometric analysis

The aim of this study was to evaluate the effectiveness of calcitonin in promoting bone growth in surgical bone defects in rat mandibles. Fifty male rats were divided into two groups: bone defect (control) and bone defect with calcitonin (experimental). A circular bone defect 4mm in diameter was made in the mandibular bone of the rats in the angle region, and covered with a polytetrafluoroethylene barrier. The experimental group received 2 IU/kg of synthetic salmon calcitonin intramuscularly three times a week, with treatment starting immediately after surgery. The animals were killed 3, 7, 14, 21 and 28 days after the surgical procedure. The bone defects were examined histologically and by histomorphometric analysis. The Student t-test was applied to the histomorphometric data, with the level of significance set at 5%. The animals of the experimental group showed a lower level of bone formation at almost all time points than the control group, but no difference between groups was observed 28 days after surgery. The volume of newly formed bone matrix was significantly greater in the control than the experimental group at 7, 14 and 21 days, as determined by both morphologic and histomorphometric analysis. Bone repair in the calcitonin-treated animals was delayed in comparison to controls, indicating the need for further studies on male rats.