Ui-Won Jung

The induction of bone formation in rat calvarial defects and subcutaneous tissues by recombinant human BMP-2, produced in Escherichia coli

We investigated the ability of recombinant human bone morphogenetic protein-2, produced from Escherichia coli (ErhBMP-2), to form orthotopic and ectopic bone in rat models. BMP-2 was expressed in E. coli and extracted from the inclusion bodies. Critical-sized calvarial defects and subcutaneous pouches were created in rats, and an absorbable collagen sponge (ACS) was loaded with different doses of ErhBMP-2 for implantation. ACS alone and sham surgery controls were also included. Implant sites were evaluated by histological and/or histometric analyses following a 2- or 8-week healing interval. In the calvarial defect model, enhanced bone formation was observed with all doses of ErhBMP-2, while only limited amounts of new bone were found in controls. In the ectopic subcutaneous implant model, bone formation was clearly observed in all animals treated with ErhBMP-2 at 2 weeks. However, at 8 weeks, less new bone formation was detected than at 2 weeks. Nevertheless, the remaining new bone showed an advanced degree of bone remodeling and more maturity than that observed at 2 weeks. These results showed that ErhBMP-2 was osteoinductive under controlled in vivo conditions. Thus, ErhBMP-2 has definite potential as an alternative to rhBMP-2 produced in a eukaryotic system for clinical use.

Spontaneous healing capacity of rabbit cranial defects of various sizes

Purpose This study evaluated the spontaneous healing capacity of surgically produced cranial defects in rabbits with different healing periods in order to determine the critical size defect (CSD) of the rabbit cranium. Methods Thirty-two New Zealand white rabbits were used in this study. Defects of three sizes (6, 8, and 11 mm) were created in each of 16 randomly selected rabbits, and 15-mm defects were created individually in another 16 rabbits. The defects were analyzed using radiography, histologic analysis, and histometric analysis after the animal was sacrificed at 2, 4, 8, or 12 weeks postoperatively. Four samples were analyzed for each size of defect and each healing period. Results The radiographic findings indicated that defect filling gradually increased over time and that smaller defects were covered with a greater amount of radiopaque substance. Bony islands were observed at 8 weeks at the center of the defect in both histologic sections and radiographs. Histometrical values show that it was impossible to determine the precise CSD of the rabbit cranium. However, the innate healing capacity that originates from the defect margin was found to be constant regardless of the defect size. Conclusions The results obtained for the spontaneous healing capacity of rabbit cranial defects over time and the underlying factors may provide useful guidelines for the development of a rabbit cranial model for in vivo investigations of new bone materials.

Osteoinductive activity of biphasic calcium phosphate with different rhBMP-2 doses in rats.

OBJECTIVE The aim of the current study was to determine whether a hydroxyapatite (HA)/beta-tricalcium phosphate (β-TCP) ratio of 20/80 impregnated with recombinant human bone morphogenetic protein (rhBMP-2) enhances new bone formation and to evaluate the dose-dependent response of rhBMP-2. STUDY DESIGN Critical-sized calvarial defects were made in rats, and biphasic calcium phosphate (BCP) with different rhBMP-2 doses was loaded into rat calvarial defects. The animals were allowed to heal for either 2 or 8 weeks. RESULTS The percentages of new bone after 2 and 8 weeks of healing were significantly greater in the rhBMP-2-treated groups (at all doses) than in the control groups. The percentage of remaining BCP was significantly lower at 8 weeks than at 2 weeks in all groups that included BCP. CONCLUSIONS rhBMP-2 administered using a BCP carrier significantly induces new bone formation. A dose-dependent response was not shown in the present study.

Periodontal wound healing/regeneration following implantation of recombinant human growth/differentiation factor‐5 in a β‐tricalcium phosphate carrier into one‐wall intrabony defects in dogs

OBJECTIVE Recombinant human growth/differentiation factor-5 (rhGDF-5) is being evaluated as a candidate therapy in support of periodontal regeneration. The objective of this study was to evaluate periodontal wound healing/regeneration following the application of rhGDF-5 on a particulate beta-tricalcium phosphate (beta-TCP) carrier using an established defect model. MATERIALS AND METHODS Bilateral 4 x 5 mm (width x depth), one-wall, critical-size, intrabony periodontal defects were surgically created at the mandibular second and fourth pre-molar teeth in 15 Beagle dogs. Unilateral defects in five animals received rhGDF-5/beta-TCP (Scil Technology GmbH); five animals received beta-TCP solo; and five animals served as sham-surgery controls. Contralateral sites received treatments reported elsewhere. The animals were sacrificed following an 8-week healing interval for histological examination. RESULTS Clinical healing was generally uneventful. Sites implanted with rhGDF-5/beta-TCP exhibited greater enhanced cementum and bone formation compared with beta-TCP and sham-surgery controls; cementum regeneration averaged (+/- SD) 3.83 +/- 0.73 versus 1.65 +/- 0.82 and 2.48 +/- 1.28 mm for the controls (p<0.05). Corresponding values for bone regeneration height averaged 3.26 +/- 0.30 versus 1.70 +/- 0.66 and 1.68 +/- 0.49 mm (p<0.05), and bone area 10.45 +/- 2.26 versus 6.31 +/- 2.41 and 3.00 +/- 1.97 mm(2) (p<0.05). Cementum regeneration included cellular/acellular cementum with or without a functionally oriented periodontal ligament. A non-specific connective tissue attachment was evident in the sham-surgery control. Controls exhibited mostly woven bone with primary osteons, whereas rhGDF-5/beta-TCP sites showed a noticeable extent of lamellar bone. Sites receiving rhGDF-5/beta-TCP or beta-TCP showed some residual beta-TCP granules apparently undergoing biodegradation without obvious differences between the sites. Sites receiving beta-TCP alone commonly showed residual beta-TCP granules sequestered in the connective tissue or fibrovascular marrow. CONCLUSION rhGDF-5/beta-TCP has a greater potential to support the regeneration of the periodontal attachment. Long-term studies are necessary to confirm the uneventful maturation of the regenerated tissues.

Osteoconductivity and biodegradation of synthetic bone substitutes with different tricalcium phosphate contents in rabbits.

Various synthetic bone substitutes have been developed to reconstruct the bony defects that clinicians often encounter during surgical procedures. Among various synthetic bone substitutes, calcium phosphate (Ca-P) ceramics have been investigated because their composition and structure are similar to those of human bone. We evaluated the bone healing and biodegradation patterns of three types of Ca-P ceramic particle with various hydroxyapatite (HA)/β-tricalcium phosphate (β-TCP) weight ratio: pure β-TCP, biphasic Ca-P (BCP) with a HA/β-TCP weight ratio of 60/40 (BCP 60/40), and BCP with an HA/β-TCP weight ratio of 20/80 (BCP 20/80). Four 8-mm-diameter defects were created in ten rabbits. Three of the defects in each rabbit were separately and randomly filled with one of the three experimental Ca-P ceramic particles, and the fourth was filled with blood clots (control). The specimens were harvested at 2 and 8 weeks post-surgery. The histologic and histometric findings revealed that the augmented space and new bone formation were significantly better for all three Ca-P ceramics than for the control group at both 2 and 8 weeks (p < 0.05). Compared to the pure β-TCP, the two BCP groups were found to provide a larger amount of newly formed bone and bone density at the 2- and 8-week post-operative periods (p < 0.05). Throughout the observation period, BCP 60/40 and BCP 20/80 exhibited a similar bone healing and biodegradation patterns with regard to both individual particles and the total augmented area in vivo.

Histologic and clinical evaluation for maxillary sinus augmentation using macroporous biphasic calcium phosphate in human.

OBJECTIVES This study evaluated both the clinical and histological aspects of bone formation in maxillary sinus augmentation using MBCP as the bone-grafting material. MATERIAL AND METHODS MBCP was used as a primary bone substitute for maxillary sinus augmentation. Fifty-two patients were selected after a medical and dental examination, and were divided into the following three groups: those augmented with MBCP only; MBCP combined with irradiated cancellous bone; and MBCP combined with intraoral autogenous bone. After a healing period (average 6.78 months after surgery), bone cores were harvested for a histological evaluation and the implant fixtures were installed. These bone cores were evaluated via light microscope and implants were followed up for at least six months after loading. RESULTS Four to ten months after surgery, new vital bone surrounding the MBCP particles was observed in 18 bone biopsies. Two out of the 130 implants installed were explanted due to a failure of osseointegration before the prosthetic procedure. All the remaining implants were functioning for 6 to 27 months (average 12.96 months). The cumulative survival rate of the implants was 98.46%. CONCLUSION These results show that MBCP can be used as a grafting material for sinus floor augmentation, whether combined with other bone graft materials or not, and lead to a predictable prognosis for dental implants in the posterior maxillary area where there is insufficient vertical height for fixture installation.

Sinus augmentation using absorbable collagen sponge loaded with Escherichia coli‐expressed recombinant human bone morphogenetic protein 2 in a standardized rabbit sinus model: a radiographic and histologic analysis

OBJECTIVES The purpose of this pilot study was to determine the osteoinductive effect of absorbable collagen sponge (ACS) loaded with Escherichia coli-expressed recombinant human bone morphogenetic protein 2 (ErhBMP-2) and evaluate structural stability of ACS in a standardized rabbit sinus model. MATERIAL AND METHODS The maxillary sinuses were prepared bilaterally in six male white rabbits. The windows were prepared using a 6 mm trephine bur, and circular bony windows were carefully removed. Following reflection of the sinus membrane, a saline-soaked ACS alone and an ErhBMP-2-loaded ACS were inserted into the left and right maxillary sinuses, respectively. After a healing period of 8 weeks, sections of the augmented sinus and surrounding bone were made and analyzed by microcomputed tomography and histologically for signs of window closure and bone augmentation. RESULTS Radiographic analysis revealed new bone formation in both groups of augmented sinus (i.e., with and without ErhBMP-2). The maximum augmented height did not differ significantly between the groups; however, window closure was significantly more advanced in the ErhBMP-2 group than in the control group (P=0.02). The defect was significantly deeper in the control group than in the ErhBMP-2-treated group (P=0.02). CONCLUSIONS In conclusion, ErhBMP-2-loaded ACS showed enhanced osteoinductive potential, particularly with regard to bone closure of a sinus window and facilitated maturation of the newly formed bone within the rabbit sinus cavity. However, the structural durability of ACS was not sufficient to maintain the augmented volume in the sinus.

Volumetric bone regenerative efficacy of biphasic calcium phosphate‐collagen composite block loaded with rhBMP‐2 in vertical bone augmentation model of a rabbit calvarium

Block-type biphasic calcium phosphate (BCP) carriers are more effective at delivering recombinant human bone morphogenetic protein-2 (rhBMP-2) in various clinical situations than are particle-type carriers, due to their potential for highly successful three-dimensional bone regeneration. The aim of this study was to confirm the bone-regenerative capabilities of three-dimensional BCP blocks with a low hydroxyapatite/β-tricalcium phosphate ratio (20/80) combined with collagen (10% wt) as an rhBMP-2 delivery system in a craniofacial vertical bone augmentation model. BCP blocks and BCP-collagen blocks (with average macropore sizes of 296 and 390 μm, respectively) with or without rhBMP-2 were fixed with osteosynthesis screws to the calvarial surface of rabbits. After 8 weeks, histologic and histomorphometric analyses were performed to evaluate the resulting new bone area, augmented area, bone density, and degree of integration. The area of new bone was significantly greater in specimens containing rhBMP-2 than in the control group (p < 0.05). Moreover, the area fractions of newly formed bone within the augmented area and a degree of integration between the regenerative bone and the calvarium were both significantly greater in the BCP-collagen/rhBMP-2 group than in the BCP/rhBMP-2 group (p < 0.05), whereas the two carrier systems exhibited similar rhBMP-2 release profiles, with sustained and linear release. The BCP and BCP/rhBMP-2 blocks exhibited excellent structural integrity, with large fragments of residual ceramic. In conclusion, the BCP-collagen composite block exhibited enhanced osteoinductive potential and could be a good candidate as a carrier of rhBMP-2 due to its characteristics of favorable volumetric stability, ease of handling, and excellent remodeling properties.

Bone formation of block and particulated biphasic calcium phosphate lyophilized with Escherichia coli-derived recombinant human bone morphogenetic protein 2 in rat calvarial defects.

The objective of this study was to evaluate bone formation in rat calvarial defects after surgical implantation of block or particulated biphasic calcium phosphate (BCP) lyophilized with Escherichia coli-derived recombinant human bone morphogenetic protein 2 (ErhBMP-2). Critical-size calvarial osteotomy defects were created in 5 groups of Sprague-Dawley rats. Each group received one of the following: 1) sham surgery control; 2) biphasic calcium phosphate particles (CPP); 3) biphasic calcium phosphate block (CPB); 4) ErhBMP-2-coated CPP; or 5) ErhBMP-2-coated CPB. ErhBMP was coated on BCP by a stepwise lyophilizing protocol. The new bone formation was significantly greater in ErhBMP-2-treated groups compared with the untreated group. In particular, the ErhBMP-2/CPB group showed stability of augmented areas during the period of healing, due to relevant space-providing capacity. Thus, it can be concluded that CPP and CPB lyophilized with ErhBMP-2 enhance the formation of new bone, and CPB appears to be a suitable carrier for ErhBMP-2 in which a 3-dimensional structural integrity is an important consideration factor.

Impact of different synthetic bone fillers on healing of extraction sockets: an experimental study in dogs

OBJECTIVES The objective of this study was to elucidate the socket healing process and biodegradation of incorporating synthetic bone fillers followed by grafting of the fresh extraction socket. MATERIALS AND METHODS Third premolars in four quadrants of eight beagle dogs were extracted and randomly treated with either one of hydroxyapatite (HA), biphasic calcium phosphate (BCP), β-tricalcium phosphate (β-TCP), or no graft (C). Histologic observations and histomorphometric analysis at three zones (apical, middle, and coronal) of the socket were performed. Socket area (S) and the proportions of newly formed bone (%NB), residual biomaterials (%RB), and fibrovascular connective tissue (%FCT) at 2, 4, and 8 weeks were measured. The numbers of osteoclast-like multinucleated cells (No.OC) were also determined at the three zones. RESULTS %NB was significantly higher in control group compared with the grafted groups at all healing periods. %NB of HA and BCP increased with time, whereas %RB showed different patterns that decreased in BCP, unlike the minimal change observed in HA. %NB of β-TCP showed smallest portion compared with other grafted groups at 2 and 4 weeks, however, significantly increased at 8 weeks. %RB of β-TCP was less than HA and BCP at all healing periods. Numbers of multinucleated cells were greater in BCP and β-TCP, followed by HA and smallest in control group. CONCLUSIONS Within the limit of this study, bone formation of the extraction socket was delayed in the sockets grafted with synthetic bone fillers and showed different healing process according to the biodegradation patterns.