SHED differentiate into functional odontoblasts and endothelium

Regenerative endodontics: barriers and strategies for clinical translation

Regenerative endodontics has encountered substantial challenges toward clinical translation. The adoption by the American Dental Association of evoked pulp bleeding in immature permanent teeth is an important step for regenerative endodontics. However, there is no regenerative therapy for most endodontic diseases. Simple recapitulation of cell therapy and tissue engineering strategies that are under development for other organ systems has not led to clinical translation in regeneration endodontics. Recent work using novel biomaterial scaffolds and growth factors that orchestrate the homing of host endogenous cells represents a departure from traditional cell transplantation approaches and may accelerate clinical translation.

Endothelial differentiation of SHED requires MEK1/ERK signaling

The discovery that dental pulp stem cells are capable of differentiating into endothelial cells raises the exciting possibility that these cells can be a single source of odontoblasts and vascular networks in dental tissue engineering. The purpose of this study was to begin to define signaling pathways that regulate endothelial differentiation of SHED. Stem cells from exfoliated deciduous teeth (SHED) exposed to endothelial growth medium (EGM-2MV) supplemented with vascular endothelial growth factor (VEGF) differentiated into VEGFR2-positive and CD31-positive endothelial cells in vitro. In vivo, VEGFR1-silenced SHED seeded in tooth slice/ scaffolds and transplanted into immunodeficient mice showed a reduction in human CD31-positive blood vessels as compared with controls (p = 0.02). Exposure of SHED to EGM2-MV supplemented with VEGF induced potent activation of ERK and Akt signaling, while it inhibited phosphorylation of STAT3. Notably, genetic (MEK1 silencing) or chemical (U0126) inhibition of ERK signaling restored constitutive STAT3 phosphorylation and inhibited the differentiation of SHED into endothelial cells. Collectively, analysis of these data unveiled the VEGF/MEK1/ERK signaling pathway as a key regulator of the endothelial differentiation of dental pulp stem cells.

A hydrogel scaffold that maintains viability and supports differentiation of dental pulp stem cells

OBJECTIVES

The clinical translation of stem cell-based Regenerative Endodontics demands further development of suitable injectable scaffolds. Puramatrix™ is a defined, self-assembling peptide hydrogel which instantaneously polymerizes under normal physiological conditions. Here, we assessed the compatibility of Puramatrix™ with dental pulp stem cell (DPSC) growth and differentiation.

METHODS

DPSC cells were grown in 0.05-0.25% Puramatrix™. Cell viability was measured colorimetrically using the WST-1 assay. Cell morphology was observed in 3D modeling using confocal microscopy. In addition, we used the human tooth slice model with Puramatrix™ to verify DPSC differentiation into odontoblast-like cells, as measured by expression of DSPP and DMP-1.

RESULTS

DPSC survived and proliferated in Puramatrix™ for at least three weeks in culture. Confocal microscopy revealed that cells seeded in Puramatrix™ presented morphological features of healthy cells, and some cells exhibited cytoplasmic elongations. Notably, after 21 days in tooth slices containing Puramatrix™, DPSC cells expressed DMP-1 and DSPP, putative markers of odontoblastic differentiation.

SIGNIFICANCE

Collectively, these data suggest that self-assembling peptide hydrogels might be useful injectable scaffolds for stem cell-based Regenerative Endodontics.

Cryopreserved dental pulp tissues of exfoliated deciduous teeth is a feasible stem cell resource for regenerative medicine

Human exfoliated deciduous teeth have been considered to be a promising source for regenerative therapy because they contain unique postnatal stem cells from human exfoliated deciduous teeth (SHED) with self-renewal capacity, multipotency and immunomodulatory function. However preservation technique of deciduous teeth has not been developed. This study aimed to evaluate that cryopreserved dental pulp tissues of human exfoliated deciduous teeth is a retrievable and practical SHED source for cell-based therapy. SHED isolated from the cryopreserved deciduous pulp tissues for over 2 years (25–30 months) (SHED-Cryo) owned similar stem cell properties including clonogenicity, self-renew, stem cell marker expression, multipotency, in vivo tissue regenerative capacity and in vitro immunomodulatory function to SHED isolated from the fresh tissues (SHED-Fresh). To examine the therapeutic efficacy of SHED-Cryo on immune diseases, SHED-Cryo were intravenously transplanted into systemic lupus erythematosus (SLE) model MRL/lpr mice. Systemic SHED-Cryo-transplantation improved SLE-like disorders including short lifespan, elevated autoantibody levels and nephritis-like renal dysfunction. SHED-Cryo amended increased interleukin 17-secreting helper T cells in MRL/lpr mice systemically and locally. SHED-Cryo-transplantation was also able to recover osteoporosis bone reduction in long bones of MRL/lpr mice. Furthermore, SHED-Cryo-mediated tissue engineering induced bone regeneration in critical calvarial bone-defect sites of immunocompromised mice. The therapeutic efficacy of SHED-Cryo transplantation on immune and skeletal disorders was similar to that of SHED-Fresh. These data suggest that cryopreservation of dental pulp tissues of deciduous teeth provide a suitable and desirable approach for stem cell-based immune therapy and tissue engineering in regenerative medicine.

Rigid matrix supports osteogenic differentiation of stem cells from human exfoliated deciduous teeth (SHED)

Stem cell fate can be induced by the grade of stiffness of the extracellular matrix, depending on the developed tissue or complex tissues. For example, a rigid extracellular matrix induces the osteogenic differentiation in bone marrow derived mesenchymal stem cells (MSCs), while a softer surface induces the osteogenic differentiation in dental follicle cells (DFCs). To determine whether differentiation of ectomesenchymal dental precursor cells is supported by similar grades of extracellular matrices (ECMs) stiffness, we examined the influence of the surface stiffness on the proliferation and osteogenic differentiation of stem cells from human exfoliated deciduous teeth (SHED). Cell proliferation of SHED was significantly decreased on cell culture surfaces with a muscle-like stiffness. A dexamethasone-based differentiation medium induced the osteogenic differentiation of SHED on substrates of varying mechanical stiffness. Here, the hardest surface improved the induction of osteogenic differentiation in comparison to that with the softest stiffness. In conclusion, our study showed that the osteogenic differentiation of ectomesenchymal dental precursor cells SHED and DFCs are not supported by similar grades of ECM stiffness.

Skeletal myogenic differentiation of human periodontal ligament stromal cells isolated from orthodontically extracted premolars

Objective

To investigate the stem cell-like characteristics of human periodontal ligament (PDL) stromal cells outgrown from orthodontically extracted premolars and to evaluate the potential for myogenic differentiation.

Methods

PDL stromal cells were obtained from extracted premolars by using the outgrowth method. Cell morphological features, self-replication capability, and the presence of cell-surface markers, along with osteogenic, adipogenic, and chondrogenic differentiation, were confirmed. In addition, myogenic differentiation was induced by the use of 5-aza-2'-deoxycytidine (5-Aza) for DNA demethylation.

Results

PDL stromal cells showed growth patterns and morphological features similar to those of fibroblasts. In contrast, the proliferation rates of premolar PDL stromal cells were similar to those of bone marrow and adipogenic stem cells. PDL stromal cells expressed surface markers of human mesenchymal stem cells (i.e., CD90 and CD105), but not those of hematopoietic stem cells (i.e., CD31 and CD34). PDL stromal cells were differentiated into osteogenic, adipogenic, and chondrogenic lineages. Myotube structures were induced in PDL stromal cells after 5-Aza pretreatment, but not in the absence of 5-Aza pretreatment.

Conclusions

PDL stromal cells isolated from extracted premolars can potentially be a good source of postnatal stem cells for oromaxillofacial regeneration in bone and muscle.

Clinical utility of stem cells for periodontal regeneration

The aim of this review is to discuss the clinical utility of stem cells in periodontal regeneration by reviewing relevant literature that assesses the periodontal-regenerative potential of stem cells. We considered and described the main stem cell populations that have been utilized with regard to periodontal regeneration, including bone marrow-derived mesenchymal stem cells and the main dental-derived mesenchymal stem cell populations: periodontal ligament stem cells, dental pulp stem cells, stem cells from human exfoliated deciduous teeth, stem cells from apical papilla and dental follicle precursor cells. Research into the use of stem cells for tissue regeneration has the potential to significantly influence periodontal treatment strategies in the future.

Transplantation of undifferentiated and induced human exfoliated deciduous teeth-derived stem cells promote functional recovery of rat spinal cord contusion injury model

Regarding both the neural crest origin and neuronal potential of stem cells from human exfoliated deciduous teeth (SHED), here, we assessed their potential in addition to neural induced SHED (iSHED) for functional recovery when transplanted in a rat model for acute contused spinal cord injury (SCI). Following transplantation, a significant functional recovery was observed in both groups relative to the vehicle and control groups as determined by the open field locomotor functional test. We also observed that animals that received iSHED were in a better state as compared with the SHED group. Immunohistofluorescence evaluation 5 weeks after transplantation showed neuronal and glial differentiation and limited proliferation in both groups. However, myelin basic protein and chondroitin sulfate proteoglycan NG2-oligodendrocyte markers-were increased and glial fibrillary acidic protein-astrocyte marker-was decreased in the iSHED group in comparison with the SHED group. These findings have demonstrated that transplantation of SHED or its derivatives could be a suitable candidate for the treatment of SCI as well as other neuronal degenerative diseases.

Dental stem cells and their sources

The search for more accessible mesenchymal stem cells than those found in bone marrow has propelled interest in dental tissues. Human dental stem/progenitor cells (collectively termed dental stem cells [DSCs]) that have been isolated and characterized include dental pulp stem cells, stem cells from exfoliated deciduous teeth, stem cells from apical papilla, periodontal ligament stem cells, and dental follicle progenitor cells. Common characteristics of these cell populations are the capacity for self-renewal and the ability to differentiate into multiple lineages. In vitro and animal studies have shown that DSCs can differentiate into osseous, odontogenic, adipose, endothelial, and neural-like tissues.

Impact of stem cells in craniofacial regenerative medicine

Interest regarding stem cell based therapies for the treatment of congenital or acquired craniofacial deformities is rapidly growing. Craniofacial problems such as periodontal disease, cleft lip and palate, ear microtia, craniofacial microsomia, and head and neck cancers are not only common but also some of the most burdensome surgical problems worldwide. Treatments often require a multi-staged multidisciplinary team approach. Current surgical therapies attempt to reduce the morbidity and social/emotional impact, yet outcomes can still be unpredictable and unsatisfactory. The concept of harvesting stem cells followed by expansion, differentiation, seeding onto a scaffold and re-transplanting them is likely to become a clinical reality. In this review, we will summarize the translational applications of stem cell therapy in tissue regeneration for craniofacial defects.

The levels of vascular endothelial growth factor and bone morphogenetic protein 2 in dental pulp tissue of healthy and diabetic patients

INTRODUCTION

Vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP 2) are growth factors (GFs) identified within the dentine-pulp complex and involved into the cellular events connected to the pulp-healing response. It is well established that the expression of these GFs is increased in different tissues in diabetes mellitus. Because there are no data concerning the levels of VEGF and BMP 2 in human dental pulp, the aim of present study was to quantify VEGF and BMP 2 levels in intact dental pulp and dental pulp that underwent reactive dentinogenesis in healthy and diabetic human subjects.

METHODS

The study was conducted on 28 healthy and 28 subjects with controlled diabetes type II who underwent pulp extirpation as a part of prosthetic rehabilitation. Pulp were collected from intact teeth and teeth treated by indirect pulp capping. The levels of VEGF and BMP 2 were determined in the pulp tissue lysates with enzyme-linked immunosorbent assay.

RESULTS

The levels of VEGF and BMP 2 were significantly higher in intact teeth pulp of diabetic than in healthy subjects. The concentrations of these GFs were significantly lowered in teeth with indirect pulp capping both in healthy and diabetic persons. Furthermore, VEGF and BMP 2 levels were in strong positive correlation.

CONCLUSIONS

Similar changes in the levels of VEGF and BMP 2 in intact and treated teeth of healthy and diabetic patients could be suggestive of associated roles of these GFs in responses of healthy and diabetic dental pulp.

The effects of human platelet lysate on dental pulp stem cells derived from impacted human third molars

Human platelet lysate (PL) has been suggested as a substitute for fetal bovine serum (FBS) in the large-scale expansion of dental pulp stem cells (DPSCs). However, the biological effects and the optimal concentrations of PL for the proliferation and differentiation of human DPSCs remain unexplored. We isolated and expanded stem cells from the dental pulp of extracted third molars and evaluated the effects of PL on the cells' proliferative capacity and differentiation potential in vitro and in vivo. Before testing, immunocytochemical staining and flow cytometry-based cell sorting showed that the cells derived from human dental pulp contained mesenchymal stem cell populations. Cells were grown on tissue culture plastic or on hydroxyapatite-tricalcium phosphate (HA/TCP) biomaterials and were incubated with either normal or odontogenic/osteogenic media in the presence or absence of various concentrations of human PL for further investigation. The proliferation of DPSCs was significantly increased when the cells were cultured in 5% PL under all testing conditions (P < 0.05). However, this enhancement was inconsistent when the cells were cultured in 1% PL or in 10% PL; 10% PL significantly inhibited cell proliferation and was therefore excluded from further differentiation testing. Culture medium containing 5% PL also significantly promoted the mineralized differentiation of DPSCs, as indicated by the measurement of alkaline phosphatase activity and calcium deposition under mineral-conditioned media (P < 0.05). Scanning electron microscopy and modified Ponceau trichrome staining showed that the cells treated with 5% PL and mineralizing media were highly capable of integrating with the HA/TCP biomaterials and had fully covered the surface of the scaffold with an extensive sheet-like structure 14 d after seeding. In addition, 5% PL showed significantly positive effects on tissue regeneration in two in vivo transplantation models. We conclude that the appropriate concentration of PL enhances the proliferation and mineralized differentiation of human DPSCs both in vitro and in vivo, which supports the use of PL as an alternative to FBS or a nonzoonotic adjuvant for cell culture in future clinical trials. However, the elucidation of the molecular complexity of PL products and the identification of both the essential growth factors that determine the fate of a specific stem cell and the criteria to establish dosing require further investigation.

Tissue engineering: from research to dental clinics

Tissue engineering is an interdisciplinary field that combines the principles of engineering, material and biological sciences toward the development of therapeutic strategies and biological substitutes that restore, maintain, replace or improve biological functions. The association of biomaterials, stem cells, growth and differentiation factors has yielded the development of new treatment opportunities in most of the biomedical areas, including Dentistry. The objective of this paper is to present the principles underlying tissue engineering and the current scenario, the challenges and the perspectives of this area in Dentistry.

SIGNIFICANCE

The growth of tissue engineering as a research field has provided a novel set of therapeutic strategies for biomedical applications. Indeed, tissue engineering may lead to new strategies for the clinical management of patients with dental and craniofacial needs in the future.

Osteoblastic/cementoblastic and neural differentiation of dental stem cells and their applications to tissue engineering and regenerative medicine

Recently, dental stem and progenitor cells have been harvested from periodontal tissues such as dental pulp, periodontal ligament, follicle, and papilla. These cells have received extensive attention in the field of tissue engineering and regenerative medicine due to their accessibility and multilineage differentiation capacity. These dental stem and progenitor cells are known to be derived from ectomesenchymal origin formed during tooth development. A great deal of research has been accomplished for directing osteoblastic/cementoblastic differentiation and neural differentiation from dental stem cells. To differentiate dental stem cells for use in tissue engineering and regenerative medicine, there needs to be efficient in vitro differentiation toward the osteoblastic/cementoblastic and neural lineage with well-defined and proficient protocols. This would reduce the likelihood of spontaneous differentiation into divergent lineages and increase the available cell source. This review focuses on the multilineage differentiation capacity, especially into osteoblastic/cementoblastic lineage and neural lineages, of dental stem cells such as dental pulp stem cells (DPSC), dental follicle stem cells (DFSC), periodontal ligament stem cells (PDLSC), and dental papilla stem cells (DPPSC). It also covers various experimental strategies that could be used to direct lineage-specific differentiation, and their potential applications in tissue engineering and regenerative medicine.

Dentin conditioning codetermines cell fate in regenerative endodontics

INTRODUCTION

Recent successes in dental pulp engineering indicate that regenerative treatment strategies in endodontics are feasible. Clinically, revascularization procedures render completion of root formation in immature teeth. The generation of a pulp-like tissue after seeding of dental pulp stem cells into dentin discs or cylinders and transplantation in vivo is possible. In this experimental setup, which mimics the situation in the root canal, the pretreatment of dentin might influence cellular behavior at the cell-dentin interface. Thus, the objective of this study was to investigate whether dentin conditioning can determine cell fate.

METHODS

Dental pulp stem cells (DPSCs) were seeded into a growth factor-laden peptide hydrogel, transferred into dentin cylinders, and transplanted subcutaneously into immunocompromised mice. Before cell seeding, dentin cylinders were either pretreated with sodium hypochloride (NaOCl) or conditioned with EDTA. The constructs were explanted after 6 weeks and subjected to histological and immunohistochemical analysis.

RESULTS

In dentin treated with NaOCl, resorption lacunae were found at the cell-dentin interface created by multinucleated cells with clastic activity. After conditioning with EDTA, DPSCs adjacent to the dentin formed an intimate association with the surface, differentiated into odontoblasts-like cells that expressed dentin sialoprotein, and extended cellular processes into the dentinal tubules. A vascularized soft connective tissue similar to dental pulp was observed inside the dentin cylinder.

CONCLUSIONS

Dentin conditioning considerably influences DPSC fate when seeded in close proximity to dentin. This information might be critical for optimized strategic planning for future regenerative endodontic treatment.

Chitosan/collagen scaffold containing bone morphogenetic protein-7 DNA supports dental pulp stem cell differentiation in vitro and in vivo

In this study, porous chitosan/collagen scaffolds were prepared through a freeze-drying process, and loaded with the plasmid vector encoding human bone morphogenetic protein-7 (BMP-7) gene. To investigate the feasibility and efficacy of this gene-activated scaffold on dental tissue engineering, human dental pulp stem cells (DPSCs) were seeded in this scaffold for in vitro and in vivo study. In vitro results indicated that cells can be transfected successfully by loaded plasmid and secrete BMP-7 until day 24. Evaluation of DNA content, ALP activity, calcium content, SEM, and real-time PCR revealed that cells on gene-activated scaffold showed better proliferation properties and odontoblastic differentiation behaviors than cells on pure scaffolds. Then, these cell-scaffold complexes were implanted subcutaneously and retrieved after 4 weeks for histology evaluation. In vivo results that gene-activated scaffold group could still trace the existence of tranfected cells at week 4 and showed the upregulated expression of DSPP compared to pure scaffold groups. On the basis of our results, chitosan/collagen-loaded BMP-7 DNA appears to be an effective substrate candidate for gene delivery and indeed enhanced DPSCs differentiation toward an odontoblast-like phenotype in vitro and in vivo. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A:, 2012.

Stem cells in dental pulp of deciduous teeth

Dental pulp from deciduous (baby) teeth, which are discarded after exfoliation, represents an advantageous source of young stem cells. Herein, we discuss the methods of deciduous teeth stem cell (DTSC) isolation and cultivation. We show that based on these methods, at least three different stem cell populations can be identified: a population similar to bone marrow-derived mesenchymal stem cells, an epithelial stem-like cells, and/or a mixed population composed of both cell types. We analyzed the embryonic origin and stem cell niche of DTSCs with respect to the advantages they can provide for their future use in cell therapies and regenerative medicine. In vitro and in vivo differentiation of the DTSC populations, their developmental potential, immunological compatibility, tissue engineering, and transplantation use in studies in animal models are also the focus of the current report. We briefly describe the derivation of induced pluripotent stem (iPS) cells from DTSCs, which can be obtained more easily and efficiently in comparison with human fibroblasts. These iPS cells represent an interesting model for the investigation of pediatric diseases and disorders. The importance of DTSC banking is also discussed.

Scaffolds for dental pulp tissue engineering

For tissue engineering strategies, the choice of an appropriate scaffold is the first and certainly a crucial step. A vast variety of biomaterials is available: natural or synthetic polymers, extracellular matrix, self-assembling systems, hydrogels, or bioceramics. Each material offers a unique chemistry, composition and structure, degradation profile, and possibility for modification. The role of the scaffold has changed from passive carrier toward a bioactive matrix, which can induce a desired cellular behavior. Tailor-made materials for specific applications can be created. Recent approaches to generate dental pulp rely on established materials, such as collagen, polyester, chitosan, or hydroxyapatite. Results after transplantation show soft connective tissue formation and newly generated dentin. For dentin-pulp-complex engineering, aspects including vascularization, cell-matrix interactions, growth-factor incorporation, matrix degradation, mineralization, and contamination control should be considered. Self-assembling peptide hydrogels are an example of a smart material that can be modified to create customized matrices. Rational design of the peptide sequence allows for control of material stiffness, induction of mineral nucleation, or introduction of antibacterial activity. Cellular responses can be evoked by the incorporation of cell adhesion motifs, enzyme-cleavable sites, and suitable growth factors. The combination of inductive scaffold materials with stem cells might optimize the approaches for dentin-pulp complex regeneration.

Dentin regeneration in vitro: the pivotal role of supportive cells

The elaboration of dentin-pulp engineering strategies requires the investigation of not only progenitor cell potentials but also their interactions with other non-progenitor "supportive" cells. Under severe caries lesions, progenitor cells may be activated by growth factors released after the acidic dissolution of carious dentin. However, dentin regeneration has also been observed after traumatic injuries without any significant dentin dissolution. This raises questions about the origin of signals involved in progenitor cell activation, migration, and differentiation. Study models such as the entire tooth culture and co-cultures of pulp and endothelial cells highlighted the role of interactions between the different pulp cell types and the pivotal role they play in dentin regeneration. Injured pulp fibroblasts secrete growth factors involved in progenitor cell activation and differentiation as well as neoangiogenesis which may pave the pathways for progenitor cell migration. This appears to be the first paper to focus on this very important field in dental pulp biology.

Comparison of mesenchymal-like stem/progenitor cells derived from supernumerary teeth with stem cells from human exfoliated deciduous teeth

Aims: Dental tissue has been the focus of attention as an easily accessible postnatal tissue source of high-quality stem cells. Since the first report on the dental pulp stem cells (DPSCs) from permanent third molar teeth, stem cells from human exfoliated deciduous teeth (SHED) were identified as a population distinct from DPSCs. In this study, we compared DPSCs from supernumerary teeth and SHED in three age- and sex-matched patients. Patients & methods: Dental samples were obtained from the three patients, who were 6 years old and male, with the parental consent of the three donors, and then isolated cells from dental pulp for comparative analysis between supernumerary DPSCs and SHED. Results: Colony-forming unit fibroblast levels and the proliferation rate of supernumerary DPSCs were slightly lower than that of SHED. The expression of cell surface antigens in supernumerary DPSCs and SHED were almost identical. Cells were mainly expressing endogenous mesodermal and ectodermal lineage markers. Differentiation capacity to osteogenic, adipogenic and chondrogenic lineage was similar in the SHED and supernumerary DPSCs. Migration assay revealed that both supernumerary DPSCs and SHED rapidly migrated toward wounded areas. Supernumerary DPSCs were altered in cell growth after storage for 2 years. Specially, the population doubling time of supernumerary DPSCs increased while that of SHED remained nearly unchanged. Conclusion: Both supernumerary teeth and deciduous teeth share many characteristics, such as highly proliferative clonogenic cells with a similar immunophenotype to that of mesenchymal stem cells, although they are inferior to SHED for long-term banking. Our findings suggest that supernumerary teeth are also easily accessible and noninvasive sources of postnatal stem cells with multipotency and regenerative capacity.

A customized self-assembling peptide hydrogel for dental pulp tissue engineering

Root canal therapy is common practice in dentistry. During this procedure, the inflamed or necrotic dental pulp is removed and replaced with a synthetic material. However, recent research provides evidence that engineering of dental pulp and dentin is possible by using biologically driven approaches. As tissue engineering strategies hold the promise to soon supersede conventional root canal treatment, there is a need for customized scaffolds for stem cell delivery or recruitment. We hypothesize that the incorporation of dental pulp-derived stem cells with bioactive factors into such a scaffold can promote cell proliferation, differentiation, and angiogenesis. In this study, we used a cell adhesive, enzyme-cleavable hydrogel made from self-assembling peptide nanofibers to encapsulate dental pulp stem cells. The growth factors (GFs) fibroblast growth factor basic, transforming growth factor β1, and vascular endothelial growth factor were incorporated into the hydrogel via heparin binding. Release profiles were established, and the influence of GFs on cell morphology and proliferation was assessed to confirm their bioactivity after binding and subsequent release. Cell morphology and spreading in three-dimensional cultures were visualized by using cell tracker and histologic stains. Subcutaneous transplantation of the hydrogel within dentin cylinders into immunocompromised mice led to the formation of a vascularized soft connective tissue similar to dental pulp. These data support the use of this novel biomaterial as a highly promising candidate for future treatment concepts in regenerative endodontics.

A hybrid approach to direct pulp capping by using emdogain with a capping material

INTRODUCTION

This study evaluated the formation of reparative hard tissues in baboon pulps after Emdogain (EMD) application in conjunction with 3 pulp-capping materials.

METHODS

Thirty-two premolars in four 3-year-old baboons were randomly assigned to 1 of 3 pulp-capping materials. A split-mouth design and intra-animal side randomization were applied to 3 experimental groups (calcium hydroxide, ProRoot White mineral trioxide aggregate, white Portland cement) and the control group (no pulp-capping material). In the hybrid EMD approach, a small drop of EMD was placed over the exposure site after arrest of hemorrhage. The designated pulp-capping material was placed over the EMD, followed by placement of resin-modified glass ionomer cement over the set/unset pulp-capping material. The animals were killed after 4 months. Histomorphometric analysis and micro-computed tomography were performed on the retrieved specimens.

RESULTS

All groups capped with EMD and 1 of the 3 capping materials exhibited similar reparative tissue thickness (P > .05). Dentin tunnel defects were absent in the mineral trioxide aggregate and Portland cement groups after the use of EMD. However, only a tubular was identified from all specimens.

CONCLUSIONS

Mineral trioxide aggregate produces a better quality reparative hard tissue response with the adjunctive use of Emdogain, when compared with the use of calcium hydroxide.

Human platelet lysate permits scale-up of dental pulp stromal cells for clinical applications

BACKGROUND AIMS. Dental pulp stromal cells (DPSC) are considered to be a promising source of stem cells in the field of regenerative therapy. However, the usage of DPSC in transplantation requires large-scale expansion to cater for the need for clinical quantity without compromising current good manufacturing practice (cGMP). Existing protocols for cell culturing make use of fetal bovine serum (FBS) as a nutritional supplement. Unfortunately, FBS is an undesirable additive to cells because it carries the risk of transmitting viral and prion diseases. Therefore, the present study was undertaken to examine the efficacy of human platelet lysate (HPL) as a substitute for FBS in a large-scale set-up. METHODS. We expanded the DPSC in Dulbecco's modified Eagle's medium-knock-out (DMEM-KO) with either 10% FBS or 10% HPL, and studied the characteristics of DPSC at pre- (T25 culture flask) and post- (5-STACK chamber) large-scale expansion in terms of their identity, quality, functionality, molecular signatures and cytogenetic stability. RESULTS. In both pre- and post-large-scale expansion, DPSC expanded in HPL showed extensive proliferation of cells (c. 2-fold) compared with FBS; the purity, immune phenotype, colony-forming unit potential and differentiation were comparable. Furthermore, to understand the gene expression profiling, the transcriptomes and cytogenetics of DPSC expanded under HPL and FBS were compared, revealing similar expression profiles. CONCLUSIONS. We present a highly economized expansion of DPSC in HPL, yielding double the amount of cells while retaining their basic characteristics during a shorter time period under cGMP conditions, making it suitable for therapeutic applications.

Regenerative endodontics in light of the stem cell paradigm

Stem cells play a critical role in development and in tissue regeneration. The dental pulp contains a small sub-population of stem cells that are involved in the response of the pulp to caries progression. Specifically, stem cells replace odontoblasts that have undergone cell death as a consequence of the cariogenic challenge. Stem cells also secrete factors that have the potential to enhance pulp vascularisation and provide the oxygen and nutrients required for the dentinogenic response that is typically observed in teeth with deep caries. However, the same angiogenic factors that are required for dentine regeneration may ultimately contribute to the demise of the pulp by enhancing vascular permeability and interstitial pressure. Recent studies focused on the biology of dental pulp stem cells revealed that the multipotency and angiogenic capacity of these cells could be exploited therapeutically in dental pulp tissue engineering. Collectively, these findings suggest new treatment paradigms in the field of endodontics. The goal of this review is to discuss the potential impact of dental pulp stem cells to regenerative endodontics.

Bioengineering of dental stem cells in a PEGylated fibrin gel

AIM

Postnatal stem cells can generate tooth-specific structures after transplantation in vivo, which makes them a valuable tool for dental tissue engineering. Scaffold materials that are compatible with dental stem cells, injectable and tunable for targeted regeneration are needed. A candidate material is fibrin, a biopolymer critical to hemostasis and wound healing. Rapid degradation of fibrin can be decelerated by modification with polyethylene glycol (PEG), thus creating a hybrid material for cell delivery. The aim of this study was to evaluate the suitability of PEGylated fibrin as a scaffold for dental stem cells.

METHODS

A PEGylated fibrin hydrogel was combined with stem cells derived from dental pulp or periodontal ligament. Cell proliferation was assessed over a 4-week period, and alkaline phosphatase activity and expression levels of mineralization-associated genes after osteogenic induction were analyzed. Cell morphology, matrix degradation, collagen production and mineral deposition were evaluated by histology. Constructs of PEGylated fibrin with dental pulp stem cells in dentin disks were transplanted in immunocompromised mice for 5 weeks and examined for new tissue formation.

RESULTS

All cell types proliferated in PEGylated fibrin. After osteogenic induction, alkaline phosphatase activity was higher and osteoblast-specific genes were upregulated. Dentin-specific markers increased in pulp-derived stem cells. Histologic analysis revealed degradation of fibrin, production of a collagenous matrix and mineral deposition. In vivo transplantation rendered a vascularized soft connective tissue similar to dental pulp.

CONCLUSION

Fibrin allows for the growth and differentiation of dental stem cells, can be inserted into small defects and thus appears to be a promising biomaterial for tissue regeneration in the oral cavity.

Tooth slice/scaffold model of dental pulp tissue engineering

Multipotency is a defining characteristic of post-natal stem cells. The human dental pulp contains a small subpopulation of stem cells that exhibit multipotency, as demonstrated by their ability to differentiate into odontoblasts, neural cells, and vascular endothelial cells. These discoveries highlight the fundamental role of stem cells in the biology of the dental pulp and suggest that these cells are uniquely suited for dental pulp tissue-engineering purposes. The availability of experimental approaches specifically designed for studies of the differentiation potential of dental pulp stem cells has played an important role in these discoveries. The objective of this review is to describe the development and characterization of the Tooth Slice/Scaffold Model of Dental Pulp Tissue Engineering. In addition, we discuss the multipotency of dental pulp stem cells, focusing on the differentiation of these cells into functional odontoblasts and into vascular endothelial cells.

Tissue engineering approaches for regenerative dentistry

Although teeth can withstand enormous abrasive forces, they are susceptible to damage due to trauma, acids and bacterial attack. Conventional treatment relies on synthetic materials to fill defects and replace whole teeth, but these remain substitutes and cannot restore the tissues' physiological architecture and function. With the isolation of postnatal stem cells from various sources in the oral cavity and the development of smart materials for cell and growth factor delivery, possibilities for alternative, biology-based treatments arise. Interdisciplinary approaches are needed to move from replacement to regeneration, involving clinicians as well as biologists, stem cell researchers and material scientists. First, in order to provide an appreciation for the complexity of the tooth as a whole, its components and surrounding structures will be described. Next, the basic principles of tooth development will be presented, which can be applied to recreate signaling events and utilize them to build whole teeth. For the regeneration of individual tooth structures, the classical tissue engineering triad can be utilized, using dental stem cells, scaffold materials and relevant growth and differentiation factors. Recent successful engineering initiatives on whole teeth as well as on specific tissues such as enamel, the dentin-pulp complex or periodontal ligament will be discussed. In projecting future research directions, we conclude with a brief discussion of key components necessary to develop effective strategies for dental tissue engineering, which might enable us to implement novel regenerative strategies in clinical practice in the near future.

Pulp tissue from primary teeth: new source of stem cells

SHED (stem cells from human exfoliated deciduous teeth) represent a population of postnatal stem cells capable of extensive proliferation and multipotential differentiation. Primary teeth may be an ideal source of postnatal stem cells to regenerate tooth structures and bone, and possibly to treat neural tissue injury or degenerative diseases. SHED are highly proliferative cells derived from an accessible tissue source, and therefore hold potential for providing enough cells for clinical applications. In this review, we describe the current knowledge about dental pulp stem cells and discuss tissue engineering approaches that use SHED to replace irreversibly inflamed or necrotic pulps with a healthy and functionally competent tissue that is capable of forming new dentin.

Mesenchymal stem cells derived from dental tissues

Regeneration of tissues occurs naturally due to the existence of stem cells with the capacity to self-regenerate and differentiate; however, regenerative capacity decreases with age, and in many cases, regeneration is not sufficient to repair the damage produced by degenerative, ischaemic, inflammatory, or tumour-based diseases. In the last decade, advances have been made in the understanding of stem cells, the genes that control the alternative fates of quiescence and differentiation, and the niches that provide specific signals that modulate cell fate decisions. Embryonic stem-cell research is shedding light on the secrets of development. Adult stem cells (AS cells) are available from several sources. Bone marrow and connective tissue have been used in preliminary clinical trials for regenerative therapy. Recently, several types of AS cells have been isolated from teeth, including dental pulp stem cells, stem cells from human exfoliated deciduous teeth, periodontal ligament stem cells, dental follicle progenitor stem cells and stem cells from apical papilla. Preliminary data suggest that these cells have the capacity to differentiate into osteoblasts, adipocytes, chondrocytes and neural cells. If confirmed, these data would support the use of these cells, which are easily obtained from extracted teeth, in dental therapies, including in regenerative endodontics, providing a new therapeutic modality.

Tooth engineering: searching for dental mesenchymal cells sources

The implantation of cultured re-associations between embryonic dental mesenchymal cells and epithelial cells from mouse molars at embryonic day 14 (ED14) allowed making full teeth with crown, root, periodontal ligament fibers, and bone. Although representing valuable tools to set up methodologies embryonic cells are not easily available. This work thus aimed to replace the embryonic cells by dental mesenchymal cell lines or cultured expanded embryonic cells, and to test their ability to mediate tooth development in vitro when re-associated with a competent dental epithelium. Histology, immunostaining and RT-PCR allowed getting complementary sets of results. Two different immortalized cell lines from ED18 dental mesenchyme failed in mediating tooth formation. The potentialities of embryonic dental mesenchymal cells decreased from ED14 to ED16 and were lost at ED18. This is likely related to a change in the mesenchymal cell phenotype and/or populations during development. Attempts to cultivate ED14 or ED16 embryonic dental mesenchymal cells prior to re-association led to the loss of their ability to support tooth development. This was accompanied by a down-regulation of Fgf3 transcription. Supplementation of the culture medium with FGF2 allowed restoring Fgf3 expression, but not the ability of mesenchymal cells to engage in tooth formation. Altogether, these observations suggest that a competent cell population exists in the dental mesenchyme at ED14, progressively decreases during development, and cannot as such be maintained in vitro. This study evidenced the need for specific conditions to maintain the ability of dental mesenchymal cells to initiate whole tooth formation, when re-associated with an odontogenic epithelium. Efforts to improve the culture conditions will have to be combined with attempts to characterize the competent cells within the dental mesenchyme.

Dental pulp tissue engineering

Dental pulp is a highly specialized mesenchymal tissue that has a limited regeneration capacity due to anatomical arrangement and post-mitotic nature of odontoblastic cells. Entire pulp amputation followed by pulp space disinfection and filling with an artificial material cause loss of a significant amount of dentin leaving as life-lasting sequelae a non-vital and weakened tooth. However, regenerative endodontics is an emerging field of modern tissue engineering that has demonstrated promising results using stem cells associated with scaffolds and responsive molecules. Thereby, this article reviews the most recent endeavors to regenerate pulp tissue based on tissue engineering principles and provides insightful information to readers about the different aspects involved in tissue engineering. Here, we speculate that the search for the ideal combination of cells, scaffolds, and morphogenic factors for dental pulp tissue engineering may be extended over future years and result in significant advances in other areas of dental and craniofacial research. The findings collected in this literature review show that we are now at a stage in which engineering a complex tissue, such as the dental pulp, is no longer an unachievable goal and the next decade will certainly be an exciting time for dental and craniofacial research.

Stem cell-based biological tooth repair and regeneration

Teeth exhibit limited repair in response to damage, and dental pulp stem cells probably provide a source of cells to replace those damaged and to facilitate repair. Stem cells in other parts of the tooth, such as the periodontal ligament and growing roots, play more dynamic roles in tooth function and development. Dental stem cells can be obtained with ease, making them an attractive source of autologous stem cells for use in restoring vital pulp tissue removed because of infection, in regeneration of periodontal ligament lost in periodontal disease, and for generation of complete or partial tooth structures to form biological implants. As dental stem cells share properties with mesenchymal stem cells, there is also considerable interest in their wider potential to treat disorders involving mesenchymal (or indeed non-mesenchymal) cell derivatives, such as in Parkinson's disease.

Angiogenic activity of dentin matrix components

Angiogenesis is key to both the development and regeneration of the dentin-pulp complex.

OBJECTIVE

We hypothesized that proangiogenic signaling molecules sequestered in dentin matrix can be solubilised to induce angiogenic events.

METHODS

Matrix components were extracted from powdered sound human dentin with EDTA and their dose-dependent (0.0001-5 mg/mL) effects examined in endothelial cells in an in vitro angiogenic tube formation assay, proliferation assay, and transcriptional regulation of the VEGF and VEGF-R2 genes.

RESULTS

Lower concentrations of dentin matrix components were found to show proangiogenic activity, whereas higher concentrations suppressed angiogenic activity.

CONCLUSION

This study highlights that the release of dentin matrix components after dental injury can contribute to the angiogenic events that support pulp regeneration.