The effect of bisphosphonate and intermittent human parathyroid hormone 1-34 treatments on cortical bone allografts in rabbits

AIM

This study compares the effect of bisphosphonate and intermittent PTH administration on haversian remodeling in cortical bone allografts in rabbits.

MATERIALS AND METHODS

An intercalary heat-treated cortical bone allograft was applied to a segment skeletal defect in the left femur of Japanese white rabbits. The rabbits were randomly assigned to one of three groups: the vehicle control group (CNT); the bisphosphonate group (B group); and the intermittent PTH treatment group (P group). Periodic radiographic evaluation was performed and peripheral quantitative computerized tomography (pQCT) was used to evaluate the total bone area (Area), bone mineral density (BMD), and bone mineral content (BMC). The allografts also underwent histological examination.

RESULTS

The P group was radiographically superior in the latter stage, compared with the other groups. pQCT analysis of the allografts showed that the B group had a significantly higher Area and BMC. These parameters in the latter stage were significantly lower in the P group than in the other groups. The allograft of the B group was histologically mostly necrotic bone, whereas allograft of the P group showed abundant newly formed bone.

CONCLUSION

In rabbits, bisphosphonate prevents resorption, but suppresses remodeling and incorporation; by contrast, PTH increases resorption and accelerates allograft remodeling and incorporation. Based on our preliminary data, we suggest that further research on the manner of administration of bisphosphonate and PTH - which have contrasting effects - can be beneficial in maintaining bone strength and in regulating remodeling and allograft incorporation.

Platelet-rich plasma diminishes calvarial bone repair associated with alterations in collagen matrix composition and elevated CD34+ cell prevalence

The interaction between platelets and both type I and III collagens plays an important role in modulating platelet adhesion and aggregation, also contributing to the chemotaxis of CD34+ cells. The interaction with type III collagen can maintain high levels of collagen and alter the biology of bone repair when the PRP is used. The aim of this study was to evaluate the effect of platelet-rich plasma (PRP) and autograft on the presence of type III and type I collagens, the ratio between them, as well as the presence of CD34+ progenitor cells, while comparing these results by means of a histomorphometric analysis of the bone tissue. Four bone defects (8.0mm in diameter and 2.0mm in depth) were produced on the calvarium of 23 rabbits. The surgical defects were treated with either autogenous bone grafts, autogenous bone grafts with PRP and PRP alone. Animals were euthanized at 2, 4 or 6 weeks post-surgery. Histological, histomorphometric and immunohistochemical analyses were performed to assess repair time, as well as the expression of type I and III collagens, and number of progenitor CD34+ cells. Data were analyzed using the ANOVA and Student-Newman-Keuls test (alpha=5%). An enlarged granulation and medullary tissue areas in the PRP groups were observed. The use of PRP in this study hindered bone deposition, also enhanced type III to type I collagen ratio and the chemotaxis of CD34+ progenitor cells, similarly to a thrombogenic effect.

Maxillary sinus augmentation using recombinant bone morphogenetic protein-2/acellular collagen sponge in combination with a mineralized bone replacement graft: a report of three cases

The objective of the following case reports was to assess whether mineralized bone replacement grafts (eg, xenografts and allografts) could be added to recombinant human bone morphogenetic protein-2/acellular collagen sponge (rhBMP-2/ACS) in an effective manner that would: (1) reduce the graft shrinkage observed when using rhBMP-2/ACS alone, (2) reduce the volume and dose of rhBMP-2 required, and (3) preserve the osteoinductivity that rhBMP-2/ACS has shown when used alone. The primary outcome measures were histomorphometric analysis of vital bone production and analysis of serial computed tomographic scans to determine changes in bone graft density and stability. Over the 6-month course of this investigation, bone graft densities tended to increase (moreso with the xenograft than the allograft). The increased density in allograft cases was likely the result of both compression of the mineralized bone replacement graft and vital bone formation, seen histologically. Loss of volume was greater with the four-sponge dose than the two-sponge dose because of compression and resorption of the sponges. Vital bone formation in the allograft cases ranged from 36% to 53% but, because of the small sample size, it was not possible to determine any significant difference between the 5.6 mL (four-sponge) dose and the 2.8 mL (two-sponge) dose. Histology revealed robust new woven bone formation with only minimal traces of residual allograft, which appeared to have undergone accelerated remodeling or rhBMP-2-mediated resorption.

Influence of osteopenia in autogenous bone graft healing with or without expanded polytetrafluoroethylene membranes: histologic and histomorphometric study in rats

PURPOSE

The aim of this study was to quantitatively evaluate and qualitatively describe autogenous bone graft healing with or without an expanded polytetrafluoroethylene (e-PTFE) membrane in ovariectomized rats.

MATERIALS AND METHODS

Eighty Wistar rats, weighing approximately 300 g each, were used. A graft was obtained from the parietal bone and fixed to the sidewall of each animal's left mandibular ramus. The animals were randomly divided into four experimental groups (n = 20 in each group): group 1, sham operated and autogenous bone graft only; group 2, sham operated and autogenous bone graft covered by e-PTFE membrane; group 3, ovariectomized (OVX) and autogenous bone graft only; group 4, OVX and autogenous bone graft covered by e-PTFE membrane. The animals were sacrificed at five different time points: immediately after grafting or at 7, 21, 45, or 60 days after grafting. Histologic examination and morphometric measurement of the sections were performed, and values were submitted to statistical analyses.

RESULTS

Both groups (sham and OVX) experienced loss of the original graft volume when it was not covered by the membrane, whereas use of the membrane resulted in additional bone formation beyond the edges of the graft and under the membrane. Histologic analysis showed integration of the grafts in all animals, although a larger number of marrow spaces was found in OVX groups.

CONCLUSIONS

Association of bone graft with an e-PTFE membrane resulted in maintenance of its original volume as well as formation of new bone that filled the space under the membrane. Osteopenia did not influence bone graft repair, regardless of whether or not it was associated with e-PTFE membrane, but descriptive histologic analysis showed larger numbers of marrow spaces in the bone graft and receptor bed and formation of new bone in the OVX animals.

Autogenous bone graft with or without perforation of the receptor bed: histologic study in rabbit calvaria

PURPOSE

To evaluate the amount of bone matrix in autogenous block bone grafts that were fixed with or without perforation of the receptor bed.

MATERIALS AND METHODS

Twelve rabbits received two 5-mm circular osteotomies each in the anterior parietal region. The bone was removed, perforated, and fixed by a titanium screw in the adjacent area, 3 mm from the border of the osteotomies. On the contralateral side, six perforations were made in the receptor site before the graft was fixated by the titanium screw. After 28 days, the animals were sacrificed and specimens were prepared for histologic study. Sections were analyzed with regard to the total area of the graft and the percentages of bone matrix in the graft, interface, and receptor bed. Analyses using the Wilcoxon test (P<.05) were performed.

RESULTS

No statistically significant differences were found between the groups with or without perforations to the area of the graft (P=.85) or the percentage of hard tissue in the grafts (P=.53), the interface (P=.65), or the receptor bed (P=.18).

CONCLUSION

Based upon this study that used a rabbit model with bone grafts placed in the parietal regions, cortical perforations of the receptor bone did not improve repair of bone grafts and did not increase the amount of bone matrix in the final grafted area.

Biomechanical effects of a maxillary implant in the augmented sinus: a three-dimensional finite element analysis

PURPOSE

The biomechanical effects of different strengths of grafted bone, bicortical anchorage, and dimensional alterations of a dental implant with maxillary sinus augmentation were investigated.

MATERIALS AND METHODS

Sixteen finite element (FE) models that included five implant lengths, two implant diameters, and grafted bone with two levels of stiffness were studied. A posterior maxillary model was constructed from computerized tomographic images of a human skull, and the implant models were created via computer-aided design software (SolidWorks 2006). All materials were assumed to be isotropic and linearly elastic. A 45-degree oblique force of 129 N was applied to the buccal cusp of the first molar.

RESULTS

The von Mises stress was highest in the 7-mm-long implant. Stresses in cortical and trabecular bone were reduced by at least 50% for all other implants (length greater than or equal to 8.5 mm) with bicortical anchorage. Increasing the length of the bicortically anchored implant did not decrease the stress in native bone, but it decreased the stress in sinus grafts by at least 20%. The use of a wide implant decreased the stress by 24% to 42% in cortical bone and 17% to 36% in trabecular bone. Increasing the elastic modulus of grafted bone decreased the stress in native bone by approximately 10%.

CONCLUSIONS

Bicortical fixation of implants and the presence of grafted bone with greater stiffness reduced the stresses in native bone. Increasing the length of the implant in grafted bone did not reduce the stress in native bone, but it did reduce the stress in grafted bone. The effects of implant diameters on reducing bone stress are primarily a result of the increased contact area between implant and bone. The results of the FE analysis imply that the success of a sinus-augmented dental implant is heavily dependent on the implant design and rigidity of the bone grafts.

Influence of ovariectomy on healing of autogenous bone block grafts in the mandible: a histomorphometric study in an aged rat model

PURPOSE

The aim of this study was to evaluate quantitatively and qualitatively the influence of estrogen deficiency on autogenous bone block grafts in aged ovariectomized rats.

MATERIALS AND METHODS

Fifty 12-month-old female Wistar rats were used in the study. They were divided into 2 groups, an ovariectomized group and a sham-operated group. After 30 days the animals received autogenous block bone grafts on the angle of the mandible, harvested from the calvaria. The animals were euthanized at 7, 14, or 28 days postoperatively.

RESULTS

Histologic analysis showed that at 7 days postsurgery, the interface between graft and recipient site in the sham-operated group appeared filled by a granulation tissue with angiogenic activity, whereas the ovariectomized group still exhibited a blood clot and a granulation tissue in organization. On the 14th postoperative day, the interface in the sham-operated group was partially filled by newly formed bone establishing a union between the graft and the recipient site. The interface in the ovariectomized group was typically filled by granulation tissue with discrete osteogenic activity in most specimens. On the 28th postoperative day, the graft in the sham-operated group appeared histologically integrated to the mandible. However, the interface in the ovariectomized group appeared partially filled by newly formed bone, with areas of interposed connective tissue. The statistical analysis revealed that bone neoformation was significantly greater in the sham-operated group (57.41% at 14 days and 68.35 at 28 days) in comparison with the ovariectomized group (40.82% at 14 days and 53.09 at 28 days) at the 5% level.

CONCLUSION

The estrogen depletion caused by the ovariectomy hindered the healing process of autogenous block bone grafts placed in the mandibles of aged rats.

Effects of demineralized freeze-dried bone allograft on gene expression of osteoblastlike MG63 cells

Demineralized freeze-dried bone allograft (DFDBA) is widely used in periodontal regeneration procedures as a scaffold for new bone formation in periodontal defects. How this biomaterial alters osteoblast activity to promote bone formation is poorly understood. We therefore attempted to address this question by using microarray techniques to identify genes that are differently regulated in osteoblasts exposed to DFDBA. By using DNA microarrays containing 20,000 genes, the authors identified in an osteoblastlike cell line (MG-63) cultured with DFDBA (Allogro, Dentsply/Friadent-Ceramed) several genes whose expression was significantly up-regulated or down-regulated. The differently expressed genes cover a broad range of functional activities: (1) cell cycle regulation, (2) immunity, (3) vesicular transport, (4) production of cytoskeletal elements, and (5) bone remodeling. The data reported are, to the authors' knowledge, the first genetic portrait of DFDBA effects. They can be relevant to a better understanding of the molecular mechanism of bone regeneration and as a model for comparing other materials with similar clinical effects.

Inflammatory mediator release following bone grafting in humans: a pilot study

AIM

The aim of this pilot study was to track markers of periodontal inflammation and bone resorption associated with decalcified freeze-dried bone allografts.

MATERIAL AND METHODS

Eleven subjects completed standardized treatment of intrabony defects > or =3 mm with allografts. Gingival crevicular fluid was collected from the defect site and an adjacent interproximal site within the surgical field at baseline, 2, 4, and 8 weeks post-operatively, and analysed for biochemical markers of inflammation/bone resorption. Probing depth, recession, bleeding on probing, plaque, and 6-month radiographic bone height change were measured.

RESULTS

Both prostaglandin E(2) (p=0.007) and bone-specific type 1 collagen (p=0.01) increased in crevicular fluid after 2 weeks in the bone graft sites. Matrix metalloproteinase-9 levels remained constant over time. There were positive correlations between prostaglandin levels during the first 8 weeks and bone height change over 6 months.

CONCLUSIONS

Periodontal bone grafts stimulate an inflammatory response during the first 2 weeks post-operatively, and the potential negative effects of inhibiting prostaglandins post-operatively should be investigated further.

A comprehensive clinical review of recombinant human bone morphogenetic protein-2 (INFUSE Bone Graft)

The combination of recombinant human bone morphogenetic protein-2 (rhBMP-2) on an absorbable collagen sponge (ACS) carrier has been shown to induce bone formation in a number of preclinical and clinical investigations. In 2002, rhBMP-2/ACS at a 1.5-mg/cc concentration (INFUSE Bone Graft, Medtronic Spinal and Biologics, Memphis, TN) was FDA-approved as an autograft replacement for certain interbody spinal fusion procedures. In 2004, INFUSE Bone Graft was approved for open tibial fractures with an intermedullary (IM) nail fixation. Most recently, in March 2007, INFUSE Bone Graft was approved as an alternative to autogenous bone grafts for sinus augmentations, and for localised alveolar ridge augmentations for defects associated with extraction sockets. The culmination of extensive preclinical and clinical research and three FDA approvals makes rhBMP-2 one of the most studied, published and significant advances in orthopaedics. This review article summarises a number of clinical findings of rhBMP-2/ACS, including the FDA-approved investigational device exemption (IDE) studies used in gaining the aforementioned approvals.

Success of dental implants placed in intraoral block bone grafts

BACKGROUND

The purpose of this study was to evaluate the survival and success of dental implants placed in alveolar bone following augmentation using intraoral block bone grafts.

METHODS

A consecutive retrospective study was conducted on patients who had onlay bone grafts for vertical or horizontal augmentations followed by dental implantation from 1999 to 2001. Files of 50 healthy patients who received 129 implants in augmented sites were reviewed. Implant survival, radiologic implant success (marginal bone loss), and complications were recorded.

RESULTS

Follow-up from time of implantation ranged from 6 to 67 months (mean: 24.3 +/- 11.2 months). Ranges of implant widths and lengths were 3.25 to 4.7 mm and 10 to 16 mm, respectively. The overall survival rate was 96.9% (four implants were removed). Marginal bone loss around implants ranged from 0 to 3.3 mm (average: 0.22 +/- 0.45 mm). Only 5% of the implants presented marginal bone loss > or =1.5 mm over the follow-up time.

CONCLUSIONS

Intraoral bone block graft surgery is a predictable operation for the use of dental implants. Implant placement in augmented areas presents high survival and radiologic success rates with minimal bone loss.

Primary Stability of Simultaneously Placed Dental Implants in Extraoral Donor Graft Sites: A Human Cadaver Study

PURPOSE

To compare the primary stability of dental implants placed in fibula, iliac crest, and scapula of human cadavers.

MATERIALS AND METHODS

Straumann Dental Implants (Institut Straumann, Basel, Switzerland) 4.1 mmx10 mm in diameter were placed into bilateral fibula, iliac crest, and scapula of 4 fresh human cadavers. For the assessment of primary stability of implants, installation torque values (ITV) and removal torque values (RTV) were measured using a custom-made strain-gauged torque wrench, and resonance frequency analysis was carried out to quantify the implant stability quotients (ISQ). Bone specimens from each donor site were harvested to perform radiographic and histomorphometric analyses. Linear distance and optical density (OD) measurements were made on digitized parallel periapical radiographs and bone area fraction (BAF) was calculated on digitized images of decalcified histologic sections.

RESULTS

Fibula donor site presented higher ITVs and RTVs and cortical bone height for implants than other sites (P<.05). BAF measurements for iliac crest were higher than fibula and scapula bone donor sites. OD was higher in the iliac crest followed by scapula and fibula.

CONCLUSION

The primary mechanical stability of implants placed in the fibula is higher than those placed in the iliac crest and the scapula, although the bone mass and density around implants in latter sites are higher.

Inhibitory Effect of Alendronate on Bone Resorption of Autogenous Free Bone Grafts in Rats

PURPOSE

This study was designed to investigate the effect of alendronate on the resorption of autogenous free bone grafts by biochemical and histopathologic methods. Alendronate is a potent inhibitor of osteoclast-mediated bone resorption with no adverse effect on the mineralization of bone.

MATERIALS AND METHODS

In this experimental study, 56 male Wistar rats were used. Autogenous free bone grafts were prepared with standard trephine bur in the right femur of each rat. The animals were then divided into 2 groups. In the first group, rats were treated with a daily subcutaneous injection of alendronate (0.25 mg/kg/day) for 2, 4, and 12 weeks, respectively. In the second group, rats were treated with saline solution injection for the same time periods. At the end of these periods, serum and overnight fasting urine samples were collected from all animals. In serum, the level of calcium, phosphate, parathyroid hormone, and 25 dihydroxyvitamin D were measured. In urine, pyridinoline, deoxypyridinoline, calcium, and creatinine were analyzed. The rats were sacrificed at 2, 4, and 12 weeks postsurgery. The number of osteoclasts and the number and size of resorptive lacunae were evaluated histopathologically.

RESULTS

Alendronate caused significant reduction in urinary pyridinoline, deoxypyridinoline levels biochemically, and the number of osteoclasts and resorptive lacunae histopathologically.

CONCLUSION

Suppression of the graft resorption occurred in the alendronate-treated group.

Viable cells survive in fresh frozen human bone allografts

BACKGROUND

Fresh frozen bone allograft is available for human recipients after at least 6 months of quarantine at -80 degrees C. It is assumed that cryopreservation without cryoprotectant removes all viable donor cells.

METHODS

We studied the in vitro cell growth from samples of fresh frozen human femoral head allografts after they had been released for patient use, and compared it with cell growth from a control group of fresh cancellous bone specimens from excised femoral heads (8 samples in each group).

RESULTS

Cell outgrowths were seen in all of the fresh cancellous bone specimens (100% of replicates, 48 replicates per specimen) but only in a small minority of replicates from 4 of the allograft samples (mean 3.1%). Reverse transcription quantitative polymerase chain reaction (RT-qPCR) investigations revealed that cell outgrowths from both groups contained mRNA for transcription factors Runx2 and Osterix, and also for matrix proteins collagen type I, osteocalcin and bone sialoprotein. This is consistent with the cells being osteoblast-related.

INTERPRETATION

This study confirms that fresh frozen human bone allograft cells have the potential to grow in vitro, but the significance of this in recipients is currently unknown.

Schwann cell graft: A method to promote sensory responses of osseointegrated implants

Osseointegrated dental implants have been widely used in clinics to restore the missing teeth of patients. Since there are no periodontal ligament and associated Ruffini endings in the peri-implant tissues, sensory thresholds of the implant are much higher than those of natural teeth, and its self-protective reflex is quit poor. Implant fracture or aggressive bone loss sometimes occurs because the patient cannot feel the overloads exerted on the implant. Until now, no available method has been issued to solve such a problem. Schwann cell is the glial cell of peripheral nerve system. It has been widely accepted to play indispensable roles during neural development and regeneration. Its mechanism includes forming Büngner's band, producing neurotrophic factors, synthesizing surface cell adhesion molecules, and elaborating basement membrane. Furthermore, Schwann cell is quite important for the periodontal Ruffini endings. Applying these functions of Schwann cells, we put forward a hypothesis that transplanting Schwann cells into the implant site can be a method to promote sensory responses of the dental implants.

Sterilization of allograft bone: effects of gamma irradiation on allograft biology and biomechanics

Gamma irradiation from Cobalt 60 sources has been used to terminally sterilize bone allografts for many years. Gamma radiation adversely affects the mechanical and biological properties of bone allografts by degrading the collagen in bone matrix. Specifically, gamma rays split polypeptide chains. In wet specimens irradiation causes release of free radicals via radiolysis of water molecules that induces cross-linking reactions in collagen molecules. These effects are dose dependent and give rise to a dose-dependent decrease in mechanical properties of allograft bone when gamma dose is increased above 25 kGy for cortical bone or 60 kGy for cancellous bone. But at doses between 0 and 25 kGy (standard dose), a clear relationship between gamma dose and mechanical properties has yet to be established. In addition, the effects of gamma radiation on graft remodelling have not been intensively investigated. There is evidence that the activity of osteoclasts is reduced when they are cultured onto irradiated bone slices, that peroxidation of marrow fat increases apoptosis of osteoblasts; and that bacterial products remain after irradiation and induce inflammatory bone resorption following macrophage activation. These effects need considerably more investigation to establish their relevance to clinical outcomes. International consensus on an optimum dose of radiation has not been achieved due to a wide range of confounding variables and individual decisions by tissue banks. This has resulted in the application of doses ranging from 15 to 35 kGy. Here, we provide a critical review on the effects of gamma irradiation on the mechanical and biological properties of allograft bone.

Effect of impact on chondrocyte viability during insertion of human osteochondral grafts

BACKGROUND

Osteochondral grafts, used to treat chondral and osteochondral defects, require high insertional forces that may affect the viability of chondrocytes in the graft. The objectives of this study were to (1) measure the loading impact during insertion of osteochondral grafts, (2) evaluate the effect of insertional loading on chondrocyte viability, and (3) assess this effect on chondrocyte apoptosis and activation of caspase-3.

METHODS

The distal parts of twelve fresh femora from six adult human cadavers were harvested within seventy-two hours after the death of the donor. From each femur, four 15-mm-diameter cylindrical osteochondral grafts were isolated; two of these grafts (a total of twenty-four grafts in the study) were transplanted with standard impact insertion into recipient sockets in the other condyle of the ipsilateral femur. The other two grafts served as unloaded controls. Loads were measured during the insertion of ten of the twenty-four transplanted grafts. Full-thickness cartilage disks were then removed from the grafts, incubated for up to forty-eight hours, and analyzed for cell viability, TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling)-positive reactivity, and caspase-3 activation, each as a function of the depth from the articular surface.

RESULTS

The insertion of an osteochondral graft was characterized, on the average (and standard deviation), by 10 +/- 4 impacts, each generating 2.4 +/- 0.9 kN of load and 13.3 +/- 4.9 MPa of stress for a duration of 0.57 +/- 0.13 ms with a 0.62 +/- 0.25 N.s impulse. Impact insertion increased cell death in the superficial 500 mum to 21% at one hour (p < 0.001) and 47% at forty-eight hours (p < 0.001) and also increased cell death in deeper layers at forty-eight hours. Some cell death was due to apoptosis, as indicated by an increase in caspase-3 activation at eight hours (p < 0.01) and TUNEL-positive cells at forty-eight hours (p < 0.05) in the superficial 500 mum of impacted cartilage.

CONCLUSIONS

Impact insertion of osteochondral grafts generates damaging loads that cause chondrocyte death, particularly in the superficial zone, mainly as a result of apoptosis mediated by the activation of caspases.

CLINICAL RELEVANCE

Chondrocyte death that occurs during impact insertion of osteochondral grafts may lead to compromised function. Understanding the mechanisms and consequences of such impact loading may provide insights into potential therapeutic interventions, or lead to changes in the insertion technique, to decrease the cell injury associated with impact loading.

Bone healing and graft resorption of autograft, anorganic bovine bone and beta-tricalcium phosphate. A histologic and histomorphometric study in the mandibles of minipigs

OBJECTIVE

The purpose was to qualitatively and quantitatively compare the bone formation and graft resorption of two different bone substitutes used in both orthopedic and oral surgery, with autogenous bone as a positive control.

MATERIALS AND METHODS

Three standardized bone defects were prepared in both mandibular angles of 12 adult minipigs. The defects were grafted with either autograft, anorganic bovine bone (ABB), or synthetic beta-tricalcium phosphate (beta-TCP). Sacrifice was performed after 1, 2, 4, and 8 weeks for histologic and histomorphometric analysis.

RESULTS

At 2 weeks, more new bone formation was seen in defects filled with autograft than with ABB (P approximately 0.0005) and beta-TCP (P approximately 0.002). After 4 weeks, there was no significant difference between beta-TCP and the two other materials. Defects grafted with ABB still exhibited less bone formation as compared with autograft (P approximately 0.004). At 8 weeks, more bone formation was observed in defects grafted with autograft (P approximately 0.003) and beta-TCP (P approximately 0.00004) than with ABB. No difference could be demonstrated between beta-TCP and autograft. beta-TCP resorbed almost completely over 8 weeks, whereas ABB remained stable.

CONCLUSION

Both bone substitutes seemed to decelerate bone regeneration in the early healing phase as compared with autograft. All defects ultimately regenerated with newly formed bone and a developing bone marrow. The grafting materials showed complete osseous integration. Both bone substitutes may have a place in reconstructive surgery where different clinical indications require differences in biodegradability.

Effect of proliferating tissue on transplanted teeth in dogs

OBJECTIVE

The objective of this study was to investigate the effect of transplanted proliferating tissue on the regeneration of periodontal ligaments (PDL) in tooth transplantation.

STUDY DESIGN

Two weeks after removing the alveolar bone, proliferating tissues were excised and examined for expression of basic fibroblast growth factor (bFGF) and alkaline phosphatase (ALP) using a LightCycler. Next, the teeth to be transplanted (first premolars) were extracted and PDLs were removed by scaling. After that, the first premolar teeth and proliferating tissues for the experimental group were transplanted into bone cavities created at the sites of the third and fourth premolars, while the control sites received teeth only. Finally, 1, 2, and 4 weeks later, the animals were sacrificed and specimens were collected and processed for histopathologic examination.

RESULTS

bFGF and ALPmRNA showed a significant increase in the transplanted proliferating tissue. Transplantation of the proliferating tissues positively affected the formation of new cementum and PDL. Moreover, application of the transplanted proliferating tissues decreased the occurrence and extent of ankylosis and root resorption at the root surface.

CONCLUSION

These results indicate that transplanted proliferating tissue may promote the regeneration of periodontal tissue and prevent ankylosis and root resorption following the transplantation of teeth.

Effects of platelet-rich plasma on the healing of autologous bone grafted mandibular defects in dogs

PURPOSE

This study was undertaken to describe both radiographically and with histomorphometric analysis the effect platelet-rich plasma (PRP) has on immediate autologous bone grafts in a dog model.

MATERIALS AND METHODS

Thirteen dogs comprised the study. Twelve adult dogs received bilateral inferior mandibular border defect resections measuring 2 cm x 1 cm. The right defect was immediately grafted with milled autologous iliac corticocancellous bone along with 2 cc of PRP that was developed in a standardized fashion. The left side was immediately grafted with the same amount of autologous iliac corticocancellous bone placed without PRP. Three animals were sacrificed at 1, 2, 3, and 6 months. A thirteenth dog underwent bilateral inferior border resections with only PRP placed in the right defect, and nothing placed in the left defect. This dog was sacrificed at 6 months. Ten and 3 days before sacrifice all animals received 10 mg/kg body weight tetracycline intravenously. At sacrifice, grafts along with adjacent native bone were harvested, fixed, radiographed, and processed for epifluorescence analysis.

RESULTS

Analysis of digitized radiographs indicated that at 1 and 2 months the non-PRP grafts were significantly more dense than the PRP grafts, and at 3 and 6 months there was no significant difference. Histomorphometric analysis showed that at 1 and 2 months there was significantly less grafted bone and more new bone in the PRP grafts than in the non-PRP grafts. At 3 and 6 months there was no difference in the amount of grafted bone or new bone between the PRP and non-PRP grafts. Histology of the control dog showed incomplete bony healing at 6 months, suggesting that this was a critical sized defect. The bone apposition rate for all times in the PRP and non-PRP graft sites did not significantly change.

CONCLUSION

PRP appeared to enhance early autologous graft healing. However, after 2 months this effect is no longer significant. The early enhanced healing occurred by increasing the amount of non-viable grafted bone that was removed and increasing the amount of new bone that was formed. PRP did not change the rate at which new bone was formed, and no increase in trabecular density was realized in these grafts.

COX-2 has a Critical Role During Incorporation of Structural Bone Allografts

Nonsteroidal anti-inflammatory drugs (NSAIDs), which inhibit cyclooxygenase (COX) activity, reduced pain and are commonly used in patients with skeletal injury. In this article we will also present data to show that selective COX-2 inhibitor delays allograft healing and incorporation. In contrast, local delivery of prostaglandin E2 (PGE2) enhanced bone formation at cortical bone graft junction. A 4-mm mid-diaphyseal segmental femoral defect was created and then repaired by frozen bone allograft of the same size. A 22-gauge metal pin was placed in the intramedullary cavity to stabilize the bone graft. Healing was evaluated weekly by X ray and by a semiquantitative histomorphometric analysis at 5 weeks postsurgery. Celecoxib (25 mg/kg/day) and Ketorolac (4 mg/kg/day) were administered daily for 2 weeks or 5 weeks. PGE2 was infused locally at a dose of 800 nmol/kg per day via osmotic minipump for 4 weeks. Inhibition of cyclooxygenase by daily administration of the Celecoxib or Ketorolac for 5 weeks reduced new bone ingrowth by about 60% (P < 0.05). The percentage of bony bridging in both drug-treated groups was significantly decreased at 5 weeks. Temporal administration of Celecoxib for 2 weeks also significantly reduced bone formation by 45% and withdrawal of the Celecoxib only led to slight recovery of bone formation at the graft side. In contrast to the inhibitory effects of NSAIDS, PGE2 infusion at the cortical bone junction increased bone formation by about twofold. These results demonstrated that COX-2 is essential for bone allograft incorporation. Furthermore, our data support the notion that COX-2-dependent PGE2 produced at the early stage of bone healing is prerequisite for efficient skeletal repair.

Changes in the volume and density of calvarial split bone grafts after alveolar ridge augmentation

OBJECTIVES

One main problem occurring after bone grafting is resorption, leading to insufficient bone volume and quality, and may subsequently cause dental implant failure. Comparison of graft volume and bone density of iliac crest and calvarial transplants determined by animal studies demonstrates significantly lower resorption of bone grafts harvested from the skull. This paper is the first clinical study evaluating bone volume and density changes of calvarial split bone grafts after alveolar ridge reconstruction.

MATERIAL AND METHODS

Bone volume and density were determined using CT scans and the software program Dicom Works in a total of 51 calvarial grafts after alveolar ridge augmentation in 15 patients. CT scans were taken in all 15 patients immediately after grafting (T0) and before implantation after a postoperative period of 6 months (T1). In five patients (26 calvarial grafts), a 1-year follow-up was performed (T2).

RESULTS

A mean volume reduction of 16.2% at T1 (15 patients) and 19.2% at T2 (five patients) was observed. Bone density was high--about 1000 Hounsfield units--and did not change during the 1-year period. At the time of implantation, 41 transplants were classified as quality 1 bone and 10 as quality 2-3 bone. Grafting area and the technique used for grafting (inlay or onlay graft) did not affect the postoperative bone volume reduction. Generalized osteoporosis did not increase the resorption rate of calvarial transplants.

CONCLUSION

Based on these findings, calvarial split bone grafts are a promising alternative for alveolar ridge reconstruction in dental implantology.

Platelet-rich fibrin (PRF): a second-generation platelet concentrate. Part V: histologic evaluations of PRF effects on bone allograft maturation in sinus lift

OBJECTIVE

Platelet-rich fibrin (PRF) belongs to a new generation of platelet concentrates, with simplified processing and without biochemical blood handling. The use of platelet gel to improve bone regeneration is a recent technique in implantology. However, the biologic properties and real effects of such products remain controversial. In this article, we therefore attempt to evaluate the potential of PRF in combination with freeze-dried bone allograft (FDBA) (Phoenix; TBF, France) to enhance bone regeneration in sinus floor elevation.

STUDY DESIGN

Nine sinus floor augmentations were performed. In 6 sites, PRF was added to FDBA particles (test group), and in 3 sites FDBA without PRF was used (control group). Four months later for the test group and 8 months later for the control group, bone specimens were harvested from the augmented region during the implant insertion procedure. These specimens were treated for histologic analysis.

RESULTS

Histologic evaluations reveal the presence of residual bone surrounded by newly formed bone and connective tissue. After 4 months of healing time, histologic maturation of the test group appears to be identical to that of the control group after a period of 8 months. Moreover, the quantities of newly formed bone were equivalent between the 2 protocols.

CONCLUSIONS

Sinus floor augmentation with FDBA and PRF leads to a reduction of healing time prior to implant placement. From a histologic point of view, this healing time could be reduced to 4 months, but large-scale studies are still necessary to validate these first results.

Stability of autogenous bone grafts after sinus lift procedures: a comparative study between anterior and posterior aspects of the iliac crest and an intraoral donor site

BACKGROUND

Autologous bone is the standard material used for augmentations in oral-maxillofacial surgery. Depending on the origin of the graft, subsequent bone resorption may vary.

STUDY DESIGN

This prospective study evaluated 57 patients receiving 2-stage sinus floor augmentations. Monocortical samples were taken at the site of bone harvesting, including the posterior (n = 28) and anterior pelvic (n = 15) and retromolar (n = 14) regions. At second-stage surgery, 6 months after the implant insertion, bone cores were harvested at the site of implant placement. All samples were analyzed by microradiography.

RESULTS

Mean retromolar mineralization was 68.7% +/- 8.75%; 35.1% +/- 7.6% in the anterior and 30.7% +/- 9.5% in the posterior iliac crest. Areas augmented with grafts originating from the retromolar region showed a significant decrease to 53.0% +/- 5.15% (P = .001). A stable mineralization of 36.1% +/- 7.59% was found in sites where bone grafts from the anterior pelvic crest were used. Grafts from the posterior pelvis showed a slight increase to 34.5% +/- 6.5%.

CONCLUSION

This prospective clinical study demonstrates the differences in mineralization depending on the origin of autogenous bone. Even after 6 months, these values could still be correlated to the transplants origin.

Incorporation of impacted morselized bone allografts in rabbits

Morselized bone allografts have been used for the treatment of bone stock loss in orthopedic revision surgery with encouraging results. However, several parameters can influence the graft incorporation including the processing treatments. This experimental work used a cavitary bone defect in 90 rabbits to evaluate the sequence of incorporation of three different kinds of morselized bone allografts: uncryopreserved cancellous bone, freeze-dried cancellous bone, and totally demineralized cortical bone each of which were prepared in accordance with our rigid protocol. Revascularization and remodeling of the transplanted bone grafts were evident upon histological evaluation. Bone apposition and bone resorption resulted in a mixture of graft and new bone. Mineralized cancellous grafts showed great osteoconductive capacity, whereas demineralized cortical grafts showed an intense osteoinductive capacity and a weak osteoconductive capacity. In a general evaluation, cryopreserved cancellous bone grafts showed superior biological efficacy for reconstruction of experimental bone defects, closely followed by freeze-dried cancellous bone grafts, and, finally, by demineralized cortical bone grafts. These results validate our protocol for the processing and preservation of these three kinds of bone grafts.

The Hydration Characteristics of Demineralized and Nondemineralized Allograft Bone: Scientific Perspectives on Graft Function

Demineralized bone matrix grafts are osteoinductive due to the increase in bioavailability of bone morphogenetic proteins that occurs from demineralization. The manner by which demineralization increases their bioavailability, however, is not known with certainty. It is known that the mineral phase of bone masks the proteins of the organic matrix. Proteins depend on their interaction with water for their three-dimensional conformation, biologic activity, and stability. It is possible that demineralization allows a more complete hydration of bone matrix, changing the local environment and allowing the bone morphogenetic proteins to desorb and form a concentration gradient, signaling the appropriate cell types to begin the process of bone regeneration. Under similar test conditions, it was discovered that hydration of demineralized bone matrix powder produces a strong exotherm on the order of 14 degrees C whereas hydration of bone powder produces a smaller exotherm of about 2 degrees C. The details of the hydration reactions of demineralized bone matrix and bone were investigated by measuring the exotherm produced under varying conditions. The results suggest that bone mineral does mask, or limit, the ability of the organic matrix to interact with water. An understanding of the hydration characteristics of demineralized bone matrix can also help in the development of carrier systems that optimize osteoinductive potential.

Statin-induced osteogenesis uses in orthodontics: a scientific review

This article summarizes the current research behind the use of statin to induce bone formation and relates that to potential uses in the field of orthodontics. It triggered BMP-2 expression in in vitro studies. In an in vivo study, the amount of new bone formed by statin mixed with a collagen carrier was quantitatively assessed and results showed that 308% more new bone was formed in defects grafted with statin than those grafted with the carrier alone. Immunolocalization studies on the early healing of the defects grafted with statin showed VEGF, BMP-2, Cbfa 1 expression, and new bone formation occurred 1 day earlier than those grafted with the carrier alone. Since statin is a commonly prescribed drug, it has great potential to be used routinely in bone grafting in the craniofacial region.

Comparison of bone formation ingrafted periosteum harvested from tibia and calvaria

Periosteum covers the bone surface and displays the potential to initiate bone formation, after injury to the bone. Numerous studies have demonstrated that the periosteum plays major roles in the healing process after bone fracture. Some reports have described that in the healing of long bone fractures, the periosteum forms new bone by intramembranous and endochondral ossification. Other researchers insist that healing of defects in membrane bone shows bone formation by intramembranous ossification. However, previous studies have not been able to clarify differences in bone formation patterns. We hypothesized that differences in bone formation pattern are associated with the periosteal potential for cell differentiation. The present study grafted periosteum, harvested from the tibia and calvaria, into the suprahyoid muscle, with the aim of interrupting release of factors from bone matrix. Bone formation, after grafting periosteum, harvested from the tibia and calvaria, was examined histologically and radiographically. Grafted tibial periosteum formed a large area of new bone by intramembranous and endochondral ossification, while grafted calvarial periosteum displayed intramembranous ossification. Grafted tibial periosteum formed a larger area of bone than grafted calvarial periosteum. Patterns of cell differentiation thus differ between grafted periosteum, harvested from the tibia and calvaria.

Evaluation of osteogenic and chondrogenic activities of prefabricated periallografts

Reconstruction of cartilage and bone defects has always been a challenging problem for the surgeon. Basic elements that are responsible for the repair process of these tissues are periost and perichondrium. Although several methods for the use of periost and perichondrium are proposed in the literature, the osteogenic and chondrogenic capacities of these tissues were shown to be the most important factor for a successful outcome. Bone and cartilage formation in acellular dermal matrix (ADM) prefabricated with periost and perichondrium was studied in 20 New Zealand rabbits. Morphologic and histologic evaluation and comparison of the newly formed tissues were evaluated. Four rabbits were excluded from the study because of infection, and specimens were obtained at 4, 6, 8, and 12 weeks after the study began from the remaining 16 rabbits. A gradual increase in bone and cartilage tissue formation through the 4th to 12th weeks was documented by reason of perichondrium and periost activation infiltrating into acellular dermal allografts. In view of the data obtained, it was concluded that periost or perichondrium prefabricated over ADM may be an alternative technique of cartilage and bone formation that may provide adequate tissue with elastic and osteo- and chondroconductive properties for the reconstruction of challenging defects.

Biological effects of rAAV-caAlk2 coating on structural allograft healing

Structural bone allografts often fracture due to their lack of osteogenic and remodeling potential. To overcome these limitations, we utilized allografts coated with recombinant adeno-associated virus (rAAV) that mediate in vivo gene transfer. Using beta-galactosidase as a reporter gene, we show that 4-mm murine femoral allografts coated with rAAV-LacZ are capable of transducing adjacent inflammatory cells and osteoblasts in the fracture callus following transplantation. While this LacZ vector had no effect on allograft healing, bone morphogenetic protein signals delivered via rAAV-caAlk2 coating induced endochondral bone formation directly on the cortical surface of the allograft by day 14. By day 28 there was evidence of remodeling of the new woven bone and massive osteoclastic resorption of the cortical surface of the rAAV-caAlk2-coated allografts only. Micro-CT analysis of rAAV-LacZ- vs rAAV-caAlk2-coated allografts after 42 days of healing demonstrated a significant increase in new bone formation (0.67 +/- 0.21 vs 2.49 +/- 0.40 mm(3); P < 0.005). Furthermore, the 3D micro-CT images of femurs grafted with rAAV-Alk2-coated allografts provided the first evidence that complete bridging of bone around a cortical allograft is possible. These results indicate that cell-free, rAAV-coated allografts have the potential to revitalize in vivo following transplantation.

[Growth defects of fibular flaps in children]

BACKGROUND

Mandibular reconstruction with fibula free flap is a challenge in pediatric patients because of the size of the bone and absence of growth without epiphyseal transplantation.

CASE REPORT

We report 2 cases of free fibula flap in children for mandibular reconstruction. The 2 patients presented with growth insufficiency of the bone graft after few years of evolution.

DISCUSSION

Growth insufficiency was treated with different surgical procedures which were discussed We review the consequences on growth after fibula free flap and the specific indications to achieve epiphyseal fibular growth in children.

Revascularization of autogenous block grafts with or without an e-PTFE membrane

PURPOSE

The aim of this study was to describe the revascularization process of autogenous bone block grafts placed with or without an expanded polytetrafluoroethylene (e-PTFE) membrane.

MATERIALS AND METHODS

Thirty Wistar male rats had their mandibles augmented by either an autogenous bone block graft (group A) or an autogenous bone block graft covered with an e-PTFE membrane (group B). The animals were sacrificed by perfusion at baseline, 3, 7, 14, and 21 days after surgery.

RESULTS

After 3 days, the presence of vascular sprouts derived from the recipient bed was observed in group A; more discrete sprouts were also observed in group B. After 7 days, revascularization continued, with vessels derived from both the recipient bed and the surrounding connective tissue in group A but only from the recipient bed in group B. At 14 days, group A showed penetration of vessels at the periphery of the graft; the vessels reached varying distances inside it. In group B, revascularization of the graft occurred mainly near its perforation, its borders, and at the recipient bed-graft interface. After 21 days, graft vascular penetration could be observed throughout the extent of the graft in group A but only approximately halfway through the graft in group B.

DISCUSSION

The results emphasized the importance of the vascular network and of the revascularization process of the autogenous bone graft in new bone formation. Early vascular penetration and nutrition of the graft are key factors in its integration with the recipient bed.

CONCLUSIONS

Revascularization of the bone graft occurred in both A and B. However, vascular sprouts originated only from the recipient bed in group A, while in group B the graft was penetrated by vessels from both the recipient bed and the surrounding connective tissue. The revascularization took place more promptly and was more intense and extensive in group A than in group B for all periods.

Revascularization of diaphyseal bone segments by vascular bundle implantation

Vascularized bone transfer is an effective, established treatment for avascular necrosis and atrophic or infected nonunions. However, limited donor sites and technical difficulty limit its application. Vascular bundle transplantation may provide an alternative. However, even if vascular ingrowth is presumed to occur in such situations, its extent in aiding revascularization for ultimate graft incorporation is not well understood. A rabbit tibia model was used to study and compare vascularized, segmental, diaphyseal, nonvascularized conventional, and vascular bundle-implanted grafts with a combination of angiographic, radiographic, histopathologic, and bone scanning techniques. Complete graft incorporation in conventional grafts was observed at 6 months, whereas it was 8 to 12 weeks with either of the vascularized grafts. The pattern of radionuclide uptake and the duration of graft incorporation between vascular segmental bone grafts (with intact endosteal blood supply) and vascular bundle-implanted segmental grafts were similar. A vascular bundle implanted in the recipient bone was found to anastomose extensively with the intraosseous circulation at 6 weeks. Effective revascularization of bone could be seen when a simple vascular bundle was introduced into a segment of bone deprived of its normal blood supply. This simple technique offers promise for improvement of bone graft survival in clinical circumstances.

Bone quality and healing in a swine vascularized bone allotransplantation model using cyclosporine-based immunosuppression therapy

Although vascularized bone and joint allotransplantation is a promising new treatment option for reconstructing large bone defects, the need for immunosuppressive agents to prevent rejection in these procedures poses a major problem. This problem stems from the fact that several of these agents can cause harmful side effects, such as alterations in bone quality and healing. Therefore, the purpose of this study was to determine what effect the commonly used immunosuppressant regimen cyclosporine A-based combination therapy has on bone quality and healing. In 10 pigs, vascularized bone allografts with skin and muscle components (osteomyocutaneous free flaps) were transplanted from size-matched donor animals. Recipient animals received oral cyclosporine A/mycophenolate mofetil/prednisone therapy for 90 days. Bone quality was studied before and after transplantation by measuring the bone's acoustic velocity and density and calculating the bone's elastic coefficient. Bone healing was assessed using radiographic analysis. Four animals were lost as a result of graft rejection or immunosuppression-related complications before the 90-day endpoint of the study. Although bone specimens taken from the six animals that completed the 90-day protocol had histological signs of rejection, they all seemed to have normal bone healing. Posttransplant bone density values were significantly decreased (p < 0.05) (1544.7 +/- 47.5 kg/m3) as compared with pretransplant values (1722.7 +/- 44.1 kg/m3). Results of the acoustic velocity and elastic coefficients measurements showed a significant decrease (p < 0.05) in posttransplant values (from 3503.0 +/- 165.1 meters/sec to 2963.0 +/- 54.6 meters/sec and from 21.6 +/- 2.2 GPa to 13.6 +/- 0.5 GPa, respectively), indicating diminished bone quality. The findings indicate that cyclosporine A/mycophenolate mofetil/prednisone combination therapy is ineffective in preventing bone rejection, that it decreases bone quality, and that it is associated with systemic toxicity, suggesting that this immunosuppressive regimen at the doses used in this study is not ideal for vascularized bone allotransplantation procedures.

Long-term radiographic assessment of secondary alveolar bone grafting outcomes in patients with alveolar clefts

OBJECTIVE

The objective of this study was to assess the outcomes of secondary alveolar bone grafting (SABG) in patients with complete, unilateral cleft lip and palate (UCLP) operated on before eruption of the permanent canine.

STUDY DESIGN

Sixty-five periapical radiographs from 41 patients with left UCLP and 24 with right UCLP (9 to 12 years old at SABG), were analyzed retrospectively for the amount of bone in the cleft site according to the Bergland and Chelsea scales, and for the occurrence of canine eruption (CE) through the neoformed bone.

RESULTS

Of the cases, 71% were classified as Bergland type I and Chelsea type A; 15% as types II/C, and 14% could not be classified. CE was observed in 95% of the cases operated on 4 years before the study.

CONCLUSIONS

SABG performed before CE is a procedure with a high rate of success. The radiographic scales proved to be important instruments for assessing surgical outcomes.

Implant prosthodontic rehabilitation of fibula free-flap reconstructed mandibles: a Memorial Sloan-Kettering Cancer Center review of prognostic factors and implant outcomes

PURPOSE

This study aimed to estimate the cumulative survival rates (CSRs) of implants placed in reconstructed mandibles and to identify prognostic factors that may influence implant survival.

MATERIALS AND METHODS

The charts of 24 patients (10 male, 14 female) who had undergone mandibular resection and reconstruction with fibula free-flaps treated with implant-supported prostheses from April 1986 through December 2001 were reviewed. Information on demographics, surgical characteristics, treatment modalities, dentition, implant parameters, prostheses, and hyperbaric oxygen therapy (HBO) was gathered. Kaplan-Meier survival estimates were generated for the 100 implants that satisfied the inclusion criteria. Multivariate Cox proportional hazards regression models accounting for correlated implants within subjects were developed to identify prognostic factors for implant survival.

RESULTS

Ninteen implants had been placed in native mandible (3 in irradiated bone) and 81 in fibula bone flap. Six implants failed during the follow-up period (mean 51.7 months). The overall 5- and 10-year CSRs were 97.0% and 79.9%, respectively. In the univariate analysis, variables associated with implant survival were age, gender, chemotherapy, radiation therapy, HBO, irradiated bone, implant diameter, xerostomia, trismus, opposing dentition, and type of prosthesis. At 5 years, the CSR of implants in patients with HBO was 86.7%; HBO was statistically associated with an increased risk for implant failure (P = .005, hazard ratio = 19.79, 95% CI: 2.42 to 161.71).

DISCUSSION

The CSR was lower when implants were placed in a previously irradiated mandible. There is still a lack of reliable clinical evidence to support the effectiveness of HBO in these patients.

CONCLUSIONS

A high survival rate was demonstrated for implants placed in fibula free-flap reconstructed mandibles. The finding that HBO was a risk factor can probably be attributed to the small sample size; further study is needed in this patient population.

Long-term results of vertical height augmentation genioplasty using autogenous iliac bone graft

OBJECTIVE

In order to clarify the clinical utility of the vertical height augmentation (VHA) genioplasty using autogenous iliac bone graft (IBG), this study examined the postsurgical changes in hard and soft tissues of the chin and the stability of the grafted bone.

STUDY DESIGN

Twenty-three patients who had undergone VHA genioplasty using autogenous IBG were evaluated radiographically and clinically. A comparison study of the changes in hard to soft tissues after surgery in all 23 patients was performed with preoperative, 1-month, 3-months, 6-months, and/or 1-year postoperative lateral cephalograms by tracing. Stability, bone healing, and complication of the grafted bone was evaluated by follow-up radiographs and clinical observation.

RESULTS

Between the preoperative and 6-month postoperative tracings, an average vertical augmentation of the osseous segment was 4.2 mm at menton and that of the soft tissue menton was 4.0 mm. There was a high predictability of 1:0.94 between the amounts of hard versus soft tissue changes with surgery in the vertical plane. The position of the genial bone segment was stable immediately after surgery and soft tissue was not changed significantly from 1 month to 1 year after operation. Clinical and radiological follow-up results of the iliac bone graft showed normal bony union and were generally stable.

CONCLUSIONS

VHA genioplasty using IBG is a reliable method for predicting hard and soft tissue changes and for maintaining postoperative soft tissue of the chin after surgery.

Osteogenic Capacities of Periost Grafts, Periost Flaps and Prefabricated Periosteal Flaps: Experimental Study

Reconstruction of the bone defects due to various causes is still one of the challenging problems in plastic and reconstructive surgery. Periosteum is accepted to be the essential source for the repair of the bone tissue, which constitutes the basis of the support and the mobility functions of the surrounding tissues. Periosteal grafts and flaps have been used for various purposes by numerous techniques. The osteogenic activity of the periosteal tissues has a great importance regarding the purposes of reconstruction. In this experimental study, 20 New Zealand rabbits were used for the evaluation and the comparison of the osteogenic activities of periosteal grafts, periosteal flaps and prefabricated periosteal flaps. Morphological, histopathological and scinthigraphical observations were carried out for the assessment and the comparison of the groups after a follow-up of 12 weeks. Two of the animals were left out as a result of infection. The results showed that periosteal flaps had a much faster and more stable reconstructive capacity of osteogenesis, whereas prefabricated periosteal flaps had an osteogenic capacity of a lower degree and periosteal grafts apparently less than the former groups. We believe that this study confirms the reconstructive capacity of prefabricated periosteal flaps as an alternative to periosteal flaps for the repair of osseous tissues as well as indicating the osteogenic capacity of the periosteal grafts, though in a lesser degree.

Nacre/bone interface changes in durable nacre endosseous implants in sheep

Raw nacre implants persist even after 9 months of implantation into bone tissue in sheep. However the nacre surface undergoes a limited biodegradation process. Smooth-surfaced nacre implants were seen to become microporous after implantation. The results of these long-term, in vivo studies show that the overall process involves bone-resorbing cells, relies on a two-phase mechanism and may correspond to a regulation process. The rate of surface change depends on the bone implantation site and the nacre/bone interaction. The in vivo biodegradability of nacre is a highly variable parameter. The size and shape of the implanted nacre and the cellular environment of the implant are key factors in determining the biodegradation kinetics of the nacre in a living system.

La greffe d’apposition à visée pré-implantaire pour édentation maxillaire antérieure

INTRODUCTION

Apposition grafting is a method of choice for reconstruction of the anterior maxillary. The purpose of this work was to evaluate the success rate, the degree of bone resorption and the osteointegration of these grafts.

MATERIAL AND METHODS

We reviewed retrospectively 36 cases of pre-maxillary bone apposition in patients operated from 1998 to 2002. Autografts were used for all patients. The harvesting site was parietal for 24 patients, intraoral for 8 and iliac for 4.

RESULTS

There was two graft failures. The success rate was 94.5%. Partial resorption with effect on implantation was noted in 3 patients. Eighty implants were inserted successfully in 234 grafted sites with on average 2.4 implants per graft. Three implants were removed. Implant survival was 96.2%.

DISCUSSION

This study demonstrated that the premaxillary apposition technique using autologous grafts provides sufficient bone volume to enable optimal implant insertion and stability.

La cicatrisation des greffes osseuses

Bone graft healing involves an invasive process where vessels and cells penetrate the graft material to enable neoformation of bone. The origin of the material and its intrinsic properties and morphology are factors which affect its resorption and replacement. The first step involve formation of bone via the osteoconductive properties of the graft. For autologous bone, graft resorption enables secondarly release of preserved bone proteins, favoring a process of osteo-induction which contributes to remodelling and graft replacement by neoformed bone.

Basic fibroblast growth factor up-regulates the expression of vascular endothelial growth factor during healing of allogeneic bone graft

Recently we reported that basic fibroblast growth factor (bFGF) improved the healing of allogeneic bone grafts. However, the mechanism of action of the bFGF was not known. Therefore, the present study was designed to identify the expression pattern of vascular endothelial growth factor (VEGF) in the presence of bFGF reconstituted in demineralized intramembranous bone matrix (DBMIM) during the healing of allogeneic bone grafts. Eighteen critical size (15 mm x 10 mm) defects were created on rabbit mandibles bilaterally. Three groups of six defects each were grafted with allogeneic bone alone, allogeneic bone and DBMIM, and allogeneic bone and bFGF reconstituted in DBMIM. Three weeks later, the defects were retrieved for immunohistochemistry and in situ hybridization for VEGF. The percentage of positive staining area was quantified by using image analyzer. The increase (517%) in the expression of VEGF mRNA was accompanied by an increase (492%) of immunoreactive VEGF protein in allogeneic bone graft augmented by bFGF reconstituted in DBMIM. A close correlation existed between levels of VEGF production and the amount of newly formed bone. The results show that bFGF reconstituted in DBMIM markedly up-regulated the expression of VEGF in the grafted area. Basic FGF augments the healing of allogeneic bone grafts by enhancing vascularization through the up-regulation of VEGF.

Proliferation and osteogenic differentiation of cells from cortical bone cylinders, bone particles from mill, and drilling dust

PURPOSE

The osteogenic potential of a graft is based on the parallel lines ability of cells to survive transplantation and to respond to local factors that stimulate new bone formation. Here we investigated the potential of cells that had grown out of porcine cortical bone grafts obtained by 3 preparation techniques to respond to mitogenic and osteogenic stimuli.

MATERIALS AND METHODS

Bone grafts were harvested from 2 pigs. Cortical bone was taken in cylindrical form and ground in a bone mill or harvested via drilling and aspiration.

RESULTS

Cell outgrowth was observed in all cortical bone cylinders, bone cylinders homogenized by mill, and 5 of 10 explants of bone dust collected upon drilling. After a 2-week culture period, the number of outgrown cells did not significantly differ among the 3 preparations. Bone cells showed increased proliferation in response to platelet-released supernatants as determined by 3 [H]-thymidine incorporation assay. When cultured under conditions that favor the expression of an osteogenic phenotype, the outgrown cells expressed alkaline phosphatase activity and transcripts of the osteoblast-specific marker osteocalcin. Individual cell preparations showed accumulation of mineral salts in their extracellular matrix. Bone cells also increased alkaline phosphatase activity in response to bone morphogenetic protein (BMP)-2, BMP-6, and BMP-7. The mitogenic and osteogenic response was obtained with cells from the mandible as well as from the maxilla, irrespective of the preparation technique.

CONCLUSION

These data show that cortical bone grafts contain cells that have the ability to proliferate and differentiate into the osteogenic lineage, suggesting that these cells can contribute to bone regeneration following transplantation.

The influence of alendronate on bone formation after autogenous free bone grafting in rats

OBJECTIVE

This study was undertaken to investigate the influence of alendronate on bone formation after autogenous free bone grafting in rats.

STUDY DESIGN

Fifty-six male Wistar-Albino rats were divided into 3 groups: baseline, saline-treated, and alendronate-treated groups, and followed up at 2, 4, and 12 weeks. In the femur of the rats, autogenous free bone grafts 3 mm in diameter and 2 mm in length were harvested with a standard trephine bur. The bone defects 3 mm in diameter and 2 mm in length were created 5 mm from the donor sites. Each graft was placed in the bone defect and stabilized by perifemoral wiring. The alendronate-treated rats were administered 0.25 mg/kg alendronate subcutaneously daily. The saline-treated rats were given daily saline solution. Serum calcium, phosphate, parathyroid hormone, 1,25-dihydroxyvitamin D, bone alkaline phosphatase (BAP), osteocalcin, and urine calcium were measured. The changes in the number of osteoblasts bordering active bone formation surface and osteoid and lamellar bone formation were evaluated to measure anabolic bone activity.

RESULTS

Alendronate caused significant increase in serum osteocalcin and BAP levels biochemically and the number of osteoblasts histopathologically.

CONCLUSION

Alendronate may be considered among therapeutic options to improve bone formation process in different bone remodeling cases. Further detailed studies should be focused on dosage- and time-dependent effects of alendronate on bone formation.

No effect of platelet-rich plasma with frozen or processed bone allograft around noncemented implants

We compared processed morselized bone allograft with fresh-frozen bone graft around noncemented titanium implants. Also, the influence of platelet-rich plasma (PRP) in combination with bone allograft was evaluated. Analysis was based on implant fixation and histomorphometry. PRP was prepared by isolating the buffy coat from autologous blood samples. Bone allograft was used fresh-frozen or processed by defatting, freeze drying, and irradiation. Cylindrical hydroxyapatite-coated titanium implants were inserted bilaterally in the femoral condyles of eight dogs. Each implant was surrounded by a 2.5-mm concentric gap, which was filled randomly according to the four treatment groups--group 1: fresh-frozen bone allograft; group 2: processed bone allograft; group 3: fresh-frozen bone allograft + PRP; group 4: processed bone allograft + PRP. Histological and mechanical evaluation demonstrated no influence of bone allograft processing. Even though the level of platelet in PRP was 7.7 times that found in whole blood, we found no improvement of bone formation or implant fixation by adding PRP.