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PubMed2007

Enhanced bone regeneration associated with decreased apoptosis in mice with partial HIF-1alpha deficiency.

UNLABELLED: HIF-1alpha activates genes under hypoxia and was hypothesized to regulate bone regeneration. Surprisingly, HIF-1alpha+/- fracture calluses are larger, stronger, and stiffer than HIF-1alpha+/+ calluses because of decreased apoptosis. These data identify apoptosis inhibition as a means to enhance bone regeneration. INTRODUCTION: Bone regeneration subsequent to fracture involves the synergistic activation of multiple signaling pathways. Localized hypoxia after fracture activates hypoxia-inducible factor 1alpha (HIF-1alpha), leading to increased expression of HIF-1 target genes. We therefore hypothesized that HIF-1alpha is a key regulator of bone regeneration. MATERIALS AND METHODS: Fixed femoral fractures were generated in mice with partial HIF-1alpha deficiency (HIF-1alpha+/-) and wildtype littermates (HIF-1alpha+/+). Fracture calluses and intact contralateral femurs from postfracture days (PFDs) 21 and 28 (N=5-10) were subjected to microCT evaluation and four-point bending to assess morphometric and mechanical properties. Molecular analyses were carried out on PFD 7, 10, and 14 samples (N=3) to determine differential gene expression at both mRNA and protein levels. Finally, TUNEL staining was performed on PFD 14 samples (N=2) to elucidate differential apoptosis. RESULTS: Surprisingly, fracture calluses from HIF-1alpha+/- mice exhibited greater mineralization and were larger, stronger, and stiffer. Microarray analyses focused on hypoxia-induced genes revealed differential expression (between genotypes) of several genes associated with the apoptotic pathway. Real-time PCR confirmed these results, showing higher expression of proapoptotic protein phosphatase 2a (PP2A) and lower expression of anti-apoptotic B-cell leukemia/lymphoma 2 (BCL2) in HIF-1alpha+/+ calluses. Subsequent TUNEL staining showed that HIF-1alpha+/+ calluses contained larger numbers of TUNEL+ chondrocytes and osteoblasts than HIF-1alpha+/- calluses. CONCLUSIONS: We conclude that partial HIF-1alpha deficiency results in decreased chondrocytic and osteoblastic apoptosis, thereby allowing the development of larger, stiffer calluses and enhancing bone regeneration. Furthermore, apoptosis inhibition may be a promising target for developing new treatments to accelerate bone regeneration.

Animals↗
PubMed1990

Bone regeneration adjacent to titanium dental implants using guided tissue regeneration: a report of two cases.

The biologic principle of guided tissue regeneration was applied to regenerate alveolar bone in conjunction with the placement of titanium dental implants. In one case, complete osseointegration of an implant was achieved by the placement of a Teflon membrane over an implant that had been inserted into an alveolus immediately following tooth extraction. In a second case, the same biologic principle was used to increase the volume (height and width) of a resorbed, edentulous alveolar ridge to provide adequate bone dimensions for implant installation. In both cases, the membranes appear to have prevented the repopulation of the wound area by cells other than those derived from surrounding bone tissue. These two different applications of the principle of guided tissue regeneration open new avenues for reconstructive osseous surgery.

Adult↗
PubMed2006

Coating of VEGF-releasing scaffolds with bioactive glass for angiogenesis and bone regeneration.

Bioactive glasses are potentially useful as bone defect fillers, and vascular endothelial growth factor (VEGF) has demonstrated benefit in bone regeneration as well. We hypothesized that the specific combination of prolonged localized VEGF presentation from a matrix coated with a bioactive glass may enhance bone regeneration. To test this hypothesis, the capacity of VEGF-releasing polymeric scaffolds with a bioactive glass coating was examined in vitro and in vivo using a rat critical-sized defect model. In the presence of a bioactive glass coating, we did not detect pronounced differences in the differentiation of human mesenchymal stem cells in vitro. However, we observed significantly enhanced mitogenic stimulation of endothelial cells in the presence of the bioactive glass coating, with an additive effect with VEGF release. This trend was maintained in vivo, where coated VEGF-releasing scaffolds demonstrated significant improvements in blood vessel density at 2 weeks versus coated control scaffolds. At 12 weeks, bone mineral density was significantly increased in coated VEGF-releasing scaffolds versus coated controls, while only a slight increase in bone volume fraction was observed. The results of this study suggest that a bioactive glass coating on a polymeric substrate participates in bone healing through indirect processes which enhance angiogenesis and bone maturation and not directly on osteoprogenitor differentiation and bone formation. The mass of bioactive glass used in this study provides a comparable and potentially additive, response to localized VEGF delivery over early time points. These studies demonstrate a materials approach to achieve an angiogenic response formerly limited to the delivery of inductive growth factors.

Animals↗
PubMed1992

Bone regeneration and tissue acceptance of human fascia lata grafts adjacent to dental implants: a preliminary case report.

The biologic principle of guided tissue regeneration (GTR) has been studied extensively in hopes of regenerating alveolar bone. Various materials have been utilized as regenerative membranes; however, all materials have disadvantages, and the ideal membrane material is yet to be identified. In this case report, human freeze-dried fascia lata strips were used as a regenerative barrier membrane in conjunction with the placement of endosseous root implants and demineralized, freeze-dried bone allograft. The major advantage in the use of human fascia lata for guided tissue regeneration is that a second procedure to remove the material is not necessary, and the fascia is accepted by the surrounding tissues without complication. There is acceptance of four endosseous root-form dental implants that were immediately placed into fresh extraction sockets and covered with demineralized freeze-dried bone allograft (DFDBA), with human freeze-dried fascia lata used to serve as a biocompatible, collagenous, regenerative augmentation membrane over the dental implants. The biologic concept of GTR is clinically applied to increase the dimensions of the edentulous, maxillary alveolar ridge with use of human freeze-dried fascia lata barrier membranes.

Adolescent↗
PubMed2006

Bone regeneration after enucleation of mandibular cysts: comparing autogenous grafts from tissue-engineered bone and iliac bone.

OBJECTIVE: The aim of this study was to compare bone regeneration after grafting enucleated mandibular cyst cavities using either autogenous osteoblasts cultured on a biomaterial or autogenous spongiose iliac bone. STUDY DESIGN: Twenty patients with 22 mandibular cysts were assessed. Eleven cysts were filled in with tissue-engineered bone (autogenous osteblasts cultured on demineralized bone matrix Osteovit) and 11 with spongiose iliac bone as controls. Panoramic radiographs were taken preoperatively, immediately postoperatively, and 3, 6, and 12 months after surgery. Radiolucency was computer analyzed using gray-level histograms. RESULTS: In both groups bone regeneration took place in a similar fashion. After 3 and 6 months there were few differences in bone density between the groups. However, in radiographic controls after 12 months ossification was considerably stronger in cysts grafted with tissue-engineered bone. CONCLUSION: These results advocate for the clinical application of tissue-engineered bone as an alternative viable filling material for cysts.

Adolescent↗
PubMed2000

Platelet derived growth factor releasing chitosan sponge for periodontal bone regeneration.

With an aim of improving bone regeneration, chitosan sponge containing platelet-derived growth factor-BB (PDGF-BB) were developed. For fabrication of chitosan sponge, chitosan solution was freeze-dried, crosslinked and freeze-dried again. PDGF-BB was incorporated into the chitosan sponge by soaking chitosan sponge into the PDGF-BB solution. Release kinetics of PDGF-BB, cell attachment, proliferation capacity and bony regenerative potentials of PDGF-BB-loaded chitosan sponge were investigated. Prepared chitosan sponge retained porous structure with 100 microm pore diameter that was suitable for cellular migration and growth. Release rate of PDGF-BB could be controlled by varying initial loading content of PDGF-BB to obtain optimal therapeutic efficacy. PDGF-BB-loaded chitosan sponge induced significantly high cell attachment and proliferation level, which indicated good cellular adaptability. PDGF-BB-loaded chitosan sponge demonstrated marked increase in new bone formation and rapid calcification. Degradation of the chitosan sponge was proceeded at defect site and subsequently replaced with new bone. Histomorphometric analysis confirmed that PDGF-BB-loaded chitosan sponge significantly induced new bone formation. These results suggested that chitosan sponge and PDGF-BB-loaded chitosan sponge may be beneficial to enhance periodontal bone regeneration.

Animals↗
PubMed2003

Effect of rhBMP-2 on guided bone regeneration in humans.

The aim of the present clinical study was to test whether or not the addition of recombinant human bone morphogenetic protein-2 (rhBMP-2) to a xenogenic bone substitute mineral (Bio-Oss) will improve guided bone regeneration therapy regarding bone volume, density and maturation. In 11 partially edentulous patients, 34 Brånemark implants were placed at two different sites in the same jaw (five maxillae, six mandibles) requiring lateral ridge augmentation. The bone defects were randomly assigned to test and control treatments: the test and the control defects were both augmented with the xenogenic bone substitute and a resorbable collagen membrane (Bio-Gide). At the test sites, the xenogenic bone substitute mineral was coated with rhBMP-2 in a lyophilization process. Following implant insertion (baseline), the peri-implant bone defect height was measured from the implant shoulder to the first implant-bone contact. After an average healing period of 6 months (SD 0.17, range 5.7-6.2), the residual defects were again measured and trephine burs were used to take 22 bone biopsies from the augmented regions. The healing period was uneventful except for one implant site that showed a wound dehiscence, which spontaneously closed after 4 weeks. Later at reentry, all implants were stable. At baseline, the mean defect height was 7.0 mm (SD 2.67, range 3-12 mm) at test and 5.8 mm (SD 1.81, range 3-8 mm) at control sites. At reentry, the mean defect height decreased to 0.2 mm (SD 0.35, range 0-1 mm) at test sites (corresponding to 96% vertical defect fill) and to 0.4 mm (SD 0.66, range 0-2 mm) at the control site (vertical defect fill of 91%). Reduction in defect height from baseline to reentry for both test and control sites was statistically significant (Wilcoxon P<0.01). Histomorphometric analysis showed an average area density of 37% (SD 11.2, range 23-51%) newly formed bone at test sites and 30% (SD 8.9, range 18-43%) at control sites. The fraction of mineralized bone identified as mature lamellar bone amounted to 76% (SD 14.4, range 47.8-94%) at test compared to 56% (SD 18.3, range 31.6-91.4%) at control sites (paired t-test P<0.05). At BMP-treated sites 57% (SD 16.2, range 29-81%) and at control sites 30% (SD 22.6, range 0-66%) of the surface of the bone substitute particles were in direct contact with newly formed bone (paired t-test P<0.05). It is concluded that the combination of the xenogenic bone substitute mineral with rhBMP-2 can enhance the maturation process of bone regeneration and can increase the graft to bone contact in humans. rhBMP-2 has the potential to predictably improve and accelerate guided bone regeneration therapy.

Adult↗
PubMedDate not supplied

Enhancement of bone regeneration and graft material resorption using surface-modified bioactive glass in cortical and human maxillary cystic bone defects.

PURPOSE: Bioactive glass bonds to bone through a calcium phosphate layer that mimics the structure of the mineral phase of bone. Formation of this layer is inhibited in the presence of serum protein. The authors hypothesize that creation of a calcium phosphate layer on the surface of bioactive glass before implantation will enhance bone regeneration and graft material resorption in bone defects. MATERIALS AND METHODS: Bioactive glass particles covered with a layer of amorphous calcium phosphate (BG-ACP), bioactive glass particles covered with a layer of hydroxycarbonate apatite (BG-HCA), and unmodified bioactive glass particles (as a control) were prepared and implanted in cortical bone defects in dogs or in human maxillary cavities. Ungrafted sites were also used as a control. RESULTS: Histomorphometric analyses showed significantly more bone tissue regeneration and graft material resorption in the defects filled with BG-HCA than in those filled with BG-ACP or unmodified bioactive glass (P < .0001). Moreover, measurements of radiographic density of the grafted areas suggested a higher rate of bone regeneration in defects filled with the modified bioactive glass than in those filled with unmodified bioactive glass or in the ungrafted control. Bone formation was significantly greater in defects filled with unmodified bioactive glass particles than in ungrafted defects. DISCUSSION: The enhancement of bone regeneration could be explained by the ability of the apatite layer to facilitate bone adsorption and enhance calcium release, which stimulates osteoblast differentiation and bone formation. CONCLUSION: Results of both the clinical and animal studies suggest that the use of surface-modified bioactive glass covered with a hydroxycarbonate apatite layer has the potential to accelerate bone formation and graft material resorption better than unmodified bioactive glass.

Adsorption↗
PubMed1979

Bone regeneration within a coralline hydroxyapatite implant.

The hypothesis that incomplete resorption of osteons in an autogenous cortical bone graft may limit its replacement by new bone regeneration was explored by implanting a hydroxyapatite replica of a coral skeletal structure into bone gaps. This implant contained channels and interconnections similar to those in osteon-evacuated bone grafts. In 6 implanted mandibular defects in dogs, two of which were examined at two, 4, and 6 months, 11 percent, 46 percent, and 88 percent of the implant areas were filled with regenerated bone. The regenerated bone was a woven type at two months, but changed to a lamellar type by 6 months. In two implanted defects examined at 12 months, biodegradation of 29 percent of the implant had occurred. The bone regeneration was physiological, the implant was biocompatible, and the biodegradation began after the bone had regenerated.

Animals↗
PubMed1997

[Histologic evaluation of bone regeneration in cases of limb lengthening by Ilizarov's technique. An experimental study in the dog].

The histology of bone regeneration in cases of limb lengthening was studied in eight adult dogs. Following an osteotomy of the right fibula, an Orthofix (four dogs) or an Ilizarov external fixator (4 dogs) was installed and an osteotomy of the right tibia performed. Lengthening was started seven days after the surgery at the rate and rhythm of 0.5 mm every 12 hours for three weeks and was then followed by compression of 1 mm. The animals were then sacrificed in pairs 3, 6, 9 and 12 weeks after the start of lengthening. Histological evaluation of regenerate bone was performed using hematoxylin and eosin, trichrome and Von Kossa stain (decalcified). New bone at the site of distraction seemed to be formed mostly through intramembranous, and to a lesser extent, through endochondral ossification as evident by the presence of cartilaginous islands within the distraction gap of old specimens. However, these foci of cartilage cells did not have the appearance of growth plates. From the third week of lengthening, collagen fibers were laid down along the longitudinal axis of distraction. Mineralization of these fibers started at the bone ends and during the following weeks, progressed towards the center of the distraction gap. New bone was formed from both the medullary cavity and the periosteum.

Animals↗
PubMed2000

Guided bone regeneration around endosseous implants using a resorbable membrane vs a PTFE membrane.

The aim of the present experimental pilot study was to assess bone regeneration underneath resorbable barrier membranes vs non-resorbable extended polytetrafluoroethylene (ePTFE) membranes in peri-implant defects. Two implants were inserted into surgically created defects on each side of the mandibles of 6 adult beagle dogs 3 months after extraction of all premolar teeth. One implant on each side was covered with a porous polylactic acid membrane or a ePTFE membrane, respectively, while the second implant served as control. Fluorochrome labelling was administered during the 1st, 5th, 12th and the 18th week. Three animals each were evaluated after 3 and 6 months. Bone regeneration was assessed by measuring the distance from the first fluorochrome label to the level of the regenerated bone immediately adjacent to the implant surface and to the top of the newly formed alveolar contour both on the lingual and buccal side. The increase in bone height was significantly higher compared to the controls under both barrier membranes after 3 months at the top of the alveolar crest but not immediately adjacent to the implant surface. After 6 months, bone height was significantly increased only at the top of the alveolar contour underneath the ePTFE membranes, while bone underneath the polylactic acid membranes showed signs of superficial resorption. It is concluded that guided bone regeneration underneath barrier membranes can restore alveolar bone contour but is not necessarily associated with a higher bone/implant contact. The use of resorbable membranes may be associated with untoward biological effects at later stages, when membrane degradation starts due to degradation products of the polymer material or decreasing membrane stability. Future efforts have to refine the relation between degradation kinetics, membrane porosity and mechanical properties of degradable barrier membranes to improve membrane performance.

Absorbable Implants↗
PubMed1999

Qualitative analysis of peripheral peri-implant bone and influence of alendronate sodium on early bone regeneration.

BACKGROUND: Alendronate sodium increases alveolar bone density with systemic use. It inhibits osteoclast activity and is thought to result in a net increase in osteoblastic activity. However, little is known about local in vivo use. The purpose of this study was to evaluate the effect of local delivery of alendronate on bone regeneration within peri-implant defects. Peri-implant bone was examined histomorphometrically to evaluate the amount of supporting bone peripheral to the bone-implant interface. METHODS: Six adult hound dogs were evenly divided into 2 groups, with one group receiving alendronate-coated dental implants and the other group serving as controls. Dental implants were placed immediately after extraction of right and left second, third, and fourth mandibular premolars. Forty-eight dental implants were placed (2 types in each dog: 24 hydroxyapatite [HA]-coated and 24 titanium machine-polished [TMP]), for a total of 4 variables. A bioabsorbable collagen membrane was secured over the implants and defects, and the flaps closed primarily. The dogs were sacrificed on day 28. Specimens were sectioned, mounted, and stained with Stevenel's blue and van Gieson's picric fuchsin. The amount of bone adjacent and 1 mm peripheral to the implant surface was recorded with a computerized microscopic digitizer. RESULTS: Locally applied alendronate resulted in significantly increased amounts of bone (P<0.0002, ANOVA) in the peripheral area with both HA and TMP implants. However, the most influential factor in the amount of peripheral bone was the type of implant surface (P<0.0001). CONCLUSIONS: Local application of alendronate is useful in increasing the amount of peripheral peri-implant bone. Also, the amount of supporting bone was not related to the bone-to-implant contact but to the surface characteristics of the implant. The findings of the present study indicate that the evaluation of dental implant-supporting bone should include peripheral bone as well as bone-to-implant interface.

Alendronate↗
PubMed1996

Self-regenerating bone implant: ectopic osteoinduction following intramuscular implantation of a combination of rhBMP-2, atelopeptide type I collagen and porous hydroxyapatite.

A combination of recombinant human bone morphogenetic protein-2 (rhBMP-2), atelopeptide Type I collagen (CL) as a carrier and porous hydroxyapatite (pHAP) was implanted in a calf muscle pouch of the rat. Three rhBMP-2-implanted groups (2, 10 and 50 micrograms; each n = 5) and the control group (n = 5), in which only CL and pHAP were implanted, were established. Three weeks later, the implants were examined.

Animals↗
PubMed2000

Strong effect of PTH (1-34) on regenerating bone: a time sequence study in rats.

This study compares the effects of parathyroid hormone (PTH) treatment on new bone formation and normal baseline remodelling in rats. To study new bone formation we used a titanium bone chamber, and to study normal remodelling we used the femur and vertebrae from the same animals. One titanium bone chamber was inserted in the proximal tibia of each of 37 rats. The rats were randomly assigned to daily injections of human PTH (1-34) 60 microg/kg) or vehicle control and killed after 2, 4 or 6 weeks. The total distance of bone growth into the chamber was slightly increased by PTH. Body weight was not affected, and there was only a minor increase in trabecular density of the vertebral and femoral cancellous bone after 6 weeks. The only dramatic effect of PTH was seen in the chambers. In the controls, a marrow cavity formed in the chamber so that the cancellous density decreased from 44% to 24%, and 11% over 2, 4 and 6 weeks. In the PTH-treated animals, a dense network of bone trabeculae was found in the entire bone chamber at all times. The cancellous density increased from 48% to 60%, and 73% at 2, 4 and 6 weeks, respectively. The results suggest that PTH treatment can reduce the development of a resorption cavity. Thus, PTH in this model had a net antiresorptive effect, probably solely because it stimulated osteoblastic activity. Even though osteoclastic activity was present throughout the PTH specimens, it was not sufficient to resorb all newly formed bone. Since PTH seemed to have a greater effect on new bone formation in the chamber than on normal bone remodeling, it might become useful for improving the incorporation of orthopedic implants and stimulating fracture repair.

Animals↗
PubMedDate not supplied

[Bone regeneration following the implantation of osteoblasts from cell cultures].

An animal model utilizing 26 inbred rats was aimed at the question if the regeneration of bone tissue is enhanced by implantation of osteoblasts previously cultured in vitro. Bone tissue was harvested from inbred rats (Lewis) and a cell line of rat osteoblasts was established. The osteoblasts were cultured in vitro and multiplied in three passages. Characterization of the cells was by various methods. Monocortical defects were created in the distal portion of the rat femurs by drilling; and the cells, embedded in 25% bone gelatine, were reimplanted into these defects. After observation periods of varying lengths, the femurs were examined radiographically and bone growth in the defect area was evaluated histologically. The results of this study indicated that there was an initial effect of the reimplanted cultured osteoblasts on the bone growth pattern. At a later point in time this effect could no longer be demonstrated in the young, healthy rats.

Animals↗