Periodontal repair in dogs: recombinant human bone morphogenetic protein-2 significantly enhances periodontal regeneration

Stem cell-based composite tissue constructs for regenerative medicine

A major task of contemporary medicine and dentistry is restoration of human tissues and organs lost to diseases and trauma. A decade-long intense effort in tissue engineering has provided the proof of concept for cell-based replacement of a number of individual tissues such as the skin, cartilage, and bone. Recent work in stem cell-based in vivo restoration of multiple tissue phenotypes by composite tissue constructs such as osteochondral and fibro-osseous grafts has demonstrated probable clues for bioengineered replacement of complex anatomical structures consisting of multiple cell lineages such as the synovial joint condyle, tendon-bone complex, bone-ligament junction, and the periodontium. Of greater significance is a tangible contribution by current attempts to restore the structure and function of multitissue structures using cell-based composite tissue constructs to the understanding of ultimate biological restoration of complex organs such as the kidney or liver. The present review focuses on recent advances in stem cell-based composite tissue constructs and attempts to outline challenges for the manipulation of stem cells in tailored biomaterials in alignment with approaches potentially utilizable in regenerative medicine of human tissues and organs.

Formation and resolution of ankylosis under application of recombinant human bone morphogenetic protein-2 (rhBMP-2) to class III furcation defects in cats

OBJECTIVES

Periodontal regeneration under application of bone morphogenetic protein (BMP) is compromised by ankylosis. Ankylosis disappearance following application of BMP has been observed in the case of a small defect, which might be beneficial change for periodontal regeneration. However, the histological observation of ankylosis disappearance has not been demonstrated in a large defect. The purpose of this present study was to confirm resolution of ankylosis during periodontal regeneration by recombinant human BMP-2 (rhBMP-2) applied to class III furcation defects.

MATERIAL AND METHODS

Class III furcation defects were created in the premolars of six adult cats. The rhBMP-2 material, prepared by applying rhBMP-2 to a combination of polylactic acid-polygricolic copolymer and gelatin sponge (PGS; 0.33 microg rhBMP-2/mm(3) PGS) or control material containing only PGS, was implanted into each defect. The cats were killed at 3, 6 or 12 weeks after surgery and serial sections were prepared for histological and histometrical observation.

RESULTS

Ankylosis was observed in some of the rhBMP-2/PGS group at 3 and 6 weeks, but not at 12 weeks. At 6 weeks, osteoclast-like cells were visible in the rhBMP-2/PGS group with ankylosis. Residual PGS was evident between the bone and root surface in the rhBMP-2/PGS group without ankylosis at 3 weeks.

CONCLUSIONS

Resolution of ankylosis by osteoclast-like cells possibly occurred under application of rhBMP-2. Residual PGS might play an important role in preventing ankylosis formation.

Assessment of Bone Repair Associated with the Use of Organic Bovine Bone and Membrane Irradiated at 830 nm

OBJECTIVE

The aim of the present investigation was to assess histologically the effect of LLLT (GaAIAs, 830 nm, 40 mW, CW, (Phi) approximately 0.6 mm, 16 J/cm(2) per session) on the repair of surgical defects created in the femur of the Wistar Albinus rat. The defects were filled to lyophilized bovine bone (Gen-ox), organic matrix) associated or not to GTR (Gen-derm).

BACKGROUND DATA

A major problem on modern Dentistry is the recovery of bone defects caused by trauma, surgical procedures or pathologies. Several types of biomaterials have been used in order to improve the repair of these defects. These materials are often associated to procedures of GTR. Previous studies have shown positive effects of LLLT on the repair of soft tissue wounds, but there are a few on its effects on bone healing.

METHODS

Surgical bone defects were created in 42 animals divided into five groups: Group I (control, 6 animals); Group II (Gen-ox, 9 animals); Group III (Gen-ox + Laser, 9 animals); Group IV (Gen-ox + Gen-derm, 9 animals); Group V (Gen-ox + Gen-derm + Laser, 9 animals). The animals on the irradiated group received 16 J/cm(2) per session divided into four points around the defect (4 J/cm(2)) being the first irradiation immediately after surgery and repeated seven times at every 48 h. The animals were humanly killed after 15, 21, and 30 days.

RESULTS

The results of the present investigation showed histological evidence of improved amount of collagen fibers at early stages of the bone healing (15 days) and increased amount of well organized bone trabeculae at the end of the experimental period (30 days) on irradiated animals compared to non irradiated ones.

CONCLUSIONS

It is concluded that a positive biomodulative effect on the healing process of one defect associated or not to the use of organic lyophilized bone and biological bovine lyophilized membrane on the femur of the rat.

Bone morphogenetic proteins in craniofacial and periodontal tissue engineering: Experimental studies in the non-human primate Papio ursinus

The bone morphogenetic and osteogenic proteins (BMPs/OPs), pleiotropic members of the transforming growth factor-beta (TGF-beta) supergene family act as soluble signals for the de novo initiation of bone formation, sculpting the multicellular mineralized structures of the bone-bone marrow organ. The strikingly pleiotropic effects of BMPs/OPs spring from amino acid sequence variations in the carboxy-terminal domain and in the transduction of distinct signalling pathways by individual Smad proteins after transmembrane serine/threonine kinase complexes of type I and II receptors. BMPs/OPs are the common molecular initiators deployed for embryonic development and the induction of bone formation and regeneration in postnatal osteogenesis. Naturally derived BMPs/OPs extracted and purified from baboon and bovine bone matrices induce complete regeneration of non-healing calvarial defects in the non-human primate Papio ursinus as well as the induction of cementogenesis and the morphogenesis of a periodontal ligament system with a faithful insertion of Sharpey's fibers into the newly formed cementum. gamma-Irradiated recombinant human osteogenic protein-1 (hOP-1) delivered by xenogeneic bovine collagenous bone matrices completely regenerated and maintained the architecture of the induced bone after treatment of calvarial defects with single applications of doses of 0.1, 0.5 and 2.5mg hOP-1 per gram of carrier matrix. The long-term implantation of hOP-1 delivered by gamma-irradiated bovine bone matrices induced the regeneration of the three essential components of the periodontium, i.e. cementum, periodontal ligament and alveolar bone. The osteogenic proteins of the TGF-beta superfamily are sculpting tissue constructs that engineer skeletal tissue regeneration in molecular terms. The pleiotropy of the signalling molecules of the TGF-beta superfamily is highlighted by the redundancy of molecular signals initiating bone formation, including the TGF-beta isoforms per se, powerful inducers of endochondral bone formation but in the primate only. The induction of bone develops a mosaic structure in which members of the TGF-beta superfamily singly, synergistically and synchronously initiate and maintain tissue induction and morphogenesis.

Preliminary Evaluation of BMP-2 Expression and Histological Characteristics During Apexification with Calcium Hydroxide and Mineral Trioxide Aggregate

Histological characteristics and bone morphogenetic protein-2 (BMP-2) expression were evaluated in apexification procedures using calcium hydroxide [Ca (OH)2] and mineral trioxide aggregate (MTA). In three of four quadrants of the mouth, monkey (Macaca fascicularis) teeth were infected by pulpal exposure to saliva. After 90 days, each group was treated with Ca (OH)2 or MTA. Infected, untreated teeth were used as negative controls and normally developing teeth were used as positive controls. Areas within the apical region of each sample were scored based upon histological findings and BMP-2 expression. Overall, BMP-2 expression in all areas was similar in the Ca (OH)2, MTA, and infection/no treatment groups, which tended to be more immunoreactive for BMP-2 than the untreated group. Use of MTA in combination with Ca (OH)2 may initiate regeneration of the periodontium more quickly than either material used alone, but further studies involving MTA use in apical closure are indicated.

Effects of bone morphogenetic protein-6 on periodontal wound healing in a fenestration defect of rats

BACKGROUND

Bone morphogenetic proteins (BMPs) may play significant roles in bone formation. The ability of BMP-6 to promote wound healing has been chosen as the subject of this investigation. In this study, a synthetic rat BMP-6 polypeptide was applied to a periodontal fenestration defect in rats to elucidate the effects of BMP-6 on periodontal wound healing.

MATERIAL AND METHODS

Following surgery to create a bony window on the buccal aspects of mandibular molar roots, 24 male Sprague Dawley rats were divided into four groups according to BMP application (0, 1, 3 and 10 microg, respectively). Animals were killed after 28 days and the mandible taken for histological examination. Histometric measurements were performed on sections selected from three levels (coronal, middle and apical levels; with 240 microm apart from the central) of the defect. New bone and cementum formation (including area and thickness) were analyzed and compared.

RESULTS

In general, minimal new bone was observed on the surgically created defects in the non-BMP group, whereas a complete osseous healing occurred in all BMP-6 treated animals. New bone formation (both in area and thickness) was significantly influenced by both the dosage and the examining level, whereas new cementum formation was affected by dosage only. An increase in bone and cementum formation was noted in all three BMP groups when compared with the control group at all examined levels. Among the BMP groups, greatest new bone and cementum formation were noted in the 3 microg group. New cementum thickness increased on the cementum surfaces of the defects compared with the dentinal surfaces in all study groups.

CONCLUSION

An increase in new bone and cementum formation was noted after applying a synthetic BMP-6 polypeptide to a periodontal fenestration defect in rats. Therefore, we suggest that BMP-6 may play a certain role in periodontal regeneration.

The Effects of a Bioabsorbable Barrier Membrane Containing Safflower Seed Extracts on Periodontal Healing of 1-Wall Intrabony Defects in Beagle Dogs

BACKGROUND

Recently, there has been much research done into the regenerative potential of materials used in oriental medicine. In several studies, evidence was found that these materials have an effect on bone regeneration. Among these materials, safflower seeds are of particular interest as they have been used for the treatment of blood stasis, bone fracture, and osteoporosis in traditional Korean medicine. In addition, they are known to have anti-inflammatory effects. The objective of this study is to evaluate the periodontal tissue regenerative effects of a bioabsorbable barrier membrane (polylactide glycolic acid electro-spun non-woven membrane) containing safflower seed extracts applied to surgically created 1-wall intrabony defects in beagle dogs.

METHODS

One-wall intrabony defects were surgically created bilaterally at the mesial and distal sides of the mandibular second premolars and mesial side of the fourth premolars. These defects were randomly assigned either to the surgical control group which received a flap operation only or to one of two experimental groups consisting of defects which received a guided tissue regenerative procedure with either a bioabsorbable membrane (PLGA) or a bioabsorbable membrane containing safflower seed extracts (SSE/PLGA). The dogs were sacrificed 8 weeks after the operation, and a comparative histological examination was done.

RESULTS

The new cementum formation was 2.49+/-0.41 mm in the surgical control group, 3.22+/-0.35 mm in the PLGA group, and 3.67+/-0.82 mm in the SSE/PLGA group. The extent of new cementum formation in barrier groups was significantly different from the surgical control group (P <0.05). The amount of intrabony cementum was 1.75+/-0.06 mm, 2.40+/-0.33 mm, and 2.70+/-0.81 mm for the surgical control group, the PLGA group, and the SSE/PLGA group, respectively; the amount of infrabony cementum in the barrier groups was significantly different from the surgical control group (P<0.05). The value of the suprabony cementum was 0.73+/-0.48 mm, 0.82+/-0.21 mm, and 0.97+/-0.09 mm for the surgical control group, the PLGA group, and the SSE/PLGA group, respectively, with no significant differences being observed among the treatments. The amount of new alveolar bone formation was 1.74+/-0.25 mm, 2.36+/-0.30 mm, and 2.64+/-0.74 mm for the surgical control group, the PLGA group, and the SSE/PLGA group, respectively, with a significant difference exhibited between the surgical control group and other groups (P <0.05). Superficial root resorption was often observed, but ankylosis was not present.

CONCLUSION

Our results suggest that surgical application of polylactide glycolic acid non-woven membrane with or without safflower seed extract could promote the regeneration of alveolar bone and cementum in intrabony periodontal defects.

Periodontal repair in dogs: evaluation of a bioresorbable calcium phosphate cement (Ceredex) as a carrier for rhBMP-2

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to induce clinically relevant bone formation for orthopedic, craniofacial, and oral indications. It appears critical, in particular for onlay indications, that the associated carrier technology exhibits structural integrity to offset compressive forces in support of rhBMP-2-induced bone formation. The objective of this study was to evaluate a calcium phosphate (CP) cement, Ceredex, as a candidate carrier for rhBMP-2 in a defect model with limited osteogenic potential.

MATERIALS

Bilateral, critical size, 6-mm, supra-alveolar, periodontal defects were created in six, adult, male, Hound Labrador mongrels. Three animals received rhBMP-2/Ceredex (rhBMP-2 at 0.20 and 0.40 mg/ml) in contralateral defect sites (implant volume/defect approximately 1 ml). One defect site in each of the three remaining animals received Ceredex without rhBMP-2 (control). The animals were euthanized at 12 weeks postsurgery for histologic and histometric analysis.

RESULTS

Mean induced bone height exceeded 80% of the defect height for supra-alveolar periodontal defects receiving rhBMP-2/Ceredex without major differences between rhBMP-2 concentrations compared with approximately 40% for the control. The newly formed bone, a mixture of lamellar and woven bone in fibrovascular tissue, circumscribed relatively large portions of the residual Ceredex biomaterial. Inflammatory lesions were associated with limited bone formation in some sites. From a periodontal perspective, sites receiving rhBMP-2/Ceredex exhibited increased cementum formation compared with control, but without a functionally oriented periodontal ligament, and increased ankylosis and root resorption. Control sites exhibited early wound failure and exposure, loss of the Ceredex biomaterial, and limited bone formation.

CONCLUSIONS

The Ceredex CP cement appears a potentially promising carrier technology for rhBMP-2 onlay indications. However, a slow resorption rate may prevent its wider use. This study does not support use of the rhBMP-2/Ceredex combination for periodontal indications.

Enhancement of Bone Formation by Bone Morphogenetic Protein-2 During Alveolar Distraction: An Experimental Study in Sheep

BACKGROUND

The purpose of this study was to perform alveolar ridge augmentation by distraction osteogenesis (DO) and to enhance bone regeneration through the use of recombinant human bone morphogenetic protein-2 (rhBMP-2), followed by implant placement.

METHODS

Alveolar segmental osteotomy was performed in the mandible of 10 sheep followed by placement of 1.5 mm alveolar distraction devices. The study group was injected on the fifth day of distraction with a single dose of 10 microg rhBMP-2. Only distraction was performed in the control group.

RESULTS

A mean alveolar augmentation of 12 mm was achieved. After 12 weeks of consolidation, the distraction devices were removed and biopsies were taken for histological and immunohistochemical characterization and morphometry of the newly formed bone. Titanium threaded cylindrical implants were then placed in the newly augmented bone. Radiological evaluation showed lifting of the transport segment and integration of the implants within both the transport segment and the regenerated bone. The histological study demonstrated that the association of DO and BMP resulted in increased trabecular bone size and volume (32.2%+/-0.95% versus 18.6%+/-0.71%; P <1 x 10(-17) after 24 days of lengthening and 63.8%+/-1.89% versus 42.5%+/-1.33%; P<1 x 10(-15) after 12 weeks of consolidation) and increased numbers of proliferating cell nuclear antigen stained cells (0.7+/-0.04 versus 0.47+/-0.04; P<1 x 10(-10)) compared with the DO only group.

CONCLUSIONS

Alveolar distraction augments atrophic alveolar ridge and creates new bone that permits implant placement. rhBMP-2 enhances bone quality and may shorten the consolidation period of distraction allowing for earlier implant placement.

Periodontal repair in dogs: effect of recombinant human bone morphogenetic protein-12 (rhBMP-12) on regeneration of alveolar bone and periodontal attachment

OBJECTIVES

Recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to stimulate alveolar bone and cementum formation in periodontal defects but not a functionally oriented periodontal ligament (PDL). Subcutaneous and intramuscular implants of BMP-12 have been shown to induce tendon formation and ligament-like tissue. The objective of this study was to evaluate rhBMP-12 for periodontal regeneration, in particular PDL formation.

METHODS

Six young adult Hound Labrador mongrel dogs were used. Routine supraalveolar periodontal defects were created around the mandibular premolar teeth. Three animals received rhBMP-12(0.04 mg/ml) in an absorbable collagen sponge (ACS) carrier vs. rhBMP-12(0.2 mg/mL)/ACS in contralateral defects. Three animals received rhBMP-12(1.0 mg/ml)/ACS vs. rhBMP-2(0.2 mg/ml)/ACS (total implant volume/defect approximately 1 ml). The animals were euthanized 8 weeks postsurgery and block biopsies were processed for histometric analysis.

RESULTS

Bone regeneration appeared increased in sites receiving rhBMP-2/ACS compared to sites receiving rhBMP-12/ACS. Cementum regeneration was similar comparing sites implanted with rhBMP-2/ACS to sites implanted with rhBMP-12/ACS. In contrast, sites receiving rhBMP-12/ACS exhibited a functionally oriented PDL bridging the gap between newly formed bone and cementum whereas this was a rare observation in sites receiving rhBMP-2/ACS. Ankylosis appeared increased in sites receiving rhBMP-2/ACS compared to those receiving rhBMP-12/ACS.

CONCLUSIONS

The outcomes of this study suggest that rhBMP-12 may have significant effects on regeneration of the PDL. Additional preclinical evaluation is needed to confirm these initial observations prior to clinical application.

Identification of genes differentially regulated in rat alveolar bone wound healing by subtractive hybridization

Periodontal healing requires the participation of regulatory molecules, cells, and scaffold or matrix. Here, we hypothesized that a certain set of genes is expressed in alveolar bone wound healing. Reciprocal subtraction gave 400 clones from the injured alveolar bone of Wistar rats. Identification of 34 genes and analysis of their expression in injured tissue revealed several clusters of unique gene regulation patterns, including the up-regulation at 1 wk of cytochrome c oxidase regulating electron transfer and energy metabolism, presumably occurring at the site of inflammation; up-regulation at 2.5 wks of pro-alpha-2 type I collagen involving the formation of a connective tissue structure; and up-regulation at 1 and 2 wks and down-regulation at 2.5 and 4 wks of ubiquitin carboxyl-terminal hydrolase l3 involving cell cycle, DNA repair, and stress response. The differential expression of genes may be associated with the processes of inflammation, wound contraction, and formation of a connective tissue structure.

Effect of recombinant human bone morphogenetic protein-12 (rhBMP-12) on regeneration of periodontal attachment following tooth replantation in dogs. A pilot study

OBJECTIVES

Subcutaneous and intramuscular implants of bone morphogenetic protein-12 (BMP-12) have been shown to induce formation of tendon and ligament tissue. BMP-12 induced a new attachment with a distinct fibrocartilaginous zone at the tendon-bone interface in the rat tendon-bone attachment model. Surgical controls showed poor healing and failure to reform the appropriate tendon-bone attachment morphologically. Application of recombinant human BMP-12 (rhBMP-12) to periodontal defects suggests that rhBMP-12 has the potential to support regeneration of the periodontal ligament (PDL). The objective of this pilot study was to evaluate this effect of rhBMP-12 in a tooth replantation model.

METHODS

Six, young adult, male Hound Labrador mongrel dogs were used. Maxillary and/or mandibular incisor and premolar teeth were extracted and the PDL was either left "intact" or removed by root planing. rhBMP-12 (1.0 mg/ml) or a buffer control was topically applied to teeth with "intact" PDL in contralateral jaw quadrants in each of 3 animals. The teeth were immersed in 1.0 ml of the rhBMP-12 or the buffer solution for 10 min and then replanted. The remaining three animals received rhBMP-12 (1.0 mg/ml) and the buffer control in a similar fashion applied to teeth instrumented to remove the PDL and cementum, and surface demineralized with citric acid. The animals were euthanized at 8 weeks postsurgery and block sections were collected and processed for histopathologic analysis.

RESULTS

No dramatic differences were found between teeth receiving topical rhBMP-12 and the buffer control. Application of rhBMP-12 did not have an apparent effect on new cementum and PDL formation in the tooth replantation model. Moreover, application of rhBMP-12 did not increase nor did it decrease the apparent presence and extent of ankylosis along the root surface compared to the control.

CONCLUSIONS

The observations from this study do not support the use of topical rhBMP-12 to support the reestablishment of the PDL including regeneration of cementum and functionally oriented fibers, and to prevent ankylosis and root resorption following replantation of teeth.

rhBMP-2 significantly enhances guided bone regeneration

BACKGROUND

Previous studies have shown a limited potential for bone augmentation following guided bone regeneration (GBR) in horizontal alveolar defects. Surgical implantation of recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable collagen sponge carrier (ACS) significantly enhances bone regeneration in such defects; however, sufficient quantities of bone for implant dentistry are not routinely obtained. The objective of this study was to evaluate the potential of rhBMP-2/ACS to enhance GBR using a space-providing, macro-porous expanded polytetrafluoroethylene (ePTFE) device.

METHODS

Bilateral, critical size, supra-alveolar, peri-implant defects were surgically created in four Hound Labrador mongrel dogs. Two turned and one surface-etched 10-mm titanium dental implant were placed 5 mm into the surgically reduced alveolar ridge creating 5-mm supra-alveolar defects. rhBMP-2/ACS (rhBMP-2 at 0.2 mg/ml) or buffer/ACS was randomly assigned to left and right jaw quadrants in subsequent animals. The space-providing, macro-porous ePTFE device was placed to cover rhBMP-2/ACS and control constructs and dental implants. Gingival flaps were advanced for primary wound closure. The animals were euthanized at 8 weeks postsurgery for histologic and histometric analysis.

RESULTS

Bone formation was significantly enhanced in defects receiving rhBMP-2/ACS compared to control. Vertical bone gain averaged (+/- SD) 4.7 +/- 0.3 and 4.8 +/- 0.1 mm, and new bone area 10.3 +/- 2.0 and 8.0 +/- 2.5 mm2 at turned and surface-etched dental implants, respectively. Corresponding values for the control were 1.8 +/- 2.0 and 1.3 +/- 1.3 mm, and 1.8 +/- 1.3 and 1.2 +/- 0.6 mm2. Bone-implant contact in rhBMP-2-induced bone averaged 6.4 +/- 1.4% and 9.6 +/- 7.5% for turned and surface-etched dental implants, respectively (P=0.399). Corresponding values for the control were 14.6 +/- 19.4% and 23.7 +/- 9.7% (P=0.473). Bone-implant contact in resident bone ranged between 43% and 58% without significant differences between dental implant surfaces.

CONCLUSIONS

rhBMP-2/ACS significantly enhances GBR at turned and surface-etched dental implants. The dental implant surface technology does not appear to substantially influence bone formation.

Effect of Recombinant Human Bone Morphogenetic Protein-2 in an Absorbable Collagen Sponge With Space-Providing Biomaterials on the Augmentation of Chronic Alveolar Ridge Defects

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable collagen sponge (ACS) carrier has been shown to support significant bone formation in the craniofacial skeleton. When used as an onlay, however, rhBMP-2/ACS may become compressed with limited resulting bone formation. The objective of this study was to evaluate the effect of two space-providing biomaterials, bioactive glass (BG) and demineralized/mineralized bone matrix (DMB), on rhBMP-2/ACS induced alveolar ridge augmentation.

METHODS

Bilateral alveolar ridge defects were produced in the mandible in six mongrel dogs. rhBMP-2/ACS with biomaterials was surgically implanted into contralateral defects in four animals. Treatments were alternated between jaw quadrants in consecutive animals. Two animals received rhBMP-2/ACS or sham-surgery in contralateral defects. The animals were injected with fluorescent bone labels to monitor bone formation. Clinical evaluations were made at ridge augmentation and 12 weeks post-implantation when the animals were euthanized and block biopsies collected for histopathologic evaluation.

RESULTS

Sham-surgery produced limited horizontal alveolar augmentation (0.1 +/- 0.6 mm). Implantation of rhBMP-2/ACS resulted in alveolar augmentation amounting to 2.2 +/- 1.8 mm. Alveolar augmentation in sites receiving rhBMP-2/ACS with DMB or BG was 2-fold greater compared to rhBMP-2/ACS alone averaging 4.4 +/- 1.3 and 4.6 +/- 1.5 mm, respectively. The DMB biomaterial appeared substituted by newly formed bone. The BG particles were observed imbedded in bone or encapsulated in dense connective tissue without associated bone metabolic activity. Fluorescent light microscopy suggested that the new bone was formed within 4 weeks.

CONCLUSION

The bioglass and demineralized/mineralized bone matrix biomaterials utilized in this study in combination with rhBMP-2/ACS supported clinical and histological ridge augmentation.

Tissue regeneration based on growth factor release

Tissue engineering is an emerging biomedical field intended to assist the regeneration of body tissue defects too large to self-repair as well as to substitute for the biological functions of damaged and injured organs by using cells with proliferative and differentiative potential. In addition to basic research on such cells, it is undoubtedly indispensable for successful tissue engineering to create an artificial environment enabling cells to induce tissue regeneration. Such an environment can be achieved by making use of a scaffold for cell proliferation and differentiation and for growth factors, as well as their combination. Growth factors are often required to promote tissue regeneration, as they can induce angiogenesis, which supplies oxygen and nutrients to cells transplanted for organ substitution to maintain their biological functions. However, the biological effects of growth factors cannot always be expected because of their poor in vivo stability, unless a drug delivery system is contrived. In this article, tissue regeneration based on the release of growth factors is reviewed to emphasize the significance of drug delivery systems in tissue engineering.

Favorable healing following space creation in rhBMP-2-induced periodontal regeneration of horizontal circumferential defects in dogs with experimental periodontitis

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is believed to be capable of inducing periodontal regeneration. However, the risk of aberrant healing events, such as root resorption and ankylosis, has been reported. We hypothesized that implantation of BMP-containing carriers directly on the root planed surface may be the cause of unfavorable healing. The purpose of this study was to evaluate the influence of a 1 mm spacer membrane, which separated the rhBMP-2 in polymer-coated gelatin sponge (PGS) and the root surface, on periodontal regeneration of experimentally induced horizontal defects in dogs.

METHODS

Horizontal circumferential periodontal defects were surgically created, and experimental periodontitis was induced in 72 maxillary and mandibular premolars of four male beagle dogs. The recipient sites of each quadrant received: 1) rhBMP-2/PGS (B group) (rhBMP-2 at 1.0 mg/ml, total implant volume/ site approximately 7.2 microl) (n = 24); 2) rhBMP-2/PGS with a spacer membrane (PB group) (n = 24); and 3) physiological saline (PS)/PGS as a control (P group) (n = 24). One quadrant was left untreated. Dogs were sacrificed at 12 weeks post-surgery, and healing was evaluated histologically.

RESULTS

Both groups treated with rhBMP-2/PGS demonstrated enhanced new bone formation and connective tissue attachment with cementum regeneration when compared to the control group. Sites treated with rhBMP-2/PGS showed a greater degree of bone formation than sites treated with rhBMP-2/PGS and spacer membrane, although the latter sites showed no ankylosis.

CONCLUSIONS

Implantation of rhBMP-2/PGS enhances bone formation and connective tissue attachment in horizontal circumferential defects. In addition, the use of a spacer membrane reduces the degree of bone formation, but minimizes ankylosis.

Effect of phosphophoryn on rhBMP-2-induced bone formation

In the present study, dentin phosphophoryn (DPP) derived from fresh bovine dentin was evaluated as a co-factor for recombinant human bone morphogenetic protein-2 (rhBMP-2) in rhBMP-2-induced bone formation in rats. A 5 microg amount of Escherichia coli-derived rhBMP-2 variant was combined with DPP cross-linked to type I collagen (2.4 microg DPP/360 microg collagen), acting as carrier. Next, rhBMP-2/DPP/collagen composites were implanted by onlay-grafting beneath the cranial periosteum in 4-week-old Wistar rats. Rats were sacrificed at 2 and 3 weeks after implantation. Throughout the experimental period, rhBMP-2/DPP/collagen composite induced more bone formation than the rhBMP-2/collagen composite. Moreover, the degradation rate of rhBMP-2/DPP/collagen composite in rat was faster than that of rhBMP-2/collagen composite. Neither DPP/collagen composite nor collagen alone conducted bone formation even at 3 weeks postimplantation. These results indicate that the bone-inducing activity of rhBMP-2 is enhanced by DPP as a co-factor of rhBMP-2 in vivo.

Enhanced Cementum Formation in Experimentally Induced Cementum Defects of the Root Surface with the Application of Recombinant Basic Fibroblast Growth Factor in Collagen Gel In Vivo

BACKGROUND

Therapies using biologically active, soluble factors such as growth factors or cytokines have been investigated for potential clinical use in regenerating lost periodontal tissue due to periodontitis. Basic fibroblast growth factor (bFGF, FGF-2) is a multifunctional growth factor that has a variety of effects including induction of proliferation and morphogenesis in a wide range of cells and tissues including periodontal ligament tissue.

METHODS

In this study, we examined the effects of bFGF on the regeneration of cementum and periodontal ligament in experimentally induced partial defects in a beagle dog model. bFGF in a collagen gel was applied to the defects and root surfaces, and the teeth were replanted.

RESULTS

Eight weeks post-surgery, formation of cementum on denuded dentin was enhanced by application of 0.1, 1, or 5 microg of bFGF in a collagen gel compared to collagen gel containing vehicle. Histological analyses revealed that at 4 weeks post-surgery, random periodontal ligament fibers had bound to dentin, but were attached only to denuded dentin to which 0.1, 1, or 5 microg of bFGF in collagen gel had been applied. At 8 weeks post-surgery, we observed the formation of dense fibers bound to alveolar bone and newly synthesized cementum in teeth treated with 1 microg of bFGF.

CONCLUSION

These results suggest that basic fibroblast growth factor in a collagen gel is a suitable therapy for damaged periodontal ligament and could lead to readily achievable methods of treatment for periodontal disease.

Effect of 830-nm laser light on the repair of bone defects grafted with inorganic bovine bone and decalcified cortical osseus membrane

OBJECTIVE

The aim of this study was to histologically assess the effect of low-level laser therapy (LLLT) (lambda830 nm) on the repair of standardized bone defects of the femur of Wistar albinus rats grafted with inorganic bovine bone and associated (or not) with decalcified bovine cortical bone membrane.

BACKGROUND DATA

Bone loss may be a result of pathology, trauma, or surgical procedure. Extensive studies on the process of bone repair have been undertaken, and several techniques for the correction of bone defects have been proposed. Amongst them is the use of several types of grafts, the use of membranes, and the combination of both techniques. There is evidence in the literature of the positive effect of LLLT on the healing of soft tissue wounds. However, its effect on bone healing is not completely understood.

MATERIALS AND METHODS

Five randomized groups were studied: group I (control); group IIA (Gen-ox); group IIB (Gen-ox + LLLT); group IIIA (Gen-ox + Gen-derm); and group IIIB (Gen-ox + Gen-derm + LLLT). Bone defects were created at the femur and were treated according to the group. The animals of irradiated groups were irradiated every 48 h for 15 days; the first irradiation was performed immediately after the procedure. The animals were irradiated transcutaneuosly at four points around the defect. At each point, a dose of 4 J/cm2 was given (phi approximately equal to 0.6 mm, 40 mW), and the total dose per session was 16 J/cm2. The animals were humanely killed at 15, 21, and 30 days after surgery. The specimens were routinely processed to wax, serially cut, stained with H&E and Picrosirius stains, and analyzed under light microscopy.

RESULTS

The results showed more advanced repair of the irradiated groups when compared to the non-irradiated ones. The repair of the irradiated group was characterized by both increased bone formation and on the amount of collagen fibers around the graft within the cavity, as early as the 15th day after surgery, considering the osteoconductive capacity of the Gen-ox and the increment of the cortical repair in specimens with Gen-derm membrane.

CONCLUSION

It is concluded that LLLT had a positive effect on the repair of bone defect by graft associated or not with the use of biological membrane.

Growth and Amelogenin-Like Factors in Periodontal Wound Healing. A Systematic Review

BACKGROUND

Regeneration of tooth-supporting structures destroyed by periodontitis is a major goal of periodontal therapy. Periodontal tissue engineering utilizing growth and amelogenin-like factors (GAFs) applies advances in materials science and biology to regenerate alveolar bone, periodontal ligament, and cementum. Amelogenin-like factors (e.g., enamel matrix derivative [EMD]) and growth factors (e.g., platelet-derived growth factor [PDGF] and bone morphogenetic proteins [BMPs, also considered morphogens]) have demonstrated pleotrophic effects on the stimulation of several key events required for tissue regeneration including DNA synthesis, chemotaxis, differentiation, and matrix synthesis.

RATIONALE

GAFs have been used for the treatment of periodontal disease as shown in preclinical and clinical studies. This systematic review evaluates the evidence to support the utilization of EMD and growth factors (GFs) for periodontal repair and regeneration associated with natural teeth.

FOCUSED QUESTION

In patients with periodontal osseous defects, what is the effect of GAFs compared with controls on clinical, radiographic, histologic, adverse, and patient-centered outcomes?

SEARCH PROTOCOL

Two investigators searched MEDLINE, pre-MEDLINE, and the Cochrane Oral Health Group trials register for clinical and preclinical studies published in English. Hand searches were performed on the International Journal of Periodontics and Restorative Dentistry, Journal of Clinical Periodontology, Journal of Dental Research, Journal of Periodontology, and Journal of Periodontal Research. Searches were performed for articles published through April 2002. In addition, investigators contacted manufacturers of GAF products for related unpublished data and studies in progress.

SELECTION CRITERIA

INCLUSION CRITERIA

Randomized controlled clinical trials (RCTs), cohort studies, case-control studies, case reports, and preclinical (animal) randomized controlled investigations that included a cohort population diagnosed with periodontal disease and presenting data on intrabony/interproximal defects and/or furcation defects were screened.

EXCLUSION CRITERIA

In vitro studies or those that did not include quantifiable data with respect to clinical or bone measures were not included.

DATA COLLECTION AND ANALYSIS

Meta-analyses were performed for studies that fulfilled the eligibility criteria for the following continuous variables: clinical attachment level (CAL), probing depth (PD), or bone level (radiographic, re-entry, or histologic). Heterogeneity was assessed to determine whether the differences among therapies were due to systematic confounding factors (as noted in study quality assessments).

MAIN RESULTS

1. Eight studies, representing 7 RCTs and 1 quasi-experimental study, representing a total population of 511 subjects were analyzed with respect to EMD. 2. The majority of the remaining papers had a low evidence rating. 3. Most reports were case studies or case series without controls. 4. There were insufficient data to conduct a meta-analysis on the effect of growth factors used in periodontal repair around teeth.

REVIEWERS' CONCLUSIONS

1. There is evidence supporting the use of EMD for periodontal osseous defects to improve CAL and reduce PD, although long-term benefits have not been established. 2. EMD has demonstrated notable consistency among the studies investigated in terms of superiority to controls (in general compared to open flap debridement [OFD]). 3. EMD appears to be safe for single and multiple administrations in terms of lack of elicitation of antibody responses or other local/systemic inflammatory events. 4. Preclinical and initial clinical data for growth factors appear promising but are insufficient to draw definitive conclusions at this time.

Effect of 830-nm Laser Light on the Repair of Bone Defects Grafted with Inorganic Bovine Bone and Decalcified Cortical Osseous Membrane

OBJECTIVE

The aim of this study was to assess histologically the effect of LLLT (lambda830 nm) on the repair of standardized bone defects on the femur of Wistar albinus rats grafted with inorganic bovine bone and associated or not to decalcified bovine cortical bone membrane.

BACKGROUND DATA

Bone loss may be a result of several pathologies, trauma or a consequence of surgical procedures. This led to extensive studies on the process of bone repair and development of techniques for the correction of bone defects, including the use of several types of grafts, membranes and the association of both techniques. There is evidence in the literature of the positive effect of LLLT on the healing of soft tissue wounds. However, its effect on bone is not completely understood.

MATERIALS AND METHODS

Five randomized groups were studied: Group I (Control); Group IIA (Gen-ox); Group IIB (Gen-ox + LLLT); Group IIIA (Gen-ox + Gen-derm) and Group IIIB (Gen-ox + Gen-derm + LLLT). Bone defects were created at the femur of the animals and were treated according to the group. The animals of the irradiated groups were irradiated every 48 h during 15 days; the first irradiation was performed immediately after the surgical procedure. The animals were irradiated transcutaneously in four points around the defect. At each point a dose of 4 J/cm2 was given (phi approximately 0.6 mm, 40 mW) and the total dose per session was 16 J/cm2. The animals were humanely killed 15, 21, and 30 days after surgery. The specimens were routinely processed to wax, serially cut, and stained with H&E and Picrosirius stains and analyzed under light microscopy.

RESULTS

The results showed evidence of a more advanced repair on the irradiated groups when compared to non-irradiated ones. The repair of irradiated groups was characterized by both increased bone formation and amount of collagen fibers around the graft within the cavity since the 15th day after surgery, through analysis of the osteoconductive capacity of the Gen-ox and the increment of the cortical repair in specimens with Gen-derm membrane.

CONCLUSION

It is concluded that LLLT had a positive effect on the repair of bone defect submitted the implantation of graft.

rhBMP-2 injected in a calcium phosphate paste (alpha-BSM) accelerates healing in the rabbit ulnar osteotomy model

This study evaluated the ability of recombinant human bone morphogenetic protein-2 (rhBMP-2) delivered in an injectable calcium phosphate carrier (alpha-BSM) to accelerate healing in a rabbit ulna osteotomy model compared to untreated surgical controls. Healing was assessed by radiography, histology and biomechanics. Bilateral mid-ulnar osteotomies were created in 16 skeletally mature rabbits. One limb in each animal was injected with either 0.1 mg rhBMP-2/alpha-BSM (BMP) (N=8) or buffer/alpha-BSM (BSM) (N=8). Contralateral osteotomies served as untreated surgical controls (SXCT). Gamma scintigraphy showed 75%, 45% and 5% of the initial 125I-rhBMP-2 dose was retained at the osteotomy site at 3 h, 1 week and 3 weeks. The biological activity of rhBMP-2 (alkaline phosphatase activity from bioassay) extracted from alpha-BSM incubated in vitro up to 30 days at 37 degrees C was unchanged. Radiographs demonstrated complete bridging of the BMP limbs at 4 weeks whereas none of the BSM or SXCT limbs were bridged. Post-mortem peripheral quantitative computed tomography determined mineralized callus area was 62% greater in BMP limbs compared to SXCT limbs. Torsional stiffness and strength were 63% and 103% greater in BMP limbs compared to SXCT limbs. There was no difference in torsional properties between BSM and SXCT limbs. Failure occurred outside the osteotomy in four out of seven of the BMP limbs. All BSM and SXCT limbs failed through the osteotomy. Histology showed bony bridging of the osteotomy and no residual carrier in the BMP limbs. BSM and SXCT groups showed less mature calluses composed of primarily fibrocartilaginous tissue and immature bone in the osteotomy gap. These data indicate rhBMP-2 delivered in alpha-BSM accelerated healing in a rabbit ulna osteotomy model compared to BSM and SXCT groups.

Effects of growth/differentiation factor-5 on human periodontal ligament cells

OBJECTIVES

Growth/differentiation factor-5 (GDF-5), a member of the transforming growth factor-beta superfamily, shows a close structural relationship to bone morphogenetic proteins and plays crucial roles in skeletal, tendon, and ligament morphogenesis. The mRNA encoding GDF-5 is also expressed during odontogenesis, especially in dental follicle tissue. While this suggests that GDF-5 participates in the formation of alveolar bone and the periodontal ligament, cementum, and dental root, the physiologic role of GDF-5 in these tissues in adulthood remains unclear. We therefore investigated GDF-5 effects upon cultures of human periodontal ligament (HPDL) cells.

MATERIAL AND METHODS

HPDL cells were obtained from healthy periodontal ligaments of individuals. Tetrazolium reduction assay was carried out for cell proliferation assay. Alkaline phosphatase (ALP) activity was estimated by measuring light absorbance at 405 nm. Reverse transcription-polymerase chain reaction (RT-PCR) and northern analysis were performed for gene expression in cultured HPDL cells. Sulfated glycosaminoglycan (sGAG) synthesis was evaluated by histochemical staining and a quantitative dye-binding method.

RESULTS

Expression of GDF-5 and its receptor was demonstrated in HPDL cells by RT-PCR. ALP activity in HPDL cells was significantly decreased by addition of rhGDF-5 at 10-1000 ng/ml (p < 0.05). Although northern analysis showed little change in gene expression for collagen alpha2(I) in rhGDF-5-stimulated HPDL cells, rhGDF-5 dose-dependently enhanced cell proliferation. This proliferative effect persisted for 16 d. Alcian blue staining and dye-binding assays indicated that sGAG synthesis was enhanced by rhGDF-5.

CONCLUSION

rhGDF-5 may provide an environment fostering periodontal healing or regeneration by affecting extracellular matrix metabolism.

Periodontal Regeneration with a Combination of Enamel Matrix Proteins and Autogenous Bone Grafting

BACKGROUND

Attempts to stimulate periodontal regeneration in the past have focused on either filling the defect with some type of material or providing a space for host cells to repopulate the site and elicit new tissue. In some cases, these approaches have been combined with the assumption that the filler material will help maintain the space necessary for the host cells to invade the area. Growth stimulating substances such as growth factors and other proteins have also been used to encourage periodontal tissue regeneration and histological evaluation supports the use of these substances. Thus, the role for and the necessity of a certain amount of space maintenance for periodontal regeneration is not exactly understood. In addition, it is not known if there is some critical size required for space maintenance or for exactly how long the space must be maintained in order for the host cells to stimulate new cementum, periodontal ligament, and bone. The goal of this study was to evaluate periodontal regeneration in intrabony defects of various sizes treated with a combination of enamel matrix proteins and autogenous bone graft.

METHODS

Periodontal defects ranging in size from 1 to 6 mm were randomized and created bilaterally beside three teeth in the mandibles of baboons. Plaque was allowed to accumulate around wire ligatures placed into the defects. After 2 months, the wire ligatures were removed, the teeth and roots scaled and root planed, and a notch was placed with a chisel at the base of the defect. On one side of the mandible, neutral ethylene diamine tetracetic acid and enamel matrix derivative (EMD) were first used to treat the defect. Autogenous bone taken from the same surgical site was treated with enamel matrix derivative in a dampen dish and then added to the EMD-treated defects. The other side of the mandible served as control with neutral ethylene diamine tetracetic acid and scaling and root planing. Flaps were sutured and the animals were allowed to heal without oral hygiene procedures. After 5 months, the animals were sacrificed and the teeth were processed for histological evaluation.

RESULTS

The results revealed new cementum, periodontal ligament with Sharpey's fibers, and new bone tissue similar to native periodontal tissues. Remnants of the autogenous bone chips were still present at this 5-month post-healing period. Thus periodontal regeneration occurred in all sizes of the periodontal defects. In general, EMD plus autogenous graft treatment resulted in greater tissue formation than controls. In fact, in many cases, very dramatic tissue formation occurred far coronal to the base of the defects in the EMD plus autogenous graft-treated lesions. In addition, horizontal bone fill occurred in the defects and was prominent in the 4 or 6 mm wide lesions. When evaluating the combined 1 and 2 mm defects, the height of new cementum with EMD plus graft was 3.88 mm versus 2.03 mm in the controls, a statistically significant (P < 0.005) difference. In the wider (4 and 6 mm) lesions, this difference was not significant and was much less between treated and control lesions with 2.78 and 2.57 mm of new cementum respectively. In the case of new bone height, in the smaller lesions EMD plus graft resulted in 4.00 mm new bone versus 2.22 mm in the controls, again a statistically significant (P < 0.005) difference. In the larger lesions, EMD plus autogenous bone graft had 3.24 mm new bone height compared to 2.71 mm in the controls, a difference that was not statistically significant. Additionally, in the smaller lesions, new cementum width at the level of the notch was twice as great (statistically significant, P < 0.015) in the EMD plus graft sites compared to control. The width of the periodontal ligament at the coronal aspect of the new bone tissue was similar in the smaller lesions between treated and control sites. The results from the wider defects must be interpreted cautiously as the interproximal bone heights were remodeled adjacent to the wider defects and likely limited the potential for regeneration.

CONCLUSIONS

The combination of enamel matrix derivative plus autogenous bone graft stimulated statistically significant periodontal regeneration in the more narrow 1 and 2 mm lesions. No statistically significant difference was observed in the wider 4 and 6 mm lesions. In many cases, dramatic amounts of new cementum, Sharpey's fibers, periodontal ligament, and bone tissue were formed far above the notch placed at the base of the contaminated defects. This was especially significant considering the width of some of the defects and the fact that no oral hygiene was performed over the 5-month healing period. This periodontal regeneration occurred in the absence of exogenous growth factors or barrier membranes. In summary, the combination of enamel matrix derivative and autogenous bone represents a therapeutic combination that can be highly effective in stimulating significant amounts of periodontal regeneration.

The application of bone morphogenetic proteins to dental tissue engineering

Progress in understanding the role of bone morphogenetic proteins (BMPs) in craniofacial and tooth development, the demonstration of stem cells in dental pulp and accumulating knowledge on biomaterial scaffolds have set the stage for tissue engineering and regenerative therapy of the craniofacial complex. Furthermore, the recent approval by the US Food and Drug Administration (FDA; Rockville, MD, USA) of recombinant human BMPs for accelerating bone fusion in slow-healing fractures indicates that this protein family may prove useful in designing regenerative treatments in dental applications. In the near term, these advances are likely to be applied to endodontics and periodontal surgery; ultimately, they may facilitate approaches to regenerating whole teeth for use in tooth replacement.

Space-Providing Expanded Polytetrafluoroethylene Devices Define Alveolar Augmentation at Dental Implants Induced by Recombinant Human Bone Morphogenetic Protein 2 in an Absorbable Collagen Sponge Carrier

BACKGROUND

Surgical implantation of recombinant human bone morphogenetic protein 2 (rhBMP-2) in an absorbable collagen sponge carrier (ACS) significantly enhances bone regeneration in horizontal alveolar defects; however, sufficient quantities of bone for implant dentistry are not routinely obtained.

PURPOSE

The objective of this proof-of-principle study was to evaluate the potential of a space-providing macroporous expanded polytetrafluoroethylene (ePTFE) device to control volume and geometry of rhBMP-2/ACS-induced alveolar bone augmentation.

MATERIALS AND METHODS

Bilateral critical-size supra-alveolar periimplant defects were created in four Hound-Labrador mongrel dogs. Two turned and one surface-etched 10 mm titanium dental implants were placed 5 mm into the surgically reduced alveolar ridge creating 5 mm supra-alveolar defects. rhBMP-2/ACS (0.4 mg rhBMP-2) was placed around the exposed dental implants. Additionally, one jaw quadrant in each animal was randomly assigned to receive the dome-shaped macroporous ePTFE device. Mucoperiosteal flaps were advanced for primary wound closure. The animals were euthanized at 8 weeks post surgery for histometric analysis.

RESULTS

The space-providing macroporous ePTFE device defined the volume and geometry of rhBMP-2/ACS-induced bone formation, whereas bone formation at sites receiving rhBMP-2/ACS alone varied considerably. Vertical bone gain at turned dental implants averaged (+/-SD) 4.7 +/-0.2 mm at sites receiving rhBMP-2/ACS and the ePTFE device compared with 3.5 +/-0.9 mm at sites receiving rhBMP-2/ACS only. The corresponding values for rhBMP-2/ACS-induced bone area were 9.6 +/- 0.7 mm2 and 7.5 +/-6.2 mm2. There was a highly significant correlation between induced bone area and the space provided by the ePTFE device (p <.001). There was no difference in induced bone density or bone-implant contact between the two technologies. These observations were consistent with those observed at surface-etched dental implants.

CONCLUSIONS

The data from this study suggest that a space-providing macroporous ePTFE device defines rhBMP-2/ACS-induced alveolar augmentation to provide adequate bone quantities for implant dentistry. The dental implant surface technology does not appear to substantially influence bone formation.

Periodontal repair in dogs: space-providing ePTFE devices increase rhBMP-2/ACS-induced bone formation

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) technologies have been shown to enhance alveolar bone formation significantly. Biomaterial (carrier) limitations, however, have restricted their biologic potential for indications where compressive forces may limit the volume of bone formed. The objective of this proof-of-principle study was to evaluate the potential of a space-providing, macroporous ePTFE device to define rhBMP-2-induced alveolar bone formation using a discriminating onlay defect model.

METHODS

Routine, critical size, 5-6 mm, supra-alveolar, periodontal defects were created around the third and fourth mandibular premolar teeth in four young adult Hound Labrador mongrel dogs. All jaw quadrants received rhBMP-2 (0.4 mg) in an absorbable collagen sponge (ACS) carrier. Contralateral jaw quadrants in subsequent animals were randomly assigned to receive additionally the dome-shaped, macroporous ePTFE device over the rhBMP-2/ACS implant or no additional treatment. The gingival flaps were advanced to cover the ePTFE device and teeth, and sutured. Animals were scheduled for euthanasia to provide for histologic observations of healing at 8 weeks postsurgery.

RESULTS

Healing was uneventful without device exposures. New bone formation averaged (+/-SD) 4.7+/-0.2 mm (98%) and 4.5+/-0.4 mm (94%) of the defect height, respectively, for jaw quadrants receiving rhBMP-2/ACS with the ePTFE device or rhBMP-2/ACS alone (p>0.05). In contrast, the regenerated bone area was significantly enhanced in jaw quadrants receiving rhBMP-2/ACS with the ePTFE device compared to rhBMP-2/ACS alone (9.3+/-2.7 versus 5.1+/-1.1 mm2; p<0.05). Cementum formation was similar for both treatment groups. Ankylosis compromised periodontal regeneration in all sites.

CONCLUSIONS

The results suggest that the novel space-providing, macroporous ePTFE device appears suitable as a template to define rhBMP-2/ACS-induced alveolar bone formation.

Periodontal repair in dogs: rhBMP-2 significantly enhances bone formation under provisions for guided tissue regeneration

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to support the regeneration of alveolar bone and periodontal attachment in surgically created periodontal defects and in defects with a history of dental plaque and calculus exposure. Periodontal regeneration has also been shown following guided tissue regeneration using space-providing expanded polytetrafluoroethylene (ePTFE) devices. The objective of this study was to evaluate the influence of rhBMP-2 on regeneration of alveolar bone and periodontal attachment used in conjunction with a space-providing ePTFE device.

METHODS

Routine, critical-size, 5-6 mm, supra-alveolar, periodontal defects were created around the third and fourth mandibular premolar teeth in four young adult Hound Labrador mongrel dogs. rhBMP-2 (0.2 mg/ml) in an absorbable collagen sponge (rhBMP-2/ACS) or buffer/ACS (control) implants were randomly assigned to be placed around the premolar teeth in the left and right jaw quadrants in subsequent animals. Space-providing ePTFE devices with 300-microm laser-drilled pores, 0.8 mm apart, were used to cover the rhBMP-2 and control implants. The gingival flaps were advanced for primary wound closure. The animals were euthanized at 8 weeks postsurgery for histologic and histometric analyses.

RESULTS

Bone regeneration and ankylosis were significantly increased in jaw quadrants receiving rhBMP-2/ACS compared to control (bone height 4.8+/-0.3 versus 2.0+/-0.2 mm, p=0.001; bone area 10.9+/-1.3 versus 1.4+/-0.1 mm2; p=0.009, and ankylosis 2.2+/-0.2 versus 0.04+/-0.7 mm; p=0.01). No differences between groups were found for cementum regeneration and root resorption.

CONCLUSIONS

rhBMP-2 significantly enhances regeneration of alveolar bone in conjunction with a space-providing, macroporous ePTFE device for GTR.

The effect of enamel matrix proteins on periodontal regeneration as determined by histological analyses

BACKGROUND

Therapeutic approaches to periodontal regeneration in the past have utilized bone replacement grafts, growth factors, barrier membranes, or combinations of these approaches. More recently, enamel extracellular matrix proteins have been introduced to stimulate periodontal regeneration. One factor thought to have an impact on the outcome of the regenerative process is the initial size of the periodontal defect. This is particularly the case when using proteins to stimulate regeneration, because the concepts of guided tissue regeneration emphasize the need for space maintenance to allow for selected cell repopulation. The goal of this study was to evaluate periodontal regeneration in intrabony defects of various sizes treated with enamel matrix proteins.

METHODS

Periodontal defects ranging in size from 1 to 6 mm were created bilaterally around 3 teeth in the mandibles of baboons. Plaque was allowed to accumulate around ligatures placed into the defects. After 2 months, the ligatures were removed, the teeth were scaled and root planed, and a notch was placed at the base of the defect. On one side of the mandible, neutral ethylene diamine tetracetic acid and enamel matrix proteins were used to treat the defects. The other side served as a control, with neutral ethylene diamine tetracetic acid treatment alone after scaling and root planing. Flaps were sutured and the animals were allowed to heal without oral hygiene procedures. After 5 months, the animals were sacrificed and the teeth were processed for histological evaluation.

RESULTS

Periodontal regeneration occurred in all sizes of the periodontal defects. Qualitatively, new cementum, periodontal ligament with Sharpey's fibers, and new bone tissue were observed. In general, enamel matrix protein treatment resulted in greater tissue formation than controls. In many instances, dramatic tissue formation occurred far coronal to the base of the defects. In addition, horizontal bone fill occurred in defects that were initially 4 or 6 mm wide. The resultant width of the periodontal ligament was similar in all defects regardless of the original defect width. The cementum width was slightly greater in the wider (4 and 6 mm) defects compared to the more narrow (1 and 2 mm) defects. When evaluating the combined 1 and 2 mm defects, the height of new cementum with enamel matrix protein treatment was 45% greater than the control, with 31% greater new bone height versus the control. In the combined wider defects (4 and 6 mm), new tissue height was more similar between enamel matrix protein-treated defects and control defects. The results from the wider defects must be interpreted cautiously, because the interproximal bone heights were resorbed more adjacent to the wider defects during the plaque accumulation period and likely limited the potential for regeneration.

CONCLUSIONS

The treatment of various sized periodontal defects with enamel matrix proteins stimulated substantial periodontal regeneration. In many cases, dramatic amounts of new cementum, Sharpey's fibers, periodontal ligament, and bone tissue were formed far coronal to the notch at the base of the defect, especially considering the width of the original defects. This periodontal regeneration occurred in the absence of exogenous growth factors, bone replacement grafts, barrier membranes, or their combination.

Gene therapy of bone morphogenetic protein for periodontal tissue engineering

BACKGROUND

The reconstruction of lost periodontal support including bone, ligament, and cementum is a major goal of therapy. Bone morphogenetic proteins (BMPs) have shown much potential in the regeneration of the periodontium. Limitations of BMP administration to periodontal lesions include need for high-dose bolus delivery, BMP transient biological activity, and low bioavailability of factors at the wound site. Gene transfer offers promise as an alternative treatment strategy to deliver BMPs to periodontal tissues.

METHODS

This study utilized ex vivo BMP-7 gene transfer to stimulate tissue engineering of alveolar bone wounds. Syngeneic dermal fibroblasts (SDFs) were transduced ex vivo with adenoviruses encoding either green fluorescent protein (Ad-GFP or control virus), BMP-7 (Ad-BMP-7), or an antagonist of BMP bioactivity, noggin (Ad-noggin). Transduced cells were seeded onto gelatin carriers and then transplanted to large mandibular alveolar bone defects in a rat wound repair model.

RESULTS

Ad-noggin treatment tended to inhibit osteogenesis as compared to the control-treated and Ad-BMP-7-treated specimens. The osseous lesions treated by Ad-BMP-7 gene delivery demonstrated rapid chrondrogenesis, with subsequent osteogenesis, cementogenesis and predictable bridging of the periodontal bone defects.

CONCLUSION

These results demonstrate the first successful evidence of periodontal tissue engineering using ex vivo gene transfer of BMPs and offers a new approach for repairing periodontal defects.

Platelet-rich plasma contains high levels of platelet-derived growth factor and transforming growth factor-beta and modulates the proliferation of periodontally related cells in vitro

BACKGROUND

Platelet-rich plasma (PRP) is a fraction of plasma, in which platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) are thought to be concentrated. It is plausible that topically-applied PRP up-regulates cellular activity and subsequently promotes periodontal regeneration in vivo. However, the concentrations of these growth factors in PRP have not been specifically determined and the biological effects of PRP at the cellular and molecular levels have not been determined.

METHODS

PRP obtained from 20 healthy subjects was prepared from plasma by centrifugation. These PRP preparations were immediately subjected to an evaluation for PDGF-AB and TGF-beta1 using enzyme-linked immunosorbent assay (ELISA) kits. The biological effects of the PRP preparations were evaluated on osteoblastic, epithelial, fibroblastic, and periodontal ligament cells. Cellular mitogenic activity was evaluated by counting cell numbers or evaluating 5-bromodeoxyuridine (BrdU) incorporation. Expression of alkaline phosphatase (ALP) was immunocytochemically evaluated.

RESULTS

In the PRP preparations, platelets were concentrated up to 70.9 x 10(4) cells/microl (283.4% of the unconcentrated plasma). The levels of PDGF-AB and TGF-beta1 were also concentrated up to 182.0 ng/ml (440.6%) and 140.9 ng/ml (346.6%), respectively. Scatter plots revealed significant correlations between platelet counts and levels of these growth factors. PRP stimulated osteoblastic DNA synthesis and cell division (138% of control), with simultaneous down-regulation of ALP, but suppressed epithelial cell division (80% of control). PRP also stimulated DNA synthesis in gingival fibroblasts and periodontal ligament cells.

CONCLUSIONS

These data demonstrated that both PDGF-AB and TGF-beta1 were highly concentrated in the PRP preparations. It is suggested PRP modulates cell proliferation in a cell type-specific manner similar to what has been observed with TGF-beta1. Since synchronized behavior of related cell types is thought to be required for successful periodontal regeneration, it is further suggested these cell type-specific actions may be beneficial for periodontal regenerative therapy.

Enhanced bone augmentation by controlled release of recombinant human bone morphogenetic protein-2 from bioabsorbable membranes

BACKGROUND

The present study was undertaken to determine the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded biodegradable membranes on bone augmentation in a rabbit calvarial model.

METHODS

Five microg of rhBMP-2 was loaded into a stiff hemispherical dome membrane made of poly(L-lactide) and tricalcium phosphate (PLLA/TCP). The release kinetics of rhBMP-2 from the membrane were determined in vitro using a human BMP-2 immunoassay. Twelve rhBMP-2-loaded dome membranes (test group) and 12 control dome membranes (control group) were placed on the partial-thickness calvarial defects of 24 rabbits. The animals were sacrificed at 4 and 8 weeks, and undecalcified ground sections were prepared. Newly formed bone area and height were measured histomorphometrically and calculated by percentage ratio to the total submembranous space area and height below the dome.

RESULTS

In vitro release results demonstrated that rhBMP-2 was released consistently over a 4-week period following a high initial burst release on the first day. At both 4 and 8 weeks, histomorphometric analysis revealed that the test group showed significantly higher newly formed bone heights and areas than the control group (P < 0.01). In the control group, new bone height was 36.3% of the dome height and the new bone area reached 8.2% of the submembranous space area at 8 weeks, while the test group reached 87.3% and 35.4%, respectively.

CONCLUSION

These results suggest that the use of rhBMP-2-loaded PLLA/TCP membranes can result in additional bone augmentation, which is due to the osteoinductive properties of rhBMP-2 released from the membrane during healing.

Effect of recombinant human bone morphogenetic protein-2 in dehiscence defects with non-submerged immediate implants: an experimental study in Cynomolgus monkeys

BACKGROUND

Alveolar ridge aberrations commonly compromise optimal dental implant installation. To offset any variance between an aberrant alveolar ridge and prosthetic designs, bone augmentation procedures become necessary. The objective of this study was to evaluate bone formation and osseointegration at alveolar dehiscence defects following augmentation of the defect site with recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable collagen sponge carrier (ACS) at dental implant installation including transmucosal positioning of the dental implant.

METHODS

Four adult male Cynomolgus monkeys received dental implants in contralateral extraction socket sites with surgically created 6 x 4 mm buccal dehiscence defects following elevation of mucoperiosteal flaps. Contralateral sites received rhBMP-2/ACS (rhBMP-2 at 1.5 mg/ml; 0.1 mg/defect) or served as sham-surgery controls. The flaps were adapted and sutured around the healing abutments leaving the implants in a transmucosal position. The animals were sacrificed at 16 weeks postsurgery and block sections of the implant sites were harvested and prepared for histometric analysis.

RESULTS

One dental implant from each treatment group failed to osseointegrate. Another 3 dental implants (sham-surgery controls) failed to osseointegrate with newly-formed bone in the defect area. Thus, 7 of 8 defect sites (4/4 animals) receiving rhBMP-2/ACS compared to 4 of 8 sites (2/4 animals) receiving sham-surgery exhibited evidence of osseointegration with newly formed bone in the defect area. Mean +/- SD defect height amounted to 5.3 +/- 0.2 and 5.4 +/- 0.1 mm for the rhBMP-2/ACS and sham-surgery sites, respectively. Vertical bone gain in rhBMP-2/ACS treated defects (3.9 +/- 0.3 mm) did not differ significantly from that in the sham-surgery control (3.7 +/- 0.4 mm; P > 0.05; paired t-test, N = 4). There were also no significant differences noted for coronal bone-implant contact (3.0 +/- 0.6 versus 3.6 +/- 0.5 mm), and bone-implant contact within the defect site (28.5% +/- 15.1% versus 27.4% +/- 31.7%) and within resident bone (46.9% +/- 26.8% versus 47.8% +/- 39.4%) for the rhBMP-2/ACS and control sites, respectively.

CONCLUSIONS

The observations in this study point to a substantial native osteogenic potential of the alveolar process that has previously not been explored and show that surgical reentry observations of new bone formation may not necessarily indicate that osseointegration has occurred. Bone formation in control defects was substantially greater than predicted, limiting the value of adding an osteoinductive biologic construct.

Periodontal repair in dogs: evaluation of a bioabsorbable space-providing macroporous membrane with recombinant human bone morphogenetic protein-2

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) technologies have been shown to significantly support alveolar bone formation. Biomaterial limitations, however, have restricted the biologic potential for onlay indications. The objective of this study was to evaluate regeneration of alveolar bone and periodontal attachment, and biomaterials reaction following surgical implantation of a space-providing, bioabsorbable, macroporous, polyglycolic acid-trimethylene carbonate (PGA-TMC) membrane combined with a rhBMP-2 construct in a discriminating onlay defect model.

METHODS

Routine supraalveolar periodontal defects were created at the mandibular premolar teeth in 9 beagle dogs. Contralateral jaw quadrants in subsequent animals were randomly assigned to receive the dome-shaped PGA-TMC (100 to 120 microm pores) membrane with rhBMP-2 (0.2 mg/mL) in a bioresorbable hyaluronan (Hy) carrier or the PGA-TMC membrane with Hy alone (control). The gingival flaps were advanced to submerge the membranes and teeth and sutured. Animals were euthanized at 8 and 24 weeks postsurgery for histologic observations.

RESULTS

Jaw quadrants receiving the PGA-TMC membrane alone experienced exposures at various time points throughout the study. Jaw quadrants receiving the PGA-TMC/rhBMP-2 combination remained intact, although one site experienced a late minor exposure. Newly formed alveolar bone approached and became incorporated into the macroporous PGA-TMC membrane in sites receiving rhBMP-2. The PGA-TMC biomaterial was occasionally associated with a limited inflammatory reaction. Residual PGA-TMC could not be observed at 24 weeks postsurgery. Residual Hy could not be observed at any time interval. Regeneration of alveolar bone height (means +/- SD) was significantly increased in sites receiving the PGA-TMC/rhBMP 2 combination compared to control (3.8 +/- 1.3 versus 0.7 +/- 0.5 mm at 8 weeks and 4.6 +/- 0.8 versus 2.1 +/- 0.4 mm at 24 weeks; P < 0.05). Limited cementum regeneration was observed for PGA-TMC/rhBMP-2 and PGA-TMC control sites. Ankylosis compromised regeneration in sites receiving PGA-TMC/rhBMP-2.

CONCLUSIONS

The bioabsorbable, space-providing, macroporous PGA-TMC membrane appears to be a compatible biomaterial for bone augmentation procedures. rhBMP-2 significantly enhances alveolar bone augmentation and soft tissue healing when combined with the PGA-TMC membrane.

Failure to induce supracrestal bone growth between and around partially inserted titanium implants using bone morphogenetic protein (BMP): an experimental study in dogs

The effect of bone morphogenetic protein on supracrestal bone growth around partially inserted implants in a dog model is described. The lower premolar teeth (P1, P2, P3 and P4) were extracted on both sides of the mandible in six dogs. At a surgical exposure 12 weeks later, two 10-mm turned titanium implants were partially inserted, approximately 15 mm apart, in the areas of the P1 and P3 in each side of the mandible, allowing five threads to protrude from the bone crest. A titanium mesh was fastened to the coronal aspect of the two fixtures and the space beneath the mesh was filled with bone morphogenetic protein (S300 BMP) in combination with an insoluble bone matrix carrier, or with the carrier alone. The mesh was covered with an ePTFE membrane. Thus, a space for potential bone formation was created between the two implants. The surgical flaps were coronally positioned and secured with vertical mattress sutures. After 16 weeks of healing, biopsy specimens were retrieved and examined histologically. Bone was not formed around the protruding implants or in the created space between the implants in any case. The carrier was incompletely resorbed. We conclude that supracrestal bone growth beyond the crestal limit with or without BMP in such a large space as in this experimental design may not be possible.

Novel approach to regeneration of periodontal tissues based on in situ tissue engineering: effects of controlled release of basic fibroblast growth factor from a sandwich membrane

To regenerate periodontal tissues, a sandwich membrane composed of a collagen sponge scaffold and gelatin microspheres containing basic fibroblast growth factor (bFGF) in a controlled-release system was developed according to the new concept of "in situ tissue engineering." A three-walled alveolar bone defect (3 x 4 x 4 mm) was made bilaterally in edentulous regions created mesially to the canines in both the maxilla and mandible of nine beagle dogs. A sandwich membrane with or without bFGF (100 microg) was implanted in each defect (each group, n = 18). During weeks 1, 2, and 4, histologic evaluation and histometric analyses were performed on three dogs. Throughout the 4 weeks, vascularization and osteogenesis were active only in the bFGF-treated group (p < 0.01). New cementum was formed (2.4 +/- 0.9 mm) on the exposed root surface at 4 weeks, and functional recovery of the periodontal ligament was indicated in part by the perpendicular orientation of regenerated collagen fibers. In the control group, epithelial downgrowth and root resorption occurred and the defects were filled with connective tissue. Thus, our sandwich membrane induced successful regeneration of the periodontal tissues in a short period of time.

Bone morphogenetic protein-2 inhibits differentiation and mineralization of cementoblasts in vitro

As an approach for improving the outcome and predictability of periodontal regenerative therapies, we have focused on determining the responses of cells within the local environment to putative regenerative factors. This study examined the effects of bone morphogenetic protein-2 (BMP-2) on murine cementoblasts in vitro. Northern blot analysis indicated that BMP-2 decreased mRNA levels of bone sialoprotein and type I collagen dose-dependently (10-300 ng/mL). At low doses, up to 100 ng/mL, BMP-2 had no effect on transcripts for osteocalcin and osteopontin, whereas at 300 ng/mL, BMP-2 greatly increased expression of these two genes. BMP-2 also inhibited cementoblast-mediated mineral nodule formation in a dose-dependent manner (inhibition was noted at 10 ng/mL). Noggin reversed the effects of BMP-2 on gene expression and on mineralization. These findings reflect the diverse responses of periodontal cells to BMP-2 and highlight the need to consider the complexity of factors involved in designing predictable regenerative therapies.

Effect of low level laser therapy on the repair of bone defects grafted with inorganic bovine bone

The aim of this study was to assess histologically the effect of LLLT (l 830 nm) on the repair of standardized bone defects on the femur of Wistar albinus rats which were grafted with inorganic bovine bone Gen-ox®. Three randomized groups were studied: group I (control, n=6); group II (Gen-ox®, n=9) and group III (Gen-ox® + LLLT, n=9). The animals were irradiated every 48 h during 15 days; the first irradiation was performed immediately after the procedure. The animals were irradiated transcutaneuosly at four points around the defect. At each point a dose of 4 J/cm² was given (Ø~0.6 mm, 40 mW) and the total dose per session was 16 J/cm². The animals were killed by an overdose of general anesthetic 15, 21 and 30 days after surgery. The specimens were routinely processed by embedding in paraffin, serially cut and stained with H&E and Picrosirius and analyzed under light microscopy. The results showed evidence of a more advanced repair in the irradiated group when compared to the non-irradiated groups. The repair of the irradiated group was characterized by both increased bone formation and amount of collagen fibers around the graft within the cavity from the 15th day after surgery, also considering the osteoconductive capacity of the Gen-ox®. We conclude that LLLT had a positive effect on the repair of bone defects implanted with inorganic bovine bone.

Effect of surgical implantation of recombinant human bone morphogenetic protein-2 in a bioabsorbable collagen sponge or calcium phosphate putty carrier in intrabony periodontal defects in the baboon

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) in a proper carrier has been shown to induce clinically relevant bone formation for several oral/maxillofacial and periodontal indications and to stimulate regeneration of the periodontal attachment. The objective of this study is to evaluate regeneration of alveolar bone, cementum, periodontal ligament, and associated root resorption and ankylosis following surgical implantation of rhBMP-2 in an absorbable collagen sponge (ACS) or a calcium phosphate putty (alphaBSM) carrier in 3-wall intrabony periodontal defects in the baboon.

METHODS

rhBMP-2/ACS and rhBMP-2/alphaBSM were implanted in surgically produced, maxillary and mandibular, large size, 3-wall intrabony defects in 4 baboons. Contralateral jaw quadrants were implanted with buffer/ACS, buffer/ alphaBSM, or served as sham-operated surgical controls. Treatments were allocated to left and right, maxillary and mandibular, jaw quadrants following a randomization schedule. Four months following implantation, block biopsies of defect sites were obtained, processed, and subjected to histologic and histometric analysis.

RESULTS

Defect sites receiving rhBMP-2/ACS and rhBMP-2/alphaBSM demonstrated significantly greater regeneration than controls. No significant differences were observed between defect sites receiving rhBMP-2/ACS or rhBMP-2/alphaBSM regarding epithelial migration and connective tissue attachment and new bone formation. However, rhBMP-2/ACS supported significantly greater new cementum formation. Ankylosis or root resorption were not observed.

CONCLUSIONS

The results of this study support the use of rhBMP-2 to enhance periodontal regeneration of intrabony periodontal defects. While this novel technology holds promise, refinement in carrier systems may provide the key to enhancement of the regenerative potential.

The effect of safflower seed extract on periodontal healing of 1-wall intrabony defects in beagle dogs

BACKGROUND

Recent interest in naturally based products has increased. Various herbal extracts are known to have a variety of medicinal properties. Among the various natural medicines, safflower seeds have beneficial effects on various bone diseases such as bone fracture, osteoporosis, and osteodysplasia. In addition, they are known to have anti-inflammatory effects. The objective of this study was to evaluate the effect of a safflower seed extract (SSE) on the regeneration of periodontal tissue in a preclinical 1-wall model in dogs.

METHODS

Preclinical 1-wall periodontal defects were surgically created in the mesial aspect of the maxillary third and mandibular fourth premolar and in the distal aspect of the maxillary first and mandibular second premolar, and were randomly assigned to receive SSE/collagen (SSE/Col), phosphate-buffered saline/collagen (buffer control), or root planing only (surgical control). The created 1-wall defect configuration was 4 mm in depth by 4 mm in width. We selected the segment showing the best activity to the osteoblast cells that was sensitive to the formation of calcified nodules among the SSE fractions extracted from various organic solvents. The animals were euthanized at 8 weeks postsurgery, and block sections of the defects were collected for histologic and histometric analysis.

RESULTS

The junctional epithelium migration did not show any statistically significant differences among the treatments. In connective tissue adhesion, the SSE/Col group and the buffer control group showed significant differences compared to the surgical control group. New cementum averaged 3.84 +/- 0.57 mm, 3.75 +/- 0.24 mm, and 1.53 +/- 1.22 mm for the SSE/Col group, the buffer control group, and the surgical control group, respectively, with the SSE/Col and buffer control groups significantly different from the surgical control group (P < 0.05). The amount of intrabony cementum in the SSE/Col group was significantly different (P < 0.01) from the surgical control group, but the amount of suprabony cementum did not demonstrate any statistical difference between the different treatments. The amount of new alveolar bone averaged 2.93 +/- 0.70 mm, 2.10 +/- 0.63 mm, and 1.20 +/- 0.65 mm for the SSE/Col group, the buffer control group, and the surgical control group, respectively. The difference in alveolar bone regeneration between the SSE/Col group and the surgical control group was significantly different (P < 0.01). Root resorption was often observed, but no ankylosis was present.

CONCLUSION

Wound conditioning with safflower seed extracts may contribute to bone formation but appears to have unpredictable potential for stimulating periodontal regeneration including new cementum.

Bone repair following recombinant human bone morphogenetic protein-2 stimulated periodontal regeneration

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable sponge (ACS) carrier is currently being evaluated as candidate therapy for periodontal regeneration. The objective of this study was to characterize, in some detail, tissue reactions following surgical implantation of rhBMP-2/ACS into periodontal defects.

METHODS

Four young adult, male beagle dogs with surgically induced, bilateral, critical size, supra-alveolar, mandibular premolar defects sequentially received rhBMP-2/ACS (rhBMP-2 at 0.2 mg/ml) in right and left jaw quadrants. After 4 or 8 weeks of healing, experimental teeth with surrounding tissues were harvested and processed for light and transmission electron microscopy.

RESULTS

Surgical implantation of rhBMP-2/ACS into large supra-alveolar periodontal defects resulted in a variable tissue response without marked difference between 4- and 8-week observations. New bone, exceeding the volume of the normal alveolar process, had formed within 4 weeks. The regenerated bone tissue consisted of finely trabeculated woven bone. Marrow spaces exhibited a continuous lining of osteoblasts, osteoclasts, and resting cells. The marrow spaces contained numerous large, thin-walled vessels but were almost devoid of collagen fibrils or fibroblasts. Large voids (seromas) encountered in the newly formed bone were free of structured elements except for occasional aggregates of effete erythrocytes. A variety of tissue reactions were observed along the root surface including areas of resorption, areas of hard tissue deposition, and areas without resorptive or appositional activity. Ankylosis was a frequent observation, although areas showing characteristics of a periodontal ligament with a fine layer of acellular fiber cementum and occasional inserting Sharpey's fibers were also observed. Osteoblasts facing the root surface often appeared to be in a highly active state judged by their cuboidal shape, well-developed endoplasmic reticulum and numerous mitochondria, and the presence of an adjacent layer of preosteoblasts. Conspicuous bundles of wide collagen fibrils near the dentin surface as well as within the marrow spaces were considered to represent remnants of the ACS. These fibrils were associated with areas of mineralization as verified by examination of undecalcified specimens.

CONCLUSIONS

rhBMP-2/ACS elicits a rapid osteoinductive process throughout the implant as well as along and onto the instrumented adjacent root surface. Lamellated trabecular bone was the predominant regenerated tissue. A typical cementum-periodontal ligament-alveolar bone relationship was a rare observation. The great variability in histological tissue response along the instrumented root surface indicates that the stimulus to hard tissue formation resided primarily in the rhBMP-2/ACS implant rather than in the root surface.

Regenerative repair of the mandible using a collagen sponge containing TGF-beta1

INTRODUCTION

Alveolar bone resorption and atrophy of the mandible are a major challenge for regeneration medicine. In the present investigation, a collagen sponge that contained TGF-beta1 was placed at a mandibular defect and the osteogenic effects of collagen-TGF-beta1, complex were evaluated.

MATERIAL AND METHODS

The Pm2, Pm3, and Pm4 teeth on both sides of the mandibles of 12 adult beagle dogs (9.0-12.0 kg) were extracted. After the extraction-site wounds healed, a bone defect (10.0 x 15.0 mm-wide, 10.0 mm-deep or 10.0 x 10.0 mm-wide, 10.0 mm-deep) was created on the mandible. A collagen sponge (10.0 x 10.0 x 10.0 mm) that contained TGF-beta1 (1.0 microg, 5.0 microg, or 10.0 microg, in physiological saline) was placed at the bottom of the defect and the overlying mucous membrane was sutured with 4-0 prolene. As a control, a collagen sponge that contained physiological saline only was placed in a defect on the opposite side. Two weeks after the surgery the wounds above the bone defects on both the control and TGF-beta1-treated sides had healed completely.

RESULTS

At four, six, or eight weeks post-operatively animals were killed. Soft X-ray and bone-salt measurement analyses confirmed clearly that there was greater calcified bone formation in the defects into which TGF-beta1 had been incorporated than with the control defects. The implanted collagen sponges were fully resorbed and the bone tissue had regenerated from the bottom of the defects on the TGF-beta1, side by four weeks. On the control side, no such regeneration was observed.

CONCLUSIONS

These results indicate that TGF-beta1, released slowly from a collagen sponge was effective in promoting bone remodeling when applied to mandibular defects in adult dogs.

Effects of simvastatin gels on murine calvarial bone

BACKGROUND

The cholesterol-lowering drug simvastatin has been shown to stimulate murine calvarial bone growth after multiple injections. The purpose of this study was to test if similar bone stimulation could be induced by 2 single-dose drug delivery systems appropriate to periodontal therapy.

METHODS

ICR Swiss mice were treated with the following protocols: 1) injection of methylcellulose gel alone, subcutaneously over the calvarium (INJ-GEL; n = 8); 2) injection of gel with simvastatin (INJ-SIM; 2.2 mg, n = 16); 3) polylactide membrane (PLA) containing gel alone implanted over calvarium (MEM-GEL; n = 10); 4) implanted PLA membrane containing gel and simvastatin (MEM-SIM; n = 10); and 5) untreated mice (n = 12). Animals were sacrificed after 22 or 44 days, calvaria decalcified and stained with hematoxylin and eosin, and images digitized and measured for bone thickness and area. Data were compared using analysis of variance.

RESULTS

INJ-SIM stimulated a 53% (P = 0.02) increase at the thickest point of calvarial bone, while MEM-SIM caused a highly significant (P < or = 0.0005) increase in bone thickness (159% to 172%) and bone area (144% to 180%) compared to gel controls. Simvastatin gels caused soft tissue inflammation, which appeared to be related to bone increases. If INJ-SIM animals showing leakage of gel and/or no inflammation were excluded from analysis, INJ-SIM resulted in more bone (58% to 83%) than gel controls. An insignificant amount of SIM-stimulated bone was lost over the long term (44 days).

CONCLUSIONS

A single, high dose of simvastatin gel can stimulate murine cranial bone apposition, particularly when delivered under an occlusive membrane. Both approaches should be investigated further for possible development for periodontal therapy.

Bone morphogenetic protein 2 induces dental follicle cells to differentiate toward a cementoblast/osteoblast phenotype

When triggered appropriately, dental follicle cells are considered to be able to differentiate toward a cementoblast/osteoblast phenotype. However, factors and mechanisms regulating follicle cell differentiation remain undefined. This study focused on determining the ability of bone morphogenetic protein (BMP) 2 to promote the differentiation of follicle cells and periodontal ligament (PDL) cells along a cementoblast/ osteoblast pathway. Follicle cells and PDL cells were isolated from the first molar region of CD-1 mice and immortalized with SV40. Both cell types expressed BMP-4 and BMP receptors (BMPR) IA and II, but only follicle cells expressed BMP-2 mRNA. Cells were exposed to recombinant human BMP (rhBMP)-2 (0-100 ng/ml) and Northern blots were used to determine the expression of mineral-associated markers. BMP-2, in a dose- and time-dependent manner, induced cementoblast/osteoblast differentiation of follicle cells, as reflected by enhanced core binding factor alpha (Cbfal), bone sialoprotein (BSP), and osteocalcin (OCN) mRNA expression and enhanced mineral formation. U0126, a specific inhibitor of MEK-1/2 members of the MAPK family, abolished BMP-2-mediated expression of BSP and OCN. In contrast, exposure of PDL cells to BMP-2 resulted in modest expression of OCN and minimal promotion of mineralization. These results suggest that BMP-2 triggers follicle cells to differentiate toward a cementoblast/osteoblast phenotype and that the MAPK pathway is involved.

Factors that modulate the effects of bone morphogenetic protein-induced periodontal regeneration: a critical review

The healing process initiated by a single molecular species of bone morphogenetic protein (BMP) such as BMP-2 or BMP-7 sets in motion a cascade of cellular events resulting in differentiation of progenitor cells into phenotypes involved in periodontal regeneration. For example, animal studies show that a single dose of recombinant human (rh) BMP-2 increases the rate of normal intramembranous bone formation and enhanced cementum formation during periodontal wound healing. However, the optimal effects of BMPs are modulated by a range of factors that need careful evaluation in clinical studies. These factors include the influence of root conditioning, occlusal loading, BMP dose, and the release characteristics of the carrier as well as the suitability of the model to evaluate the efficacy of BMPs. Each of these factors may affect the rate of BMP-induced osteogenesis and cementogenesis and subsequent periodontal ligament (PDL) formation during the early and late stages of periodontal wound healing. Although BMP-2 initiates stem cells along an osteogenic pathway, the dose may have to be of sufficient concentration to ensure other growth and differentiation factors do not redirect or retard the osteogenic potential of the cell. Understanding when to manipulate the cell's differentiation pathway with the application of single or multiple doses of BMPs at the appropriate concentration is required to optimize the effect of BMPs in periodontal wound healing. Therefore, different release profiles from the same carrier may be particularly important in tissues with mixed cell populations such as in the periodontium, where similar tissues like bone and cementum grow at different rates. Furthermore, treatment of intrabony defects with BMPs are likely to not only require appropriate temporal release of the BMP(s), but also a carrier that can serve as a template for new tissue formation providing space maintenance and supporting the mucoperiosteal flap. Many of these issues have not been adequately addressed from a periodontal standpoint; therefore the purpose of this review is to clarify our current understanding of the factors that are likely to modulate the effects of BMP-induced periodontal regeneration. Moreover, assessing the importance of these factors is essential prior to conducting expensive human clinical trials.

Hard tissue formation on dentin surfaces applied with recombinant human bone morphogenetic protein-2 in the connective tissue of the palate

The purpose of this study was to evaluate whether hard tissue might be formed on dentin surfaces applied with recombinant human bone morphogenetic protein-2 (rhBMP-2) in palatal connective tissue. Fifty-eight dentin blocks were prepared from rat roots, demineralized with 24% EDTA (pH 7.0), applied with 0, 50 and 100 microgram/ml rhBMP-2, and labeled as groups 0, 50 and 100. The dentin blocks were then transplanted into palatal connective tissue of rats, and specimens were prepared at two and four weeks after surgery for histologic and histomorphometric examinations. The results showed that the percentage of newly formed hard tissue in relation to the total dentin block surface length in groups 0, 50 and 100 was 0.0%, 2.8% and 4.4% at two weeks, and 0.0%, 1.6% and 12.8% at four weeks, respectively. New hard tissue formation in groups 50 and 100 was significantly promoted as compared to group 0 (p < 0.01). These findings thus indicate that rhBMP-2 application to dentin enhanced new hard tissue formation on dentin surfaces in the connective tissue of the palate.

Peri-implant bone regeneration using recombinant human bone morphogenetic protein-2 in a canine model: a dose-response study

The objective of this study was to evaluate the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) dose on alveolar ridge augmentation and dental implant osseointegration. Bilateral, 5 mm supraalveolar, peri-implant defects were surgically created in 6 beagle dogs. rhBMP-2 (0.05, 0.1 or 0.2 mg/ml) in an absorbable collagen sponge (ACS) carrier was molded around the fixtures and wounds were closed. Treatment variations were alternated between animals (incomplete block design). Animals were sacrificed at week 8 postsurgery. Nine of twelve jaw quadrants healed uneventfully. Two jaw quadrants exhibited wound failure by week 4 and one by week 8 postsurgery. Radiographic bone regeneration was observed in defects without wound failure from week 4 postsurgery. Radiolucent voids of variable size and shape were observed and regressed over time. In weeks 6 through 8, there was an apparent increase in bone density and trabecular structure, while bone height and volume decreased. Histometric analysis revealed limited differences in bone regeneration between experimental conditions. Bone regeneration area averaged (+/- SD) 1.0 +/- 0.5, 3.5 +/- 1.4 and 2.3 +/- 0.4 mm2 for the 0.05, 0.1 and 0.2 mg/ml dose, respectively. There were no significant differences in osseointegration. Osseointegration in newly formed bone averaged 19 +/- 4%, 18 +/- 10% and 21 +/- 6% for the 0.05, 0.1 and 0.2 mg/ml rhBMP-2 sites, respectively. Collectively, the data suggest that there are no dramatic differences in bone induction and osseointegration within the selected dose and observation interval.