no abstract available

Purpose: Successful repair and regeneration in bone tissue engineering vastly depends on proper interaction between the tissue-engineered construct and the recipient's immune system. In clinical application, adverse responses to bioartificial implants may result in chronic inflammation and loss of the implant. It is known that prolonged inflammation linked to NF-κB inflammatory pathways inhibits bone-forming activity of osteoblast cells. Contributing to orchestrate inflammatory processes, the ligand-activated transcription factor peroxisome proliferator-activated receptor alpha (PPARα) holds inhibitory effects on NF-κB and CEBß activity. Sp1, a widely expressed transcription factor, has been linked to PPAR pathways, cellular homeostasis, and responsiveness to environmental perturbation. Formerly not being characterized, the role of PPARα in inflammatory-mediated bone loss requires further investigation. The aim of the present study was to identify regulatory transcription factor binding sites (TFBS) on the PPAR alpha promoter and to assess the role of Sp1 and associated proteins in its regulation.
Materials and Methods: In a first set of experiments, polymerase chain reaction assessed the presence of PPARα gene expression in isolated murine bone tissue. Deletion mutagenesis was performed on the human PPARα (hPPARα) promoter gene, and the deletion constructs were transiently transfected to murine osteoblasts to identify important TFBS. PPARα promoter-driven reporter gene expression was monitored in response to overexpression and repression of Sp1 to analyze functional transcription factor recruitment to the PPARα promoter.
Results: This study could demonstrate that the full-length hPPARα promoter contains inhibiting promoter regions and that hPPARα basal expression can be significantly increased by deletion mutagensis. Sp1 TFBS proved functional in the regulation of PPARα promoter activity, and the first five Sp1 motifs on the PPARα promoter were sufficient to significantly increase PPARα expression. Additional transient co-transfection experiments could not detect any direct effect of NF-κB/IκB downstream pathway on the regulation of PPARα promoter activity. Taken together, we could demonstrate that Sp1 plays a key role in transcriptional regulation of PPARα promoter activity and gene expression.
Conclusion: This study provides further insight on Sp1-dependent PPARα regulatory mechanisms and suggests that Sp1-regulated PPARα expression plays a key role in inflammatory mediated bone loss.

Keywords: bone tissue engineering, inflammation, NF-κB, PPARα, osteoblast, Sp1

Purpose: The objective of this study was to establish a method for accurate cell counting from matrix-rich cell sheets in the clinical setting.
Materials and Methods: Human periodontal ligament (HPDL) cells were obtained from healthy donors to prepare PDL cell sheets. To obtain single cell suspensions, the cell sheets were treated with three different enzymatic formulations: collagenase alone, trypsin-ethylenediaminetetraacetic acid (EDTA) alone, and a combination of collagenase and trypsin-EDTA. After cell dispersion, cell numbers and cell survival rates were measured. To evaluate damage to the cell surfaces from the enzymes, the dispersed cells were analyzed by a flow cytometer with an anti-alkaline phosphatase antibody.
Results: Treatment with collagenase alone or trypsin-EDTA alone dispersed few cells from HPDL cell sheets. In contrast, combined treatment with collagenase and trypsin-EDTA successfully produced a large amount of single cells from cell sheets. Flow cytometry analysis showed that single cells obtained by combined use of collagenase and trypsin-EDTA preserved alkaline phosphatase epitopes on the cell surfaces.
Conclusions: Cell sheets rich with extracellular matrix were dispersed via combined treatment with collagenase and trypsin-EDTA without destroying the expression of cell surface markers. The results suggest that this method would be useful for determining the accurate cell number of cell sheets for cell therapies and should also be applicable for other kinds of matrix-rich cell sheets.

Keywords: cell sheet, collagenase, extracellular matrix, human periodontal ligament cells, trypsin-ethylenediaminetetraacetic acid

Purpose: To determine whether a collagen scaffold could provide an environment for mesenchymal stem cell (MSC)-related bone repair of critical-size bone defects in rat calvaria.
Materials and Methods: Craniotomy defects were created in 28 adult Sprague-Dawley rats. Two additional rats were used as MSC donors by means of femoral bone marrow lavage and culture. The rats were randomly divided into four groups: (1) empty/no graft; (2) collagen scaffold (matrix) + saline; (3) matrix + MSCs; (4) matrix + bone morphogenetic protein. The animals were euthanized 28 days after surgery. Microcomputed tomographic reconstructions were obtained to measure bone fill. The specimens were processed for histologic examination, and the total defect and bone fill areas were measured.
Results: Mean bone fill (± standard deviation) of 9.25% ± 10.82%, 19.07% ± 17.38%, 44.21% ± 3.93%, and 66.06% ± 15.08%, respectively, was observed for the four groups; the differences were statistically significant. Bone repair was statistically significant for groups 3 and 4. No significant difference was seen for bone repair between groups 1 and 2 or between groups 3 and 4. Bone formation differed significantly across the four groups. Statistically significant changes in radiodensity were observed between groups 1 and 3, groups 1 and 4, and groups 2 and 4. Significant differences were not observed between groups 1 and 2, groups 2 and 3, or groups 3 and 4.
Conclusion: After grafting of adult MSCs adherent within a collagen matrix, repair of bone was significant. Expanded three-dimensional collagen represents a radiolucent, resorbable, biocompatible scaffold that is capable of supporting MSC repair of bone.

Keywords: adult mesenchymal stem cell, bone repair, collagen matrix, osteogenesis, rat calvaria model, tissue engineering

Paranasal bone affects the decision-making process for placement of implants for immediate function in the highly resorbed maxilla. The most important bone for apical fixation of implants in this setting is the lateral nasal bone mass. Maximum available bone mass found at the pyriform above the nasal fossa, designated M point, can most often engage two implants placed at 30-degree angles. The second most important area of paranasal bone mass is the subnasal bone of the premaxilla, which is required to engage an angled implant at the alveolar crest. However, only 4 to 5 mm in height is needed when implants are angled posterior to engage M point. The third most important paranasal bone site for implant fixation is the midline nasal crest extending upward to the vomer. This site, which is usually type 1/2 bone, can engage implants apically and provide enough fixation for immediate function even if implants are short. These anatomical bone sites enable placement of implants to obtain a 12- to 15-mm anterior-posterior spread, which is favorable for immediate function.

Keywords: anterior-posterior spread, immediate function, M-4, M point, pyriform rim, V point, vomer/nasal crest, zygomatic implants

Purpose: To present a retrospective report of eight significant alveolar defects in which the alveolus was regenerated with recombinant human bone morphogenetic protein 2 (rhBMP-2) combined with anorganic bovine bone and contoured using titanium mesh to facilitate implantsupported restorations.
Materials and Methods: A total of seven patients underwent extractions and debridement of the compromised alveolar sites with simultaneous grafting using a mixture of rhBMP-2 and anorganic bovine bone. The three-dimensional contour of the compromised alveolus was reestablished using titanium mesh with rigid screw fixation. Implants were placed a minimum of 6 months after healing and subsequently were restored.
Results: The treated defects were successfully regenerated and did not require any additional surgery prior to implant placement or prosthetic restoration. A total of 14 implants were placed and restored with fixed single or multiple restorations. Thirteen of the 23 treated sites were in the anterior esthetic zone.
Conclusion: Vertical and horizontal alveolar bone defects can be predictably regenerated by grafting with a combination of rhBMP-2 and anorganic bovine bone contained by titanium mesh to successfully accommodate implant placement.

Keywords: bone grafting, bone regeneration, rhBMP-2, titanium mesh

Purpose: Different forms of dentin, including untreated, undemineralized, demineralized, boiled, or mixed with other materials, have been evaluated for efficacy as bone substitutes. However, the effects of application of liquid nitrogen-treated dentin for bone grafting remain unknown. The objective of this study was to chronologically evaluate bone healing following grafting with liquid nitrogen-treated dentin in a rabbit model.
Materials and Methods: Autogenous dentin treated with liquid nitrogen at -196°C for 20 minutes was used. In 16 New Zealand White rabbits, a bone defect (5 mm in diameter) was created in each femur and randomly grafted with either autogenous dentin (experimental group) or autogenous bone grafts (positive control). In another four rabbits (negative control), a similar defect in each femur was left empty. The rabbits were sacrificed at 2, 4, 8, and 12 weeks. Explants of grafted sites were harvested for histologic and histomorphometric analysis.
Results: At 2 and 4 weeks in both the experimental and positive control groups, accelerated formation of new bone was observed, which was undergoing remodeling at 8 and 12 weeks. The mean new bone score was higher in the experimental than in the negative control groups, but this was not statistically significant.
Conclusion: The present results demonstrated that liquid nitrogen-treated autogenous dentin has both osteoconductive and osteoinductive properties and therefore has potential as a bone substitute.

Keywords: autogenous bone graft, autogenous dentin graft, bone regeneration, bone substitute, liquid nitrogen

This paper presents the results of a structured review of the literature concerning in vitro molecular assessment of osseointegration at the level of cell-surface topography interactions. A search of the electronic databases was performed up to and including November 2010, with 320 articles meeting the inclusion criteria. Characteristics of the included in vitro reports were model systems used, genes examined, techniques used for molecular assessment of the osseointegration process, and wide gene expression profiling studies. There exists a growing body of in vitro evidence to support a role for surface topography in the direct influence of cellular phenotypes as related to the process of osseointegration. Most recently, functional or mechanistic studies have provided evidence that particular topographic cues can be specifically integrated among the many extracellular signals received by the cell in its signal transduction network. Such investigations begin to define linkages between the character of the implant surface and adherent cellular responses, including cells from extravasated blood (eg, platelets) and of the immune system (eg, monocytes). In vitro studies involving cell culture on endosseous implant-related biomaterials offer important and beneficial insight into the clinical control of the implant-bone interface.

Keywords: cell culture, gene profiling, molecular regulation, osseointegration

no abstract available

no abstract available