Bone morphogenetic proteins: background and implications for oral reconstruction. A review

Advantage of leaky expression, acid solubilization and CHAPS in the production of cost-effective bone morphogenetic Protein-2

The aim of this study was to purify BMP-2 in an easy and time-efficient way. We have developed a new method in which BMP-2 is produced through leaky expression in E. coli BL21 (DE3) cells as inclusion bodies, eliminating the need for inducer Isopropyl β-D-1-thiogalactopyranoside (IPTG). Inclusion bodies were solubilized by the acid denaturation method. Several refolding agents, along with a reducing and oxidizing environment, were tried to produce a correctly folded dimer, which is the biologically active form of BMP-2. CHAPS was found to be the most effective refolding agent at a concentration of 20 mM. The activity of the purified protein was confirmed by alkaline phosphatase assay and calcium deposition assay on C2C12 cells and native PAGE analysis was done to check binary complex formation upon binding between BMP-2 and ALK-3 receptor. These results demonstrate that the synthesized BMP-2 protein is biologically active and has potential clinical applications.

Efficient Delivery of Transducing Polymer Nanoparticles for Gene-Mediated Induction of Osteogenesis for Bone Regeneration

Developing non-viral gene therapy vectors that both protect and functionally deliver nucleic acid cargoes will be vital if gene augmentation and editing strategies are to be effectively combined with advanced regenerative medicine approaches. Currently such methodologies utilize high concentrations of recombinant growth factors, which result in toxicity and off-target effects. Herein we demonstrate the use of modified cell penetrating peptides (CPPs), termed Glycosaminoglycan (GAG)-binding Enhanced Transduction (GET) peptides with plasmid DNA (pDNA) encapsulated poly (lactic-co-glycolic acid) PLGA nanoparticles (pDNA-encapsulated PLGA NPs). In order to encapsulate the pDNA, it was first condensed with a cationic low molecular weight Poly L-Lysine (PLL) into 30-60 nm NPs followed by encapsulation in PLGA NPs by double emulsion; yielding encapsulation efficiencies (EE) of ∼30%. PLGA NPs complexed with GET peptides show enhanced intracellular delivery (up to sevenfold) and transfection efficiencies (up to five orders of magnitude). Moreover, the pDNA cargo has enhanced protection from nucleases (such as DNase I) promoting their translatability. As an example, we show these NPs efficiently deliver pBMP2 which can promote osteogenic differentiation in vitro. Gene delivery to human Mesenchymal Stromal Cells (hMSCs) inducing their osteogenic programming was confirmed by Alizarin red calcium staining and bone lineage specific gene expression (Q RT-PCR). By combining simplistic and FDA-approved PLGA polymer nanotechnology with the GET delivery system, therapeutic non-viral vectors could have significant impact in future cellular therapy and regenerative medicine applications.

Gene expression changes in bioceramic paste-treated human dental pulp cells

We evaluated the gene expression profiles of human dental pulp cells exposed to iRoot BP using microarray after 24 and 72 h. The results were verified using quantitative reverse transcriptase PCR analysis. Of the 36,000 transcripts arrayed, 21 were up-regulated and 15 were down-regulated by more than two fold. The largest group of up-regulated genes included those involved in nucleobase-containing compound metabolic processes, cell communication, protein metabolic processes, developmental processes, and biological regulation. The largest groups of down-regulated genes were those involved in cell communication, development, and biological regulation processes. In conclusion, iRoot BP affects the expression of genes involved in different biological processes in human dental pulp cells. (J Oral Sci 58, 307-315, 2016).

Severe mandibular atrophy treated with a subperiosteal implant and simultaneous graft with rhBMP-2 and mineralized allograft: a case report

A 71-year-old patient was successfully rehabilitated by means of a 3D model-derived, hydroxyapatite-coated titanium subperiosteal mandibular implant. The implant was specifically designed to allow bone augmentation. The deficient bone was simultaneously grafted with mineralized bone allograft and recombinant bone morphogenetic protein -2 (rhBMP-2). The 32-month postoperative cone beam computerized tomography follow-up showed vertical bone augmentation beneath the implant frame.

Understanding the advances in biology of orthodontic tooth movement for improved ortho-perio interdisciplinary approach

This article provides an insight on detailed current advances in molecular understandings of periodontal ligament cells and the influence of orthodontic force on them in the light of recent advances in molecular and genetic sciences. It sequentially unfolds the cellular events beginning from the mechanical force initiated events of cellular responses to bone remodeling. It also highlights the risks and limitations of orthodontic treatment in certain periodontal conditions, the important areas of team work, orthodontic expectations from periodontal treatment and the possibility of much more future combined research to improve the best possible periodontal health and esthetic outcome of the patient.

Effect of recombinant human bone morphogenetic protein 2 associated with a variety of bone substitutes on vertical guided bone regeneration in rabbit calvarium

BACKGROUND

A major challenge for dental implantology is to consistently obtain appropriate bone augmentation before implant placement. The aim of this study is to evaluate the effect of recombinant human bone morphogenetic protein 2 (rhBMP-2) associated with bone substitute materials beta-tricalcium phosphate (β-TCP), biphasic calcium phosphate (BCP), and bovine bone mineral on vertical guided bone regeneration (GBR) in rabbit calvarium.

METHODS

Four titanium cylinders were fixed to the calvarium of 22 rabbits. In group 1 (n = 10), three cylinders were randomly filled with one of the test materials, and one cylinder was filled with a blood clot (CL). In group 2 (n = 12), the cylinders were randomly assigned to the same materials and CL but with the addition of rhBMP-2. Bone labels were injected over the course of 13 weeks, and euthanasia was performed 14 weeks after surgery in both groups.

RESULTS

The mean volume and area of tissue growth was greater in group 2 (with rhBMP-2) than in group 1 (without rhBMP-2), irrespective of the material used (P <0.001). The mean volume of tissue growth in the CL cylinder was smaller than that observed with all other materials (P <0.001) in both groups. The mean area of regenerated bone in the CL cylinder was smaller than that observed in the β-TCP cylinder (P = 0.028). The histologic study revealed more lamellar bone in the rhBMP-2 group, with a greater level of biodegradation of all the bone substitute materials tested.

CONCLUSION

The use of rhBMP-2/absorbable collagen sponge (ACS) combined with all of the bone substitute materials tested resulted in a greater amount of bone formation than that produced with the bone substitute materials alone or rhBMP-2/(ACS) and CL using the rabbit calvarium GBR model.

The optimal dose of recombinant human osteogenic protein-1 enhances differentiation of mouse osteoblast-like cells: an in vitro study

OBJECTIVE

There is no certain conclusion on the effect of recombinant human Osteogenic Protein-1 (OP-1, BMP-7) on the proliferation of the osteoblast-like cell line, MC3T3-E1. Furthermore, the optimal dose of rhOP-1 on cell differentiation still needs to be elucidated. This investigation aims to delineate the biofunctional characteristics of rhOP-1 in inducing osteoblastogenesis of MC3T3-E1 through in vitro time-course and dose-response studies.

DESIGN

MC3T3-E1 cells were cultured for 1, 4, 7 days with the addition of different rhOP-1 concentrations (0, 10, 20, 50, 100, 200, 400 ng/ml), and cell proliferation and cell differentiation were examined.

RESULTS

MC3T3-E1 cell proliferation was stimulated by rhOP-1 in a dose-dependent manner (0-400 ng/ml) on day 1, whereas on day 4 and 7, it was still stimulated at low concentrations (10, 20, 50 ng/ml) but inhibited at high ones (200, 400 ng/ml). The alkaline phosphatase (ALP) activity, osteocalcin (OC) production, collagen deposition and extracellular matrix mineralization were dramatically elevated by rhOP-1 treatment, as a function of culture time and rhOP-1 concentration, and all of them reached a plateau at the concentration of 200 ng/ml. Real-time quantitative RT-PCR results showed Runx2, AKP-2, OC and Nog mRNA expressions increased in a dose- and time-dependent manner, and their expressions were significantly higher at high rhOP-1 concentrations than that of low ones. No significant differences were found between the effects of 200 ng/ml rhOP-1 and 400 ng/ml rhOP-1 on the differentiation of MC3T3-E1 cells, except the expression of Nog mRNA, whose expression level was much higher at 400 ng/ml than that at 200 ng/ml.

CONCLUSIONS

These results suggest that cell proliferation of MC3T3-E1 is depended on culture time and rhOP-1 concentration, rhOP-1 could stimulate the differentiation of MC3T3-E1 cells and the optimal concentration could be 200 ng/ml.

Effect of rhTGF-β1 combined with bone grafts on human periodontal cell differentiation

Various techniques and materials have been proposed for the treatment of periodontal defects. In periodontal regeneration, periodontal ligament (PDL) cell differentiation as well as certain growth factors and their delivery system applied are critical. The purpose of this study was to evaluate the in vitro effect of recombinant human transforming growth factor-beta 1 (rhTGF-β1) combined with two different bone grafts on human PDL (hPDL) cell differentiation. The hPDL cells were treated with TGF-β1 alone or in combination with a calcified freeze-dried bone allograft (FDBA) and a porous biphasic calcium phosphate (BC) bone graft. Cell differentiation effect was estimated by measuring alkaline phosphatase (ALPase) activity and osteocalcin secretion. Results demonstrated that rhTGF-β1 alone or in combination with FDBA and BC provoked a significant (p<0.05) increase in ALPase activity as compared with controls. The findings of this study confirmed the beneficial role of rhTGF-β1 combined with FDBA and BC as carriers in periodontal regeneration.

Comparison of applying particulate demineralized bone matrix (DBM), putty DBM and open flap debridement in periodontal horizontal bone defects. A 12-month longitudinal, multi-center, triple-blind, split-mouth, randomized, controlled clinical study. Part 1 - clinical and radiographic evaluation

Putty form graft materials may have additional favourable effects when compared with particulate ones in periodontal bone defects. The purpose of this study was to assess clinical and also radiographic changes following application of (i) putty form demineralized bone matrix (DBM), (ii) particulate form DBM and (iii) open flap debridement (control), using modified curtain suturing technique in the treatment of interproximal suprabony (horizontal) defects. Twenty-five chronic periodontitis patients with 125 sites (radiologically >or=4 mm horizontal bone defect) were selected to participate in this triple-blind, split mouth, randomized, controlled clinical trial. Putty and particulate form DBM grafts were placed at experimental sites. Clinical measurements included probing depth (PD), relative attachment level (RAL), gingival recession and bone probing depth (BPD) were made at baseline and repeated 12 months after the operations. Standardized digital radiographs were also taken to measure radiographic bone level (RBL) at baseline and 12 months later to be compared in a software. Probing depth reductions and RAL gains were significantly improved in all treatment groups (P < 0.001). No significant differences in soft tissue parameters were found among three groups (P > 0.05). Bone probing depth measurements indicated comparable significant bone gain in graft applied groups (P < 0.01) and a significant bone resorption in open flap debridement group (P < 0.01). Radiographic evaluation did not show any significant bone gain or resorption in all treatment groups (P > 0.05). The results of this study indicate that either putty or particulate DBM demonstrates similar enhancements in soft and hard tissue parameters. Applying putty or particulate form DBM results with slight bone formation when compared with open flap debridement in horizontal bone defects at 1-year post-operative examination according to BPD measurements.

Regenerative approaches in the craniofacial region: manipulating cellular progenitors for oro-facial repair

This review aims to highlight the potential for regeneration that resides within the bony tissues of the craniofacial region. We examine the five main cues which determine osteogenic differentiation: heritage of the cell, mechanical cues, the influence of the matrix, growth factor stimulation and cell-to-cell contact. We review how successful clinical procedures, such as guided tissue regeneration and distraction osteogenesis exploit this resident ability. We explore the developmental origins of the flat bones of the skull to see how such programmes of differentiation may inform new therapies or regenerative techniques. Finally we compare and contrast existing approaches of hard tissue reconstruction with future approaches inspired by the regenerative medicine philosophy, with particular emphasis on the potential for using chondrocyte-inspired factors and replaceable scaffolds.

Bone repair in rat mandible by rhBMP-2 associated with two carriers

This study evaluated the quantity and quality of newly formed bone, stimulated by rhBMP-2 in combination with monoolein or chitosan gel as carriers, in critical bone defects created in 36 Wistar rat mandibles. Two weeks after surgery, the animals were anesthetized with 37.5% urethane submitted to perfusion and the hemi-mandibles removed for histological and histomorphometrical analysis. The results showed that there was a statistical difference between groups of animals receiving or not rhBMP-2 (p<0.05). Newly formed bone was more intense in the occlusal region, followed by the basal and middle regions, respectively. Both carriers, monoolein and chitosan gels were adequate for defect filling and control of protein release.

Role of growth factors on periodontal repair

Regeneration of periodontal structures lost during periodontal diseases constitutes a complex biological process regulated among others by interactions between cells and growth factors. Growth factors are biologically active polypeptides affecting the proliferation, chemotaxis and differentiation of cells from epithelium, bone and connective tissue. They express their action by binding to specific cell-surface receptors present on various target cells including osteoblasts, cementoblasts and periodontal ligament fibroblasts. The observation that growth factors participate in all cell functions led to exogenous application during periodontal tissue repair aiming to their use as an alternative therapeutic approach to periodontal therapy. Cell types and cultures conditions, dose, carrier materials, application requirements are of critical importance in the outcome of periodontal repair. The purpose of this article is to review the literature with respect to the biological actions of PDGF, TGF, FGF, IGF and EGF on periodontal cells and tissues, which are involved in periodontal regeneration.

Influence of platelet-rich plasma on a bioglass and autogenous bone in sinus augmentation. An explorative study

Platelet-rich plasma (PRP) has been introduced to the field of oral and maxillofacial surgery for a decade, but its beneficial effects on maxillary sinus augmentation remain unclear. The aim of this study was to evaluate the short- and long-term effects of PRP on osseointegration following single-stage sinus augmentation in a randomized prospective animal study. The maxillary premolars of 24 minipigs were extracted bilaterally and allowed to heal for 2 months. Consecutively all animals underwent bilateral sinus floor elevation using autogenous bone, Biogran as well as a combination of the materials with PRP. Three dental implants (Ankylos, Dentsply Co., Mannheim, Germany) were installed in each sinus simultaneously. Four animals were sacrificed at each period of observation (1, 2, 8 and 12 months). Microradiographic images of the specimens were made for quantitative evaluation of the bone-implant contact (BIC) and light microscopic images were made for qualitative analysis. An increment of the BIC during the observation time could be seen over the observation time in all groups. Autogenous bone exhibited a level of BIC from 25.1 +/- 9.96% at 1 month to 55.1 +/- 13.10% at 12 months; on adding PRP, the BIC ranged from 28.4 +/- 4.64% to 52.5 +/- 17.06%. Biogran with and without PRP led to BIC levels from 16.3 +/- 4.64% to 37.6 +/- 16.40% and 21.7 +/- 4.33% to 46.6 +/- 19.37%, respectively. The results of this study did not show a significantly positive effect of PRP on the BIC following sinus augmentation in both groups.

Evaluation of bone healing enhancement by lyophilized bone grafts supplemented with platelet gel: A standardized methodology in patients with tibial osteotomy for genu varus

Orthopedic practice may be adversely affected by an inadequate bone repair that might compromise the success of surgery. In recent years, new approaches have been sought to improve bone healing by accelerating the rate of new bone formation and the maturation of the matrix. There is currently great interest in procedures involving the use of platelet gel (PG) to improve tissue healing, with satisfactory results both in vitro and in maxillofacial surgery. Otherwise, to our knowledge, only a preliminary clinical study was undertaken in the orthopedic field [Kitoh et al., Bone 2004;35:892-898] and the efficacy of PG is still controversial. Our paper focuses on the effect on bone regeneration by adding PG to lyophilized bone chips used for orthopedic applications. The clinical model and the laboratory methodology were standardized. As a clinical model, we employed the first series of patients of a randomized case-control study undergoing high tibial osteotomy (HTO) for genu varus. Ten subjects were enrolled: in 5 patients lyophilized bone chips supplemented with PG were inserted during tibial osteotomy (group A); 5 patients were used as a control (group B) and lyophilized bone chips without gel were applied. Forty-five days after surgery, computed tomography scan guided biopsies of grafted areas were obtained and the bone maturation was evaluated by a standardized methodology: the osteogenic and angiogenic processes were semi-quantitatively characterized by using histomorphometry, and the mineral component of the lyophilized and host bone was analyzed by using X-ray diffraction technique with sample microfocusing and microradiography. Lyophilized bone with PG seems to accelerate the healing process, as shown by new vessel formation and deposition of newly formed bone, with no evidence of inflammatory cell infiltrate, when compared with lyophilized bone without gel. On the contrary, lyophilized bone undergo a resorption process, and a fibrous tissue often fills the spaces between chips. A histiocytic/giant-cell reaction is sometimes present. Otherwise, no differences have been found concerning microstructure. Our findings show the reliability of the methodology used to monitor early bone repair. The completion of the study and the evaluation of the ultimate clinical outcome are necessary in order to verify PG in vivo effects in orthopedic surgery.

Establishment of immortalized clonal cells derived from periodontal ligament cells by induction of the hTERT gene

Since the periodontal ligament (PDL) contains a heterogeneous cell population, it is challenging to identify all cell types within the tissue and to determine whether they function alone to produce tissue components or interact with other cell types. Further, it is difficult to isolate and expand single cell clones from PDL cells, as normal cells have a limited life span and are phenotypically unstable. In the present study, we inserted the human telomerase reverse transcriptase (hTERT) gene, which encodes the catalytic subunit of the telomerase holoenzyme, into normal human periodontal ligament (HPL) cells and successfully obtained single cell clones. Expression of the inserted gene and telomerase activity in each of the clones was confirmed. Unlike the original HPL cells, at the end of the study (day 120), clone populations continued to actively double without phenotypic alteration. Osteogenic characteristics were present in some but not all clones. In conclusion, immortalization of HPL cells was successfully accomplished by transduction with the hTERT gene. This is the first report of immortalization of different cell types derived from PDL.

O papel da proteína morfogenética óssea na reparação do tecido ósseo

Este estudo de revisão da literatura aborda os avanços do uso da proteína morfogenética óssea (BMP) na reparação do tecido ósseo e seus mecanismos de ação no tecido lesionado. As BMPs são moléculas pleiotrópicas que são envolvidas na quimiotaxia, mitose e diferenciação de células mesenquimais no tecido ósseo.

Effect of platelet-rich plasma on bone regeneration in autogenous bone graft

In this study, we evaluated the effect of platelet-rich plasma (PRP) on bone regeneration in an autogenous bone graft in a canine model. The mandibular premolar teeth had been bilaterally extracted previously, and the ridges had been allowed to heal for 3 months. After this period, continuity resection was performed on both sides of the mandible. One defect (the PRP group) was reconstructed with the original particulate bone mixed with PRP. As a control, the contralateral defect (non-PRP group) was reconstructed with the original particulate bone alone. Biopsies after 6 weeks showed lower levels of bone formation in the PRP group than in the non-PRP group, and fluorescence microscopy revealed a delay in the remodelling of grafts loaded with PRP. These findings suggest that the addition of PRP does not appear to enhance new bone formation in autogenous bone grafts.

Novel in vivo method for evaluation of healing around implants in bone

A material implanted in bone is always inserted into coagulating blood. Protein and cell interactions during this initial implantation time will govern later healing. Many studies have focused on the tissue surrounding implants. We have developed a method for evaluation of healing around implants in bone by studying cells adhering to the implant surface. Hydrophilic titanium discs were inserted into rat tibiae. Samples were retrieved after 1, 2, 4, and 8 days of implantation and were analyzed by fluorescence microscopy techniques and scanning electron microscopy. Both proliferating and apoptotic cells were found on the surface. Generally, cells closest to the implant surface were nonviable whereas cells in the fibrin network a distance from the surface were viable. Bone morphogenetic protein-2 (BMP-2) is an osteogenic substance. An increase in BMP-2-positive cells was seen during the implantation period, and a population of large BMP-2-positive cells appeared on the surface after 4 days of implantation. The method developed here is a suitable tool for rapid evaluation of the initial healing around implant material.

Bone morphogenetic protein 2 induces the expression of cementum attachment protein in human periodontal ligament clones

Cementum is continuously formed during the lifetime of a tooth. The paravascular zones in the adult periodontal ligament (PL) comprise the progenitors for the fibroblastic (Fb) lineage and mineralized tissue-forming (MTF) cell lineages--the osteoblastic (Ob) and cementoblastic (Cb) lineages. Recent studies indicate that cementum attachment protein (CAP) is related to the differentiation of the Cb lineage and is instrumental in differentiating between the three periodontal cell lineages. The purpose of this study was to assess the effect of bone morphogenetic protein 2 (BMP2) on the expression of cementum attachment protein (CAP) and on the differentiation of cloned PL progenitors. The effect of BMP2 on CAP expression and on the differentiation of cloned Fb and MTF progenitors was tested by assessing the expression of alkaline phosphatase (ALP), CAP, and bone sialoprotein (BSP) by immunochemistry and by determining the CAP-binding capacity of these clones. Untreated Fb clones were negative for all tested markers and had low CAP-binding capacity. Untreated MTF clones had a high CAP-binding capacity and were positive for the three markers. BMP2 enhanced the CAP-binding potential of both Fb and MTF clones. BMP2 induced the expression of CAP, ALP, and BSP in the Fb clones and enhanced the expression of CAP and BSP in the MTF clones. These results indicate for the first time that BMP2 can recruit progenitors to the Cb lineage and regulate the differentiation of the Cb lineage by inducing and enhancing the expression of CAP, a cell lineage-specific regulator. Furthermore, the results suggest that the MTF and Fb lineages may originate from a common early progenitor cell.

Osteogenesis by guided tissue regeneration and demineralized bone matrix

AIM

To evaluate in a discriminating capsule model whether bone formation by guided tissue regeneration (GTR) may be influenced by concomitant implantation of demineralized bone matrix (DBM).

MATERIALS AND METHODS

Thirty 4-month-old male albino rats of the Wistar strain were used in the study. Following surgical exposure of the mandibular ramus, a hemispherical, Teflon capsule (5.0 mm in diameter), loosely packed with a standardized amount of DBM, was placed with its open part facing the lateral bone surface of the ramus. At the contralateral side, an empty capsule was placed, serving as control. After healing periods of 15, 30, and 120 days, groups of 10 animals were sacrificed and 40-70 microm thick undecalcified sections of the capsules were produced. In the sections, the cross-sectional areas of (1) the space created by the capsule, (2) newly formed bone, (3) DBM particles, (4) loose connective tissue as well as the (5) height of the capsules, and (6) that of the newly formed bone were measured.

RESULTS

Increasing bone fill was observed in both test and control sites from 30 to 120 days. After 30 days of healing, the mean amount of bone was approx. 3% of the cross-sectional area of the capsules at the test sites while it was 8% in the control sites (p<0.05). However, no statistically significant differences were observed between the test (46%) and control (64%) sites after 120 days regarding any of the measured parameters (p>0.05). The newly formed bone in the DBM group at 120 days, on the other hand, appeared more dense than that in the control capsules.

CONCLUSION

DBM used as an adjunct to GTR did not provide any added effect on bone formation but increased the density of the newly formed bone.

New paradigms in prosthodontic treatment planning: a literature review

New treatment modalities have expanded the choices available to prosthodontists and their patients. At the same time, an explosion of data has called into question the validity and efficacy of certain forms of traditional prosthodontic treatment. Together, these factors have greatly complicated the treatment-planning process. The purpose of this article is to provide a framework for the prosthodontic treatment-planning process that incorporates the latest evidence-based information available. A review of the literature was undertaken through a Medline search. Articles published in English from 1975 through 2001 were evaluated; selected articles were chosen for review on the basis of a subjective judgment of their relevancy and significance to the clinician.

Periodontal tissue regeneration by combined applications of recombinant human osteogenic protein-1 and bone morphogenetic protein-2. A pilot study in Chacma baboons (Papio ursinus)

Native and recombinant human bone morphogenetic/osteogenic proteins (BMPs/ OPs) singly initiate bone induction in vivo. The finding of synchronous but spatially different BMPs/OPs expression during periodontal tissue morphogenesis suggests novel therapeutic approaches using morphogen combinations based on recapitulation of embryonic development. Twelve furcation defects prepared in the first and second mandibular molars of three adult baboons (Papio ursinus) were used to assess whether qualitative histological aspects of periodontal tissue regeneration could be enhanced and tissue morphogenesis modified by combined or single applications of recombinant hOP-1 and hBMP-2. Doses of BMPs/OPs were 100 microg of each protein per 1 g of insoluble collagenous bone matrix as carrier. Approximately 200 mg of carrier matrix was used per furcation defect. Undecalcified sections cut for histological analysis 60 d after healing of hOP-1-treated specimens showed substantial cementogenesis with scattered remnants of the collagenous carrier. hBMP-2 applied alone induced greater amounts of mineralized bone and osteoid when compared to hOP-1 alone or to combined morphogen applications. Combined applications of hOP-1 and hBMP-2 did not enhance alveolar bone regeneration or new attachment formation over and above the single applications of the morphogens. The results of this study, which is the first to attempt to address the structure-activity relationship amongst BMP/OP family members, indicate that tissue morphogenesis induced by hOP-1 and hBMP-2 is qualitatively different when the morphogens are applied singly, with hOP-1 inducing substantial cementogenesis. hBMP-2 treated defects, on the other hand, showed limited cementum formation but a temporal enhancement of alveolar bone regeneration and remodelling. The demonstration of therapeutic mosaicism in periodontal regeneration will require extensive testing of ratios and doses of recombinant morphogen combinations for optimal tissue engineering in clinical contexts.

Expression of bone matrix protein mRNAs by primary and cloned cultures of the regenerative phenotype of human periodontal fibroblasts

The successful regeneration of periodontal tissues is dependent, in part, on the ability of cells to reconstitute the mineralized tissues of cementum and bone. The aim of the present study was to characterize regeneration-associated cells in terms of their ability to express mineralized tissue macromolecules. Following guided tissue regeneration, cell cultures were established from regenerating tissue, periodontal ligament, and gingiva. Additionally, these cells were transfected, and single-cell-derived clones were established. Following treatment with platelet-derived growth factor-BB and insulin-derived growth factor-1, the presence of mRNA for alkaline phosphatase, osteocalcin, bone sialoprotein, osteopontin, and bone morphogenetic proteins-2 and -4 was assessed. The three cell types expressed similar mRNA levels for alkaline phosphatase, bone morphogenetic protein-2, and bone morphogenetic protein-4, whereas the expression of osteopontin, osteocalcin, and bone sialoprotein was greater in the periodontal ligament and regenerating tissue fibroblasts compared with the gingival fibroblasts. The two growth factors did not affect the expression of any of the genes. This study has identified markers that correlate with the known ability of periodontal ligament and regenerating tissue-derived fibroblasts to facilitate regeneration of the mineralized tissues of the periodontium.

Preliminary in vivo studies on the osteogenic potential of bone morphogenetic proteins delivered from an absorbable puttylike polymer matrix

This article describes preliminary in vivo studies evaluating the osteogeneic potential of bone morphogenetic proteins (BMPs) delivered from an absorbable puttylike polymer matrix. In the first study, bovine-derived bone morphogenetic proteins were incorporated in an polymer matrix consisting of 50:50 poly(DL-lactide-co-glycolide) dissolved in N-methyl-2-pyrrolidone. The matrix was implanted in an 8 mm critical-size calvarial defect created in the skull of adult Sprague-Dawley rats (n = 5 per treatment group). After 28 days, the implant sites were removed and examined for new bone formation, polymer degradation, and tissue reaction. Gamma-irradiated polymer matrices appeared to give more bone formation than nonirradiated samples (histological analysis; 2. 76 + 1.34 mm(2) of bone versus 1.30 + 0.90 mm(2) of bone, respectively and x-ray analysis; 27.2 + 15.9 mm(2) of bone versus 20. 7 + 16.7 mm(2) of bone, respectively) and less residual polymer (0.0 + 0.0 versus 0.2 + 0.4, respectively). The polymer implants with bone morphogenetic protein also gave less inflammatory response than the polymer controls (gamma irradiated polymer/BMP = 1.8 + 0.4 and nonirradiated polymer/BMP = 1.2 + 0.4 versus polymer only = 3.0 + 1. 2, respectively). However, despite trends in both the x-ray and histological data there was no statistical difference in the amount of new bone formed among the four treatment groups (P > 0.05). This was most likely due to the large variance in the data scatter and the small number of animals per group. In the second animal study, bovine-derived BMPs and the polymeric carrier were gamma irradiated separately, at doses of 1.5 or 2.5 Mrad, and their ability to form bone in a rat skull onlay model was evaluated using Sprague-Dawley rats (n = 5 per treatment group). Histomorphometry of skull caps harvested 28 days after implantation showed no significant differences as compared to non-irradiated samples, in implant area, new bone area, and percent new bone (P > 0.05). These results suggest gamma irradiation may be useful in sterilization of the bovine-derived BMPs and the polymeric carrier for potential bone repair and/or regeneration applications.

Biological effects of cementum and bone extracts on human periodontal fibroblasts

BACKGROUND

Non-collagenous proteins of mineralized tissues play important roles in bone induction during mineralization and in regulating the activity of many types of mesenchymal cells. This study was conducted to determine the effects of acetic acid extracts of bone and cementum on alkaline phosphatase (ALPase) activity and in vitro mineralization of cultured human periodontal fibroblasts (hPF).

METHODS

Alveolar bone and cementum obtained from clinically healthy subjects were extracted by a solution containing 0.5 M acetic acid and enzyme inhibitors. Osteoblastic phenotypes of hPF were assayed by ALPase activity, gene expression of bone marker proteins, and the ability to produce in vitro mineralization in culture media containing 50 microg/ml ascorbic acid, 10 mM sodium beta-glycerophosphate, and 10(-7) M dexamethasone. The effects of cementum and bone extracts on the expression of osteoblastic phenotypes in hPF were also determined.

RESULTS

Many protein components, varying in molecular weight from 10 to 14 to 120 kDa, were detectable in 10% SDS-PAGE of both cementum and alveolar bone extracts. The hPF cells were found to exhibit a moderate ALPase activity when compared with rat osteosarcoma (ROS) 17/2.8 cells under the same experimental conditions. Gene expression for ALPase, osteocalcin bone sialoprotein, osteopontin, and BMP-7 at mRNA message was detected by RT-PCR in hPF and ROS 17/2.8 cells. The confluent hPF and ROS 17/2.8 cells showed evidence of calcium deposition in the extracellular milieu at 30 and 15 to 30 days' cultures, respectively, under a mineralization medium. The hPF appeared to form mineralized foci with morphological characteristics different from the mineralized nodules produced by ROS 17/2.8 cells. The addition of low concentrations (5 microg/ml) of either cementum or bone extract produced an increase in the size and number of mineralization spots, as well as greater ALPase activity in both hPF and ROS 17/2.8 cultures during the observation periods.

CONCLUSIONS

These results suggest that hPF possess certain mineralizing phenotypes, and that acetic acid extracts of bone and cementum contain components capable of stimulating osteogenic differentiation of hPF.

Biological activity of rhBMP-2 released from PLGA microspheres

Human recombinant bone morphogenetic protein-2 (rhBMP-2) has been proven effective in stimulating the regeneration of bone in both skeletal and extraskeletal locations. Through encapsulation within, and release from, biodegradable poly(DL-lactic-co-glycolic acid) (PLGA) microspheres, a proven vehicle for sustained delivery of various proteins, the local concentrations of rhBMP-2 could be maintained at optimal levels to stimulate bone regeneration and remodeling at the site of healing in diverse clinical settings. Thus the purpose of this work was to investigate the encapsulation of rhBMP-2 in PLGA microspheres and its biologic activity upon release. Using in vitro tests in simulated body fluids, the effect of rhBMP-2 released from PLGA microspheres upon osteoblast cell cultures was found to be statistically similar to the effect produced by positive controls consisting of nonencapsulated aqueous rhBMP-2 in simulated body fluids. This clarifies an important step in skeletal tissue engineering strategies aimed at the use of encapsulated rhBMP-2 to stimulate bone regeneration and remodeling.

BMP receptors in limb and tooth formation

Members of the TGF-beta superfamily signal through receptor complexes comprised of type I and type II receptors. These receptors, which are serine/threonine kinases, form two new classes of transmembrane receptor kinases. The activity of both of the kinases is necessary for signal transduction in response to ligand binding. Bone morphogenetic proteins (BMPs), which are members of the TGF-beta superfamily, bind to multiple type I and type II receptors. There is growing evidence to support the hypothesis that the BMP receptors are differentially regulated during development and that they have both unique and overlapping functions. Thus, the nature and distribution of the BMP receptors, which are reviewed here in the context of the development of limbs and teeth, appear to be critical in the control of the diverse activities of BMPs.

Current and potential pulp therapies for primary and young permanent teeth

OBJECTIVES

This paper aims to alert the dental practitioner to the rapidly evolving therapies for treating the pulps of primary and young permanent teeth.

DATA SOURCES

Experimental research on animals, clinical studies and case reports.

STUDY SELECTION

Indirect pulp capping, direct pulp capping, pulpotomies, and pulpectomies are standard procedures for treating primary teeth. However, direct pulp capping, heretofore not very successful, is being revisited. Based on studies in animals and clinical findings in humans, there has been a movement in pediatric dentistry to find alternatives to formocresol and calcium hydroxide for pulpotomy therapy. Venues range from eradication by cautery to the possibility of healing with growth factors. New studies with iodoform paste for pulpectomies are confirming the success rates of previous publications. The new dental adhesives are being tested as agents for direct pulp capping, as well as partial and complete pulpotomy protocols.

CONCLUSIONS

More thought is being given by clinicians to preserving pulp, either through more ambitious indirect pulp therapy or partial pulpotomy. Formocresol and calcium hydroxide pulpotomies, while still popular, may soon be challenged by other chemical treatments, electrocautery or stimulation of reparative dentine by growth factors. Iodoform pastes are promising easier and more successful pulpectomy therapy. Total etch direct bonding materials could soon transform direct pulp capping, as well as partial and complete pulpotomy protocols.

Role of intramarrow penetration in osseous repair: a pilot study in the rabbit calvaria

BACKGROUND

The use of intramarrow penetration in combination with osseous reconstructive surgery has been recommended in various periodontal and oral surgical applications. The purpose of this pilot study was to evaluate the effect of intramarrow penetration on the rate of bone neogenesis in protected spaces created on the calvarial bone using occlusive titanium domes in 16 adult white rabbits.

METHODS

In each rabbit, 2 standardized circular 1 mm deep slits were prepared in the bone, one on each side of the midline using a trephine. Within the perimeter of one of the slits, the external cortical surface of the skull bone was mechanically perforated using a carbide round bur (experimental site), while the bone surface within the other slit (control site) was left intact. Subsequently, 2 prefabricated titanium domes with an inner diameter of 4.8 mm and an inner height of 3.0 mm were anchored in the prepared slits. The animals were divided into 4 groups of 4 rabbits each and were sacrificed at 10, 21, 42, and 60 days. The specimens were assessed for the percentage bone fill and density of the newly formed bone within the boundaries of the domes.

RESULTS

Histomorphometric analysis showed significantly increased bone neogenesis within the experimental domes at 10, 21, 42, and 60 days. A mean total area of 29% newly formed bone was demonstrated in the experimental sites at 21 days, while negligible bone formation (9%) occurred with the control domes at the same evaluation interval. Bone density was consistently higher in experimental domes at all healing intervals.

CONCLUSIONS

Within the limits of this study, the results demonstrate that intramarrow penetration accelerates initial bone neogenesis and results in increased bone fill and density, suggesting that its use can be beneficial in bone regenerative procedures.

Growth factors regulate expression of osteoblast-associated genes

BACKGROUND

The goal of periodontal regenerative therapies is to reconstruct periodontal tissues such as bone, cementum, and periodontal ligament cells (PDL). The need to establish predictable treatment modalities is important for reconstruction of these tissues. The aim of this study was to determine the effects of a low molecular extract of bovine bone protein (BP) containing bone morphogenetic proteins (BMPs) 2, 3, 4, 6, 7, 12, and 13, alone or in combination with platelet-derived growth factor (PDGF) and/or insulin-like growth factor (IGF) on osteoblast differentiation in vitro.

METHODS

BP, mixed with a collagen matrix, was added to a poly (DL-lactide-co-glycolide) polymer (PLG) and placed at orthotopic sites in the skullcaps of Sprague-Dawleys rats. At day 28, rats were sacrificed for histological analysis. All sites treated with the polymer/BP produced bone while control sites (without BP) showed no bone formation. Having established the biological activity of BP, in vitro studies were initiated using MC3T3-E1 cells, a mouse osteoprogenitor cell line. The ability of BP and other growth factors to alter cell proliferation was determined by Coulter counter, and differentiation was determined by Northern analysis for specific genes.

RESULTS

When compared with cells treated with 2% serum alone, PDGF enhanced cell numbers at 10 and 20 ng/ml; IGF produced no significant effect at these doses; and BP at 10 and 20 microg/ml decreased cell proliferation. Northern analysis revealed that PDGF blocked gene expression of osteopontin (OPN) and osteocalcin (OCN), while BP and IGF promoted gene expression of bone sialoprotein (BSP) and OPN. The combination of BP and IGF enhanced expression of OPN beyond that of either BP or IGF alone. PDGF was able to block the effects of IGF on gene expression, but not those of BP.

CONCLUSIONS

These results indicate that BP, PDGF, and IGF influence cell activity differently, and thus raise the possibility that combining factors may enhance the biological activity of cells.

Biological mediators for periodontal regeneration

A review of the literature on the use of growth-regulatory molecules in the oral cavity permits a model in which to consider approaches to oral tissue engineering. These concepts apply to periodontal regeneration and to regeneration of alveolar bone. In either case, the formation of tissues is complex but proceeds in a deliberate and orderly sequence. In these sequence of events resulting in either bone or cementum formation, periodontal ligament and bone can be stimulated at various points. Different signals can apparently be used to stimulate tissue formation including mitogenic signals and differentiation factors. Additionally, both hard and soft tissue stimulatory molecules appear to be permissive. Classic receptor-mediated peptides or extracellular matrix molecules for soft and hard tissues appear to allow stimulation of tissue formation cascades. Importantly, it also appears that the stimulatory event is transitory (that is, short-lived) and leads itself to a sequence of cellular events. These cellular events in turn stimulate a number of subsequent events (such as chemotaxis, proliferation, differentiation or angiogenesis), which lead to further progression of tissue formation. While a solid scientific rationale exists for the use of a variety of growth and attachment factors in regeneration of oral tissues, only a small number are being pursued clinically. Many therapeutic regimens have failed in preclinical testing or have resulted in limited regenerative capacity. The mitogenic polypeptides that stimulate soft tissue growth (such as platelet-derived growth factor) and both hard and soft tissue growth (such as transforming growth factor-beta) appear to have not led to successful enough outcomes to facilitate further work towards regulatory approval. The demonstrated ability of bone morphogenetic proteins to generate substantial quantities of bone suggest many applications in the oral cavity where this is the only tissue desired. Another therapeutic candidate is enamel matrix derivative, a set of matrix proteins. Enamel matrix derivative appears to stimulate first acellular cementum formation, which may allow for functional periodontal ligament formation. It will be of interest in the future to determine whether the protein matrix contains classic mitogenic or differentiation factors as well as the amelogenins. It is also evident that the bone morphogenetic proteins permit periodontal ligament formation. The conditions for stimulating predictable periodontal ligament tissues with bone morphogenetic proteins however are not known. It is clear that the bone morphogenetic proteins are excellent molecules for stimulating oral bone formation. The results of all these studies will determine the future therapeutic potential for these growth molecules such that they may be used to optimally stimulate and direct specific points along tissue formation cascades.

Progress toward understanding craniofacial malformations

Significant advances in the study of the human face have revealed the genetic and gene-environment bases of numerous common and rare craniofacial disorders. Classification of craniofacial malformations based on clinical phenotypes is sometimes quite different from the genetic findings of patients. Different mutations in a single gene can cause distinct syndromes, and mutations in different genes can cause the same syndrome. The extracellular signaling molecule SHH, fibroblast growth factor receptors, and transcription factors GLI3, MSX2, and TWIST are discussed as examples of molecules involved in interrelated signal transduction networks regulating craniofacial development. Progress in the understanding of normal and abnormal craniofacial development, through the study of morphoregulatory signaling pathways, has benefited from multifactorial approaches recommended 40 years ago at the National Institute of Dental Research-sponsored landmark Gatlinburg Conference. The utilization of biochemistry, protein structure analyses, tissue culture, and animal model systems for developmental genetics has resulted in remarkable scientific advances. The evolutionary conservation of morphoregulatory pathways has revealed the homology of genes associated with human craniofacial malformations and their counterparts that regulate the morphogenesis of fruit flies. The continued investments in basic, translational, and patient-oriented research regarding normal and abnormal craniofacial development will translate into substantial improvements in the prevention, diagnosis, and treatment of craniofacial diseases and disorders.