Experimental reconstruction of the mandible using polylactic acid tubes and basic fibroblast growth factor in alloplastic scaffolds

Regeneration of alveolar bone defects in the experimental pig model: A systematic review and meta-analysis

OBJECTIVE

Pigs are emerging as a preferred experimental in vivo model for bone regeneration. The study objective was to answer the focused PEO question: in the pig model (P), what is the capacity of experimental alveolar bone defects (E) for spontaneous regeneration in terms of new bone formation (O)?

METHODS

Following PRISMA guidelines, electronic databases were searched for studies reporting experimental bone defects or extraction socket healing in the maxillae or mandibles of pigs. The main inclusion criteria were the presence of a control group of untreated defects/sockets and the assessment of regeneration via 3D tomography [radiographic defect fill (RDF)] or 2D histomorphometry [new bone formation (NBF)]. Random effects meta-analyses were performed for the outcomes RDF and NBF.

RESULTS

Overall, 45 studies were included reporting on alveolar bone defects or extraction sockets, most frequently in the mandibles of minipigs. Based on morphology, defects were broadly classified as 'box-defects' (BD) or 'cylinder-defects' (CD) with a wide range of healing times (10 days to 52 weeks). Meta-analyses revealed pooled estimates (with 95% confidence intervals) of 50% RDF (36.87%-63.15%) and 43.74% NBF (30.47%-57%) in BD, and 44% RDF (16.48%-71.61%) and 39.67% NBF (31.53%-47.81%) in CD, which were similar to estimates of socket-healing [48.74% RDF (40.35%-57.13%) and 38.73% NBF (28.57%-48.89%)]. Heterogeneity in the meta-analysis was high (I2 > 90%).

CONCLUSION

A substantial body of literature revealed a high capacity for spontaneous regeneration in experimental alveolar bone defects of (mini)pigs, which should be considered in future studies of bone regeneration in this animal model.

Role of periosteum during healing of alveolar critical size bone defects in the mandible: a pilot study

OBJECTIVES

Minipigs present advantages for studying oral bone regeneration; however, standardized critical size defects (CSD) for alveolar bone have not been validated yet. The objectives of this study are to develop a CSD in the mandibular alveolar bone in Aachen minipigs and to further investigate the specific role of periosteum.

MATERIALS AND METHODS

Three female Aachen minipigs aged 17, 24, and 84 months were used. For each minipig, a split-mouth design was performed: an osteotomy (2 cm height × 2.5 cm length) was performed; the periosteum was preserved on the left side and removed on the right side. Macroscopic, cone beam computed tomography (CBCT), microcomputed tomography (µCT), and histological analyses were performed to evaluate the bone defects and bone healing.

RESULTS

In both groups, spontaneous healing was insufficient to restore initial bone volume. The macroscopic pictures and the CBCT results showed a larger bone defect without periosteum. µCT results revealed that BMD, BV/TV, and Tb.Th were significantly lower without periosteum. The histological analyses showed (i) an increased osteoid apposition in the crestal area when periosteum was removed and (ii) an ossification process in the mandibular canal area in response to the surgical that seemed to increase when periosteum was removed.

CONCLUSIONS

A robust model of CSD model was developed in the alveolar bone of minipigs that mimics human mandibular bone defects. This model allows to further investigate the bone healing process and potential factors impacting healing such as periosteum.

CLINICAL RELEVANCE

This model may be relevant for testing different bone reconstruction strategies for preclinical investigations.

Potential of Bone-Marrow-Derived Mesenchymal Stem Cells for Maxillofacial and Periodontal Regeneration: A Narrative Review

Bone-marrow-derived mesenchymal stem cells (BM-MSCs) are one of the most widely studied postnatal stem cell populations and are considered to utilize more frequently in cell-based therapy and cancer. These types of stem cells can undergo multilineage differentiation including blood cells, cardiac cells, and osteogenic cells differentiation, thus providing an alternative source of mesenchymal stem cells (MSCs) for tissue engineering and personalized medicine. Despite the ability to reprogram human adult somatic cells to induced pluripotent stem cells (iPSCs) in culture which provided a great opportunity and opened the new door for establishing the in vitro disease modeling and generating an unlimited source for cell base therapy, using MSCs for regeneration purposes still have a great chance to cure diseases. In this review, we discuss the important issues in MSCs biology including the origin and functions of MSCs and their application for craniofacial and periodontal tissue regeneration, discuss the potential and clinical applications of this type of stem cells in differentiation to maxillofacial bone and cartilage in vitro, and address important future hopes and challenges in this field.

The use of rhBMP2 for augmentation of established horizontal/vertical defects may require additional use of rhVEGF to achieve significant bone regeneration: An in vivo experimental study

AIM

To test the hypothesis that the use of rhBMP2 in established defects requires additional growth factors such as rhVEGF to accomplish effective bone repair.

MATERIALS AND METHODS

Horizontal/vertical defects of 2 cm length and 1 cm height were created bilaterally in the alveolar crest of the maxillae of 18 minipigs together with the extraction of all premolar teeth and one molar tooth on both sides. After 3 months of healing, defects were augmented with 0.5 g particulate PDLLA/CaCO3 composite loaded with 400 µg rhBMP2/50 µg rhVEGF165 on one side and 800 µg rhBMP2 on the other in 12 test animals, whereas defects in six control animals were sham operated and left unfilled on one side and augmented with blank carriers on the other. After 4 and 13 weeks, the animals were evaluated each for area of new bone formation (mm²) and bone density (area %).

RESULTS

Augmentations with carriers loaded with 800 g µrhBMP2 failed to induce significantly more bone than in the augmentations with unloaded carrier after 4 and 13 weeks (p = .1000, p = .381). Augmentations with carriers loaded with 400 µg rhBMP2 and 50 µg erhVEGF165 resulted in significantly increased bone formation after 13 weeks (p = .024) compared to blank carriers. Soft tissue in augmentations with combined rhBMP2/rhVEGF165 loading exhibited numerous microvessels compared to soft tissue in augmentations with rhBMP2.

CONCLUSIONS

It is concluded that effective bone regeneration in augmentations of established alveolar ridge defects may require the application of rhVEGF additionally to rhBMP2.

Alloplastic Bone Substitutes for Periodontal and Bone Regeneration in Dentistry: Current Status and Prospects

Various bone graft products are commercially available worldwide. However, there is no clear consensus regarding the appropriate bone graft products in different clinical situations. This review is intended to summarize bone graft products, especially alloplastic bone substitutes that are available in multiple countries. It also provides dental clinicians with detailed and accurate information concerning these products. Furthermore, it discusses the prospects of alloplastic bone substitutes based on an analysis of the current market status, as well as a comparison of trends among countries. In this review, we focus on alloplastic bone substitutes approved in the United States, Japan, and Korea for use in periodontal and bone regeneration. According to the Food and Drug Administration database, 87 alloplastic bone graft products have been approved in the United States since 1996. According to the Pharmaceuticals and Medical Devices Agency database, 10 alloplastic bone graft products have been approved in Japan since 2004. According to the Ministry of Health and Welfare database, 36 alloplastic bone graft products have been approved in Korea since 1980. The approved products are mainly hydroxyapatite, β-tricalcium phosphate, and biphasic calcium phosphate. The formulations of the products differed among countries. The development of new alloplastic bone products has been remarkable. In the near future, alloplastic bone substitutes with safety and standardized quality may be the first choice instead of autologous bone; they may offer new osteoconductive and osteoinductive products with easier handling form and an adequate resorption rate, which can be used with growth factors and/or cell transplantation. Careful selection of alloplastic bone graft products is necessary to achieve predictable outcomes according to each clinical situation.

Tissue-engineered mandibular bone reconstruction for continuity defects: a systematic approach to the literature

BACKGROUND

Despite significant surgical advances over the last decades, segmental mandibular bone repair remains a challenge. In light of this, tissue engineering might offer a next step in the evolution of mandibular reconstruction.

PURPOSE

The purpose of the present report was to (1) systematically review preclinical in vivo as well as clinical literature regarding bone tissue engineering for mandibular continuity defects, and (2) to analyze their effectiveness.

MATERIALS AND METHODS

An electronic search in the databases of the National Library of Medicine and ISI Web of Knowledge was carried out. Only publications in English were considered, and the search was broadened to animals and humans. Furthermore, the reference lists of related review articles and publications selected for inclusion in this review were systematically screened. Results of histology data and amount of bone bridging were chosen as primary outcome variables. However, for human reports, clinical radiographic evidence was accepted for defined primary outcome variable. The biomechanical properties, scaffold degradation, and clinical wound healing were selected as co-outcome variables.

RESULTS

The electronic search in the databases of the National Library of Medicine and ISI Web of Knowledge resulted in the identification of 6727 and 5017 titles, respectively. Thereafter, title assessment and hand search resulted in 128 abstracts, 101 full-text articles, and 29 scientific papers reporting on animal experiments as well as 11 papers presenting human data on the subject of tissue-engineered reconstruction of mandibular continuity defects that could be included in the present review.

CONCLUSIONS

It was concluded that (1) published preclinical in vivo as well as clinical data are limited, and (2) tissue-engineered approaches demonstrate some clinical potential as an alternative to autogenous bone grafting.

Release kinetics of VEGF165 from a collagen matrix and structural matrix changes in a circulation model

Background

Current approaches in bone regeneration combine osteoconductive scaffolds with bioactive cytokines like BMP or VEGF. The idea of our in-vitro trial was to apply VEGF₁₆₅ in gradient concentrations to an equine collagen carrier and to study pharmacological and morphological characteristics of the complex in a circulation model.

Methods

Release kinetics of VEGF₁₆₅ complexed in different quantities in a collagen matrix were determined in a circulation model by quantifying protein concentration with ELISA over a period of 5 days. The structural changes of the collagen matrix were assessed with light microscopy, native scanning electron microscopy (SEM) as well as with immuno-gold-labelling technique in scanning and transmission electron microscopy (TEM).

Results

We established a biological half-life for VEGF₁₆₅ of 90 minutes. In a half-logarithmic presentation the VEGF₁₆₅ release showed a linear declining gradient; the release kinetics were not depending on VEGF₁₆₅ concentrations. After 12 hours VEGF release reached a plateau, after 48 hours VEGF₁₆₅ was no longer detectable in the complexes charged with lower doses, but still measurable in the 80 μg sample. At the beginning of the study a smear layer was visible on the surface of the complex. After the wash out of the protein in the first days the natural structure of the collagen appeared and did not change over the test period.

Conclusions

By defining the pharmacological and morphological profile of a cytokine collagen complex in a circulation model our data paves the way for further in-vivo studies where additional biological side effects will have to be considered. VEGF₁₆₅ linked to collagen fibrils shows its improved stability in direct electron microscopic imaging as well as in prolonged release from the matrix. Our in-vitro trial substantiates the position of cytokine collagen complexes as innovative and effective treatment tools in regenerative medicine and and may initiate further clinical research.

Establishment of cocultures of osteoblasts, Schwann cells, and neurons towards a tissue-engineered approach for orofacial reconstruction

In orofacial reconstruction not only the osseous structures themselves but also neighboring cranial nerves need to be regenerated. To replace autologous bone implants, biocompatible tissue-engineered scaffolds are under investigation at least for bone replacement but until now these studies have not focused on parallel reconstruction of injured cranial nerves. The present study contributes to the development of optimized tissue-engineered products that will enable regeneration of both bone and nervous tissue. For the first time, cocultures of primary osteoblasts (rat or human) and primary Schwann cells (rat or human) were established. The suitability of monocultures of osteoblasts and cocultures of osteoblasts plus Schwann cells as substrate for sensory neurons as well as motoneurons was tested here. The results suggest that whereas osteoblasts provide a good substrate for sensory neurons, motoneurons depend on the presence of Schwann cells for survival and neurite outgrowth. For prolonged availability of regeneration-promoting growth factors at the site of the graft, those proteins should be delivered by the transplanted cells themselves. To enable this, we established electroporation-based nonviral transfection of osteoblasts as well as Schwann cells. Our new cell culture system will enable investigations of the effect of graft-derived growth factors on osteoblasts and Schwann cells as well as on neurite outgrowth from cocultured neurons of the sensory and motor system.

Contour and volume assessment of repairing mandibular osteoperiosteal continuity defects in sheep using recombinant human osteogenic protein 1

BACKGROUND

This study describes the contour and volume of reconstructed mandibles using recombinant human osteogenic protein 1.

MATERIAL AND METHODS

The investigation was conducted on six adult sheep, where a unilateral 35 mm parasymphyseal osteoperiosteal continuity defect of the mandible was created. Recombinant human osteogenic protein 1 and type-I collagen (as carrier) were applied to the defects. Radiographic and ultrasonographic examinations were carried out at day 1 of the surgery and 2, 4, 8, and 12 weeks following the surgery. The animals were then sacrificed 3 months after the operation. Postmortem CT-scan was performed for volumetric, cross-sectional area, height and width measurements.

RESULTS

Ultrasound was more efficient than radiographs in demonstrating early callus formation at 2 weeks, while radiographic evidence of bone formation was consistently detectable only after 4 weeks. Using the combination of recombinant human osteogenic protein type 1 and type-I collagen resulted in twice the volume, cross-sectional surface area, and height when compared with those of the corresponding region of the contra-lateral non-operated side of the mandible.

CONCLUSION

Within 3 months, recombinant human osteogenic protein type 1 on type-I collagen carrier failed to restore the original contour and volume of mandibular osteoperiosteal continuity defects.

Effect of platelet-released growth factors and collagen type I on osseous regeneration of mandibular defects. A pilot study in minipigs

OBJECTIVE

To study the effects of platelet-released growth factors (PRGF) and collagen type I on bone defect healing in minipig mandibles.

MATERIAL AND METHODS

In eight adult minipigs defects were trephined in the facial mandibular wall from extra-oral and filled with collagen+PRGF or with collagen alone. Control defects were left untreated. PRGF were defined as the supernatants obtained after centrifugation of washed, thrombin-activated allogenic cells of platelet-rich plasma. The animals were sacrificed at 4 and 8 weeks. For histological analysis, undecalcified ground specimens stained with the Levai-Laczko stain were used.

RESULTS

For the entire follow-up, the amount of newly formed bone was 35.49 +/- 3.84% in the collagen+PRGF group, 46.34 +/- 3.84% in the collagen-only group and 33.83 +/- 4.11% in the controls. The differences between the collagen+PRGF and the collagen-only group (p = 0.0343), and between the collagen-only group and the controls (p = 0.0305) were significant. Histologically, defects filled with collagen+PRGF showed inflammatory reactions at 4 weeks, and new bone formation near the remnants of the filler collagen was reduced.

CONCLUSION

The data suggest that collagen type I alone, but not its combination with PRGF can support the early stages of cortical bone repair.

Protein adsorption, attachment, growth and activity of primary rat osteoblasts on polylactide membranes with defined surface characteristics

The adsorption of proteins and growth and activity of primary rat osteoblasts cultured for 1, 2 and 3 weeks on nonporous and porous resorbable poly(L/DL-lactide) 80/20% membranes with defined surface characteristics were investigated. The growth and activity of cells were estimated from the measurements of DNA, alkaline phosphatase activity and the total amount of protein in the cell lysate. The cell morphology was assessed from scanning electron microscopy and rhodamine staining. The protein adsorption to the membrane surface was assessed from the amide I peak at 1640-1660 cm(-1) and the amide II peak at 1540-1560 cm(-1) in the attenuated total reflection infrared spectra. The relative amount of proteins adsorbed on the nonporous and porous membranes was comparable. The cells growing on the nonporous and porous membranes maintained the phenotype and revealed morphology typical for osteoblasts. The mineralized noduli were larger in size on the porous membranes. The number of cells, the amount of DNA, the alkaline phosphatase activity, and the total amount of protein increased with time of the experiment and were higher for the porous membranes than for the nonporous ones.

The effect of pentosan polysulphate on bone healing of rat cranial defects

The purpose of the study was to determine the efficacy of pentosan polysulphate, used in combination with guided bone regeneration on rat skull defects. The study was conducted on 45 adult Wistar rats. On each animal two symmetrical 6 mm wide, full-thickness, skull defects were created in the parietal regions. The right defect was chosen as the experimental site and the left one was left empty to provide a control. Each experimental site was covered by an inner and outer polytetrafluoroethylene membrane. The 45 rats were divided into 3 groups: in group I (n = 15), carboxymethyl cellulose, used as a delivery vehicle, was injected between the two membranes; in group II (n = 15), 1 mg of pentosan polysulfate was added to the carboxymethyl cellulose vehicle; in group III (n = 15), purified micronized eggshell powder was added to the mixture of pentosan polysulfate and carboxymethyl cellulose between the two membranes. In each group, the animals were sacrificed at 42 days. The harvested specimens were processed for contact radiography and standard histological examination. The results were assessed by a Fisher's exact test. All animals, except one, healed uneventfully. In group I, partial bone healing was observed in 14 out of 15 animals. In group II, partial bone healing was observed in 13 out of 15 animals, and complete bone healing in 1 out of 15 cases. In group III, partial resorption of the eggshell implant was observed with a partial bone healing in only 2 cases (P < 0.001). In conclusion, significant bone regeneration was observed with the membranes alone. The use of pentosane polysulphate did not result in additional bone gain. The use of particulate material as a space maintainer is also questionable.