Evaluation of a diphenylphosphorylazide-crosslinked collagen membrane for guided bone regeneration in mandibular defects in rats

Collagen-Based Medical Devices for Regenerative Medicine and Tissue Engineering

Assisted reproductive technologies are key to solving the problems of aging and organ defects. Collagen is compatible with living tissues and has many different chemical properties; it has great potential for use in reproductive medicine and the engineering of reproductive tissues. It is a natural substance that has been used a lot in science and medicine. Collagen is a substance that can be obtained from many different animals. It can be made naturally or created using scientific methods. Using pure collagen has some drawbacks regarding its physical and chemical characteristics. Because of this, when collagen is processed in various ways, it can better meet the specific needs as a material for repairing tissues. In simpler terms, collagen can be used to help regenerate bones, cartilage, and skin. It can also be used in cardiovascular repair and other areas. There are different ways to process collagen, such as cross-linking it, making it more structured, adding minerals to it, or using it as a carrier for other substances. All of these methods help advance the field of tissue engineering. This review summarizes and discusses the current progress of collagen-based materials for reproductive medicine.

Use of Plant Extracts in Polymeric Scaffolds in the Regeneration of Mandibular Injuries

Severe loss of bone mass may require grafting, and, among the alternatives available, there are natural biomaterials that can act as scaffolds for the cell growth necessary for tissue regeneration. Collagen and elastin polymers are a good alternative due to their biomimetic properties of bone tissue, and their characteristics can be improved with the addition of polysaccharides such as chitosan and bioactive compounds such as jatoba resin and pomegranate extract due to their antigenic actions. The aim of this experimental protocol was to evaluate bone neoformation in experimentally made defects in the mandible of rats using polymeric scaffolds with plant extracts added. Thirty rats were divided into group 1, with a mandibular defect filled with a clot from the lesion and no graft implant (G1-C, n = 10); group 2, filled with collagen/chitosan/jatoba resin scaffolds (G2-CCJ, n = 10); and group 3, with collagen/nanohydroxyapatite/elastin/pomegranate extract scaffolds (G3-CHER, n = 10). Six weeks after surgery, the animals were euthanized and samples from the surgical areas were submitted to macroscopic, radiological, histological, and morphometric analysis of the mandibular lesion repair process. The results showed no inflammatory infiltrates in the surgical area, indicating good acceptance of the scaffolds in the microenvironment of the host area. In the control group (G1), there was a predominance of reactive connective tissue, while in the grafted groups (G2 and G3), there was bone formation from the margins of the lesion, but it was still insufficient for total bone repair of the defect within the experimental period standardized in this study. The histomorphometric analysis showed that the mean percentage of bone volume formed in the surgical area of groups G1, G2, and G3 was 17.17 ± 2.68, 27.45 ± 1.65, and 34.07 ± 0.64 (mean ± standard deviation), respectively. It can be concluded that these scaffolds with plant extracts added can be a viable alternative for bone repair, as they are easily manipulated, have a low production cost, and stimulate the formation of new bone by osteoconduction.

Microenvironment-targeted strategy steers advanced bone regeneration

Treatment of large bone defects represents a great challenge in orthopedic and craniomaxillofacial surgery. Traditional strategies in bone tissue engineering have focused primarily on mimicking the extracellular matrix (ECM) of bone in terms of structure and composition. However, the synergistic effects of other cues from the microenvironment during bone regeneration are often neglected. The bone microenvironment is a sophisticated system that includes physiological (e.g., neighboring cells such as macrophages), chemical (e.g., oxygen, pH), and physical factors (e.g., mechanics, acoustics) that dynamically interact with each other. Microenvironment-targeted strategies are increasingly recognized as crucial for successful bone regeneration and offer promising solutions for advancing bone tissue engineering. This review provides a comprehensive overview of current microenvironment-targeted strategies and challenges for bone regeneration and further outlines prospective directions of the approaches in construction of bone organoids.

In Vivo Evaluation of Collagen and Chitosan Scaffold, Associated or Not with Stem Cells, in Bone Repair

Natural polymers are increasingly being used in tissue engineering due to their ability to mimic the extracellular matrix and to act as a scaffold for cell growth, as well as their possible combination with other osteogenic factors, such as mesenchymal stem cells (MSCs) derived from dental pulp, in an attempt to enhance bone regeneration during the healing of a bone defect. Therefore, the aim of this study was to analyze the repair of mandibular defects filled with a new collagen/chitosan scaffold, seeded or not with MSCs derived from dental pulp. Twenty-eight rats were submitted to surgery for creation of a defect in the right mandibular ramus and divided into the following groups: G1 (control group; mandibular defect with clot); G2 (defect filled with dental pulp mesenchymal stem cells-DPSCs); G3 (defect filled with collagen/chitosan scaffold); and G4 (collagen/chitosan scaffold seeded with DPSCs). The analysis of the scaffold microstructure showed a homogenous material with an adequate percentage of porosity. Macroscopic and radiological examination of the defect area after 6 weeks post-surgery revealed the absence of complete repair, as well as absence of signs of infection, which could indicate rejection of the implants. Histomorphometric analysis of the mandibular defect area showed that bone formation occurred in a centripetal fashion, starting from the borders and progressing towards the center of the defect in all groups. Lower bone formation was observed in G1 when compared to the other groups and G2 exhibited greater osteoregenerative capacity, followed by G4 and G3. In conclusion, the scaffold used showed osteoconductivity, no foreign body reaction, malleability and ease of manipulation, but did not obtain promising results for association with DPSCs.

Complications in bone-grafting procedures: Classification and management

Bone-regenerative interventions aiming to restore deficient alveolar ridges, such as the use of block grafts or through the application of guided bone-regeneration principles, have reported positive outcomes in the published scientific literature. These interventions, however, are invasive, and hence, intraoperative and/or postoperative complications may occur. The types of complications and their severity may vary from the exposure of the biomaterial (membrane or graft) to postsurgical infections, neurosensorial disturbances, occurrence of hemorrhage, and pain, etc. The aim of the present narrative review was to search the available scientific evidence concerning the incidence of these complications, their effect on treatment outcomes, their clinical management and, finally, strategies aimed at prevention. Exposure of the barrier membrane or the block graft is the most common complication associated with oral regenerative interventions. To manage these complications, depending on the extent of the exposure and the presence or absence of concomitant infections, therapeutic measures may vary, from the topical application of antiseptics to the removal of the barrier membrane or the block graft. Regardless of their treatment, the occurrence of these complications has been associated with patient selection, with compliant patients (eg, nonsmokers) having a lower reported incidence of complications. Similarly, surgical factors such as correct flap elevation and a tensionless closure are of obvious importance. Finally, to prevent the incidence of complications, it appears prudent to utilize whenever possible less invasive surgical interventions.

Efficacy of a novel membrane comprising a copolymer of L-lactic acid and glycolic acid in osteoblasts in vitro

In guided bone regeneration (GBR), a barrier membrane is applied to provide a space for bone regeneration to promote cell adhesion, cell proliferation, and bone regeneration by inducing cell migration to the surface of the bone-deficient site. We prepared a non-woven absorbable membrane for GBR comprised of a copolymer of L-lactic acid and glycolic acid (PLLGA) using the dry spinning method. A thin and dense membrane comprising unsintered hydroxyapatite (uHA) and poly-L-lactic acid (PLLA) was used for comparison. Osteoblast TMS-12 cells were seeded onto the membranes, and cell adhesion and proliferation rates were examined. Calcification levels were quantified by Alizarin Red S staining after cell culture in calcification induction medium. Osteoblastic gene expression was examined by RT-PCR. Cell adhesion and proliferation rates and calcification on PLLGA membranes were significantly higher than those on uHA/PLLA membranes. PLLGA membranes upregulated osteogenic gene expression compared to on uHA/PLLA membranes. Non-woven PLLGA membranes may be useful in GBR for promoting bone formation and maturation.

Evaluation of 1-Ethyl-3-(3-Dimethylaminopropyl) Carbodiimide Cross-Linked Collagen Membranes for Guided Bone Regeneration in Beagle Dogs

The purpose of this study was to evaluate the bone regeneration efficacy of an 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-cross-linked collagen membrane for guided bone regeneration (GBR). A non-cross-linked collagen membrane (Control group), and an EDC-cross-linked collagen membrane (Test group) were used in this study. In vitro, mechanical, and degradation testing and cell studies were performed. In the animal study, 36 artificial bone defects were formed in the mandibles of six beagles. Implants were inserted at the time of bone grafting, and membranes were assigned randomly. Eight weeks later, animals were sacrificed, micro-computed tomography was performed, and hematoxylin-eosin stained specimens were prepared. Physical properties (tensile strength and enzymatic degradation rate) were better in the Test group than in the Control group. No inflammation or membrane collapse was observed in either group, and bone volumes (%) in defects around implants were similar in the two groups (p > 0.05). The results of new bone areas (%) analysis also showed similar values in the two groups (p > 0.05). Therefore, it can be concluded that cross-linking the collagen membranes with EDC is the method of enhancing the physical properties (tensile strength and enzymatic degradation) of the collagen membranes without risk of toxicity.

Selection of Collagen Membranes for Bone Regeneration: A Literature Review

Several treatment modalities have been proposed to regenerate bone, including guided bone regeneration (GBR) where barrier membranes play an important role by isolating soft tissue and allowing bone to grow. Not all membranes biologically behave the same way, as they differ from their origin and structure, with reflections on their mechanical properties and on their clinical performance. Collagen membranes have been widely used in medicine and dentistry, because of their high biocompatibility and capability of promoting wound healing. Recently, collagen membranes have been applied in guided bone regeneration with comparable outcomes to non-resorbable membranes. Aim of this work is to provide a review on the main features, application, outcomes, and clinical employment of the different types of collagen membranes. Comparisons with non-resorbable membranes are clarified, characteristics of cross-linked collagen versus native collagen, use of different grafting materials and need for membrane fixation are explored in order to gain awareness of the indications and limits and to be able to choose the right membrane required by the clinical condition.

Analysis of bone formation and membrane resorption in guided bone regeneration using deproteinized bovine bone mineral versus calcium sulfate

Guided Bone Regeneration (GBR) is a technique based on the use of a physical barrier that isolates the region of bone regeneration from adjacent tissues. The objective of this study was to compare GBR, adopting a critical-size defect model in rat calvaria and using collagen membrane separately combined with two filling materials, each having different resorption rates. A circular defect 8 mm in diameter was made in the calvaria of Wistar rats. The defects were then filled with calcium sulfate (CaS group) or deproteinized bovine bone mineral (DBBM group) and covered by resorbable collagen membrane. The animals were killed 15, 30, 45 and 60 days after the surgical procedure. Samples were collected, fixed in 4% paraformaldehyde and processed for paraffin embedding. The resultant sections were stained with H&E for histological and histomorphometric study. For the histomorphometric study, the area of membrane was quantified along with the amount of bone formed in the region of the membrane. Calcium sulfate was reabsorbed more rapidly compared to DBBM. The CaS group had the highest percentages of remaining membrane at 15, 30, 45 and 60 days, compared to the DBBM group. The DBBM group had the highest amount of new bone at 45 and 60 days compared to the CaS group. Based on these results, it was concluded that the type of filling material may influence both the resorption of collagen membrane and amount of bone formed.

Evaluation of the Safety and Efficacy of Soft Tissue Augmentation With a Compressive-Resistant Collagen Matrix in a Nonhuman Primate Model

PURPOSE

The purpose of the present study was to evaluate the safety and efficacy of the compression-resistant collagen-based cross-linked matrix for augmentation of maxillary and mandibular soft tissue defects in an animal model.

MATERIALS AND METHODS

Six rhesus macaque monkeys were subjected to soft tissue grafting in 4 sites intraorally; the anterior maxilla was subjected to hard and soft tissue grafting with implant placement. Each site was randomly assigned 1 of 3 treatments: a compressive-resistant collagen matrix membrane (CM), a subepithelial connective tissue autograft (SCTG), or sham treatment, in which a partial-thickness flap was elevated and then sutured closed with no further treatment (control). The following methods were used for data collection: in vivo evaluation by periodontal probing, ultrasound, shear modulus elasticity, polyether impressions for volumetric analysis, and in vitro analysis by histologic biopsy examinations. In vitro analysis provided by histologic measurements and evaluations was performed on nondecalcified sections. The follow-up period was 6 months.

RESULTS

The SCTG and CM showed favorable tissue integration. No adverse reaction to or deviation from the normal healing processes was detected. The CM integrated well in all sites, with a variable range of soft tissue volume increases. Volumetric discrepancies were appreciated in the histologic analyses and differences were found when the CM and SCTG were applied in the anterior maxilla in combination with hard tissue grafting and implant placement. Histologic evaluation showed favorable integration, no immunogenic response to the CM, and stable volumetric retention in autograft and CM sites during the experimental period.

CONCLUSION

The compressive-resistant CM could be a safe and efficacious alternative for soft tissue augmentation by obviating a donor site and the consequent morbidity. Although a similar performance between the CM and SCTG was observed, further studies will be necessary to estimate the clinical potentiality and describe the limits of the technique.

Guided bone regeneration using a hydrophilic membrane made of unsintered hydroxyapatite and poly(L-lactic acid) in a rat bone-defect model

The effectiveness of a previously developed unsintered hydroxyapatite (uHA) and poly(L-lactic acid) (PLLA) hydrophilic membrane as a resorbable barrier for guided bone regeneration (GBR) was evaluated. Critical-size 8-mm diameter bone defects were surgically generated in the parietal bones of 24 12-week-old male Wistar rats, which were then divided into three groups in which either a uHA/PLLA or a collagen membrane or no membrane (control) was placed onto the bone defect. Following sacrifice of the animals 2 or 4 weeks after surgery, bone defects were examined using microcomputed tomography and histological analysis. Bone mineral density, bone mineral content, and relative bone growth area values 2 or 4 weeks after surgery were highest in the uHA/PLLA group. Four weeks after surgery, the relative bone growth area in the uHA/PLLA group was larger than that in the collagen group. The resorbable uHA/PLLA membrane is thus potentially effective for GBR.

* Engineering Membranes for Bone Regeneration

This review is focused on the use of membranes for the specific application of bone regeneration. The first section focuses on the relevance of membranes in this context and what are the specifications that they should possess to improve the regeneration of bone. Afterward, several techniques to engineer bone membranes by using "bulk"-like methods are discussed, where different parameters to induce bone formation are disclosed in a way to have desirable structural and functional properties. Subsequently, the production of nanostructured membranes using a bottom-up approach is discussed by highlighting the main advances in the field of bone regeneration. Primordial importance is given to the promotion of osteoconductive and osteoinductive capability during the membrane design. Whenever possible, the films prepared using different techniques are compared in terms of handability, bone guiding ability, osteoinductivity, adequate mechanical properties, or biodegradability. A last chapter contemplates membranes only composed by cells, disclosing their potential to regenerate bone.

Effect of cross-linked vs non-cross-linked collagen membranes on bone: A systematic review

The aim of this study was to conduct a systematic review to compare the clinical outcomes of two different resorbable collagen membranes in terms of regenerated bone volume, postoperative complications and membrane degradation during bone regeneration procedures. Randomized controlled trials (RCT) or controlled trials (CT) that compared both techniques were reviewed on four electronic databases up to December 2015, a manual search was performed on the bibliography of the collected articles and the authors were contacted for additional references if undetected on the electronic and manual search. Membrane exposure was evaluated as a dichotomous outcome and the statistical unit was the membrane. The results were presented as relative risk (RR) with a 95% confidence interval. Eight RCTs and one CT were included in this study. The majority of the studies depicted a bone augmentation area, which ranged from 46.15% to 94.6% for the non-cross-link membranes and from 44% to 92.6% for the cross-link membranes at the 4-6 month re-entry surgery. From a total of 289 patients, a forest plot concerning the membrane exposure was constructed using the obtained RR of the included studies. The overall RR was 1.43 (95% CI: 0.85-2.39) with no statistically significant differences between the two groups, although with a marginal tendency towards higher exposure in the cross-link membrane group. This systematic review suggests the different membranes present themselves as appropriate for bone regeneration procedures, although cross-link membranes present higher rates of postoperative complications. However, more RCT with higher sample sizes are needed to evaluate the different membranes. The suggested lack of clinical differences between the compared membranes suggest that further cost-benefit ratio, tissue integration and postoperative complication oriented studies should be performed so that clinicians can take a patient-centred, evidence-based decision.

Microarray gene expression during early healing of GBR-treated calvarial critical size defects

OBJECTIVES

To investigate the gene expression and molecular pathways implicated in the regulation of the osseous healing process following guided bone regeneration (GBR).

MATERIAL AND METHODS

Six 6-month-old Wistar male rats were used. Standardized 5-mm critical size defects were created in the parietal bones of each animal and treated with an extracranial and intracranial ePTFE membrane, according to the GBR principle. Three animals were randomly sacrificed after 7 and 15 days of healing. Total RNA was extracted from each sample and prepared for gene expression analysis. RNA quality and quantity were assessed, followed by hybridization of the cRNA to Affymetrix GeneChip Rat Genome 230 2.0 Arrays. The Affymetrix data were processed, and first-order analysis, quality control and statistical analysis were performed. Biological interpretation was performed via pathway and Gene Ontology (GO) analysis.

RESULTS

Between the 7- and 15-day samples, 538 genes were differently regulated. At day 7, inflammatory and immune responses were clearly upregulated. In addition, GO terms related to angiogenesis and cell cycle regulation were overexpressed. At day 15, a more complex cellular activity and cell metabolism were evident. The bone formation processes were significantly overexpressed, with several genes encoding growth factors, enzyme activity, and extracellular matrix formation found as upregulated. Remarkably, a negative regulation of Wnt signalling pathway was observed at 15 days.

DISCUSSION

The gene expression profile of the cells participating in osseous formation varied depending on the healing stage. A number of candidate genes that seem differentially expressed during early stages of intramembranous bone regeneration was suggested.

Treatment of Orally Handicapped Edentulous Older Adults Using Dental Implants

The oral handicap of complete edentulism is the terminal outcome of a multifactorial process involving biological factors and patient-related factors. Fully edentulous orally handicapped older adults have been neglected because removable acrylic dentures have been the classic therapy for complete edentulism but are only rehabilitative, not therapeutic. Not replacing missing teeth with stable dentures could prevent adequate food intake. Osseointegrated endosseous implants used as a therapeutic adjunct can reduce the problem of long-term bone resorption to less than 0.1 mm per year. Implant-borne prostheses substantially increase the overall health and quality of life of orally handicapped fully edentulous older adults.

Comparison of unprocessed silk cocoon and silk cocoon middle layer membranes for guided bone regeneration

Background

Silk cocoon is composed of multiple layers. The natural silk cocoon containing all layers was cut as a rectangular shape as defined as total group. The inner and outermost layers were removed from the total group and the remained mat was defined as the middle group. The objectives of this study was to compare the total group with the middle group as a barrier membrane for the guided bone regeneration.

Methods

The effects of these materials on the cellular proliferation and alkaline phosphatase (ALP) expression of MG63 cells were explored. For comparing bone regeneration ability, bilateral bone defects were created in calvarial areas in ten adult New Zealand white rabbits. The defects were covered with silk membranes of the middle group, with silk membrane of the total group used as the control on the contralateral side. The defects were allowed to heal for 4 and 8 weeks. Micro-computerized tomography (μCT) and histological examination were performed.

Results

The middle group exhibited a higher MTT value 48 and 72 h after treatment compared to the total group. ALP expression was also higher in the middle group. The results of μCT and histologic examination showed that new bone formation was significantly higher in the middle group compared to the total group 8 weeks postoperatively (P < 0.05).

Conclusions

In conclusion, the middle layer of the silk cocoon supports guided bone regeneration better than unprocessed silk cocoon.

Guided bone regeneration using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-cross-linked type-I collagen membrane with biphasic calcium phosphate at rabbit calvarial defects

Background

In-vitro and animal studies using EDC cross-linked membranes have shown great resistance to enzymatic digestion as well as low cytotoxicity, and indicated its potential expediency as a barrier membrane for guided bone regeneration (GBR). The purpose of this study was to evaluate the efficacy, biocompatibility and degradation kinetics of a novel 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-cross-linked type I collagen membrane for regeneration of rabbit calvarial defects. EDC cross-linked type I collagen membrane and macroporous biphasic calcium phosphate (MBCP) consisting of 60 % hydroxyapatite and 40 % β-tricalcium phosphate were used in this study. Four circular defects (ø = 8 mm) were created in each calvarium of 12 male white rabbits. The experimental groups randomly allocated to the defects were as follows – (1) sham control, (2) EDC-cross-linked collagen membrane (EDC membrane), (3) bone graft (BG), and (4) bone graft with collagen membrane (B-EDC membrane). Specimens were harvested at 2 weeks (n = 6) and 8 weeks (n = 6) postoperatively for observational histology and histometrical analysis.

Result

The histologic observation showed close adaptation of the EDC membrane to the defect perimeters along with vascularization of the membrane at 2 weeks. Direct apposition of new bone on to the collagen matrix could be observed displaying adequate tissue integration. Collapsing of the central portion of the membrane could be seen in the EDC membrane group, and both BG and B-EDC membrane groups showed greater total augmented area and new bone area than the EDC membrane group. The membrane was largely unresorbed at 2 weeks; and at 8 weeks the overall shape of the membrane was still maintained suggesting sustained barrier function at 8 weeks.

Conclusion

Within the limits of this study, it may be concluded that EDC-cross-linked collagen membrane is a safe biomaterial with adequate tissue integration and resorption kinetics to support bone regeneration when used in conjunction with bone filler.

To cross-link or not to cross-link? Cross-linking associated foreign body response of collagen-based devices

Collagen-based devices, in various physical conformations, are extensively used for tissue engineering and regenerative medicine applications. Given that the natural cross-linking pathway of collagen does not occur in vitro, chemical, physical, and biological cross-linking methods have been assessed over the years to control mechanical stability, degradation rate, and immunogenicity of the device upon implantation. Although in vitro data demonstrate that mechanical properties and degradation rate can be accurately controlled as a function of the cross-linking method utilized, preclinical and clinical data indicate that cross-linking methods employed may have adverse effects on host response, especially when potent cross-linking methods are employed. Experimental data suggest that more suitable cross-linking methods should be developed to achieve a balance between stability and functional remodeling.

Comparative study of two collagen membranes for guided tissue regeneration therapy in periodontal intrabony defects: a randomized clinical trial

PURPOSE

THE PURPOSE OF THIS STUDY WAS TO ASSESS AND COMPARE THE CLINICAL AND RADIOGRAPHIC OUTCOMES OF GUIDED TISSUE REGENERATION THERAPY FOR HUMAN PERIODONTAL INTRABONY DEFECTS USING TWO DIFFERENT COLLAGEN MEMBRANES: a porous nonchemical cross-linking collagen membrane (NC) and a bilayer collagen membrane (BC).

METHODS

Thirty subjects were randomly assigned and divided into the following 3 groups: a test group (NC+BM), in which a NC was used with xenograft bone mineral (BM), a positive control group (BC+BM), in which a BC was used with xenograft BM, and a negative control group (BM), in which only xenograft BM was used. The following clinical measurements were taken at baseline and 3 months after surgery: plaque index, gingival index, probing pocket depth, gingival recession, and clinical attachment level. Radiographic analysis was performed at baseline, 1 week and 3 months after surgery.

RESULTS

Membrane exposure was not observed in any cases. Significant probing depth reduction, attachment-level gain and bone fill were observed for both test and control groups compared to baseline at 3 months after surgery (P<0.05). However, there were no statistically significant differences in clinical improvement and radiographic bone fill between treatment protocols (P>0.05).

CONCLUSIONS

Within the limitations of this study, the results suggest that both NC and BC were comparable in terms of clinical and radiographic outcomes for the treatment of periodontal intrabony defects in human subjects.

Influence of sterilisation methods on collagen-based devices stability and properties

Sterilisation is essential for any implantable medical device in order to prevent infection in patients. The selection of the most appropriate sterilisation method depends on the nature and the physical state of the material to be sterilised; the influence of the sterilisation method on the properties of the device; and the type of the potential contaminant. In this context, herein we review the influence of ethylene oxide, γ-irradiation, e-beam irradiation, gas plasma, peracetic acid and ethanol on structural, biomechanical, biochemical and biological properties of collagen-based devices. Data to-date demonstrate that chemical approaches are associated with cytotoxicity, whilst physical methods are associated with degradation, subject to the device physical characteristics. Thus, the sterilisation method of choice is device dependent.

The role of barrier membranes for guided bone regeneration and restoration of large bone defects: current experimental and clinical evidence

Treatment of large bone defects represents a great challenge in orthopedic and craniomaxillofacial surgery. Although there are several methods for bone reconstruction, they all have specific indications and limitations. The concept of using barrier membranes for restoration of bone defects has been developed in an effort to simplify their treatment by offering a single-staged procedure. Research on this field of bone regeneration is ongoing, with evidence being mainly attained from preclinical studies. The purpose of this review is to summarize the current experimental and clinical evidence on the use of barrier membranes for restoration of bone defects in maxillofacial and orthopedic surgery. Although there are a few promising preliminary human studies, before clinical applications can be recommended, future research should aim to establish the 'ideal' barrier membrane and delineate the need for additional bone grafting materials aiming to 'mimic' or even accelerate the normal process of bone formation. Reproducible results and long-term observations with barrier membranes in animal studies, and particularly in large animal models, are required as well as well-designed clinical studies to evaluate their safety, efficacy and cost-effectiveness.

Alveolar ridge augmentation in irradiated rabbit mandibles

Oral carcinomas are frequently treated with a nonsegmental mandibulectomy plus radiotherapy. Improving the quality of life of these patients depends on the possibilities for dental rehabilitation. The aim of this study was to increase the alveolar ridge height. Twelve white New Zealand rabbits underwent surgery to produce a 11 x 9 x 7 mm(3) horizontal bicortical full-thickness defect at the alveolar ridge of the left mandible. Six were implanted with a composite associating resorbable collagen membrane filled with micro-macroporous biphasic calcium phosphate granules. After a daily radiation delivery schedule for 4 weeks, a total autologous bone marrow graft was injected percutaneously into the center of the implant. All animals were sacrificed at 16 weeks. Successful osseous colonization was observed in all implants. Significant ridge augmentation was observed (p = 0.0349) in the implanted group compared with the control group. This study contributed to producing an experimental model for oncological mandible defects in rabbits.

Bio-degradation of a resorbable collagen membrane (Bio-Gide) applied in a double-layer technique in rats

OBJECTIVE

The aim of this study was to evaluate histologically the bio-degradation of two layers of Bio-Gide((R)) (BG) membrane, as compared with that of a single layer.

MATERIAL AND METHODS

Two circular calvarial bony defects, 5 mm in diameter, were made in 24 Wistar rats. BG membrane, labeled with biotin, was cut into 5-mm-diameter disks, and placed in defects either as a mono-layer membrane (MLM) or as a double-layer membrane (DLM). Rats were sacrificed after 4 or 9 weeks and histology was performed. Membranes were stained with horseradish peroxidase-conjugated streptavidin and aminoethyl carbazole as a substrate for detection of biotinylated collagen. The area of collagen and thickness of the residual membranes were measured by image analysis software. Statistical analysis was performed using the non-parametric Wilcoxon's signed-ranks test.

RESULTS

At 4-week collagen area per measurement window within the DLM sites (0.09+/-0.05 mm(2)) was significantly greater (P<0.01) than that in the MLM sites (0.047+/-0.034 mm(2)). At 9 weeks, the collagen area was also greater in the DLM sites (0.037+/-0.026 mm(2)) compared with that of the MLM sites (0.025+/-0.016 mm(2)); however, this difference did not reach statistical significance. The rate of membrane degradation, calculated as percent membrane lost compared with baseline, was similar for the DLM and MLM at both time points ( approximately 60% at 4 weeks and approximately 80% at 9 weeks). In addition, the residual DLM thickness at 4 weeks (475.5+/-73.77 mum) was significantly (P<0.01) greater than that of MLM (262.38+/-48.01 mum). At 9 weeks, membrane thickness was also greater in the DLM sites (318.22+/-70.45 mum) compared with that of the MLM sites (183.32+/-26.72 mum); however, this difference did not reach statistical significance. The reduction in thickness between 4 and 9 weeks was 30% for MLM and 33% for DLM.

DISCUSSION

The use of a double layer of BG membrane results in a barrier of increased collagen area and thickness, compared with application of a single layer.

Angiogenesis pattern of native and cross-linked collagen membranes: an immunohistochemical study in the rat

The aim of the present study was to immunohistochemically evaluate angiogenesis pattern of native and cross-linked collagen membranes after subcutaneous implantation in rats. Five commercially available and three experimental membranes (VN) were included: (1) BioGide (BG), (2) BioMend (BM), (3) BioMend Extend (BME), (4) Ossix (OS), (5) TutoDent (TD), and (6-8) VN(1-3). Specimens were randomly allocated in unconnected subcutaneous pouches (n=4) separated surgically on the back of 40 wistar rats, which were divided into five groups (2, 4, 8, 16, and 24 weeks), including eight animals each. Pattern of angiogenesis was labelled using primary mouse monoclonal antibody to transglutaminase II. For each membrane, the period of time, needed for a complete and homogeneous transmembraneous vascularization, was assessed immunohistomorhometrically. Differences between the membranes were found regarding the initial pattern of transmembraneous angiogenesis, as evaluated 2 weeks following implantation. Mean cross- and longitudinal-sectional area of blood vessels (%) was highest for VN(3) (5.27+/-2.73), followed by BG (2.45+/-0.88), VN(1) (2.07+/-0.29), VN(2) (1.91+/-0.55), TD (1.44+/-0.53), BME (0.35+/-0.29) and BM (0.25+/-0.4). In contrast to BG and VN(1-3), BM, BME and TD exhibited a homogeneous transmembraneous formation of blood vessels merely 4-8 weeks following implantation. OS, however, exhibited no signs of angiogenesis throughout the whole study period. Within the limits of the present study, it may be concluded that pattern of transmembraneous angiogenesis markedly differs among the membranes investigated.

Electron beam irradiation modification of collagen membrane

A critical observation of reconstituted collagen membrane radiated by electron beam (EB) indicated that these collagenous fibers become cross-linked network when the irradiation is carried out in greater than melt temperature and nitrogen atmosphere. Studies on the membrane properties showed that glass transformation temperature (Tg) and melt point (Tm) of reconstituted collagen have no changes, but thermal gravity curves and infrared (IR) spectra become obviously different before and after irradiation. Cross-linking density calculated by the equation based on the theory of Flory-Rehner proved further that the densities increase with radiation doses increasing. Resistance to enzymatic digestions in vitro and implantation in vivo were determined to evaluate the physicochemical properties of cross-linked matrices. Based on the above results, it was concluded that EB radiation inducing cross-linking in greater than melt temperature and nitrogen atmosphere condition is an attractive, effective method, which introduce into intermolecular covalent cross-linkings.

Biodegradation of differently cross-linked collagen membranes: an experimental study in the rat

The aim of the present study was to compare the biodegradation of differently cross-linked collagen membranes in rats. Five commercially available and three experimental membranes (VN) were included: (1) BioGide (BG) (non-cross-linked porcine type I and III collagens), (2) BioMend (BM), (3) BioMendExtend (BME) (glutaraldehyde cross-linked bovine type I collagen), (4) Ossix (OS) (enzymatic-cross-linked bovine type I collagen), (5) TutoDent (TD) (non-cross-linked bovine type I collagen, and (6-8) VN(1-3) (chemical cross-linked porcine type I and III collagens). Specimens were randomly allocated in unconnected subcutaneous pouches separated surgically on the back of 40 wistar rats, which were divided into five groups (2, 4, 8, 16, and 24 weeks), including eight animals each. After 2, 4, 8, 16, and 24 weeks of healing, the rats were sacrificed and explanted specimens were prepared for histologic and histometric analysis. The following parameters were evaluated: biodegradation over time, vascularization, tissue integration, and foreign body reaction. Highest vascularization and tissue integration was noted for BG followed by BM, BME, and VN(1); TD, VN(2), and VN(3) showed prolongated, while OS exhibited no vascularization. Subsequently, biodegradation of BG, BM, BME and VN(1) was faster than TD, VN(2), and VN(3). OS showed only a minute amount of superficial biodegradation 24 weeks following implantation. Biodegradation of TD, BM, BME, VN(2), and VN(3) was associated with the presence of inflammatory cells. Within the limits of the present study, it was concluded that cross-linking of bovine and porcine-derived collagen types I and III was associated with (i) prolonged biodegradation, (ii) decreased tissue integration and vascularization, and (iii) in case of TD, BM, BME, VN(2), and VN(3) foreign body reactions.

Mandibular defect repair by TGF-β and IGF-1 released from a biodegradable osteoconductive hydrogel

PURPOSE

Bone regeneration is crucial in the healing of defects in the craniofacial complex. The ability of transforming growth factor-beta1 (TGF-beta1) and insulin-like growth factor-1 (IGF-1), incorporated into a hydrogel scaffold to induce bone regeneration, was evaluated in a rat mandible defect model.

MATERIAL AND METHODS

Hydrogel scaffolds containing either transforming growth factor-beta1 (TGF-beta1), insulin-like growth factor-1 (IGF-1), TGF-beta+ IGF-1, or saline, were implanted in rat mandibular bone defects. In a control group the defects were treated by saline alone. Bone defect healing was tested after 3 and 6 weeks by radiology and morphology.

RESULTS

Soft tissue radiographs indicated that the area of new bone formation increased gradually after 3 and at 6 weeks. The percentage of closure after 3 weeks was less than the percentage closure after 6 weeks. The amount of calcified material in the TGF-beta and TGF-beta+IGF-1-treated groups had increased more than in the saline-containing hydrogel and control (saline-treated) defects. The percentages of defect closures were 37, 38, 24, 14, and 11% after 3 weeks, and 94, 91, 84, 72, and 29% after 6 weeks, in the TGF-beta+IGF-1, TGF-beta, IGF-1, saline containing hydrogel and saline-treated animals, respectively. Three-dimensional computerized tomography (3D CT) images showed that the 3D shape of the bones was restored. Morphological analysis of the defects treated with hydrogel containing TGF-beta, IGF-1 or TGF-beta+IGF-1 revealed significant bone formation after 6 weeks.

CONCLUSION

It is concluded that the hydrogel scaffold impregnated with growth factors can induce bone regeneration and is therefore a promising surgical tool for enhancement of surgical repair of bone defects.

Biocompatibility of various collagen membranes in cultures of human PDL fibroblasts and human osteoblast-like cells

The aim of the present study was to evaluate the biocompatibility of differently cross-linked collagen membranes in cultures of human PDL fibroblasts and human osteoblast-like cells. Four collagen membranes [BioGide (BG), BioMend (BM), Ossix (OS) and TutoDent (TD)] were tested. Cells plated on culture dishes (CD) served as positive controls. Six specimens of each membrane were incubated with (1) human PDL fibroblasts [2 x 10(4) cells] (n=24), and (2) human osteoblast-like cells (SaOs-2) [2 x 10(4) cells] (n=24) under standardized conditions. After 7 days, adherent cells were stained with hematoxylin and counted using a reflected light microscope and the cell density per square millimeter was calculated. Additionally, cell morphology was investigated using scanning electron microscopy (SEM). Cell counts were presented as means and standard deviations (cells/mm(2)) and analyzed for statistical difference using the Wilcoxon test: (1) CD (434+/-76)>BG (64+/-19)=OS (61+/-8)>TD (44+/-4)>BM (12+/-5); (2) CD (453+/-92)>BG (94+/-46)=TD (84+/-49)>OS (41+/-23)>BM (0). SEM examination revealed that PDL fibroblasts adherent on BG, TD and OS appeared spindle-shaped and flat, like cells on CD. SaOs-2 osteoblasts adherent on CD were star shaped and flat, but mostly round in shape on BG, OS and TD. BM appeared to be incompatible with the attachment and proliferation of SaOs-2 cells; however, a few PDL fibroblasts were found in a round shape. Within the limits of the present study, it was concluded that (i) BG, TD and OS promoted, and (ii) BM inhibited the attachment and proliferation of human PDL fibroblasts and human SaOs-2 osteoblasts.

Characteristics of ovine articular chondrocytes in a three-dimensional matrix consisting of different crosslinked collagen

The purpose of this study was to evaluate the (ultra-) morphology, biochemical behavior, and activity of ovine chondrocytes seeded on a matrix consisting of three types of collagen (I, II, III) with two different degrees of UV crosslinking. Ovine articular chondrocytes were isolated from stifle joints and seeded on both types of UV-crosslinked collagen matrices, as well as on non-crosslinked sponges, and cultured for 12 h, 7 days, 14 days, and 21 days. Histological analysis, electron microscopy, biochemical assays for glycosaminoglycans, and real-time quantitative PCR for collagens were performed for cell-seeded and unseeded matrices. There was no dramatic difference in the morphology and bioactivity of the cells; however, concerning handling characteristics and integrative stability, both types of crosslinked sponges were superior to non-crosslinked constructs. The results demonstrate that ovine articular chondrocytes express their phenotype in a sponge consisting of collagen; furthermore, because of mechanical reasons, non-crosslinked matrices cannot be recommended for implantation in vivo.

Guided tissue regeneration in human Class II furcation defects using a diphenylphosphorylazide-cross-linked collagen membrane: a consecutive case series

BACKGROUND

Several bioabsorbable collagen membranes are either currently available or under investigation for use in guided tissue regeneration (GTR) procedures. The aim of this 12-month reentry study was to evaluate a diphenylphosphorylazide (DPPA)-cross-linked bovine type I collagen membrane in the healing of mandibular Class II furcation defects. The DPPA technique prevents the inclusion of foreign cytotoxic cross-linking substances in the reticulated molecules, thus providing a more biocompatible product.

METHODS

Forty non-smoking periodontally compromised adult subjects volunteered for this study, and one defect was randomly selected in each patient. At baseline, plaque index (PI), gingival index (GI), probing depth (PD), gingival margin location (GML), clinical attachment level (CAL), and width of the attached gingiva (AG) were measured. Intrasurgical hard tissue measurements consisted of the vertical open probing attachment level (V-OPAL) and horizontal open probing attachment level (H-OPAL), as well as furcation entrance width (FW) and height (FH) and subclassification of defects according to vertical bone loss. All soft tissue measurements were repeated 12 months after membrane placement using conservative flap reentry surgeries; hard tissue parameters were also assessed at this time.

RESULTS

DPPA-cross-linked collagen membranes demonstrated good handling characteristics, and no postoperative adverse tissue reactions or clinically detectable localized allergic responses were observed. GI and PI remained low during the entire study period. When the one year reentry values were compared to the baseline measurements, a significant reduction in PD (1.9 +/- 1.4), FW (2.1 +/- 1.7), FH (2.9 +/- 1.6), and gain in CAL (1.7 +/- 1.5), V-OPAL (2.1 +/- 1.9), and H-OPAL (4.7 +/- 1.4) were observed (P < or = 0.05). However, there were no significant differences in GML or AG. Hard tissue improvements resulted in the complete closure of 30% (12) of the defects, and transformation of 67.5% (27) of the defects to Class I, while one defect remained a Class II (2.5%).

CONCLUSIONS

Based on this 12-month clinical reentry study, a DPPA-cross-linked collagen membrane could be beneficial in GTR treatment of Class II mandibular furcation involvements, both in terms of soft and hard tissue improvements.

Comparison of calcium alginate film with collagen membrane for guided bone regeneration in mandibular defects in rabbits

PURPOSE

We sought to compare calcium alginate film (CAF) with collagen membrane (CM) regarding their effects on guided bone regeneration.

MATERIALS AND METHODS

Circular bone defects with 5-mm diameter were created in the region anterior to both mandibular angles in 34 rabbits. The defects on one side were covered with a CAF, and the contralateral side with CM. Healing condition was analyzed with gross, radiographic, electromicroscopic, histologic, and immunohistochemical studies and image pattern analysis system after 1, 2, 4, 6, and 8 weeks.

RESULTS

CM absorbed more slowly but collected fewer osteoinductive factors (P <.05) in the early period. CAF induced dense bone formation, whereas CM produced less newly formed bone.

CONCLUSION

CAF is more efficacious than CM in guided bone regeneration in this animal model.

Guided bone regeneration (GBR) using membranes and calcium sulphate after apicectomy: a comparative histomorphometrical study

AIM

The purpose of the present study was to evaluate the effects of resorbable and non-resorbable membranes, and calcium sulphate on bone regeneration in osseous defects in conjunction with apicectomy.

METHODOLOGY

The mandibular third and fourth premolars of 12 beagle dogs were root treated, and apicectomies were performed. The osseous defects were divided randomly into five groups. In groups A, B and C the osseous defects were covered with e-PTFE membranes, PLGA membranes, and collagen membranes, respectively. In group D, defects were filled with calcium sulphate. Nothing was used in group E, which served as controls. The dogs were sacrificed 4, 8, and 16 weeks after the surgery. Undemineralized sections were obtained and evaluated histomorphometrically.

RESULTS

Newly formed cortical bone had closed the defect in the cortical plate in all groups at 16 weeks. The degree of concavity of the new cortical bone at 16 weeks in groups A and D was significantly less than in group B (P < 0.01). The percentage of regenerated bone in group A was significantly greater than in groups B (P < 0.01), C (P < 0.05) and E (P < 0.05). In group D, it was significantly greater than in groups B (P < 0.01) and E (P < 0.05).

CONCLUSIONS

The data suggests that e-PTFE membrane is more effective compared to resorbable membranes and controls for bone regeneration after apicectomy, and that calcium sulphate could be substituted for e-PTFE membrane.

Treatment of gingival recessions by combined periodontal regenerative technique, guided tissue regeneration, and subpedicle connective tissue graft. A comparative clinical study

BACKGROUND

Many surgical techniques have been shown to be effective in correcting gingival recessions by covering the exposed root with soft tissue; however, the thickness of the gingival tissue over the root surface probably plays an important role in preventing the recurrence of tissue recession. The aim of the present study was to compare the results of a mucogingival bilaminar technique (BT), guided tissue regeneration (GTR), and a combined periodontal regenerative technique (CPRT) in achieving root coverage and increasing the gingival thickness 1 year after surgical treatment.

METHODS

In 45 systemically healthy, non-smoking patients aged 33.6 +/- 4.3 years with no periodontal pockets >4 mm, a Miller's Class I or II gingival recession was treated for root coverage: 15 patients underwent BT (connective tissue with partial-thickness double pedicle graft), 15 GTR by a bioabsorbable membrane, and 15 CPRT by a collagen membrane and collagen-incorporated hydroxyapatite. Before and 1 year after surgical treatments, the following clinical parameters were recorded: gingival recession (GR), probing depth (PD), clinical attachment level (CAL), keratinized tissue width (KT), and gingival thickness (GT); the percentage of root coverage was also calculated and the data were statistically analyzed.

RESULTS

All 3 techniques yielded significant improvements in terms of GR decrease, CAL and KT gain, and GT increase compared to baseline values. Mean root coverage was 90.0%, 81.01%, and 87.12% in BT, GTR, and CPRT groups, respectively. Complete root coverage was observed in 60%, 40%, and 53.3% of subjects from the BT, GTR, and CPRT groups, respectively. No significant differences were observed among the 3 techniques in GR or CAL improvements; however, BT produced a significantly (P<0.01) greater increase of KT, and BT and CPRT groups showed a significantly (P<0.01) greater increase of GT compared to the GTR group.

CONCLUSIONS

BT, GTR, and CPRT successfully treated gingival recession defects, obtaining comparable percentages of root coverage, but BT and CPRT created a thick gingival tissue significantly greater than that achieved with GTR.

Repair of a critical size defect in the rat mandible using allogenic type I collagen

Mandibular fractures, resulting from either trauma or reconstructive surgery, can be challenging craniofacial problems. The morbidity of failed fracture healing is significant and may require bone grafting. Donor site morbidity and finite amounts of autogenous bone are major drawbacks of autogenous bone grafting. Similarly, the use of allografts and xenografts may be associated with an increased risk of rejection, infection, and nonunion. To circumvent the limitations of bone grafting, research efforts have focused on formulating a suitable bone substitute. The purpose of our study was to evaluate the efficacy of type I collagen implants in repairing critical sized mandibular defects in rats. Twelve male Sprague-Dawley rats (200-300g) were divided equally into control and experimental groups. Full thickness, round, four millimeter in diameter defects were created in the ramus of the right mandible of all rats using an electrical burr at low speed. The defects were irrigated of all bone chips, and either filled with a precisely fitted disk of allogenic collagen type I gel (experimental animals) or left empty (control animals). Animals were killed 6 weeks after surgery and healing of the bone defects was assessed in a blinded fashion using radiologic and histologic analysis. Radiologic analysis of the control group revealed a clear circular right mandibular defect in all animals, whereas the collagen disk implant group revealed an indistinct to nonexistent right mandibular defect in all animals. Densitometric analysis revealed a significant difference between these groups (* P = 0.01). Similarly, gross analysis of control mandibles revealed a 4mm round, soft-tissue filled defect, while implanted defects demonstrated gross bone spanning the defect. Finally, histologic analysis of all control mandibles revealed clearly demarcated bony edges at the defect border with connective tissue spanning the defect. In contrast, histological analysis of all implanted mandibles revealed indistinct bony edges at the defect border with a thin layer of osteoblasts and viable bone spanning the defects. We have demonstrated the ability of type I collagen to promote healing of a membranous bony defect that would not otherwise heal at 6 weeks. The suitability of type I collagen as a carrier matrix provides ample opportunity for tissue-engineered approaches to further facilitate bony defect healing. Promoting bone formation through tissue engineering matrices offers great promise for skeletal healing and reconstruction.

Lateral ridge augmentation using different bone fillers and barrier membrane application. A histologic and histomorphometric pilot study in the canine mandible

Lateral ridge augmentation has become a standard treatment option to enhance the bone volume of deficient recipient sites prior to implant placement. In order to avoid harvesting an autograft and thereby eliminating additional surgical procedures and risks, bone grafting materials and substitutes are alternative filler materials to be used for ridge augmentation. Before clinical recommendations can be made, such materials must be extensively studied in experimental models simulating relevant clinical situations. The present pilot study was conducted in three dogs. Different grafting procedures were evaluated for augmentation of lateral, extended (8 x 10 x 14 mm) and chronic bone defects in the mandibular alveolar ridge. Experimental sites received tricalcium phosphate (TCP) granules or demineralized freeze-dried bone allograft (DFDBA) particles. Barrier membranes (ePTFE) were placed for graft protection. These approaches were compared to ridge augmentation using autogenous cortico-cancellous block grafts, either with or without ePTFE-membrane application. After a healing period of six months, the sites were analyzed histologically and histomorphometrically. Autografted sites with membrane protection showed excellent healing results with a well-preserved ridge profile, whereas non-protected block grafts underwent bucco-crestal resorption, clearly limiting the treatment outcome. The tested alloplastic (TCP) and allogenic (DFDBA) filler materials presented inconsistent findings with sometimes encapsulation of particles in connective tissue, thereby reducing the crestal bone width. The present pilot study supports the use of autografts with barrier membranes for lateral ridge augmentation of extended alveolar bone defects.

Bioabsorbable materials for guided bone regeneration prior to implant placement and 7-year follow-up: report of 14 cases

BACKGROUND

The purpose of the present study was to evaluate the efficacy of a guided bone regeneration (GBR) procedure prior to implant placement and the long-term outcome of the inserted implants.

METHODS

Prior to dental implant placement, GBR procedure was performed on 14 patients (mean age 48 years) using a synthetic hydroxyapatite (HA) spacer under a collagen membrane. After a mean healing period of 8 months, bone biopsies were obtained during the placement of 14 implants. The specimens were processed for histology without demineralization in order to assess bone quality and quantity of the regenerated bone.

RESULTS

Both the bone density and the resorption degree of HA particles were relatively varied between samples. The different phenotypes of osteoclasts and multinucleated giant cells and the individual host response could partially explain the unpredictable results in terms of bone remodeling and biomaterial resorption. However, the presence of HA particles in the regenerated bone had no influence on the osseointegration of implants presenting a success rate of 86% after a 7-year observation period.

CONCLUSIONS

These results confirm the possibility of regenerating bone by means of bioabsorbable materials, assuring at the same time the long-term success for implants inserted in regenerated sites.