Effects of bone morphogenetic protein 2 gene therapy on new bone formation during mandibular distraction osteogenesis at rapid rate in rabbits

Applications of Biotechnology to the Craniofacial Complex: A Critical Review

BACKGROUND

Biotechnology shows a promising future in bridging the gap between biomedical basic sciences and clinical craniofacial practice. The purpose of the present review is to investigate the applications of biotechnology in the craniofacial complex.

METHODS

This critical review was conducted by using the following keywords in the search strategy: "biotechnology", "bioengineering", "craniofacial", "stem cells", "scaffolds", "biomarkers", and "tissue regeneration". The databases used for the electronic search were the Cochrane Library, Medline (PubMed), and Scopus. The search was conducted for studies published before June 2022.

RESULTS

The applications of biotechnology are numerous and provide clinicians with the great benefit of understanding the etiology of dentofacial deformities, as well as treating the defected areas. Research has been focused on craniofacial tissue regeneration with the use of stem cells and scaffolds, as well as in bioinformatics with the investigation of growth factors and biomarkers capable of providing evidence for craniofacial growth and development. This review presents the biotechnological opportunities in the fields related to the craniofacial complex and attempts to answer a series of questions that may be of interest to the reader.

CONCLUSIONS

Biotechnology seems to offer a bright future ahead, improving and modernizing the clinical management of cranio-dento-facial diseases. Extensive research is needed as human studies on this subject are few and have controversial results.

Experimental Study on the Bone Morphogenetic Protein 1-Modified Bone Marrow Mesenchymal Stem Cell Sheets to Promote Mandibular Distraction Osteogenesis

Objective

The present study aims to increase the concentration of genetically modified bone marrow mesenchymal stem cells (BMSCs) in the distraction osteogenesis (DO) interstitial space and induce the conversion of BMSCs to osteoblasts to improve the osteogenic efficiency in DO and shorten the treatment period.

Methods

Bone morphogenetic protein 1 (BMP-1) and green fluorescent protein (GFP) gene-modified cell sheets of BMSCs were constructed by tissue engineering. Thirty-six New Zealand white rabbits were randomly divided into three groups: group A (the blank control group), group B (the GFP group) with the injection of GFP gene-modified BMSC sheets into the DO gap, and group C (the BMP-1 group) with the injection of BMP-1 gene-modified BMSC sheets into the DO gap. Rabbits in all three groups were distracted for 5 days at a distraction rate of 2.0 mm/d, once/day. After distraction, the above-mentioned cell sheet suspension was injected into the distraction gap to observe osteogenesis, which was observed by gross specimen observation, micro-computed tomography (Micro-CT) scanning, and histomorphology.

Results

The gross specimen observation showed that all animals had smooth and continuous bone cortex in the distraction region with relatively high hardness. The osteogenesis quality or hardness was ranked from the highest to the lowest, as Group C > Group B > Group A. Micro-CT and histomorphological observation revealed that group C had better maturation and bone volume of the new bone in the DO region at weeks 3 and 6 than groups B and A.

Conclusion

BMP-1 gene-modified BMSC sheets could effectively promote the formation of new bone during rapid DO in the mandible, compensating for the poor osteogenesis caused by rapid distraction and providing a new approach to shorten the DO treatment period in clinical practice.

Enhancing the Efficiency of Distraction Osteogenesis through Rate-Varying Distraction: A Computational Study

Distraction osteogenesis (DO) is a mechanobiological process of producing new bone and overlying soft tissues through the gradual and controlled distraction of surgically separated bone segments. The process of bone regeneration during DO is largely affected by distraction parameters. In the present study, a distraction strategy with varying distraction rates (i.e., "rate-varying distraction") is proposed, with the aim of shortening the distraction time and improving the efficiency of DO. We hypothesized that faster and better healing can be achieved with rate-varying distractions, as compared with constant-rate distractions. A computational model incorporating the viscoelastic behaviors of the callus tissues and the mechano-regulatory tissue differentiation laws was developed and validated to predict the bone regeneration process during DO. The effect of rate-varying distraction on the healing outcomes (bony bridging time and bone formation) was examined. Compared to the constant low-rate distraction, a low-to-high rate-varying distraction provided a favorable mechanical environment for angiogenesis and bone tissue differentiation, throughout the distraction and consolidation phase, leading to an improved healing outcome with a shortened healing time. These results suggest that a rate-varying clinical strategy could reduce the overall treatment time of DO and decrease the risk of complications related to the external fixator.

Effect of bone marrow stromal cells in combination with biomaterials in early phases of distraction osteogenesis: An experimental study in a rabbit femur model

Acceleration of the consolidation of the distracted bone is a relevant medical need. As a platform to improve in vivo bone engineering, we developed a novel distraction osteogenesis (DO) model in a rabbit large bone (femur) and tested if the application of cultured bone marrow stromal cells (BMSCs) immediately after the osteotomy promotes the formation of bone. This report consists of two components, an animal study to evaluate the quality of the regenerate following different treatments and an in vitro study to evaluate osteogenic potential of BMSC cultures. To illuminate the mechanism of action of injected cells, we tested stem cell cultures enriched in osteogenic-BMSCs (O-BMSCs) as compared with cultures enriched in non-osteogenic BMSCs (NO-BMSCs). Finally, we included a group of animals treated with biomaterials (fibrin and ground cortical bone) in addition to cells. Injection of O-BMSCs promoted the maturity of distracted callus and decreased fibrosis. When combined with biomaterials, O-BMSCs modified the ossification pattern from endochondral to intramembranous type. The use of NO-BMSCs not only did not increase the maturity but also increased porosity of the bone. These preclinical results indicate that the BMSC cultures must be tested in vitro prior to clinical use, since a number of factors may influence their outcome in bone formation. We hypothesize that the use of osteogenic BMSCs and biomaterials could be clinically beneficial to shorten the consolidation period of the distraction and the total period of bone lengthening.

Changes in osteogenic gene expression in hypertrophic chondrocytes induced by SIN-1

The molecular mechanisms underlying osteoarthritis (OA) and Kashin-Beck disease (KBD) remain poorly understood. Hypertrophic chondrocytes serve an important role in the development of both OA and KBD, whereas oxidative stress can contribute to the pathological progression of cartilage damage. Therefore, the aim of the present study was to detect altered expression of osteogenesis-related genes in hypertrophic chondrocytes, following treatment with 3-morpholinosydnonimine (SIN-1). ATDC5 cells were induced to develop into hypertrophic chondrocytes via Insulin-Transferrin-Selenium. The appropriate concentration and time of SIN-1 treatment was determined via MTT assay. Following hypertrophic chondrocyte stimulation with SIN-1, a liquid chip was analyzed using a polymerase chain reaction (PCR) array. Reverse transcription-quantitative PCR was conducted on individual genes to validate the array-based data. Analyses of protein-protein interactions, gene ontology functions and Kyoto Encyclopedia of Genes and Genomes pathway enrichment of the differentially expressed genes were also performed. A total of 6 upregulated and 34 downregulated genes were identified, including the mothers against decapentaplegic homolog (Smad) family (Smad1-4), bone morphogenetic proteins and their receptors (Bmp2, Bmp3, Bmpr1α and Bmpr1β), and matrix metalloproteinases (MMP2,−9 and−10). These genes are associated with collagen biology, transcriptional control, skeletal development, bone mineral metabolism, and cell adhesion. SIN-1 induced death of hypertrophic chondrocytes likely through TGF-β/Smad or BMP/Smad pathways. Oxidative-stress-dependent induction of abnormal gene expression may be associated with chondronecrosis in the cartilage of patients with OA or KBD.

Applications of stem cells in orthodontics and dentofacial orthopedics: Current trends and future perspectives

A simple overview of daily orthodontic practice involves use of brackets, wires and elastomeric modules. However, investigating the underlying effect of orthodontic forces shows various molecular and cellular changes. Also, orthodontics is in close relation with dentofacial orthopedics which involves bone regeneration. In this review current and future applications of stem cells (SCs) in orthodontics and dentofacial orthopedics have been discussed. For craniofacial anomalies, SCs have been applied to regenerate hard tissue (such as treatment of alveolar cleft) and soft tissue (such as treatment of hemifacial macrosomia). Several attempts have been done to reconstruct impaired temporomandibular joint. Also, SCs with or without bone scaffolds and growth factors have been used to regenerate bone following distraction osteogenesis of mandibular bone or maxillary expansion. Current evidence shows that SCs also have potential to be used to regenerate infrabony alveolar defects and move the teeth into regenerated areas. Future application of SCs in orthodontics could involve accelerating tooth movement, regenerating resorbed roots and expanding tooth movement limitations. However, evidence supporting these roles is weak and further studies are required to evaluate the possibility of these ideas.

[Research of enhanced green fluorescent protein gene transfer with ultrasound-mediated microbubble destruction in bone defects]

Objective

To investigate the effect of ultrasonic irradiation time on enhanced green fluorescent protein (EGFP) gene transfection efficiency and local tissue in bone defects using ultrasound-mediated microbubble destruction.

Methods

Thirty 3-month-old New Zealand rabbits (2.5-3.0 kg in weight) were randomly divided into 5 groups ( n=6) and bone defect models were made on the right ulna. At 10 days after modeling, suspension of microbubbles and EGFP plasmids were locally injected (0.3 mL/kg) and then ultrasound was performed on defect at a frequency of 1 MHz, a intensity of 0.5 W/cm 2, and a duty ratio of 20% for 1, 2, 3, 4, and 5 minutes respectively (in 1, 2, 3, 4, and 5 minutes groups respectively). The survival condition was observed. Rabbits were sacrificed for gross observation at 7 days after transfer. The gene expression was observed by fluorescence staining. HE staining and transmission electron microscopy were used to observe the local tissue damage.

Results

The animals all survived. New soft tissue formed in bone defects area at 1 week after transfer, the surrounding muscle tissue was partly filled in it. Green fluorescence expression was observed in all rabbits. The expression was the strongest in 2 minutes group, and was the weakest in 1 minute group. The absorbance ( A) value showed significant differences when compared 1 minute and 2 minutes groups with other groups ( P<0.05), but no significant difference was found between 3, 4, and 5 minutes groups ( P>0.05). Tissue damage was observed in all groups and it was aggravated with the increase of irradiation time.

Conclusion

EGFP transfection efficiency in bone defect by ultrasound-mediated microbubble destruction is related to irradiation time. EGFP gene can be efficiently transfected without obvious toxicity at 1 MHz, 0.5W/cm 2, and duty ratio of 20% for 2 minutes in bone defects of rabbits.

Gene Therapy for Bone Defects in Oral and Maxillofacial Surgery: A Systematic Review and Meta-Analysis of Animal Studies

Craniofacial bone defects are challenging problems for maxillofacial surgeons over the years. With the development of cell and molecular biology, gene therapy is a breaking new technology with the aim of regenerating tissues by acting as a delivery system for therapeutic genes in the craniofacial region rather than treating genetic disorders. A systematic review was conducted summarizing the articles reporting gene therapy in maxillofacial surgery to answer the question: Was gene therapy successfully applied to regenerate bone in the maxillofacial region? Electronic searching of online databases was performed in addition to hand searching of the references of included articles. No language or time restrictions were enforced. Meta-analysis was done to assess significant bone formation after delivery of gene material in the surgically induced maxillofacial defects. The search identified 2081 articles, of which 57 were included with 1726 animals. Bone morphogenetic proteins were commonly used proteins for gene therapy. Viral vectors were the universally used vectors. Sprague-Dawley rats were the frequently used animal model in experimental studies. The quality of the articles ranged from excellent to average. Meta-analysis results performed on 21 articles showed that defects favored bone formation by gene therapy. Funnel plot showed symmetry with the absence of publication bias. Gene therapy is on the top list of innovative strategies that developed in the last 10 years with the hope of developing a simple chair-side protocol in the near future, combining improvement of gene delivery as well as knowledge of the molecular basis of oral and maxillofacial structures.

Scaffold-Based Delivery of Bone Marrow Mesenchymal Stem Cell Sheet Fragments Enhances New Bone Formation In Vivo

PURPOSE

Stem cell therapy is becoming a potent strategy to shorten the consolidation time and reduce potential complications during distraction osteogenesis (DO). However, the conventional local injection or scaffold-based delivery of bone marrow mesenchymal stem cell (BMSC) suspension deprives the cells of their endogenous extracellular matrix, which might dampen cell differentiation and tissue regeneration after implantation. Therefore, in our study, a BMSC sheet was established and was then minced into fragments and loaded onto a hydroxyapatite (HA) scaffold for grafting.

MATERIALS AND METHODS

The purified and characterized BMSCs were grown into a cell sheet, and bone formation and mineralization capacity, as well as the cell sheet composition, were analyzed. Afterward, the in vivo osteogenic ability of cell sheet fragments (CSFs) was evaluated in immunocompromised mouse and rabbit models of DO.

RESULTS

The BMSC sheet exhibited higher alkaline phosphatase activity than osteogenic cell suspension cultures. Alkaline phosphatase activity and mineral particles in the cell sheet increased further after osteogenic induction. Moreover, calcium and phosphorus were present only in the osteogenic cell sheet, along with the common elements carbon, oxygen, chlorine, sodium, and sulfur, as indicated by x-ray photoelectron spectroscopy analysis. In a mouse model, the CSF-HA complex was injected subcutaneously. Micro-computed tomography analysis showed that the osteogenic CSF-HA complex led to a considerably higher bone volume than the BMSC-HA or CSF-HA complex. The osteogenic CSF-HA specimens showed increased angiogenesis and deposition of type I collagen compared with the non-osteogenic CSF-HA or BMSC-HA specimens. Moreover, the osteogenic CSF-HA markedly improved bone consolidation and increased bone mass in DO rabbits.

CONCLUSIONS

Collectively, the incorporation of osteogenic BMSC sheets into HA particles greatly promoted bone regeneration, which offers therapeutic alternatives for DO.

Mandibular distraction osteogenesis assisted by cell-based tissue engineering: a systematic review

OBJECTIVES

To review the advances and limitations of recent investigations on mandibular distraction osteogenesis (MDO) assisted by mesenchymal stem cell (MSC) transplantation.

MATERIALS AND METHODS

Following the preferred reporting items for systematic reviews and meta-analysis (PRISMA) guidelines, the PubMed, Scopus, and Cochrane electronic databases were systematically searched and screened from their inception through August 2014. Searching terms included the following: 'distraction osteogenesis', 'mandible OR mandibular OR jaw', and 'cells', without any other limitations.

RESULTS

Nineteen studies meeting the eligibility criteria were selected from 227 published articles and used for qualitative synthesis. Fifteen of the studies used small animal models (rats or rabbits), while the other four used large animal models (dogs, pigs or sheep). Among these studies, large variations exist in MDO protocol, cell transplantation time, route and quantity, as well as methodology of outcome assessment. Additionally, all studies had certain biases. Nevertheless, the majority of studies found that MSC transplantation enhanced MDO bone regeneration.

CONCLUSION

Evidence from animal studies indicates that MDO may be enhanced by mesenchymal stem cell transplantation, but many questions related to animal models, MDO protocols, and cell transplantation remain to be investigated.

A New Way to Accelerate the Distraction of the Transpalatal Suture in Growing Dogs Using Recombinant Human Bone Morphogenetic Protein-2

OBJECTIVE

The purpose of this study was to evaluate the administration of recombinant human bone morphogenetic protein-2 (rhBMP-2) on trans-sutural distraction osteogenesis (TSDO) of the transverse palatal suture in growing dogs.

STUDY DESIGN

A total of 36 growing dogs were used in this study. The experimental animals were treated with different elastic force and rhBMP-2. The bone regeneration was determined with X-ray, histology, and clinical evaluation. The computed values underwent statistical analyses using analysis of variance.

RESULTS

The maxillary complex was most noticeably advanced with an applied elastic force of 600 g (22.4 ± 5.0 mm) and 800 g + rhBMP-2 (24 ± 5.1 mm). Immunohistochemical staining showed that the expression of bone morphogenetic protein-2 and bone morphogenetic protein-4 varied with different elastic force. These changes were statistically significant when 600 g and 800 g + rhBMP-2 were applied within 2 weeks of distraction when compared with controls (P < .05).

CONCLUSIONS

The results of this study suggest that TSDO in the growing dog should be safe and well tolerated when inducing bony lengthening of the maxilla. rhBMP-2 plays an important role in bone regeneration using TSDO.

Transport distraction osteogenesis with recombinant human bone morphogenic protein-2 for large calvarial defect reconstruction

BACKGROUND

Transport distraction osteogenesis (TDO) has been used in attempts to treat large calvarial defects but has, until now, lacked consistency and reliability. To achieve sufficient bone formation, the effect of TDO was compared to the effect of TDO combined with recombinant human bone morphogenic protein-2 (rhBMP-2).

METHODS

Fourteen dogs were divided into 2 groups; 6 animals in the control group received TDO only, and 8 received TDO combined with rhBMP-2. A calvarial defect 33 × 35 mm in size was generated, and the drug-delivering internal distractor was applied. After a 5-day latency period, distraction with rhBMP-2 at 10 μg/day was initiated at a rate of 2 mm/day. This was followed by a consolidation period of 3 months, after which areas of osteogenesis and strength were measured and histologic examinations were conducted.

RESULTS

The average area of osteogenesis was higher in the experimental group (P < 0.01). Regenerated bone of the experimental group showed increased strength (P < 0.05). Histological examination showed typical mature bone in the experimental group. Prominent osteoblastic rimming was observed in the bone marrow of the experimental group.

CONCLUSIONS

TDO with an internal distraction device delivering rhBMP-2 can enhance bone regeneration of large calvarial defects in a dog model. These results suggest the potential for human clinical testing of TDO combined with rhBMP-2.

Necessity of latency period in craniofacial distraction: Investigations with in vitro microdistractor and clinical outcomes

BACKGROUND

To determine the need for latency period in membranous bone distraction, we performed 1) in vitro comparison of preosteoblasts suspended in a 3D microdistraction model and 2) a clinical study comparing mandibular distraction cases with/without latency.

METHODS

In the In Vitro study, Preosteoblasts polymerized in 3D-collagen gel were placed in a microdistractor and separated into three groups: 1) distraction with latency, 2) distraction without latency, and 3) static. After 2, 4, 6, and 8 days, cell proliferation, total protein levels, alkaline phosphatase activity, and osteogenic gene expression were assessed through RT-PCR. In the clinical study, patients underwent mandibular distraction in two groups: 1) latency and 2) no latency (n = 45). The rest of the distraction protocol was identical. Outcome was based on clinical examination, radiographs at six months, and 3D CT scans.

RESULTS

In the In Vitro study, The distraction without latency group compared to the latency group had delays in: proliferation, total protein count, alkaline phosphatase activity, osteogenic gene expression in CBFA-1 (fourfold vs. eighteenfold), and in osteocalcin (twofold vs. sixfold). The distraction without latency group had higher apoptotic levels during the first four days compared to the latency group (68% vs. 14%). For the clinical study, similar perioperative complications (5% vs. 6%), X-ray mineralization (93% vs. 94%), bone volume, (8.6 vs. 9.1 cc) and bone density of central distraction zone (78% vs. 81%) were observed with or without latency.

CONCLUSIONS

In vitro studies showed poorer results in cell survival, proliferation and osteogenic activity compared to distraction with latency; yet, clinically, there were no differences in distraction with latency versus without.

New bone formation enhanced by ADSCs overexpressing hRunx2 during mandibular distraction osteogenesis in osteoporotic rabbits

Promoting new bone formation during distraction osteogenesis (DO) in elderly patients with osteoporosis is still a challenge. In this study, we investigated the effect of gene therapy using local Runt-related gene 2 on new bone formation during osteoporotic mandibular DO in rabbits. First, we successfully established a mandibular osteoporotic animal model by ovariectomizing rabbits. Second, the right mandibles of the osteoporotic rabbits were distracted after corticotomy. The distraction gap of the rabbits in Group A2 and B2 were injected with Adv-hRunx2-GFP-transfected adipose-derived stromal cells (ADSCs) and Adv-GFP-transfected ADSCs, respectively. Rabbits in Groups C2 (ovariectomized control) and D2 (sham surgery control) were injected with physiologic saline. New-generation bone tissue in the distraction gap was analyzed via plain radiographic examinations, micro-computed tomography, histological examinations, and biomechanical testing at weeks 3, 6, and 9 of the consolidation period. Results of above examinations showed that no ideal new bone formation was observed in Groups B2 and C2, but obvious ideal new bone formation was observed in Group A2 and D2. The results suggested that gene therapy using rhRunx2-modified ADSCs promoted new bone formation during osteoporotic mandibular DO and effectively compensated for the detrimental effects of systemic osteoporosis on new bone formation.

In-vitro analysis of rhBMP-2 effects in human osteogenic cells

This study evaluated the in vitro expression of bone-related proteins by osteoblasts in the presence of different concentrations of human recombinant bone morphogenetic protein-2 (rhBMP-2). Immortalized human fetal osteoblastic cell line 1.19 (hFOB) were exposed to different concentrations of rhBMP-2 (10, 50, or 100 ng/mL) for 72 h. Cell proliferation and viability (MTT assay), as well as the expression of fibronectin, osteonectin, and osteopontin were assessed by indirect immunofluorescence and Western blot. Neither of the 3 concentrations of rhBMP-2 caused statistically significant alterations in cell proliferation and viability, although the concentration of 100 ng/mL showed lower values for both assays after both 48 and 72 h of exposure. There was no alteration in the expression of noncollagenous proteins, as analyzed by immunofluorescence, when compared with the control group. Furthermore, in the Western blot assay we observed a statistically significant decrease in fibronectin and osteonectin at 100 ng rhBMP-2/mL (p < 0.05) by comparison with the medium alone. The expression of osteopontin decreased slightly in all 3 concentrations of rhBMP-2 tested; however, the change was not statistically significant (p > 0.05). In this in-vitro study, the tested concentrations of rhBMP-2 appeared to decrease the expression of important bone-related molecules in pre-osteoblast cells.

Scaffold-based delivery of autologous mesenchymal stem cells for mandibular distraction osteogenesis: preliminary studies in a porcine model

Purpose

Bone regeneration through distraction osteogenesis (DO) is promising but remarkably slow. To accelerate it, autologous mesenchymal stem cells have been directly injected to the distraction site in a few recent studies. Compared to direct injection, a scaffold-based method can provide earlier cell delivery with potentially better controlled cell distribution and retention. This pilot project investigated a scaffold-based cell-delivery approach in a porcine mandibular DO model.

Materials and Methods

Eleven adolescent domestic pigs were used for two major sets of studies. The in-vitro set established methodologies to: aspirate bone marrow from the tibia; isolate, characterize and expand bone marrow-derived mesenchymal stem cells (BM-MSCs); enhance BM-MSC osteogenic differentiation using FGF-2; and confirm cell integration with a gelatin-based Gelfoam scaffold. The in-vivo set transplanted autologous stem cells into the mandibular distraction sites using Gelfoam scaffolds; completed a standard DO-course and assessed bone regeneration by macroscopic, radiographic and histological methods. Repeated-measure ANOVAs and t-tests were used for statistical analyses.

Results

From aspirated bone marrow, multi-potent, heterogeneous BM-MSCs purified from hematopoietic stem cell contamination were obtained. FGF-2 significantly enhanced pig BM-MSC osteogenic differentiation and proliferation, with 5 ng/ml determined as the optimal dosage. Pig BM-MSCs integrated readily with Gelfoam and maintained viability and proliferative ability. After integration with Gelfoam scaffolds, 2.4–5.8×10⁷ autologous BM-MSCs (undifferentiated or differentiated) were transplanted to each experimental DO site. Among 8 evaluable DO sites included in the final analyses, the experimental DO sites demonstrated less interfragmentary mobility, more advanced gap obliteration, higher mineral content and faster mineral apposition than the control sites, and all transplanted scaffolds were completely degraded.

Conclusion

It is technically feasible and biologically sound to deliver autologous BM-MSCs to the distraction site immediately after osteotomy using a Gelfoam scaffold to enhance mandibular DO.

Non-viral gene therapy for bone tissue engineering

The possibilities of using gene therapy for bone regeneration have been extensively investigated. Improvements in the design of new transfection agents, combining vectors and delivery/release systems to diminish cytotoxicity and increase transfection efficiencies have led to several successful in vitro, ex vivo and in vivo strategies. These include growth factor or short interfering ribonucleic acid (siRNA) delivery, or even enzyme replacement therapies, and have led to increased osteogenic differentiation and bone formation in vivo. These results provide optimism to consider use in humans with some of these gene-delivery strategies in the near future.

The rabbit as experimental model for research in implant dentistry and related tissue regeneration

The use of rabbits for experimental research has a long historical tradition. The aim of this review consists in outlining the use of the rabbit for research in implant dentistry and related tissue regeneration. Rabbits appear as a first-hand choice for fundamental implant design studies because of their size, easy handling, short life span, and economical aspects in purchasing and sustaining. In the following, the various anatomical sites in the rabbit will be summarized to provide an overview of current possibilities and limitations of this model for bone research in oral implantology.

Transsutural distraction and tissue regeneration of the midfacial skeleton: experimental studies in growing dogs

Objective : The purpose of this study was to evaluate the effect of different mechanical forces on the expansion of the palatine suture using transsutural distraction osteogenesis. Methods : A total of 48 dogs were used in this study. The experimental groups were treated with a custom-designed internal distractor. Bone regeneration was determined with x-rays and histology. The computed values underwent statistical analyses using analysis of variance. Results : The maxillary complex was most noticeably advanced with an applied mechanical force of 600 g (20.15 ± 1.36 mm), compared with forces of 400 g (19.88 ± 1.41 mm) and 800 g (2.24 ± 0.93 mm). Immunohistochemical staining showed that the expression of bone morphogenetic protein-2 and bone morphogenetic protein-4 fluctuated with different mechanical forces. These changes were statistically significant when 600 g of force was applied within 30 days of distraction (P < .05). Conclusions : Transsutural distraction osteogenesis in the growing dog should be safe and well tolerated in inducing bony lengthening of the maxilla, and the optimal force is 600 × g. Bone morphogenetic protein-2 and bone morphogenetic protein-4 may play an important roles in the signaling pathways that link mechanical forces and biological responses.

Heal thyself: using endogenous regeneration to repair bone

Bone has the capacity to repair itself after an injury, and this occurs in normal fracture repair. This reparative process can be harnessed to regenerate segments of bone using distraction osteogenesis, in which the healing bone is slowly stretched. The use of animal models is identifying the important sources of cells for this endogenous bone regeneration, signaling molecules that regulate this reparative process, and the environmental cues important for success bone regeneration. A more complete understanding of the cells and pathways involved in this process can be applied to improve the outcome of distraction osteogenesis and to the development of methods to enhance endogenous bone regeneration.