Pulp regeneration by transplantation of dental pulp stem cells in pulpitis: a pilot clinical study

Parenchymal and stromal tissue regeneration of tooth organ by pivotal signals reinstated in decellularized matrix

Cells are transplanted to regenerate an organs' parenchyma, but how transplanted parenchymal cells induce stromal regeneration is elusive. Despite the common use of a decellularized matrix, little is known as to the pivotal signals that must be restored for tissue or organ regeneration. We report that Alx3, a developmentally important gene, orchestrated adult parenchymal and stromal regeneration by directly transactivating Wnt3a and vascular endothelial growth factor. In contrast to the modest parenchyma formed by native adult progenitors, Alx3-restored cells in decellularized scaffolds not only produced vascularized stroma that involved vascular endothelial growth factor signalling, but also parenchymal dentin via the Wnt/β-catenin pathway. In an orthotopic large-animal model following parenchyma and stroma ablation, Wnt3a-recruited endogenous cells regenerated neurovascular stroma and differentiated into parenchymal odontoblast-like cells that extended the processes into newly formed dentin with a structure-mechanical equivalency to native dentin. Thus, the Alx3-Wnt3a axis enables postnatal progenitors with a modest innate regenerative capacity to regenerate adult tissues. Depleted signals in the decellularized matrix may be reinstated by a developmentally pivotal gene or corresponding protein.

Apical Papilla Cells Are Capable of Forming a Pulplike Tissue with Odontoblastlike Cells without the Use of Exogenous Growth Factors

INTRODUCTION

Dental pulp is a complex tissue with highly differentiated cells, which makes its reconstruction a challenging task. The apical papilla is an undifferentiated tissue considered as the remnant of the dental papilla that forms the dentin-pulp complex. Aiming to analyze morphologic features of the tissue formed in an in vivo pulp model, we used human apical papilla as a cell source without the use of exogenous growth factors.

METHODS

A construct was built using newborn mice molar crowns treated with TrypLE (Fisher Scientific, Loughborough, UK) and EDTA. The crowns were filled with PuraMatrix (Corning Inc, Corning, NY) and a pool population of human apical papilla cells. As a control, we used crowns filled only with PuraMatrix and empty crowns. The constructs were transplanted under severe combined immunodeficient mice kidney capsules. Immunohistochemistry for lamin A, dentin sialophosphoprotein, and dentin matrix protein 1 was performed.

RESULTS

Morphologic analysis of all transplanted crowns showed the formation of a loose connective tissue of variable cellularity with the presence of well-formed functional vessels. In the study group, lamin A-positive cells represented the majority of cells within the pulp chamber and a few cells in the vessel lining. We also found positivity for dentin sialophosphoprotein and dentin matrix protein 1, an indicator of odontoblast differentiation.

CONCLUSIONS

In our study model, human transplanted apical papilla cells mixed with the host cells and formed a vascularized viable tissue, and these cells were able to differentiate into odontoblastlike cells without the use of exogenous growth factors.

Animal Models for Stem Cell-Based Pulp Regeneration: Foundation for Human Clinical Applications

IMPACT STATEMENT

Animal models are essential for tissue regeneration studies. This review summarizes and discusses the small and large animal models, including mouse, ferret, dog, and miniswine that have been utilized to experiment and to demonstrate stem cell-mediated dental pulp tissue regeneration. We describe the models based on the location where the tissue regeneration is tested-either ectopic, semiorthotopic, or orthotopic. Developing and utilizing optimal animal models for both mechanistic and translational studies of pulp regeneration are of critical importance to advance this field.

Clinical Potential and Current Progress of Dental Pulp Stem Cells for Various Systemic Diseases in Regenerative Medicine: A Concise Review

Dental pulp stem cells (DPSCs) are mesenchymal stem cells (MSCs) that have multipotent differentiation and a self-renewal ability. They have been useful not only for dental diseases, but also for systemic diseases. Extensive studies have suggested that DPSCs are effective for various diseases, such as spinal cord injuries, Parkinson's disease, Alzheimer's disease, cerebral ischemia, myocardial infarction, muscular dystrophy, diabetes, liver diseases, eye diseases, immune diseases, and oral diseases. DPSCs have the potential for use in a cell-therapeutic paradigm shift to treat these diseases. It has also been reported that DPSCs have higher regenerative potential than the bone marrow-derived mesenchymal stem cells known as representative MSCs. Therefore, DPSCs have recently gathered much attention. In this review, the therapeutic potential of DPSCs, the latest progress in the pre-clinical study for treatment of these various systemic diseases, and the clinical applications of DPSCs in regenerative medicine, are all summarized. Although challenges, including mechanisms of the effects and establishment of cell processing and transplantation methods for clinical use, still remain, DPSCs could be promising stem cells sources for various clinical applications, because of their easy isolation by a noninvasive procedure without ethical concerns.

Cellular senescence in dental pulp stem cells

OBJECTIVE

This short review summarizes our current knowledge about dental stem cell aging and about possible targets for the regulation of cellular senescence.

DESIGN

A literature search was performed using a combination of keywords, e.g., stem cells, replicative senescence, differentiation potential, dental pulp, dental follicle and periodontal ligament.

RESULTS

Previous studies have shown that cellular senescence occurs while the proliferation of dental stem cells. Moreover, the differentiation potential was significantly decreased in senescent stem cells and senescent cells secrete also factors that are harmful to the adjacent tissue cells. Moreover, many targets for the regulation of cellular senescence are considered; for example pathways related to the nutrient sensing such as the 5' adenosine monophosphate-activated protein kinase (AMPK) pathway.

CONCLUSIONS

The regulation of cellular senescence will play a crucial role in the clinical use of stem cells. However, there is no cell culture protocol available that prevents dental stem cell senescence. Therefore, more knowledge about molecular processes in stem cells is needed before and after the induction of senescence.

Pulp Stem Cell-Mediated Functional Pulp Regeneration

The preservation of vital dental pulp with vasculature and nerve components remains one of the most significant challenges in modern dentistry. Due to the immense potential for neurovascularization, mesenchymal stem cell (MSC) transplantation has shown emerging promise in regenerative medicine and dental translational practice. Actually, pulp mesenchymal stem cells, including postnatal dental pulp stem cells (from permanent teeth) and stem cells from human exfoliated deciduous teeth, possess unique properties based on their origins from neural crest or glial cells. Furthermore, they reside in a neurovascular niche and have the potential for neurogenesis, angiogenesis, and neurovascular inductive activity. According to current pulp regeneration strategies, pulp stem cell-mediated approaches to regeneration have demonstrated convincing evidence that they can rebuild the complex histologic structure of native pulp in situ with highly organized physiologic patterns or even achieve de novo regeneration of complete dental pulp tissues. More importantly, recent clinical studies emphasized in situ neurovascularization outcomes in successful regeneration of vitalized pulp via pulp stem cell transplantation. In this review, we summarize recent breakthroughs in pulp stem cell-mediated pulp regeneration, emphasizing the crucial achievement of neurovascularization. This functional pulp regeneration represents an innovative and promising approach for future regenerative endodontics.

Recycle the dental fairy's package: overview of dental pulp stem cells

Adult stem cells are excellent cell resource for cell therapy and regenerative medicine. Dental pulp stem cells (DPSCs) have been discovered and well known in various application. Here, we reviewed the history of dental pulp stem cell study and the detail experimental method including isolation, culture, cryopreservation, and the differentiation strategy to different cell lineage. Moreover, we discussed the future potential application of the combination of tissue engineering and of DPSC differentiation. This review will help the new learner to quickly get into the DPSC filed.

Comparison of the biological characteristics of human mesenchymal stem cells derived from exfoliated deciduous teeth, bone marrow, gingival tissue, and umbilical cord

Different sources of mesenchymal stem cells (MSCs) may differ in their biological characteristics, which are important for their clinical application. In the present study, MSCs were isolated from human exfoliated deciduous teeth (SHED), bone marrow, gingival tissue and umbilical cord tissue, and their biological characteristics including surface markers, proliferation capacity, tumorigenicity and immunogenicity were analyzed by flow cytometric analysis, ELISA and co‑culture with human lymphocytes, respectively. The results indicated that all four types of stem cells obtained from different sources expressed MSC surface markers, and they did not show tumorigenicity either in vivo or in vitro. Stem cells from SHED exhibited the strongest proliferation capacity. Umbilical cord‑derived MSCs displayed the strongest immunomodulatory ability, while bone marrow MSCs exhibited the best antigen‑presenting potential in response to interferon‑γ stimulation. These results provide information on MSCs derived from different tissues, which may be helpful in their clinical application.

Magnetic resonance imaging in endodontics: a literature review

OBJECTIVES

Magnetic resonance imaging (MRI) has recently been used for the evaluation of dental pulp anatomy, vitality, and regeneration. This study reviewed the recent use of MRI in the endodontic field.

METHODS

Literature published from January 2000 to March 2017 was searched in PubMed using the following Medical Subject Heading (MeSH) terms: (1) MRI and (dental pulp anatomy or endodontic pulp); (2) MRI and dental pulp regeneration. Studies were narrowed down based on specific inclusion criteria and categorized as in vitro, in vivo, or dental pulp regeneration studies. The MRI sequences and imaging findings were summarized.

RESULTS

In the in vitro studies on dental pulp anatomy, T1-weighted imaging with high resolution was frequently used to evaluate dental pulp morphology, demineralization depth, and tooth abnormalities. Other sequences such as apparent diffusion coefficient mapping and sweep imaging with Fourier transformation were used to evaluate pulpal fluid and decayed teeth, and short-T2 tissues (dentin and enamel), respectively. In the in vivo studies, pulp vitality and reperfusion were visible with fat-saturated T2-weighted imaging or contrast-enhanced T1-weighted imaging. In both the in vitro and in vivo studies, MRI could reveal pulp regeneration after stem cell therapy. Stem cells labeled with superparamagnetic iron oxide particles were also visible on MRI. Angiogenesis induced by stem cells could be confirmed on enhanced T1-weighted imaging.

CONCLUSION

MRI can be successfully used to visualize pulp morphology as well as pulp vitality and regeneration. The use of MRI in the endodontic field is likely to increase in the future.

Impaired angiogenic differentiation of dental pulp stem cells during exposure to the resinous monomer triethylene glycol dimethacrylate

OBJECTIVE

Dental pulp stem cells (DPSCs) can differentiate into tissue specific lineages to support dental pulp regeneration after injuries. Triethylene glycol dimethacrylate (TEGDMA) is a widely used co-monomer in restorative dentistry with adverse effects on cellular metabolism. Aim of this study was to analyze the impact of TEGDMA on the angiogenic differentiation potential of DPSCs.

METHODS

DPSCs were characterized by flow cytometry. Short-term (max. 72h) cytotoxicity of TEGDMA was assessed by MTT assay. To evaluate TEGDMA effects on angiogenic differentiation, DPSCs were cultivated in angiogenic differentiation medium (ADM) in the presence or absence of short-term non-toxic TEGDMA concentrations (0.1mM and 0.25mM). Subsequently, angiogenic differentiation was analyzed by qRT-PCR analysis of mRNA markers and in vitro spheroid sprouting assays.

RESULTS

DPSCs treated with 0.25mM TEGDMA revealed downregulation of angiogenesis-related marker genes PECAM1 (max. 3.8-fold), VEGF-A (max. 2.4-fold) and FLT1 (max. 2.9-fold) compared to respective untreated control. In addition, a reduction of the sprouting potential of DPSCs cultured in the presence of 0.25mM TEGDMA was detectable. Larger spheroidal structures were detectable in the untreated control in comparison to cells treated with 0.25mM TEGDMA. In contrast, TEGDMA at 0.1mM was not affecting angiogenic potential in the investigated time period (up to 28 days).

SIGNIFICANCE

The results of the present study show that TEGDMA concentration dependently impair the angiogenic differentiation potential of DPSCs and may affect wound healing and the formation of granulation tissue.

Tooth Repair and Regeneration

PURPOSE OF REVIEW

Current dental treatments are based on conservative approaches, using inorganic materials and appliances.This report explores and discusses the newest achievements in the field of "regenerative dentistry," based on the concept of biological repair as an alternative to the current conservative approach.

RECENT FINDINGS

The review covers and critically analyzes three main approaches of tooth repair: the re-mineralization of the enamel, the biological repair of dentin, and whole tooth engineering.

SUMMARY

The development of a concept of biological repair based on the role of the Wnt signaling pathway in reparative dentin formation offers a new translational approach into development of future clinical dental treatments.In the field of bio-tooth engineering, the current focus of the researchers remains the establishment of odontogenic cell-sources that would be viable and easily accessible for future bio-tooth engineering.

Current and future options for dental pulp therapy

Dental pulp is a connective tissue and has functions that include initiative, formative, protective, nutritive, and reparative activities. However, it has relatively low compliance, because it is enclosed in hard tissue. Its low compliance against damage, such as dental caries, results in the frequent removal of dental pulp during endodontic therapy. Loss of dental pulp frequently leads to fragility of the tooth, and eventually, a deterioration in the patient’s quality of life. With the development of biomaterials such as bioceramics and advances in pulp biology such as the identification of dental pulp stem cells, novel ideas for the preservation of dental pulp, the regenerative therapy of dental pulp, and new biomaterials for direct pulp capping have now been proposed. Therapies for dental pulp are classified into three categories; direct pulp capping, vital pulp amputation, and treatment for non-vital teeth. In this review, we discuss current and future treatment options in these therapies.

Growth Factors and Cell Homing in Dental Tissue Regeneration

Purpose of Review

To summarize current views on the role and therapeutic potential of growth factors (GFs) within endodontic cell homing.

Recent Findings

Cell homing/revitalization techniques aim to regenerate dentin and pulp using endogenous cells. Clinically, revitalization has successfully created new vital tissue in necrotic permanent teeth with an open apex; however, there is no evidence of new odontoblasts, pulp tissue, or predictable extension in root length. Although the response is reparative rather than regenerative, exciting opportunities to improve these biologically-based strategies remain by (1) efficiently sequestering dentin-matrix-components (DMCs) using irrigants and dental materials (2) designing next-generation GF-releasing scaffold materials and (3) utilizing other sources of GF such as cells and plasma-rich plasma and plasma-rich fibrin.

Summary

GFs can promote reparative-dentinogenesis and pulp-like tissue formation. The future development and clinical approval of GF-functionalized-scaffolds is a priority; however, current focus should be to harness DMCs and target the interaction of stem cells and GFs.

Novel Biological and Technological Platforms for Dental Clinical Use

Human teeth have a limited capacity to regenerate and thus biological reconstruction of damaged or lost dental tissues remains a significant challange in modern dentistry. Recent efforts focus on alternative therapeutic approaches for partial or whole tooth regeneration that complement traditional dental treatments using sophisticated materials and dental implants. These multidisciplinary approaches are based on the combination of stem cells with advanced tissue engineer products and computing technology, and they hold great promise for future applications in dentistry. The administration to patients of dynamic biological agents composed by stem cells and scaffolds will certainly increase the regenerative capacity of dental pathological tissues. The design of innovative materials for tissue restoration, diagnostics, imaging, and targeted pharmaceutical treatment will significantly improve the quality of dental care and will have a major societal impact. This review depicts the current challenges in dentistry and describes the possibilities for novel and succesful therapeutic applications in the near future.

Regenerative endodontics: a comprehensive review

The European Society of Endodontology and the American Association for Endodontists have released position statements and clinical considerations for regenerative endodontics. There is increasing literature on this field since the initial reports of Iwaya et al. (Dental Traumatology, 17, 2001, 185) and Banchs & Trope (Journal of Endodontics, 30, 2004, 196). Endogenous stem cells from an induced periapical bleeding and scaffolds using blood clot, platelet rich plasma or platelet-rich fibrin have been utilized in regenerative endodontics. This approach has been described as a 'paradigm shift' and considered the first treatment option for immature teeth with pulp necrosis. There are three treatment outcomes of regenerative endodontics; (i) resolution of clinical signs and symptoms; (ii) further root maturation; and (iii) return of neurogenesis. It is known that results are variable for these objectives, and true regeneration of the pulp/dentine complex is not achieved. Repair derived primarily from the periodontal and osseous tissues has been shown histologically. It is hoped that with the concept of tissue engineering, namely stem cells, scaffolds and signalling molecules, that true pulp regeneration is an achievable goal. This review discusses current knowledge as well as future directions for regenerative endodontics. Patient-centred outcomes such as tooth discolouration and possibly more appointments with the potential for adverse effects needs to be discussed with patients and parents. Based on the classification of Cvek (Endodontics and Dental Traumatology, 8, 1992, 45), it is proposed that regenerative endodontics should be considered for teeth with incomplete root formation although teeth with near or complete root formation may be more suited for conventional endodontic therapy or MTA barrier techniques. However, much is still not known about clinical and biological aspects of regenerative endodontics.

Allogeneic transplantation of mobilized dental pulp stem cells with the mismatched dog leukocyte antigen type is safe and efficacious for total pulp regeneration

Background

We recently demonstrated that autologous transplantation of mobilized dental pulp stem cells (MDPSCs) was a safe and efficacious potential therapy for total pulp regeneration in a clinical study. The autologous MDPSCs, however, have some limitations to overcome, such as limited availability of discarded teeth from older patients. In the present study, we investigated whether MDPSCs can be used for allogeneic applications to expand their therapeutic use.

Methods

Analysis of dog leukocyte antigen (DLA) was performed using polymerase chain reaction from blood. Canine allogeneic MDPSCs with the matched and mismatched DLA were transplanted with granulocyte-colony stimulating factor in collagen into pulpectomized teeth respectively (n = 7, each). Results were evaluated by hematoxylin and eosin staining, Masson trichrome staining, PGP9.5 immunostaining, and BS-1 lectin immunostaining performed 12 weeks after transplantation. The MDPSCs of the same DLA used in the first transplantation were further transplanted into another pulpectomized tooth and evaluated 12 weeks after transplantation.

Results

There was no evidence of toxicity or adverse events of the allogeneic transplantation of the MDPSCs with the mismatched DLA. No adverse event of dual transplantation of the MDPSCs with the matched and mismatched DLA was observed. Regenerated pulp tissues including neovascularization and neuronal extension were quantitatively and qualitatively similar at 12 weeks in both matched and mismatched DLA transplants. Regenerated pulp tissue was similarly observed in the dual transplantation as in the single transplantation of MDPSCs both with the matched and mismatched DLA.

Conclusions

Dual allogeneic transplantation of MDPSCs with the mismatched DLA is a safe and efficacious method for total pulp regeneration.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0855-8) contains supplementary material, which is available to authorized users.

Dental Mesenchymal Stem/Stromal Cells and Their Exosomes

Stem cells derived from human dental pulp tissue (DP-MSC) differ from the other mesenchymal stem cells prepared from bone marrow or adipose tissue due to their embryonic origin from the neural crest and are of special interest because of their neurotropic character. Furthermore, the therapeutic potential of DP-MSCs is realized through paracrine action of extracellularly released components, for which exosomes play an important role. In this review, we intend to explore the properties of these cells with an emphasis on exosomes. The therapeutic applicability of these cells and exosomes in dental practice, neurodegenerative diseases, and many other difficultly treatable diseases, like myocardial infarction, focal cerebral ischemia, acute lung or brain injury, acute respiratory distress syndrome, acute inflammation, and several others is concisely covered. The use of cellular exosomes as an important diagnostic marker and indicator of targeted cancer therapies is also discussed, while the importance of stem cells from human exfoliated deciduous teeth as a source of evolutionally young cells for future regenerative therapies is stressed. We conclude that exosomes derived from these cells are potent therapeutic tools for regenerative medicine in the near future as clinical administration of DP-MSC-conditioned medium and/or exosomes is safer and more practical than stem cells.

KDM1A regulated the osteo/dentinogenic differentiation process of the stem cells of the apical papilla via binding with PLOD2

OBJECTIVES

Dental tissue-derived mesenchymal stem cells (MSCs)-mediated pulp-dentin regeneration is considered a potential approach for the regeneration of damaged teeth. Enhancing MSC-mediated pulp-dentin regeneration is based on an understanding of the molecular mechanisms underlying directed cell differentiation process. Histone demethylation enzyme, lysine demethylase 1A (KDM1A) can regulate the differentiation of some MSCs, but its role in dental tissue-derived MSCs is unclear.

MATERIAL AND METHODS

We obtained SCAPs from immature teeth. Alkaline phosphatase (ALP) activity assay, Alizarin red staining, quantitative calcium analysis, osteogenesis-related genes expression and in vivo transplantation experiment were used to explore the osteo/dentinogenic differentiation. Co-immunoprecipitation (Co-IP) assay was used to investigate the binding protein.

RESULTS

Knock-down of KDM1A reduced ALP activity and mineralization, promoted the expressions of osteo/dentinogenic differentiation markers DSPP, DMP1, BSP and key transcript factors, RUNX2, OSX, DLX2 in SCAPs, and also enhanced the osteo/dentinogenesis in vivo. In addition, KDM1A could associate with PLOD2 to form protein complex. And knock-down of PLOD2 inhibited ALP activity and mineralization, and promoted the expressions of DSPP, DMP1, BSP, RUNX2, OSX and DLX2 in SCAPs.

CONCLUSIONS

KDM1A might have different role in different stages of osteo/dentinogenic differentiation process by binding partner with PLOD2, and finally resulted in the inhibited function for the osteo/dentinogenesis in SCAPs. Our studies provided a further understanding of the regulatory mechanisms of dynamic osteo/dentinogenic differentiation process in dental tissue MSCs.

Characterization of human dental pulp cells grown in chemically defined serum-free medium

Dental pulp cells (DPCs) are promising candidates for use as transplantable cells in regenerative medicine. However, ex vivo expansion of these cells typically requires culture media containing fetal bovine serum, which may cause infection and immunological reaction following transplantation. In addition, the proliferation and differentiation of DPCs markedly depend upon serum batches. Therefore, the present study examined whether DPCs could be expanded under serum-free conditions. DPCs obtained from four donors were identified to proliferate actively in the serum-free medium, STK2, when compared with those cells in control medium (Dulbecco's modified Eagle's medium containing 10% serum). The high proliferative potential with STK2 was maintained through multiple successive culture passages. DNA microarray analyses demonstrated that the gene expression profile of DPCs grown in STK2 was similar to that of cells grown in the control medium; however, a number of genes related to cell proliferation, including placental growth factor and inhibin-βE, were upregulated in the STK2 cultures. Following induction of osteogenesis, DPCs grown in STK2 induced alkaline phosphatase activity and calcification at higher levels compared with the control medium cultures, indicating maintenance of differentiation potential in STK2. This serum-free culture system with DPCs may have applications in further experimental studies and as a clinical strategy in regenerative medicine.

Progress in the use of dental pulp stem cells in regenerative medicine

The field of tissue engineering is emerging as a multidisciplinary area with promising potential for regenerating new tissues and organs. This approach requires the involvement of three essential components: stem cells, scaffolds and growth factors. To date, dental pulp stem cells have received special attention because they represent a readily accessible source of stem cells. Their high plasticity and multipotential capacity to differentiate into a large array of tissues can be explained by its neural crest origin, which supports applications beyond the scope of oral tissues. Many isolation, culture and cryopreservation protocols have been proposed that are known to affect cell phenotype, proliferation rate and differentiation capacity. The clinical applications of therapies based on dental pulp stem cells demand the development of new biomaterials suitable for regenerative purposes that can act as scaffolds to handle, carry and implant stem cells into patients. Currently, the development of xeno-free culture media is emerging as a means of standardization to improve safe and reproducibility. The present review aims to describe the current knowledge of dental pulp stem cells, considering in depth the key aspects related to the characterization, establishment, maintenance and cryopreservation of primary cultures and their involvement in the multilineage differentiation potential. The main clinical applications for these stem cells and their combination with several biomaterials is also covered.

Establishment of xenogeneic serum-free culture methods for handling human dental pulp stem cells using clinically oriented in-vitro and in-vivo conditions

Background

Currently, ex-vivo handling of stem cells, including transport after harvest and therapeutic preparation, is generally done in culture media containing fetal bovine serum (FBS), which promotes cell attachment, proliferation, and differentiation. However, because of safety concerns associated with the use of FBS, including potential transmission of zoonotic agents and transplant rejection because of the incorporation of foreign proteins into the stem cells, there is a need for xenogeneic serum-free culture media for clinical handling of stem cells.

Methods

Dental pulp stem cells were derived from wisdom teeth donated by eight healthy volunteers and cultured in xenogeneic serum-free culture medium (XFM) or xenogeneic serum-containing culture medium (SCM). Cells were subjected to morphological, proliferation, karyotype, differentiation, marker expression, cryopreservation, and cytotoxic susceptibility analyses in vitro, as well as transplantation in vivo.

Results

In primary culture, XFM cells showed lower adhesion and slightly different morphology, although the single-cell size was similar to that of SCM cells. XFM cells exhibited typical mesenchymal stem cell (MSC) characteristics in vitro and in vivo, including marker gene/protein expression, trilineage differentiation potential, and hard, osteo-dentin tissue formation. Additionally, XFM cells maintained a normal karyotype in vitro and nontumorigenic potential in vivo; however, XFM cells were more susceptible to H₂O₂ and ultraviolet cytotoxic stimuli. XFM cells formed a multilayered structure showing excessive cell death/division in contrast to the monolayered structure of SCM cells when reaching overconfluence. Proliferation was disrupted in overconfluent XFM cells, and these cells could not be subcultured. Dimethyl sulfoxide-free cryopreserved XFM cells yielded similar results in all of the experiments.

Conclusions

This study is the first reporting successful isolation and expansion of an MSC population from donor-derived tissue (dental pulp) under xenogeneic serum-free culture conditions, as well as the application of cryopreservation, using a research strategy based on clinically oriented in-vitro and in-vivo experiments.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0761-5) contains supplementary material, which is available to authorized users.

A dentin-derived hydrogel bioink for 3D bioprinting of cell laden scaffolds for regenerative dentistry

Recent studies in tissue engineering have adopted extracellular matrix (ECM) derived scaffolds as natural and cytocompatible microenvironments for tissue regeneration. The dentin matrix, specifically, has been shown to be associated with a host of soluble and insoluble signaling molecules that can promote odontogenesis. Here, we have developed a novel bioink, blending printable alginate (3% w/v) hydrogels with the soluble and insoluble fractions of the dentin matrix. We have optimized the printing parameters and the concentrations of the individual components of the bioink for print accuracy, cell viability and odontogenic potential. We find that, while viscosity, and hence printability of the bioinks, was greater in the formulations containing higher concentrations of alginate, a higher proportion of insoluble dentin matrix proteins significantly improved cell viability; where a 1:1 ratio of alginate and dentin (1:1 Alg-Dent) was most suitable. We further demonstrate high retention of the soluble dentin molecules within the 1:1 Alg-Dent hydrogel blends, evidencing renewed interactions between these molecules and the dentin matrix post crosslinking. Moreover, at concentrations of 100 μg ml^-1, these soluble dentin molecules significantly enhanced odontogenic differentiation of stem cells from the apical papilla encapsulated in bioprinted hydrogels. In summary, the proposed novel bioinks have demonstrable cytocompatibility and natural odontogenic capacity, which can be a used to reproducibly fabricate scaffolds with complex three-dimensional microarchitectures for regenerative dentistry in the future.

A Miniature Swine Model for Stem Cell-Based De Novo Regeneration of Dental Pulp and Dentin-Like Tissue

The goal of this study was to establish mini-swine as a large animal model for stem cell-based pulp regeneration studies. Swine dental pulp stem cells (sDPSCs) were isolated from mini-swine and characterized in vitro. For in vivo studies, we first employed both ectopic and semi-orthotopic study models using severe combined immunodeficiency mice. One is hydroxyapatite-tricalcium phosphate (HA/TCP) model for pulp-dentin complex formation, and the other is tooth fragment model for complete pulp regeneration with new dentin depositing along the canal walls. We found that sDPSCs are similar to their human counterparts exhibiting mesenchymal stem cell characteristics with ability to form colony forming unit-fibroblastic and odontogenic differentiation potential. sDPSCs formed pulp-dentin complex in the HA/TCP model and showed pulp regeneration capacity in the tooth fragment model. We then tested orthotopic pulp regeneration on mini-swine including the use of multi-rooted teeth. Using autologous sDPSCs carried by hydrogel and transplanted into the mini-swine root canal space, we observed regeneration of vascularized pulp-like tissue with a layer of newly deposited dentin-like (rD) tissue or osteodentin along the canal walls. In some cases, dentin bridge-like structure was observed. Immunohistochemical analysis detected the expression of nestin, dentin sialophosphoprotein, dentin matrix protein 1, and bone sialoprotein in odontoblast-like cells lining against the produced rD. We also tested the use of allogeneic sDPSCs for the same procedures. Similar findings were observed in allogeneic transplantation. This study is the first to show an establishment of mini-swine as a suitable large animal model utilizing multi-rooted teeth for further cell-based pulp regeneration studies.

EDTA Treatment for Sodium Hypochlorite-treated Dentin Recovers Disturbed Attachment and Induces Differentiation of Mouse Dental Papilla Cells

INTRODUCTION

The disturbance of cellular attachment to dentin by sodium hypochlorite (NaOCl) may hamper pulp tissue regeneration. The aims of this study were to examine the recovering effect of EDTA on the attachment/differentiation of stemlike cells and to address the mechanisms of EDTA-induced recovery under the hypothesis that attachment to the exposed dentin matrix and the subsequent activation of integrin/phosphatidylinositol 3-kinase (PI3K) signaling play a crucial role.

METHODS

Mouse dental papilla (MDP) cells were cultured on bovine dentin disks treated with NaOCl (0%, 1.5%, or 6%) followed by EDTA (0%, 3%, or 17%). Cell attachment was evaluated by cell density, viability, and scanning and transmission electron microscopy. Odonto-/osteoblastic gene expression in attached MDP cells was analyzed with or without a pan-PI3K inhibitor (LY294002) using real-time polymerase chain reaction.

RESULTS

NaOCl treatment (1.5%, 10 minutes) significantly diminished attached MDP cells (P < .00001), but EDTA treatment (3% and 17%, ≥10 minutes) of NaOCl-pretreated dentin induced a significant increase in attached cells (P < .05). Ultrastructurally, MDP cells on EDTA-treated dentin showed attachment to exposed collagen fibers. MDP cells cultured on EDTA-treated disks (with or without 1.5% NaOCl pretreatment) showed significant up-regulation of alkaline phosphatase, dentin matrix protein 1, and dentin sialophosphoprotein messenger RNAs (P < .05). Alkaline phosphatase expression was down-regulated by LY294002 (P < .05).

CONCLUSIONS

Under the present experimental conditions, 10 minutes of EDTA treatment was sufficient to recover attachment/differentiation of MDP cells on 1.5% NaOCl-pretreated dentin. EDTA-induced exposure of collagen fibers and subsequent activation of integrin/PI3K signaling may contribute, at least partly, to the recovery.

Dental stem cells: recent progresses in tissue engineering and regenerative medicine

Since the disclosure of adult mesenchymal stem cells (MSCs), there have been an intense investigation on the characteristics of these cells and their potentialities. Dental stem cells (DSCs) are MSC-like populations with self-renewal capacity and multidifferentiation potential. Currently, there are five main DSCs, dental pulp stem cells (DPSCs), stem cells from exfoliated deciduous teeth (SHED), stem cells from apical papilla (SCAP), periodontal ligament stem cells (PDLSCs) and dental follicle precursor cells (DFPCs). These cells are extremely accessible, prevail during all life and own an amazing multipotency. In the past decade, DPSCs and SHED have been thoroughly studied in regenerative medicine and tissue engineering as autologous stem cells therapies and have shown amazing therapeutic abilities in oro-facial, neurologic, corneal, cardiovascular, hepatic, diabetic, renal, muscular dystrophy and auto-immune conditions, in both animal and human models, and most recently some of them in human clinical trials. In this review, we focus the characteristics, the multiple roles of DSCs and its potential translation to clinical settings. These new insights of the apparently regenerative aptitude of these DSCs seems quite promising to investigate these cells abilities in a wide variety of pathologies. Key messages Dental stem cells (DSCs) have a remarkable self-renewal capacity and multidifferentiation potential; DSCs are extremely accessible and prevail during all life; DSCs, as stem cells therapies, have shown amazing therapeutic abilities in oro-facial, neurologic, corneal, cardiovascular, hepatic, diabetic, renal, muscular dystrophy and autoimmune conditions; DSCs are becoming extremely relevant in tissue engineering and regenerative medicine.

Dental stem cells in tooth regeneration and repair in the future

INTRODUCTION

Human dental stem cells can be obtained from postnatal teeth, extracted wisdom teeth or exfoliated deciduous teeth. Due to their differentiation potential, these mesenchymal stem cells are promising for tooth repair. Therefore, the development of dental tissue regeneration represents a suitable but challenging, target for dental stem cell therapies. Areas covered: Expert opinion:

AREAS COVERED

In this review, the authors provide an overview of human dental stem cells and their properties for regeneration medicine. Numerous preclinical studies have shown that dental stem cells improve bone augmentation and healing of periodontal diseases. Clinical trials are ongoing to validate the clinical feasibility of these approaches. Dental stem cells are also important for basic research.

EXPERT OPINION

Dental stem cells offer numerous advantages for tooth repair and regeneration. Data obtained from different studies are encouraging. In the next few years, investigations on dental stem cells in basic research, pre-clinical research and clinical studies will pave the way to optimizing patient-tailored treatments for repair and regeneration of dental tissues.

Effect of iRoot Fast Set root repair material on the proliferation, migration and differentiation of human dental pulp stem cells in vitro

The present study investigated the effect of iRoot Fast Set root repair material (iRoot FS) on the proliferation, migration and differentiation of human dental pulp stem cells (hDPSCs). The hDPSCs were treated with eluates of iRoot FS at concentrations of 0.2 and 2 mg/mL, referred to as FS0.2 and FS2, respectively, and Biodentine (BD; Septodont, Saint Maur des Faussés, France) eluates at the corresponding concentrations as positive controls. A CCK8 assay was performed to determine cell proliferation. Wound healing and transwell assays were conducted to examine cell migration. Osteogenic differentiation was evaluated based on alkaline phosphatase activity, Alizarin Red S staining and quantitative real-time reverse-transcriptase polymerase chain reaction (qRT-PCR) to analyze the mRNA expression of differentiation gene markers. Cell proliferation was higher in the FS and BD groups than in the blank controls at 3 and 7 days. Moreover, FS0.2 enhanced cell migration and significantly promoted the osteogenic differentiation of hDPSCs. These findings suggested that iRoot FS is a bioactive material that promotes the proliferation, migration and osteogenic differentiation of hDPSCs.

Advanced Scaffolds for Dental Pulp and Periodontal Regeneration

No current therapy promotes root canal disinfection and regeneration of the pulp-dentin complex in cases of pulp necrosis. Antibiotic pastes used to eradicate canal infection negatively affect stem cell survival. Three-dimensional easy-to-fit antibiotic-eluting nanofibers, combined with injectable scaffolds, enriched or not with stem cells and/or growth factors, may increase the likelihood of achieving predictable dental pulp regeneration. Periodontitis is an aggressive disease that impairs the integrity of tooth-supporting structures and may lead to tooth loss. The latest advances in membrane biomodification to endow needed functionalities and technologies to engineer patient-specific membranes/constructs to amplify periodontal regeneration are presented.

Implanted Dental Pulp Cells Fail to Induce Regeneration in Partial Pulpotomies

Cell-based partial pulp regeneration is one of the promising approaches to obtain newly formed functional dentin-pulp complex. It relies on the preservation of the healthy tissue while regenerating the damaged pulp. The aim of this study was to investigate whether this regenerative process could be achieved by implanting porcine dental pulp cells (pDPCs) in pulp defects in the minipig. By split-mouth model, self-assembling injectable nanopeptide hydrogel, with and without pDPCs, was implanted after cameral pulpotomy in premolars and molars. At day 21 after surgery, 3-dimensional morphometric characterization, Masson's trichrome staining, and immunolabeling for DSP and BSP (dentin sialoprotein and bone sialoprotein) were performed on treated teeth. This study demonstrated no pulp regeneration but systematic reparative dentinogenesis. In fact, regardless of the presence of pDPCs in the scaffold, an osteodentin bridge-the microarchitecture of which significantly differed from the native dentin-was systematically obtained. Furthermore, the presence of pDPCs significantly affected the microstructure of the dentin bridges. In the radicular area of each treated tooth, hyperemia in the remaining pulp and external root resorptions were observed. Under the conditions tested in this work, pulp regeneration was not achieved, which highlights the need of further investigations to develop favorable regenerative microenvironment.

The cell cycle regulator protein P16 and the cellular senescence of dental follicle cells

Cellular senescence is a restricting factor for regenerative therapies with somatic stem cells. We showed previously that the onset of cellular senescence inhibits the osteogenic differentiation in stem cells of the dental follicle (DFCs), although the mechanism remains elusive. Two different pathways are involved in the induction of the cellular senescence, which are driven either by the cell cycle protein P21 or by the cell cycle protein P16. In this study, we investigated the expression of cell cycle proteins in DFCs after the induction of cellular senescence. The induction of cellular senescence was proved by an increased expression of β-galactosidase and an increased population doubling time after a prolonged cell culture. Cellular senescence regulated the expression of cell cycle proteins. The expression of cell cycle protein P16 was up-regulated, which correlates with the induction of cellular senescence markers in DFCs. However, the expression of cyclin-dependent kinases (CDK)2 and 4 and the expression of the cell cycle protein P21 were successively decreased in DFCs. In conclusion, our data suggest that a P16-dependent pathway drives the induction of cellular senescence in DFCs.

Recent Progress in Translation from Bench to a Pilot Clinical Study on Total Pulp Regeneration

Based on a preclinical bench study in dogs, a pilot clinical study was completed. Dental pulp stem cell (DPSC) subsets were isolated by mobilization by granulocyte colony-stimulating factor and expanded in good manufacturing practice conditions. The safety and efficacy of their autologous transplantation for total pulp regeneration was assessed in 5 patients with irreversible pulpitis. The quality control of the DPSC subsets was ensured by the absence of contamination and karyotype aberrations, and positive expression of stem cell markers. The clinical safety assessment was based on laboratory and radiographic evaluations, demonstrating no evidence of toxicity and adverse events. The efficacy was determined by the recovery of a sound positive response to the electric pulp test within 4 weeks and by the robust signal intensity of magnetic resonance imaging in the root canal at 24 weeks. The functional recovery of pulp tissue was determined by lateral mineralized tissue formation detected by cone beam computed tomography. This review presents a summary of the accumulating data in translation from bench to a pilot clinical study, demonstrating potential clinical utility of DPSC subsets for total pulp regeneration in endodontics.

Chitosan Biomaterials for Current and Potential Dental Applications

Chitosan (CHS) is a very versatile natural biomaterial that has been explored for a range of bio-dental applications. CHS has numerous favourable properties such as biocompatibility, hydrophilicity, biodegradability, and a broad antibacterial spectrum (covering gram-negative and gram-positive bacteria as well as fungi). In addition, the molecular structure boasts reactive functional groups that provide numerous reaction sites and opportunities for forging electrochemical relationships at the cellular and molecular levels. The unique properties of CHS have attracted materials scientists around the globe to explore it for bio-dental applications. This review aims to highlight and discuss the hype around the development of novel chitosan biomaterials. Utilizing chitosan as a critical additive for the modification and improvement of existing dental materials has also been discussed.