Histology of human alveolar bone regeneration with a porous tricalcium phosphate. A report of two cases

A tissue engineered 3D printed calcium alkali phosphate bioceramic bone graft enables vascularization and regeneration of critical-size discontinuity bony defects in vivo

Introduction: Recently, efforts towards the development of patient-specific 3D printed scaffolds for bone tissue engineering from bioactive ceramics have continuously intensified. For reconstruction of segmental defects after subtotal mandibulectomy a suitable tissue engineered bioceramic bone graft needs to be endowed with homogenously distributed osteoblasts in order to mimic the advantageous features of vascularized autologous fibula grafts, which represent the standard of care, contain osteogenic cells and are transplanted with the respective blood vessel. Consequently, inducing vascularization early on is pivotal for bone tissue engineering. The current study explored an advanced bone tissue engineering approach combining an advanced 3D printing technique for bioactive resorbable ceramic scaffolds with a perfusion cell culture technique for pre-colonization with mesenchymal stem cells, and with an intrinsic angiogenesis technique for regenerating critical size, segmental discontinuity defects in vivo applying a rat model. To this end, the effect of differing Si-CAOP (silica containing calcium alkali orthophosphate) scaffold microarchitecture arising from 3D powder bed printing (RP) or the Schwarzwalder Somers (SSM) replica fabrication technique on vascularization and bone regeneration was analyzed in vivo. In 80 rats 6-mm segmental discontinuity defects were created in the left femur. Methods: Embryonic mesenchymal stem cells were cultured on RP and SSM scaffolds for 7d under perfusion to create Si-CAOP grafts with terminally differentiated osteoblasts and mineralizing bone matrix. These scaffolds were implanted into the segmental defects in combination with an arteriovenous bundle (AVB). Native scaffolds without cells or AVB served as controls. After 3 and 6 months, femurs were processed for angio-µCT or hard tissue histology, histomorphometric and immunohistochemical analysis of angiogenic and osteogenic marker expression. Results: At 3 and 6 months, defects reconstructed with RP scaffolds, cells and AVB displayed a statistically significant higher bone area fraction, blood vessel volume%, blood vessel surface/volume, blood vessel thickness, density and linear density than defects treated with the other scaffold configurations. Discussion: Taken together, this study demonstrated that the AVB technique is well suited for inducing adequate vascularization of the tissue engineered scaffold graft in segmental defects after 3 and 6 months, and that our tissue engineering approach employing 3D powder bed printed scaffolds facilitated segmental defect repair.

Appropriate pore size for bone formation potential of porous collagen type I-based recombinant peptide

Introduction

In this study, we developed porous medium cross-linked recombinant collagen peptide (mRCP) with two different ranges of interconnected pore sizes, Small-mRCP (S-mRCP) with a range of 100–300 μm and Large-mRCP (L-mRCP) with a range of 200–500 μm, to compare the effect of pore size on bone regeneration in a calvarial bone defect.

Methods

Calvarial bone defects were created in Sprague–Dawley rats through a surgical procedure. The rats were divided into 2 groups: S-mRCP implanted group and L-mRCP implanted group. The newly formed bone volume and bone mineral density (BMD) was evaluated by micro-computed tomography (micro-CT) immediately after implantation and at 1, 2, 3, and 4 weeks after implantation. In addition, histological analyses were carried out with hematoxylin and eosin (H&E) staining at 4 weeks after implantation to measure the newly formed bone area between each group in the entire defect, as well as the central side, the two peripheral sides (right and left), the periosteal (top) side and the dura matter (bottom) side of the defect.

Results

Micro-CT analysis showed no significant differences in the amount of bone volume between the S-mRCP and L-mRCP implanted groups at 1, 2, 3 and 4 weeks after implantation. BMD was equivalent to that of the adjacent native calvaria bone at 4 weeks after implantation. H&E images showed that the newly formed bone area in the entire defect was significantly larger in the S-mRCP implanted group than in the L-mRCP implanted group. Furthermore, the amount of newly formed bone area in all sides of the defect was significantly more in the S-mRCP implanted group than in the L-mRCP implanted group.

Conclusion

These results indicate that the smaller pore size range of 100–300 μm is appropriate for mRCP in bone regeneration.

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This study confirmed the regenerative potential of mRCP as novel bone substitute.

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mRCP with 2 different interconnected pores sizes have been developed.

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The smaller pore size range of 100–300 μm was optimal for calvarial bone regeneration.

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The slower absorption rate of smaller pore size mRCP influenced its effectiveness.

Chemical Properties of Human Dentin Blocks and Vertical Augmentation by Ultrasonically Demineralized Dentin Matrix Blocks on Scratched Skull without Periosteum of Adult-Aged Rats

Vertical augmentation is one of the most challenging techniques in bone engineering. Several parameters, such mechano-chemical characteristics, are important to optimize vertical bone regeneration using biomaterials. The aims of this study were to chemically characterize human dentin blocks (calcified demineralized dentin matrix: CDM, partially demineralized dentin matrix: PDDM and completely demineralized dentin matrix: CDDM) (2 × 2 × 1 mm³) chemically and evaluate the behavior of PDDM blocks on non-scratched or scratched skulls without periosteum of adult rats (10–12 months old, female) as a vertical augmentation model. The dissolved efficiency of CDM showed 32.3% after ultrasonic demineralization in 1.0 L of 2% HNO₃ for 30 min. The 30 min-demineralized dentin was named PDDM. The SEM images of PDDM showed the opening of dentinal tubes, nano-microcracks and the smooth surface. In the collagenase digestion test, the weight-decreasing rates of CDM, PDDM and CDDM were 9.2%, 25.5% and 78.3% at 12 weeks, respectively. CDM inhibited the collagenase digestion, compared with PDDM and CDDM. In the PDDM onlay graft on an ultrasonically scratched skull, the bone marrow-space opening from original bone was found in the bony bridge formation between the human PDDM block and dense skull of adult senior rats at 4 and 8 weeks. On the other hand, in the cases of the marrow-space closing in both non-scratched skulls and scratched skulls, the bony bridge was not formed. The results indicated that the ultrasonic scratching into the compact parietal bone might contribute greatly to the marrow-space opening from skull and the supply of marrow cells, and then bony bridge formation could occur in the vertical augmentation model without a periosteum.

Accelerated Bone Induction of Adult Rat Compact Bone Plate Scratched by Ultrasonic Scaler Using Acidic Electrolyzed Water

Fresh compact bone, the candidate graft material for bone regeneration, is usually grafted for horizontal bone augmentation. However, the dense calcified structure inhibits the release of growth factors and limits cellular and vascular perfusion. We aimed to create mechano-chemically altered dense skull bone by ultrasonic treatment, along with partial demineralization using commercially available acidic electrolyzed water (AEW). The parietal skull bone of an 11-month-old Wistar rat was exposed and continuously treated with a piezoelectric ultrasonic scaler tip for 1 min, using AEW (pH 2.3) or distilled water (DW, pH 5.6) as irrigants. Treated parietal bone was removed, cut into plates (5 × 5 × 1 mm³), grafted into the back subcutaneous tissues of syngeneic rats, and explanted at 1, 2, and 3 weeks. AEW bone showed an irregular surface, deep nano-microcracks, and decalcified areas. SEM-EDS revealed small amounts of residual calcium content in the AEW bone (0.03%) compared to the DW bone (0.86%). In the animal assay, the AEW bone induced bone at 2 weeks. Histomorphometric analysis showed that the area of new bone in the AEW bone at 2 and 3 weeks was significantly larger. This new combination technique of AEW-demineralization with ultrasonic treatment will improve the surface area and three-dimensional (3D) architecture of dense bone and accelerate new bone synthesis.

Bio-Absorption of Human Dentin-Derived Biomaterial in Sheep Critical-Size Iliac Defects

The aim of this study was to evaluate the bio-absorption and bone regeneration of human tooth-derived dentin scaffold, entitled as perforated root-demineralized dentin matrix (PR-DDM), after in vivo implantation into the critical-size iliac defects. The dentin scaffolds were prepared from human vital, non-functional teeth. Thirty artificial macro-pores (Ø 1 mm) were added after removing the enamel portion. The modified teeth were supersonically demineralized in 0.34 N HNO₃ for 30 min. The microstructure was observed by scanning electron microscope (SEM). The 3D micro-CT and histological analysis were carried out to evaluate the bio-absorption of PR-DDM at 2 and 4 months. A smooth dentin collagen surface with symmetrical macro-pores and tube-type dentinal tubules (Ø 1–2 µm) with micro-cracks were observed on the perforated region. A significant number of custom-made macro-pores disappeared, and the size of the macro-pores became significantly wider at 4 months compared with the 2 months (p < 0.05) evaluated by 3D micro-CT. Histological images revealed the presence of multinucleated giant cells attached to the scalloped border of the PR-DDM. The morphological changes due to bio-absorption by the cellular phagocytes were comparable to the 3D micro-CT and histological images at 2 and 4 months. Altogether, the results demonstrated that the PR-DDM block was gradually absorbed by multinucleated giant cells and regenerated bone. Human PR-DDM might serve as a unique scaffold for extraoral bone regeneration.

Bone formation potential of collagen type I-based recombinant peptide particles in rat calvaria defects

Introduction

This study aimed to examine the bone-forming ability of medium-cross-linked recombinant collagen peptide (mRCP) particles developedbased on human collagen type I, contains an arginyl-glycyl-aspartic acid-rich motif, fabricated as bone filling material, compared to that of the autologous bone graft.

Methods

Calvarial bone defects were created in immunodeficient rats though a surgical procedure. The rats were divided into 2 groups: mRCP graft and tibia bone graft (bone graft). The bone formation potential of mRCP was evaluated by micro-computed tomography and hematoxylin-eosin staining at 1, 2, 3, and 4 weeks after surgery, and the data were analyzed and compared to those of the bone graft.

Results

The axial volume-rendered images demonstrated considerable bony bridging with the mRCP graft, but there was no significant difference in the bone volume and bone mineral density between the mRCP graft and bone graft at 4 weeks. The peripheral new bone density was significantly higher than the central new bone density and the bottom side score was significantly higher than the top side score at early stage in the regenerated bone within the bone defects.

Conclusion

These results indicate that mRCP has a high potential of recruiting osteogenic cells, comparable to that of autologous bone chips.

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Bone formation potential of mRCP were comparable to that of autogenous bone.

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mRCP particles exhibit high new bone formation potential in the calvaria defect.

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Bone bridging was observed over the entire defect in mRCP graft at 4 weeks.

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mRCP has a high potential of recruiting osteogenic cells comparable to bone graft.

Biomaterials preparation by electrospinning of gelatin and sodium hyaluronate/gelatin nanofibers with non-toxic solvents

Gelatin (Ge) based fibers have been produced by electrospinning with a non-toxic solvent for preparing membranes usable in maxillofacial surgery. Ge and Ge/sodium hyaluronate (SH) nanofibers were successfully electrospun to produce membranes whose thickness was around 150 to 200μm. The mean fiber diameter reached a maximum of 660nm for Ge fibers and 210nm for Ge/SH fibers. The presence of Ge and SH was confirmed in the membranes by Raman spectroscopy. Ge membranes had low mechanical properties and only small samples of 0.5cm in size could be retrieved from the collector as larger sample tended to tear and break. Ge/SH membranes could be retrieved from the collector slightly easily. Membranes could be handled carefully but in vivo implantation could not be planned due to poor mechanical resistance. Crosslinking by glutaraldehyde vapors reduced the mean porosity of Ge membranes; it totally prevents membranes to be retrieved from the collector. Beta tricalcium phosphate (β-TCP) particles were added with Ge during electrospinning to increase osseointegration of the membranes and promote bone formation. β-TCP particles formed agglomerates outside the fibers, and we could not obtain β-TCP particles inside the Ge fibers due to their low diameter. In general, electrospun membranes lacked reproducibility. Despite the great interest of Ge-based membranes and Ge/β-TCP membranes, the low mechanical properties of the fibers, the lack of reproducibility and the difficulty to retrieve the membranes from the collector did not allow our biomaterials to be implanted or to be envisaged for industrial production.

3D Printing of Bioceramics for Bone Tissue Engineering

Bioceramics have frequent use in functional restoration of hard tissues to improve human well-being. Additive manufacturing (AM) also known as 3D printing is an innovative material processing technique extensively applied to produce bioceramic parts or scaffolds in a layered perspicacious manner. Moreover, the applications of additive manufacturing in bioceramics have the capability to reliably fabricate the commercialized scaffolds tailored for practical clinical applications, and the potential to survive in the new era of effective hard tissue fabrication. The similarity of the materials with human bone histomorphometry makes them conducive to use in hard tissue engineering scheme. The key objective of this manuscript is to explore the applications of bioceramics-based AM in bone tissue engineering. Furthermore, the article comprehensively and categorically summarizes some novel bioceramics based AM techniques for the restoration of bones. At prior stages of this article, different ceramics processing AM techniques have been categorized, subsequently, processing of frequently used materials for bone implants and complexities associated with these materials have been elaborated. At the end, some novel applications of bioceramics in orthopedic implants and some future directions are also highlighted to explore it further. This review article will help the new researchers to understand the basic mechanism and current challenges in neophyte techniques and the applications of bioceramics in the orthopedic prosthesis.

Rat Palatine Fissure: A Suitable Experimental Model for Evaluating Bone Regeneration

IMPACT STATEMENT

The rat palatine fissure is anatomically similar to human alveolar cleft. In this study, we examined potential bone repair by an autologous bone implant and beta-tricalcium phosphate (β-TCP) using rat palatine fissure as a model. Autologous bone chips or β-TCP granules were implanted into the rat palatine fissure. Our model demonstrated that higher bone volume and bone mineral density were achieved with autologous bone graft than with β-TCP. We have provided the first demonstration of the suitability of the rat palatine fissure as the implant site to simulate the transplantation of bone graft materials into human alveolar cleft.

Treatment of Critical-Sized Calvarial Defects in Rats with Preimplanted Transplants

The local environment and the defect features have made the skull one of the most difficult regions to repair. Finding alternative strategies to repair large cranial defects, thereby avoiding the current limitations of autograft or polymeric and ceramic prostheses constitute an unmet need. In this study, the regeneration of an 8 mm critical-sized calvarial defect treated by autograft or by a monetite scaffold directly placed in the defect or preimplanted (either cranial bone transplant or subcutaneous pocket) and then transplanted within the bone defect is compared. The data reveal that transplantation of preimplanted monetite transplant scaffolds greatly improves the skull vault closure compared to subcutaneously preimplanted or directly placed materials. Autografts, while clearly filling the defect volume with bone appear effective since bone volume inside the defect volume is obviously high, but are not well fused to the skull. The preimplantation site has a large influence on the regeneration of the defect. Transplantation of induced bone inside materials has the potential to reduce the need for autograft harvest without damaging the skeleton. This first demonstration indicates that cranial repair may be possible without recourse to bioactives or cultured cell therapies.

Biomaterial selection for bone augmentation in implant dentistry: A systematic review

In the present study, a systematic review was conducted to evaluate the biomaterials and their effectiveness for bone augmentation in implant dentistry. The databases of Cochrane Library, Google Scholar, PubMed (National Center for Biotechnology Information), and Scopus were searched for published studies between 2006 and March 30, 2018. We only included clinical studies in this research. Due to a lack of quantitative evidence and the vast heterogeneity of the biomaterials, implant surgery sites, implant types, follow-up periods, and various implant placement techniques (1-stage or 2-stage), we could not manage to do a meta-analysis on the 13 included studies. Several techniques can result in vertical bone augmentation. Complications can be seen in vertical bone augmentation and especially in the autogenous bone grafting; however, some biomaterials showed promising results to be practical substitutes for autogenous bone. Bio-Oss and beta-tricalcium phosphate are our second-level candidates for vertical bone augmentation due to their promising clinical results with the least infection and immunologic response risk. The gold standard, however, remains the autogenous bone graft. Further clinical studies in the future with exact report of bone measures are needed to develop new comparisons and quantitative analyses.

EZH1 Is Associated with TCP-Induced Bone Regeneration through Macrophage Polarization

Macrophages have been found to regulate the effects of biomaterials throughout the entire tissue repair process as an antigen-presenting cell. As a well-defined osteoconductive biomaterial for bone defect regeneration, tricalcium phosphate (TCP) has been found to facilitate a favourable osteoimmunomodulatory response that can shift macrophage polarization towards the M2 phenotype. In the present study, our group discovered that a histone methyltransferase enhancer of zeste1 (EZH1) was drastically downregulated in Thp1 cells stimulated by TCP, indicating that EZH1 may participate in the macrophage phenotype shifting. Furthermore, the NF-κB pathway in macrophages was significantly downregulated through stimulation of TCP, suggesting a potential interaction between EZH1 and the NF-κB pathway. Utilizing gene knock-down therapy in macrophages, it was found that depletion of EZH1 induced M2 macrophage polarization but did not downregulate NF-κB. When the NF-κB pathway was inhibited, the expression of EZH1 was significantly downregulated, suggesting that the inhibition of EZH1 may be regulated by the NF-κB pathway. These novel findings provide valuable insights into a potential gene target system that controls M2 macrophage polarization which ultimately favours a microenvironment suitable for bone repair.

Escherichia coli-derived BMP-2-absorbed β-TCP granules induce bone regeneration in rabbit critical-sized femoral segmental defects

PURPOSE

This study investigated whether Escherichia coli-derived bone morphogenetic protein (BMP)-2 (E-BMP-2) adsorbed onto β-tricalcium phosphate (β-TCP) granules can induce bone regeneration in critical-size femoral segmental defects in rabbits.

METHODS

Bone defects 20 mm in size and stabilized with an external fixator were created in the femur of New Zealand white rabbits, which were divided into BMP-2 and control groups. E-BMP-2-loaded β-TCP granules were implanted into defects of the BMP-2 group, whereas defects in the controls were implanted with β-TCP granules alone. At 12 and 24 weeks after surgery, radiographs were obtained of the femurs and histological and biomechanical assessments of the defect area were performed. Bone regeneration was quantified using micro-computed tomography at 24 weeks.

RESULTS

Radiographic and histologic analyses revealed bone regeneration in the BMP-2 group but not the control group; no fracturing of newly formed bone occurred when the external fixator was removed at 12 weeks. At 24 weeks, tissue mineral density, the ratio of bone volume to total volume, and volumetric bone mineral density of the callus were higher in the BMP-2 group than in control animals. In the former, ultimate stress, extrinsic stiffness, and failure energy measurements for the femurs were higher at 24 weeks than at 12 weeks.

CONCLUSION

E-BMP-2-loaded β-TCP granules can effectively promote bone regeneration in long bone defects.

Periodontal regenerative management of residual tunnel osseous defect results from the enucleation of lateral periodontal cyst in anterior maxilla: A rare case report

The lateral periodontal cyst (LPC) is a nonkeratinized, noninflammatory developmental cyst occurring adjacent or lateral to tooth root. It is a relatively uncommon lesion found in the maxillary incisors and found mostly in adults during 5^th to 7^th decades. In this case, 45-year-old male patient reported with occasional mild discomfort between left maxillary central and lateral incisor region since 1 year. Interproximally, a well-defined round radiolucent area with corticated borders was determined radiographically between vital tooth #21 and #22. Preliminary diagnosis of LPC was established based on clinical and radiographical findings. Following enucleation of the lesion, an anticipated residual tunnel osseous defect was observed, which was managed successfully utilizing bone graft and guided tissue regeneration-assisted technique. Cystic tissue removed was examined histologically; hematoxylin- and eosin-stained sections showed features suggestive of LPC. Complete healing of tunnel defect was achieved at 1 year follow-up.

Autologous Bone Marrow-Derived Mononuclear Cells Combined With β-TCP for Maxillary Bone Augmentation in Implantation Procedures

Replacing missing bone or adding mass to existing bone is often essential to the success of a dental implant. A large variety of graft materials have been used for maxillary and mandibular atrophy. To date there has been no graft material, which can be regarded as completely satisfactory. Our experience with freshly isolated autologous bone marrow-derived mononuclear cells combined with β-tricalcium phosphate for augmentation of the extremely atrophied maxilla is presented. These techniques are based on stimulation of natural events continuously present in living bone (ie, the process of bone remodeling). The property of the mixture material for bone augmentation to place dental implant was discussed.

Current bone substitutes for implant dentistry

PURPOSE

Alveolar ridge augmentation is essential for success in implant therapy and depends on the biological performance of bone graft materials. This literature review aims to comprehensively explain the clinically relevant capabilities and limitations of currently available bone substitutes for bone augmentation in light of biomaterial science.

STUDY SELECTION

The biological performance of calcium phosphate-based bone substitutes was categorized according to space-making capability, biocompatibility, bioabsorption, and volume maintenance over time. Each category was reviewed based on clinical studies, preclinical animal studies, and in vitro studies.

RESULTS

Currently available bone substitutes provide only osteoconduction as a scaffold but not osteoinduction. Particle size, sensitivity to enzymatic or chemical dissolution, and mechanical properties affect the space-making capability of bone substitutes. The nature of collagen fibers, particulate size, and release of calcium ions influence the biocompatibility of bone substitutes. Bioabsorption of bone substitutes is determined by water solubility (chemical composition) and acid resistance (integrity of apatite structure). Bioabsorption of remnant bone substitute material and volume maintenance of the augmented bone are inversely related.

CONCLUSION

It is necessary to improve the biocompatibility of currently available bone substitutes and to strike an appropriate balance between bioabsorption and volume maintenance to achieve ideal bone remodeling.

Filling bone defects with β-TCP in maxillofacial surgery: A review

Reconstruction of bone defects prior to implant placement now involves synthetic substitutes such as β-TCP because of its ability to promote bone remodeling. Its capacity to be progressively substituted by the patient's bone allows to regenerate a dense bone volume. In addition, its availability in large quantities, avoiding the morbidity observed with harvesting autogenous bone, widens the operative indications. In this paper, the main indications of β-TCP in maxillofacial surgery (dentistry, parodontology and dental implant surgery) are reviewed. They include periodontal bone disease, bone disjunction, pre-implant surgery (sinus floor elevation and lateralization of the inferior alveolar nerve).

Evaluation of perforated demineralized dentin scaffold on bone regeneration in critical-size sheep iliac defects

OBJECTIVES

Regenerating critical-size bone injury is a major problem that continues to inspire the design of new graft materials. Therefore, tissue engineering has become a novel approach for targeting bone regeneration applications. Human teeth are a rich source of stem cells, matrix, trace metal ions, and growth factors. A vital tooth-derived demineralized dentin matrix is acid-insoluble and composed of cross-linked collagen with growth factors. In this study, we recycled human non-functional tooth into a unique geometric dentin scaffold, entitled perforated root-demineralized dentin matrix (PR-DDM). The aim of this study was to evaluate the feasibility of PR-DDM as the scaffold for regenerating bone in critical-size iliac defects.

MATERIAL AND METHODS

Artificial macro-pores (1 mm in diameter) were added to human vital wisdom tooth after removing the enamel and pulp portions. The modified tooth was demineralized in 0.34 N HNO₃ for 30 min and is referred to as PR-DDM scaffold. Critical-size defect (10 mm × 15 mm × 9 mm Ø) was created in the iliac crest of six adult sheep. The in vivo bone regeneration by the scaffold was evaluated by micro-CT, 3D micro-CT, and histological examination at 2 and 4 months post-implantation.

RESULTS

PR-DDM exhibited better bone ingrowth, especially in the artificial macro-pores. The results of micro-CT and 3D micro-CT revealed good union between scaffold and native bone. New bone formation was observed in almost all portions of PR-DDM. Higher bone volume inside the scaffold was detected at 4 months compared with 2 months. New bone ingrowth was ankylosed with PR-DDM, and both osteoinduction and osteoconduction capability of PR-DDM were confirmed histologically. The ratio of new bone formation was higher at 4 months compared with 2 months by histomorphometric analysis.

CONCLUSIONS

Altogether, these results demonstrated that the human tooth-derived graft material with a unique geometric structure, PR-DDM, contributed to active bone ingrowth in critical-size bone defects. This novel scaffold may have great utility in the near-future clinical application.

Socket preservation by beta-tri-calcium phosphate with collagen compared to platelet-rich fibrin: A clinico-radiographic study

Objectives:

This study was primarily designed to determine the clinico-radiographic efficacy of platelet-rich fibrin (PRF) and beta-tri-calcium phosphate with collagen (β-TCP-Cl) in preserving extraction sockets.

Materials and Methods:

For Group I (PRF), residual sockets (n = 15) were filled with autologous PRF obtained from patients' blood; and for Group II (β-TCP-Cl), residual sockets (n = 15) were filled with β-TCP-Cl. For the sockets randomly selected for Group II (β-TCP-Cl), the reshaped Resorbable Tissue Replacement cone was inserted into the socket.

Results:

Clinically, there was a significantly greater decrease in relative socket depth, but apposition in midcrestal height in Group II (β-TCP-Cl) as compared to Group I (PRF), whereas more decrease in buccolingual width of Group I (PRF) than Group II (β-TCP-Cl) after 6 months. Radiographically, the mean difference in socket height, residual ridge, and width (coronal, middle, and apical third of socket) after 6 months was higher in Group I (PRF) as compared to Group II (β-TCP-Cl). The mean density (in Hounsfield Units) at coronal, middle, and apical third of socket was higher in Group I (PRF) as compared to Group II (β-TCP-Cl). There were statistically significant apposition and resorption for Group I (PRF) whereas nonsignificant resorption and significant apposition for Group II (β-TCP-Cl) in buccal and lingual/palatal cortical plate, respectively, at 6 months on computerized tomography scan.

Conclusion:

The use of either autologous PRF or β-TCP-Cl was effective in socket preservation. Results obtained from PRF were almost similar to β-TCP-Cl; therefore being autologous, nonimmune, cost-effective, easily procurable regenerative biomaterial, PRF proves to be an insight into the future biofuel for regeneration.

Bone substitutes for peri-implant defects of postextraction implants

Placement of implants in fresh sockets is an alternative to try to reduce physiological resorption of alveolar ridge after tooth extraction. This surgery can be used to preserve the bone architecture and also accelerate the restorative procedure. However, the diastasis observed between bone and implant may influence osseointegration. So, autogenous bone graft and/or biomaterials have been used to fill this gap. Considering the importance of bone repair for treatment with implants placed immediately after tooth extraction, this study aimed to present a literature review about biomaterials surrounding immediate dental implants. The search included 56 articles published from 1969 to 2012. The results were based on data analysis and discussion. It was observed that implant fixation immediately after extraction is a reliable alternative to reduce the treatment length of prosthetic restoration. In general, the biomaterial should be used to increase bone/implant contact and enhance osseointegration.

Evaluation of horizontal ridge augmentation using beta tricalcium phosphate and demineralized bone matrix: A comparative study

Objectives: To evaluate the effectiveness of beta tricalcium phosphate (β-TCP) alone compared to β-TCP and Demineralized Bone Matrix (DBM) in regenerating localized horizontal maxillary alveolar ridge deficiencies prior to implant placement. Study Design: The study included 20 patients with horizontal maxillary ridge deficiencies limited to one or more neighbouring teeth and initial ridge width of ≤ 5mmm. Patients were divided equally into two equal groups. Ridge augmentation was performed using Guided Bone Regeneration (GBR) principals. In group I GBR was performed using β-TCP only, while in group II both β-TCP and DBM were used. Following a 6 months healing period, bone cores from both groups were retrieved and implants were inserted. Specimens were examined histologically to calculate percentage of mineralized bone. Apical and crestal changes in ridge dimensions were calculated by digital subtraction using Cone Beam Computed Tomography (CBCT) immediately after graft placement and six months later. Results: There was a statistically significant difference between the mean area percentage of mineralized bone between both groups where it was 40.1 % (range: 27.76-% 66.29 %) for group I and 68.96 % (range: 60.07 % - 87.33 %) for group II. Radiograpically, the mean ridge width in group I increased crestally to 4.66 mm (range:3.5-5mm) and apically to 6.12 mm (range: 4.1-6.7 mm). In group II the mean ridge width increased crestally to 5.2 mm (range 4.9-5.4mm) and apically to 6.9 mm (range 6.0-7.8 mm). Group II showed more bone gain with a mean of 1.37 mm crestally and 2.44 mm apically. This difference however was not statistically significant Conclusion: Within the limitations of this study the combination of DBM and β-TCP can be used effectively in cases exhibiting minimal alveolar ridge defects.

Key words:Guided bone regeneration, equine bone, alloplast, bone graft.

Implantation of silicon dioxide-based nanocrystalline hydroxyapatite and pure phase beta-tricalciumphosphate bone substitute granules in caprine muscle tissue does not induce new bone formation

BACKGROUND

Osteoinductive bone substitutes are defined by their ability to induce new bone formation even at heterotopic implantation sites. The present study was designed to analyze the potential osteoinductivity of two different bone substitute materials in caprine muscle tissue.

MATERIALS AND METHODS

One gram each of either a porous beta-tricalcium phosphate (β-TCP) or an hydroxyapatite/silicon dioxide (HA/SiO2)-based nanocrystalline bone substitute material was implanted in several muscle pouches of goats. The biomaterials were explanted at 29, 91 and 181 days after implantation. Conventional histology and special histochemical stains were performed to detect osteoblast precursor cells as well as mineralized and unmineralized bone matrix.

RESULTS

Both materials underwent cellular degradation in which tartrate-resistant acid phosphatase (TRAP)-positive osteoclast-like cells and TRAP-negative multinucleated giant cells were involved. The ß-TCP was completely resorbed within the observation period, whereas some granules of the HA-groups were still detectable after 180 days. Neither osteoblasts, osteoblast precursor cells nor extracellular bone matrix were found within the implantation bed of any of the analyzed biomaterials at any of the observed time points.

CONCLUSIONS

This study showed that ß-TCP underwent a faster degradation than the HA-based material. The lack of osteoinductivity for both materials might be due to their granular shape, as osteoinductivity in goat muscle has been mainly attributed to cylindrical or disc-shaped bone substitute materials. This hypothesis however requires further investigation to systematically analyze various materials with comparable characteristics in the same experimental setting.

Composite materials based on poly(trimethylene carbonate) and β-tricalcium phosphate for orbital floor and wall reconstruction

Poly(trimethylene carbonate) and β-tricalcium phosphate (PTMC/β-TCP) composite materials were prepared by coprecipitation and compression molding. The effect of different amounts of the ceramic component (15 and 30 vol %) on the properties was investigated. The effect of lamination with minimal amounts of poly(D,L-lactide) (PDLLA) was assessed as well. It was hypothesized that these composites would be suitable for orbital floor reconstruction, as the polymer component resorbs enzymatically without the formation of acidic compounds, while the ceramic component could induce bone formation. To asses their suitability as load bearing devices, the flexural properties of the prepared (laminated) composites were determined in three point bending experiments and compared with those of currently used reconstruction devices. The flexural modulus of PTMC composites increased from 6-17 MPa when introducing 30 vol % β-TCP. A laminate of this composite with PDLLA (with respective layer thicknesses of 0.8 and 0.2 mm) had a flexural modulus of 64 MPa. When evaluated in a mechanical engineering model of the orbital floor the (laminated) composites materials showed similar behavior compared to the currently used materials. The results suggest that from a mechanical point of view these (laminated) composite sheets should be well suited for use in orbital floor reconstruction.

Autologous bone marrow derived mononuclear cells combined with β-tricalcium phosphate and absorbable atelocollagen for a treatment of aneurysmal bone cyst of the humerus in child

Aneurysmal bone cyst is a benign, locally destructive lesion of bone. Based on progressive cortical thinning pathological fractures are common, and are often the presenting feature. Despite the long experience of orthopaedists, radiologists and pathologists with aneurysmal bone cyst there is limited knowledge regarding the cause of the lesion and optimal treatment. Common methods of treatment vary considerably in the literature, particularly in children. A large variety of bone substitutes have been used to fill the cystic lesions. To date there has been no graft material which can be regarded as completely satisfactory. Our experience with freshly isolated autologous bone marrow derived mononuclear cells combined with β-tricalcium phosphate and absorbable atelocollagen for bone formation is presented. The concept of this treatment is based on stimulation of natural events continuously present in living bone appear to be a reasonable and beneficial alternative to promote healing of bone cysts and offering both osteoinduction and osteoconductive features.

Nanocrystalline hydroxyapatite bone substitute leads to sufficient bone tissue formation already after 3 months: histological and histomorphometrical analysis 3 and 6 months following human sinus cavity augmentation

PURPOSE

In this study the de novo bone formation capacity of a nanocrystalline hydroxyapatite bone substitute was assessed 3 and 6 months after its insertion into the human sinus cavity.

MATERIALS AND METHODS

Sinus cavity augmentation was performed in a total of 14 patients (n = 7 implantation after 3 months; n = 7 implantation after 6 months) with severely atrophic maxillary bone. The specimens obtained after 3 and 6 months were analyzed histologically and histomorphometrically with special focus on bone metabolism within the residual bone and the augmented region.

RESULTS

This study revealed that bone tissue formation started from the bone-biomaterial-interface and was directed into the most cranial parts of the augmented region. There was no statistically significant difference in new bone formation after 3 and 6 months (24.89 ± 10.22% vs 31.29 ± 2.29%), respectively.

CONCLUSIONS

Within the limits of the present study and according to previously published data, implant insertion in regions augmented with this bone substitute material could be considered already after 3 months. Further clinical studies with bone substitute materials are necessary to validate these findings.

Jaw cysts - filling or no filling after enucleation? A review

INTRODUCTION

Jaw cysts are common lesions in the oral and maxillofacial region. Enucleation of the lesions and primary closure of the defects, the so-called "cystectomy", has evolved as the treatment of choice. In order to reduce infections and to accelerate bone regeneration, different types of bone grafts are increasingly investigated for defect filling.

MATERIAL AND METHODS

The present review reflects the most recent studies using autogenous, allogenic, xenogenic and alloplastic bone grafts and compares the results to current investigations about conservative cyst enucleation without using any filling materials. Relevant studies with significant patient sample sizes were electronically searched in PubMed and Medline.

RESULTS

Simple cyst enucleation and blood clot healing show low complication rates and sufficient bone regeneration even in large defects. Prospective randomized trials comparing the additional use of filling materials to the "cystectomy" are rare. Currently available data do not indicate the superiority of additional bone grafts.

CONCLUSION

Enucleation of jaw cysts and primary closure without bone substitutes remains "state of the art" in most cases.

Macroporous bioceramics: A remarkable material for bone regeneration

This review summarises the major developments of macroporous bioceramics used mainly for repairing bone defects. Porous bioceramics have been receiving attention ever since their larger surface area was reported to be beneficial for the formation of more rigid bonds with host tissues. The study of porous bioceramics is important to overcome the less favourable bonds formed between dense bioceramics and host tissues, especially in healing bone defects. Macroporous bioceramics, which have been studied extensively, include hydroxyapatite, tricalcium phosphate, alumina, and zirconia. The pore size and interconnections both have significant effects on the growth rate of bone tissues. The optimum pore size of hydroxyapatite scaffolds for bone growth was found to be 300 µm. The existence of interconnections between pores is critical during the initial stage of tissue ingrowth on porous hydroxyapatite scaffolds. Furthermore, pore formation on β-tricalcium phosphate scaffolds also allowed the impregnation of growth factors and cells to improve bone tissues growth significantly. The formation of vascularised tissues was observed on macroporous alumina but did not take place in the case of dense alumina due to its bioinert nature. A macroporous alumina coating on scaffolds was able to improve the overall mechanical properties, and it enabled the impregnation of bioactive materials that could increase the bone growth rate. Despite the bioinertness of zirconia, porous zirconia was useful in designing scaffolds with superior mechanical properties after being coated with bioactive materials. The pores in zirconia were believed to improve the bone growth on the coated system. In summary, although the formation of pores in bioceramics may adversely affect mechanical properties, the advantages provided by the pores are crucial in repairing bone defects.

Maxillary sinus floor elevation using BMP-2 and Nell-1 gene-modified bone marrow stromal cells and TCP in rabbits

This study evaluated the synergistic osteogenic effect of bone morphogenetic protein-2 (BMP-2) and Nel-like molecule-1 (Nell-1) genes in a rabbit maxillary sinus floor elevation model. Bone marrow stromal cells (bMSCs) were cultured and transduced with AdEGFP, AdNell-1, AdBMP-2, or AdNell-1 + AdBMP-2 overexpression virus. These gene-modified autologous bMSCs were then combined with a β-tricalcium phosphate (β-TCP) granule scaffold and used to elevate the maxillary sinus floor in rabbits. bMSCs cotransduced with AdNell-1 + AdBMP-2 demonstrated a synergistic effect on osteogenic differentiation as detected by real-time PCR analysis on markers of runt-related transcription factor-2, osteocalcin, collagen type 1, alkaline phosphatase activity, and calcium deposits in vitro. As for maxillary sinus floor elevation in a rabbit model in vivo, AdNell-1 + AdBMP-2 gene-transduced autologeous bMSCs/β-TCP complex had the largest bone area and most mature bone structure among the groups, as detected by HE staining and immunohistochemistry at weeks 2 and 8 after implantation. Our data suggested that the BMP-2 and Nell-1 genes possessed a synergistic effect on osteogenic differentiation of bMSCs, while bMSCs modified with the BMP-2 and Nell-1 genes could promote new bone formation and maturation in the rabbit maxillary sinus model.

Preimplantation filling of tooth socket with beta-tricalcium phosphate/polylactic-polyglycolic acid (beta-TCP/PLGA) root analogue: clinical and histological analysis in a patient

INTRODUCTION

Bone resorption is a physiological process after tooth extraction. The use of bone substitutes to fill the tooth socket is suggested to prevent bone resorption and establish good bone architecture for implant placement. A pure beta-tricalcium phosphate coated with copolymer (polylactic-polyglycolic acid) as a root analogue, is suitable for filling tooth sockets.

CASE REPORT

We presented a patient successfully treated with root analogue after extraction of the right second lower premolar. Three months later, the patient was planned for the placement of six TE ITI dental implants into the mandible. During the sugery, the biopsy of bone-like tissue from the previously treated socket was taken. All the implants were immediately loaded due to good primary stability. Histological analysis of the specimen revealed fibrous healing in the area treated with root analogue.

CONCLUSION

The use of beta-tricalcium phosphate coated with copolymers after tooth extraction enables satisfactory bone architecture for consequent implant treatment.

Beta-tricalcium phosphate/type I collagen cones with or without a barrier membrane in human extraction socket healing: clinical, histologic, histomorphometric, and immunohistochemical evaluation

The aim of this study was to investigate the healing of human extraction sockets filled with β-tricalcium phosphate and type I collagen (β-TCP/Clg) cones with or without a barrier membrane. Twenty patients were divided in two groups: (A) β-TCP/Clg non-membrane and (B) β-TCP/Clg + barrier membrane. Clinical examination and biopsies from the grafted sites were collected 9 months later. Bone samples were analyzed using histomorphometry and immunohistochemistry. The horizontal dimension of the alveolar ridge was significantly reduced 9 months after socket preservation in the non-membrane group. There was bone formation with no significant differences between the two groups in the areas occupied by new bone (A = 42.4%; B = 45.3%), marrow (A = 42.7%; B = 35.7%), or residual graft (A = 9.7%; B = 12.5%). Immunohistochemistry revealed osteonectin expression in both groups. Both groups demonstrated sufficient amounts of vital bone and socket morphology to support dental implant placement after the 9-month healing period. A future trial to evaluate the alveolar outcomes at an earlier 6-month time point rather than the 9 months used in this study would be of interest.

Connexin 43 expression at an early stage in dog mandibles by β-TCP

β-TCP was implanted into bone defects of dog mandibles, and gene expression profiles were examined using DNA microarray. An implant drill was used to make bone defects, and then β-TCP was filled into bone defects. All specimens were taken out, total RNA was isolated, and levels were analyzed using Affymetrix GeneChip. Higher mRNA levels of connexin 43 (Cx43) and Cx45 were observed in β-TCP-implanted samples compared with controls. The enhancement of Cx43 and Cx45 by β-TCP was confirmed by RT-PCR and real-time RT-PCR. Since Cx43 is known to express in bone-forming regions and is involved in osteogenesis through gap junctional intercellular bone-cell communication (GJIB), immunohistochemical staining was also examined and demonstrated Cx43 protein expression was increased in β-TCP-implanted bone. Cx43 plays a role in osteogenesis through GJIB; therefore, the stimulation of Cx43 expression by β-TCP might be a mechanism of accelerating wound healing and bone formation.

A meta-analysis of histomorphometric results and graft healing time of various biomaterials compared to autologous bone used as sinus floor augmentation material in humans

BACKGROUND

To date, no studies have been published in which histomorphometric data from a large group of patients comparing various biomaterials for sinus floor augmentation procedures were evaluated.

MATERIALS AND METHODS

A meta-analysis of the English literature from January 1993 till April 2009 was carried out. Out of 147 titles, according to our criteria, 64 articles were selected for analysis describing the use of autologous bone and their alternatives, such as allogenic, xenogenic, and alloplastic materials.

RESULTS

On the basis of autologous bone grafting, a reference value for total bone volume (TBV) of 63% was found. Particulation of the bone graft resulted in a general reduction of −18% in TBV. Delayed implant placement reduced the TBV with −7%. Overall TBV was 8% or 6% higher if a biopsy was, respectively, taken before 4.5 months or after 9.0 months after initial sinus augmentation surgery. Allogenic, xenogenic, alloplastic, or combinations of graft materials all resulted in a significant lower amount of TBV compared to autologous bone grafting ranging from −7% to −26%. Inventorying the effect of "biopsy time" for autologous bone, the TBV was significantly higher before 4.5 and after 9.0 months of healing time compared to period in between. Surprisingly, no significant differences in TBV with respect to "biopsy time" for bone substitutes were found.

CONCLUSIONS

On the basis of the aspect of TBV autologous bone still has to be considered to be the gold standard in sinus augmentation surgery. However, the consequence of the TBV for implant survival is still unraveled yet.

A non-steroidal anti-inflammatory drug (ketoprofen) does not delay beta-TCP bone graft healing

Beta-tricalcium phosphate (beta-TCP) is a suitable biomaterial in oral and maxillofacial surgery since it can induce a rapid proliferation of woven bone. Granules, prepared by the polyurethane foam method, were implanted in critical size defects performed in the femoral condyles of New Zealand rabbits. Animals were studied after 8 and 28 days. Ketoprofen (a non-steroidal anti-inflammatory drug (NSAID)) was given for 8 and 28 days to evaluate its effects on the healing of the graft. Before euthanasia, the rabbits received an intravenous injection of fluorescent microbeads. Bones were analyzed by microcomputed tomography. beta-TCP granules induced metaplastic bone trabeculae as early as 8 days post-surgery. At 28 days, the amount of bone was increased and the biomaterial volume decreased due to simultaneous macrophagic resorption. The amount of macrophages labeled with microbeads was less in the grafted area than in the vicinal intact marrow spaces. Ketoprofen had no effect on the amount of bone formed and on the number of labeled macrophages. The influence of small doses of NSAID, given in a short duration period, did not present deleterious effects on bone graft healing.

[The use of beta-tricalcium phosphate and bovine bone matrix in the guided tissue regeneration treatment of deep infra-bony defects]

INTRODUCTION

The primary goal of bone regeneration procedures with application of various regenerative biologic agents and biomaterials is to facilitate the formation of periodontal tissues lost as a result of periodontitis.

OBJECTIVE

The aim of the study was to compare clinical outcome of the guided tissue regeneration (GTR) treatment with the use of beta-tricalcium phosphate and with bovine bone matrix in human deep intra-osseous defects.

METHODS

Twenty-one systemically healthy subjects with moderate to advanced periodontitis, between 30 and 56 years of age, 11 females and 10 males, were selected. Patients having two similar inter-proximal defects with pocket probing depths following initial therapy greater than 5 mm were recruited for the study. Experimental sites were grafted with pure beta-tricalcium phosphate biomaterial (Cerasorb) and a biomembrane, while control sites were treated with bovine-bone hydroxiapatite xenograft (Bio-oss) and a biomembrane. Immediately before surgery and 12 months after surgery, pocket probing depth (PPD), epithelial attachment level (EAL) and gingival recession (GR) were evaluated.

RESULTS

In the experimental group PPD amounted to 6.76 +/- 0.83 mm before surgery, and decreased significantly to 2.67 +/- 0.48 mm 12 months following surgery, while in the control group PPD significantly decreased from 7.14 +/- 0.65 mm presurgically to 2.85 +/- 0.57 mm postsurgically. After one year, EAL gain was 2.76 +/- 0.99 mm in the experimental group, and 3.24 +/- 0.16 mm in the control group. After twelve months postoperatively GR amounted to 1.33 +/- 0.79 mm in the experimental group and to 1.05 +/- 0.80 mm in the control group. No statistically significant differences for PPD reduction, EAL gain and GR increase were detected between the groups.

CONCLUSION

Results from the present study indicate that GTR treatment of deep intra-osseous defects with Bio-oss and Cerasorb resulted in clinically and statistically significant improvement of EAL gain and PPD reduction. A GR was slightly increased, with no statistical significance.

Systematic evaluation of a tissue-engineered bone for maxillary sinus augmentation in large animal canine model

The objective of this study is to systematically evaluate the effects of a tissue-engineered bone complex for maxillary sinus augmentation in a canine model. Twelve sinus floor augmentation surgeries in 6 animals were performed bilaterally and randomly repaired with the following 3 groups of grafts: group A consisted of tissue-engineered osteoblasts/beta-TCP complex (n=4); group B consisted of beta-TCP alone (n=4); group C consisted of autogenous bone obtained from iliac crest as a positive control (n=4). All dogs had uneventful healings following the surgery. Sequential polychrome fluorescent labeling, maxillofacial CT, microhardness tests, as well as histological and histomorphometric analyses indicated that the tissue-engineered osteoblasts/beta-TCP complex dramatically promoted bone formation and mineralization and maximally maintained the height and volume of elevated maxillary sinus. By comparison, both control groups of beta-TCP or autologous iliac bone showed considerable resorption and replacement by fibrous or fatty tissue. We thus conclude that beta-TCP alone could barely maintain the height and volume of the elevated sinus floor, and that the transplantation of autogenous osteoblasts on beta-TCP could promote earlier bone formation and mineralization, maximally maintain height, volume and increase the compressive strength of augmented maxillary sinus. This tissue engineered bone complex might be a better alternative to autologous bone for the clinical edentulous maxillary sinus augmentation.

Appositional Bone Formation by OCP-Collagen Composite

Synthetic octacalcium phosphate (OCP) has been shown to enhance bone formation and to biodegrade if implanted into bone defects. Here, we hypothesized that an OCP-atelocollagen complex (OCP/Col) is biodegradable and can induce bone formation in a thickness-dependent manner when implanted into the calvaria. OCP/Col disks (diameter, 9 mm; thickness, 1 or 3 mm) were implanted into a subperiosteal pocket in the calvaria of 12-week-old Wistar rats for 4, 8, and 12 weeks and subsequent bone formation was monitored. X-ray diffraction analysis and Fourier transform infrared spectroscopy showed that OCP in the OCP/Col implants was converted into a carbonate-rich apatite after 4 weeks. Although thinner disks tended to be replaced by new bone, thicker disks were progressively resorbed by osteoclast-like cells until 12 weeks, possibly via the increased mechanical load in the subperiosteal pocket. Therefore, OCP/Col can increase appositional intra-membranous bone formation if the appropriate size of the implant is applied.

A new biphasic osteoinductive calcium composite material with a negative Zeta potential for bone augmentation

The aim of the present study was to analyze the osteogenic potential of a biphasic calcium composite material (BCC) with a negative surface charge for maxillary sinus floor augmentation. In a 61 year old patient, the BCC material was used in a bilateral sinus floor augmentation procedure. Six months postoperative, a bone sample was taken from the augmented regions before two titanium implants were inserted at each side. We analyzed bone neoformation by histology, bone density by computed tomography, and measured the activity of voltage-activated calcium currents of osteoblasts and surface charge effects. Control orthopantomograms were carried out five months after implant insertion. The BCC was biocompatible and replaced by new mineralized bone after being resorbed completely. The material demonstrated a negative surface charge (negative Zeta potential) which was found to be favorable for bone regeneration and osseointegration of dental implants.

A histomorphometric meta-analysis of sinus elevation with various grafting materials

Several grafting materials have been used in sinus augmentation procedures including autogenous bone, demineralized freeze-dried bone (DFDBA), hydroxyapatite, beta-tricalcium phosphate (beta-TCP), anorganic deproteinized bovine bone and combination of these and others. Up to now a subject of controversy in maxillofacial surgery and dentistry is, what is the most appropriate graft material for sinus floor augmentation.

PURPOSE

The aim of this study is to provide a body of evidence-based data regarding grafting materials in external sinus floor elevation concerning the fate of the augmented material at the histomorphological level, through a meta-analysis of the available literature.

MATERIALS AND METHODS

The literature searches were performed using the National Library of Medicine. The search covered all English and German literature from 1995 until 2006. For analyzing the amount of bone the parameter "Total Bone Volume" (TBV) was assessed. TBV is determined as the percentage of the section consisting of bone tissue.

RESULTS

In a relatively early phase after implantation the autogenous bone shows the highest TBV values. Interestingly, the different TBV levels approximate during the time. After 9 months no statistically significant differences can be detected between the various grafting materials.

CONCLUSION

From a clinical point of view, the use of autogenous bone is advantageous if a prosthetic rehabilitation (with functional loading) is expected within 9 months. In other cases the use of anorganic deproteinized bovine bone in combination with autogenous bone seems to be preferable. Donor side morbidity is ignored in this conclusion.