Current Approaches and Challenges in Making a Bio-Tooth

Subcutaneous implantation of tooth germ stem cells over the masseter muscle in mice: An in vivo pilot study

Objectives

This study aimed to explore the potential of tooth germ stem cells for regenerating tooth-like structures by subcutaneously implanting first molar tooth germ stem cells over the masseter muscle in mice.

Methods

Five pairs of house mice, Mus musculus, were selected for mating. At gestational day 14 (E14), the fetuses were extracted, and the first molar tooth germ at the cap stage was isolated. Tooth germ stem cells were prepared into a suspension and seeded onto scaffolds, which were then implanted subcutaneously over the masseter muscle in male mice. The control group (n = 5 male mice) received acellular scaffolds implanted at the same site. After 20 days, the regenerated tissues were resected and analyzed histologically using hematoxylin and eosin (H & E) staining, Masson's trichrome staining, and immunohistochemical (IHC) staining for cytokeratin (CK) and vimentin markers.

Results

H & E staining showed the formation of integrated oval structures at the implant site in all samples. Masson's trichrome staining identified dispersed accumulations of cellular mineralized matrix within the connective tissue. IHC staining was positive for vimentin, confirming the mesenchymal origin of the loose tissue at the center, indicating future dental pulp development. Positive CK staining indicated the ectodermal origin of dense peripheral tissues, suggesting the future formation of inner enamel epithelium. The combined immunohistochemical results for vimentin and CK confirmed the ecto-mesenchymal origin of the regenerated tissue, which resembled a late bell-stage tooth germ observed around gestational days 17.5-18 and showed early indications of dentin formation (D0).

Conclusion

The study indicates that tooth germ stem cells may have the potential to produce dense, tooth-like structures when implanted subcutaneously in mice. These findings provide preliminary insights into the possible applications of tooth germ stem cells in regenerative dental tissue engineering.

Influence of extracellular matrix scaffolds on histological outcomes of regenerative endodontics in experimental animal models: a systematic review

BACKGROUND

Decellularized extracellular matrix (dECM) from several tissue sources has been proposed as a promising alternative to conventional scaffolds used in regenerative endodontic procedures (REPs). This systematic review aimed to evaluate the histological outcomes of studies utilizing dECM-derived scaffolds for REPs and to analyse the contributing factors that might influence the nature of regenerated tissues.

METHODS

The PRISMA 2020 guidelines were used. A search of articles published until April 2024 was conducted in Google Scholar, Scopus, PubMed and Web of Science databases. Additional records were manually searched in major endodontic journals. Original articles including histological results of dECM in REPs and in-vivo studies were included while reviews, in-vitro studies and clinical trials were excluded. The quality assessment of the included studies was analysed using the ARRIVE guidelines. Risk of Bias assessment was done using the (SYRCLE) risk of bias tool.

RESULTS

Out of the 387 studies obtained, 17 studies were included for analysis. In most studies, when used as scaffolds with or without exogenous cells, dECM showed the potential to enhance angiogenesis, dentinogenesis and to regenerate pulp-like and dentin-like tissues. However, the included studies showed heterogeneity of decellularization methods, animal models, scaffold source, form and delivery, as well as high risk of bias and average quality of evidence.

DISCUSSION

Decellularized ECM-derived scaffolds could offer a potential off-the-shelf scaffold for dentin-pulp regeneration in REPs. However, due to the methodological heterogeneity and the average quality of the studies included in this review, the overall effectiveness of decellularized ECM-derived scaffolds is still unclear. More standardized preclinical research is needed as well as well-constructed clinical trials to prove the efficacy of these scaffolds for clinical translation.

OTHER

The protocol was registered in PROSPERO database #CRD42023433026. This review was funded by the Science, Technology and Innovation Funding Authority (STDF) under grant number (44426).

Current Trends, Advances, and Challenges of Tissue Engineering-Based Approaches of Tooth Regeneration: A Review of the Literature

INTRODUCTION

Tooth loss is a significant health issue. Currently, this situation is often treated with the use of synthetic materials such as implants and prostheses. However, these treatment modalities do not fully meet patients' biological and mechanical needs and have limited longevity. Regenerative medicine focuses on the restoration of patients' natural tissues via tissue engineering techniques instead of rehabilitating with artificial appliances. Therefore, a tissue-engineered tooth regeneration strategy seems like a promising option to treat tooth loss.

OBJECTIVE

This review aims to demonstrate recent advances in tooth regeneration strategies and discoveries about underlying mechanisms and pathways of tooth formation.

RESULTS AND DISCUSSION

Whole tooth regeneration, tooth root formation, and dentin-pulp organoid generation have been achieved by using different seed cells and various materials for scaffold production. Bioactive agents are critical elements for the induction of cells into odontoblast or ameloblast lineage. Some substantial pathways enrolled in tooth development have been figured out, helping researchers design their experiments more effectively and aligned with the natural process of tooth formation.

CONCLUSION

According to current knowledge, tooth regeneration is possible in case of proper selection of stem cells, appropriate design and manufacturing of a biocompatible scaffold, and meticulous application of bioactive agents for odontogenic induction. Understanding innate odontogenesis pathways play a crucial role in accurately planning regenerative therapeutic interventions in order to reproduce teeth.

Adipose-derived stromal/stem cells are verified to be potential seed candidates for bio-root regeneration in three-dimensional culture

BACKGROUND

Bio-root regeneration is a promising treatment for tooth loss. It has been reported that dental-derived stem cells are effective seed cells for bio-root construction, but further applications are limited by their few sources. Human adipose tissues have a wide range of sources and numerous studies have confirmed the ability of adipose-derived stromal/stem cells (ASCs) in regenerative medicine. In the current study, the odontogenic capacities of ASCs were compared with dental-derived stem cells including dental follicle cells (DFCs), and stem cells from human exfoliated deciduous teeth (SHEDs).

METHODS

The biological characteristics of ASCs, DFCs, and SHEDs were explored in vitro. Two-dimensional (2D) and three-dimensional (3D) cultures were compared in vitro. Odontogenic characteristics of porcine-treated dentin matrix (pTDM) induced cells under a 3D microenvironment in vitro were compared. The complexes (cell/pTDM) were transplanted subcutaneously into nude mice to verify regenerative potential. RNA sequencing (RNA-seq) was used to explore molecular mechanisms of different seed cells in bio-root regeneration.

RESULTS

3D culture was more efficient in constructing bio-root complexes. ASCs exhibited good biological characteristics similar to dental-derived stem cells in vitro. Besides, pTDM induced ASCs presented odontogenic ability similar to dental-derived stem cells. Furthermore, 3D cultured ASCs/pTDM complex promoted regeneration of dentin-like, pulp-like, and periodontal fiber-like tissues in vivo. Analysis indicated that PI3K-Akt, VEGF signaling pathways may play key roles in the process of inducing ASCs odontogenic differentiation by pTDM.

CONCLUSIONS

ASCs are potential seed cells for pTDM-induced bio-root regeneration, providing a basis for further research and application.

Microstructured Hyaluronic Acid Hydrogel for Tooth Germ Bioengineering

Tooth loss has been found to adversely affect not just masticatory and speech functions, but also psychological health and quality of life. Currently, teeth replacement options include dentures, bridges, and implants. However, these artificial replacement options remain inferior to biological replacements due to their reduced efficiency, the need for replacements, and the risk of immunological rejection. To this end, there has been a heightened interest in the bioengineering of teeth in recent years. While there have been reports of successfully regenerated teeth, controlling the size and shape of bioengineered teeth remains a challenge. In this study, methacrylated hyaluronic acid (MeHA) was synthesized and microstructured in a hydrogel microwell array using soft lithography. The resulting MeHA hydrogel microwell scaffold resembles the shape of a naturally developing human tooth germ. To facilitate the epithelial-mesenchymal interactions, human adult low calcium high temperature (HaCaT) cells were seeded on the surface of the hydrogels and dental pulp stem cells (DPSCs) were encapsulated inside the hydrogels. It was found that hydrogel scaffolds were able to preserve the viability of both types of cells and they appeared to favor signaling between epithelial and mesenchymal cells, which is necessary in the promotion of cell proliferation. As such, the hydrogel scaffolds offer a promising system for the bioengineering of human tooth germs in vitro.

Biological tooth root reconstruction with a scaffold of swine treated dentin matrix

Treated dentin matrix (TDM) is an ideal scaffolding material with odontogenic ability, which is important for supporting cell growth and regeneration of dental tissue.

Histologic Analysis of the Influence of a Gelatin-based Scaffold in the Repair of Immature Dog Teeth Subjected to Regenerative Endodontic Treatment

INTRODUCTION

Regenerative endodontic treatment is a new and promising approach to manage immature teeth with necrotic pulps and apical periodontitis. The use of scaffolds is essential to treatment success, but many materials are difficult to acquire and have a high cost. This study assessed tissue repair in immature dog teeth with necrotic pulps and apical periodontitis after using a gelatin-based scaffold (Gelfoam; Pharmacia & Upjohn Co, Kalamazoo, MI).

METHODS

Apical periodontitis was induced in 20 immature dog teeth. After disinfection with triple antibiotic paste for 2 weeks, canals were irrigated, dried, and filled with a blood clot alone (10 teeth) or combined with Gelfoam (10 teeth). Another 10 teeth were used as negative controls (no intervention). After 7 months, the dogs were euthanized. Histologic sections were stained with hematoxylin-eosin and analyzed in relation to tissue repair. Categoric data were analyzed using the Fisher exact test (P < .05), numeric data (histomorphometric analysis), and the Mann-Whitney U test.

RESULTS

Histologic analysis revealed a higher percentage of roots with new cementumlike mineralized tissue and connective tissue inside the canal in the blood clot + Gelfoam group (P < .001). Histomorphometric analysis showed a higher area of mineralized tissue in the same group (P = .029). Apical extension of root and inflammation were similar between the experimental groups. The new tissue formed onto canal walls and in the root canal space showed characteristics of cementum and periodontal ligament, respectively.

CONCLUSIONS

The use of a gelatin-based scaffold (Gelfoam) combined with a blood clot improved repair in immature dog teeth with apical periodontitis subjected to regenerative endodontic treatment.

Proliferation and osteo/odontoblastic differentiation of stem cells from dental apical papilla in mineralization-inducing medium containing additional KH(2)PO(4)

OBJECTIVES

Stem cells from the dental apical papilla (SCAPs) can be induced to differentiate along both osteoblast and odontoblast lineages. However, little knowledge is available concerning their differentiation efficiency in osteogenic media containing additional KH2 PO4 .

MATERIALS AND METHODS

Stem cells from the dental apical papilla were isolated from apical papillae of immature third molars and treated with two kinds of mineralization-inducing media, MM1 and MM2, differing in KH2 PO4 concentration. Proliferation and osteo/odontogenic differentiation capacity of MM1/MM2-treated SCAPs were investigated and compared both in vitro and in vivo.

RESULTS

Cell counting and flow cytometry demonstrated that MM2 containing 1.8 mm additional KH2 PO4 significantly enhanced proliferative potential of SCAPs, compared to MM1. Osteo/odontogenic capacity of SCAPs was much better in MM2 medium than in MM1, as indicated by elevated alkaline phosphatase activity, increased calcium deposition and upregulated expression of osteo/odontoblast-specific genes/proteins (for example, runt-related transcription factor 2, osterix, osteocalcin, dentin sialoprotein, and dentin sialophosphoprotein). In vivo transplantation findings proved that SCAPs in MM2 group generated more mineralized tissues, and presented higher expression of osteo/odontoblast-specific proteins (osteocalcin and dentin sialoprotein) than those in the MM1 group.

CONCLUSION

Mineralization-inducing media supplemented with 1.8 mm additional KH2 PO4 significantly enhanced cell proliferation and improved differentiation capacity of SCAPs along osteo/odontogenic cell lineages, compared to counterparts lacking additional KH2 PO4 .

Skin epithelial cells as possible substitutes for ameloblasts during tooth regeneration

The disappearance of ameloblasts in erupted teeth hampers the implementation of tissue engineering-based tooth regeneration. We aimed at utilizing skin epithelial cells as the appropriate substitute for ameloblasts. The conversion potential of 1 day postnatal rat skin epithelial cells to ameloblasts was investigated under the induction of dental papillae mesenchymal cells (DPMCs). Induction strategies had been designed both in vitro and in vivo. Markers for ameloblasts had been detected in skin epithelial cells, which showed a columnar appearance with the nuclei located at one side, under indirect co-culture with DPMCs in vitro. An enamel-dentine-like and tooth germ-like structure was formed by recombining skin epithelial pieces or cells with DPMCs after 14 days of implantation in rat renal capsule. Immunohistochemistry and cell labelling analysis further demonstrated that the enamel-forming cells were skin epithelium-derived. These results indicated that the skin epithelium-derived cells from postnatal rats have the potential to convert to functional ameloblasts under effective induction.

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.

Fibrin glue mixed with platelet-rich fibrin as a scaffold seeded with dental bud cells for tooth regeneration

Odontogenesis is a complex process with a series of epithelial-mesenchymal interactions and odontogenic molecular cascades. In tissue engineering of teeth from stem cells, platelet-rich fibrin (PRF), which is rich in growth factors and cytokines, may improve regeneration. Accordingly, PRF was added into fibrin glue to enrich the microenvironment with growth factors. Unerupted second molar tooth buds were harvested from miniature swine and cultured in vitro for 3 weeks to obtain dental bud cells (DBCs). Whole blood was collected for the preparation of PRF and fibrin glue before surgery. DBCs were suspended in fibrin glue and then enclosed with PRF, and the DBC-fibrin glue-PRF composite was autografted back into the original alveolar sockets. Radiographic and histological examinations were used to identify the regenerated tooth structure 36 weeks after implantation. Immunohistochemical staining was used to detect proteins specific to tooth regeneration. One pig developed a complete tooth with crown, root, pulp, enamel, dentin, odontoblast, cementum, blood vessels, and periodontal ligaments in indiscriminate shape. Another animal had an unerupted tooth that expressed cytokeratin 14, dentin matrix protein-1, vascular endothelial growth factor, and osteopontin. This study demonstrated, using autogenic cell transplantation in a porcine model, that DBCs seeded into fibrin glue-PRF could regenerate a complete tooth.

Characterization of rat apical tissues in different root development stage

In this study, we try to compare the histological characteristics and the odontogenic capability of apical tissues (AT) at different root development stages of rat molar teeth. AT of mandibular first molars from 8-day-old, 21-day-old, and 35-day-old Sprague-Dawley rats were selected as being representative of root-initiating, root-forming, and root-completing stages, respectively. Cell counting, flow cytometry assays, alkaline phosphatase activity, alizarin red staining, and reverse transcription polymerase chain reaction were performed to assess the proliferation and mineralization potential of apical tissue cells at different stages of root development in vitro. In vivo transplantation of apical tissue cells combined with ceramic bovine bone was used to characterize the differentiation capacity. It was shown that there was a structurally and functionally dynamic change in the apical tissue of developing tooth root of rats, of which the unique developmental potential will reduce gradually with the ending up of root development. The AT of root-initiating and root-forming stage exhibited much higher proliferation and tissue-regenerative capacity than those of root-completing stage. Our present results indicate that the apical tissue, with the sustainable developmental ability throughout almost the whole process of tooth development, can yet be regarded as a competent candidate source for root/periodontal tissues regeneration.

Dentinogenic capacity: immature root papilla stem cells versus mature root pulp stem cells

BACKGROUND INFORMATION

Immature dental papilla stem cells and mature dental pulp stem cells are capable of performing the dentinogenesis under suitable circumstances. However, a dentinogenic comparison between immature and mature dental root stem cells remains unknown.

RESULTS

iRPSCs (immature root papilla stem cells) at the root-forming stage and mRPSCs (mature root pulp stem cells) at the root-completed stage were isolated from 16-day-old and 8-week-old rat first molar roots, respectively. Growth kinetics and flow cytometry results showed that iRPSCs presented more active proliferation properties than mRPSCs. Their odontoblastic differentiation and dentinogenic potential were subsequently compared both in vitro and in vivo. iRPSCs exhibited a more potent odontoblastic differentiation than mRPSCs in vitro, as indicated by the higher levels of gene expression for dentin sialophosphoprotein and ALP (alkaline phosphatase), increased protein expression of dentin sialoprotein and runt-related transcription factor 2, decreased gene/protein expression for osterix/osteocalcin (osteogenic markers), elevated ALP activity and enhanced calcium deposition in the mineralization-inducing media. Allotransplantation results demonstrated that all iRPSCs pellets in vivo performed typical dentinogenesis, whereas mRPSCs pellets mainly produced bone-like tissues.

CONCLUSION

iRPSCs presented stronger dentinogenesis but weaker osteogenesis than did mRPSCs, suggesting that the dentinogenic competence of root mesenchymal stem cells decreases, whereas their osteogenic potential the increases following the maturation of the tooth root.

Biological approaches toward dental pulp regeneration by tissue engineering

Root canal therapy has been the predominant approach in endodontic treatment, wherein the entire pulp is cleaned out and replaced with a gutta-percha filling. However, living pulp is critical for the maintenance of tooth homeostasis and essential for tooth longevity. An ideal form of therapy, therefore, might consist of regenerative approaches in which diseased/necrotic pulp tissues are removed and replaced with regenerated pulp tissues to revitalize the teeth. Dental pulp regeneration presents one of the most challenging issues in regenerative dentistry due to the poor intrinsic ability of pulp tissues for self-healing and regrowth. With the advent of modern tissue engineering and the discovery of dental stem cells, biological therapies have paved the way to utilize stem cells, delivered or internally recruited, to generate dental pulp tissues, where growth factors and a series of dentine extracellular matrix molecules are key mediators that regulate the complex cascade of regeneration events to be faithfully fulfilled.

Bone marrow combined with dental bud cells promotes tooth regeneration in miniature pig model

Growth factors and morphogens secreted by bone marrow mesenchymal stem cells (BMSCs) of bone marrow fluid may promote tooth regeneration. Accordingly, a tissue engineering approach was utilized to develop an economical strategy for obtaining the growth factors and morphogens from BMSCs. Unerupted second molar tooth buds harvested from miniature pigs were cultured in vitro to obtain dental bud cells (DBCs). Bone marrow fluid, which contains BMSCs, was collected from the porcine mandible before operation. DBCs suspended in bone marrow fluid were seeded into a gelatin/chondoitin-6-sulfate/hyaluronan tri-copolymer scaffold (GCHT scaffold). The DBCs/bone marrow fluid/GCHT scaffold was autografted into the original alveolar sockets of the pigs. Radiographic and histological examinations were applied to identify the structure of regenerated tooth at 40 weeks postimplantation. The present results showed that one pig developed a complete tooth with crown, root, pulp, enamel, dentin, odontoblast, cementum, blood vessel, and periodontal ligament in indiscriminate shape. Three animals had an unerupted tooth that expressed dentin matrix protein-1, vascular endothelial growth factor, and osteopontin; and two other pigs also had dental-like structure with dentin tubules. This study reveals that DBCs adding bone marrow fluid and a suitable scaffold can promote the tooth regeneration in autogenic cell transplantation.

Three dimensional dental epithelial-mesenchymal constructs of predetermined size and shape for tooth regeneration

While it is known that precise dental epithelial-mesenchymal (DE-DM) cell interactions provide critical functions in tooth development, reliable methods to establish proper DE-DM cell interactions for tooth regeneration have yet to be established. To address this challenge, and to generate bioengineered teeth of predetermined size and shape, in this study, we characterize three dimensional (3D) pre-fabricated DE-DM cell constructs. Human dental pulp cell seeded Collagen gel layers were co-cultured with porcine DE cells suspended in Growth Factor Reduced (GFR) Matrigel. The resulting 3D DE-DM cell layers were cultured in vitro, or implanted and grown subcutaneously in vivo in nude rats. Molecular, histological and immunohistochemical (IHC) analyses of harvested implants revealed organized DE-DM cell interactions, the induced expression of dental tissue-specific markers Amelogenin (AM) and Dentin Sialophosphoprotein (DSPP), and basement membrane markers Laminin 5 and collagen IV, and irregular mineralized tissue formation after 4 weeks. We anticipate that these studies will facilitate the eventual establishment of reliable methods to elaborate dental tissues, and full sized teeth of specified sized and shape.

Periodontal tissue engineering and regeneration: current approaches and expanding opportunities

The management of periodontal tissue defects that result from periodontitis represents a medical and socioeconomic challenge. Concerted efforts have been and still are being made to accelerate and augment periodontal tissue and bone regeneration, including a range of regenerative surgical procedures, the development of a variety of grafting materials, and the use of recombinant growth factors. More recently, tissue-engineering strategies, including new cell- and/or matrix-based dimensions, are also being developed, analyzed, and employed for periodontal regenerative therapies. Tissue engineering in periodontology applies the principles of engineering and life sciences toward the development of biological techniques that can restore lost alveolar bone, periodontal ligament, and root cementum. It is based on an understanding of the role of periodontal formation and aims to grow new functional tissues rather than to build new replacements of periodontium. Although tissue engineering has merged to create more opportunities for predictable and optimal periodontal tissue regeneration, the technique and design for preclinical and clinical studies remain in their early stages. To date, the reconstruction of small- to moderate-sized periodontal bone defects using engineered cell-scaffold constructs is technically feasible, and some of the currently developed concepts may represent alternatives for certain ideal clinical scenarios. However, the predictable reconstruction of the normal structure and functionality of a tooth-supporting apparatus remains challenging. This review summarizes current regenerative procedures for periodontal healing and regeneration and explores their progress and difficulties in clinical practice, with particular emphasis placed upon current challenges and future possibilities associated with tissue-engineering strategies in periodontal regenerative medicine.

Differentiation potential of STRO-1+ dental pulp stem cells changes during cell passaging

Background

Dental pulp stem cells (DPSCs) can be driven into odontoblast, osteoblast, and chondrocyte lineages in different inductive media. However, the differentiation potential of naive DPSCs after serial passaging in the routine culture system has not been fully elucidated.

Results

DPSCs were isolated from human/rat dental pulps by the magnetic activated cell sorting based on STRO-1 expression, cultured and passaged in the conventional culture media. The biological features of STRO-1⁺ DPSCs at the 1^st and 9^th passages were investigated. During the long-term passage, the proliferation ability of human STRO-1⁺ DPSCs was downregulated as indicated by the growth kinetics. When compared with STRO-1⁺ DPSCs at the 1^st passage (DPSC-P1), the expression of mature osteoblast-specific genes/proteins (alkaline phosphatase, bone sialoprotein, osterix, and osteopontin), odontoblast-specific gene/protein (dentin sialophosphoprotein and dentin sialoprotein), and chondrocyte-specific gene/protein (type II collagen) was significantly upregulated in human STRO-1⁺ DPSCs at the 9^th passage (DPSC-P9). Furthermore, human DPSC-P9 cells in the mineralization-inducing media presented higher levels of alkaline phosphatase at day 3 and day 7 respectively, and produced more mineralized matrix than DPSC-P9 cells at day 14. In vivo transplantation results showed that rat DPSC-P1 cell pellets developed into dentin, bone and cartilage structures respectively, while DPSC-P9 cells can only generate bone tissues.

Conclusions

These findings suggest that STRO-1⁺ DPSCs consist of several interrelated subpopulations which can spontaneously differentiate into odontoblasts, osteoblasts, and chondrocytes. The differentiation capacity of these DPSCs changes during cell passaging, and DPSCs at the 9^th passage restrict their differentiation potential to the osteoblast lineage in vivo.

Differentiation of dermal multipotent cells into odontogenic lineage induced by embryonic and neonatal tooth germ cell-conditioned medium

Stem cell-based therapy represents a novel and more advantageous modality of treatment for tooth defect or loss. However, this strategy is challenged in the circumstances where tooth-derived stem cells are not readily accessible. In present study we sought to explore the possibility of utilizing dermal multipotent cells (DMCs) easily available from skin tissue for odontogenic induction. Using the limiting dilution technique, colony-forming cell population was isolated and characterized by proliferative activity and multilineage differentiation potential. By exposure to conditioned medium of embryonic and neonatal tooth germ cells in culture, the proliferation and mineralization activity of DMCs was elevated, while the embryonic tooth germ cell-conditioned medium (ETGC-CM) produced more significant effects. Meanwhile, ETGC-CM-treated DMCs phenocopied the odontoblasts in vitro as indicated by specific lineage markers. Following in vivo transplantation as cell pellet, ETGC-CM-treated DMCs were capable of producing blocks of mineralized tissues, which resembled those of dental pulp stem cell (DPSC) explants in the same subcutaneous pockets environment. These observations suggest that although more sufficient and continuous inductive microenvironment may be needed for undifferentiated DMCs to perform as odontoblasts, ETGC-CM-treated DMCs indeed acquire properties as those of DPSCs. Our work highlights the potential utility of DMCs as an alternative candidate cell source in hopes of developing more practical strategy of tooth regeneration research and offering promising opportunities for therapeutic approach.

Differentiation of mouse embryonic stem cells into dental epithelial-like cells induced by ameloblasts serum-free conditioned medium

Embryonic stem cells (ESCs) possess an intrinsic self-renewal ability and can differentiate into numerous types of functional tissue cells; however, whether ESCs can differentiate toward the odontogenic lineage is still unknown. In this study, we developed an efficient culture strategy to induce the differentiation of murine ESCs (mESCs) into dental epithelial cells. By culturing mESCs in ameloblasts serum-free conditioned medium (ASF-CM), we could induce their differentiation toward dental epithelial cell lineages; however, similar experiments with the tooth germ cell-conditioned medium (TGC-CM) did not yield effective results. After culturing the cells for 14days in the differentiation-inducing media, the expression of ameloblast-specific proteins such as cytokeratin (CK)14, ameloblastin (AMBN), and amelogenin (AMGN) was markedly higher in mESCs obtained with embryoid body (EB) formation than in mESCs obtained without EB formation. We observed that immunocompromised mice implanted with induced murine EBs (mEBs) showed tissue regenerative capacity and produced odontogenic epithelial-like structures, whereas those implanted with mSCE monolayer cells mainly formed connective tissues. Thus, for the first time, we report that ASF-CM provides a suitable microenvironment for inducing mESC differentiation along the odontogenic epithelial cell lineage. This result has important implications for tooth tissue engineering.

Isolation and differentiation of nestin positive cells from rat oral mucosal lamina propria

Despite successes in the isolation and characterization of stem cells from the oral mucosal epithelium, there have been few studies on progenitor cells from the oral mucosal lamina propria. In this study, we isolate rat oral mucosal lamina propria cells (OMLPC) using nestin as a marker in an immunomagnetic sorting technique. The OMLPCs was negative for cytokeratin. Nestin and vimentin were expressed in the OMLPCs. And CD44 and STRO-1 were expressed in a subset of the OMLPCs, which suggest that the nestin positive OMLPCs be heterogeneous. Otherwise, OMLPCs express Oct4, which is a critical gene for pluripotency. The OMLPCs proliferated actively in vitro. A colony forming study demonstrated that OMLPCs exhibited colony-generating capacity. When cultured in defined medium, OMLPCs generated cells characteristic of osteoblast, adipocyte and astrocyte-like cells. In addition, OMLPCs seeded into three dimensional scaffolds form bone-like structures in vivo after 8 weeks. All of the results demonstrate that OMLPCs are a population of mesenchymal progenitor cells existing in rat oral mucosal lamina propria. Nestin is shown to be a useful molecular marker for these cells. In certain environments, OMLPCs can form hard tissue. Thus, OMLPCs may serve as a suitable source of cells for future bone or tooth tissue engineering applications.

Reclaiming a natural beauty: whole-organ engineering with natural extracellular materials

The ability to engineer whole organs as replacements for allografts and xenografts is an ongoing pursuit in regenerative medicine. While challenges remain, including systemic tissue integration with angiogenesis, lymphatiogenesis and neurogenesis, ongoing efforts are working to develop novel technologies to produce implantable engineered scaffolds and potentially engineered whole organs. Natural extracellular matrix materials, commonly utilized in vitro, are now being used as effective, natural, acellular allografts, and are being integrated into nanoscale scaffolds and matrices with programmable responsiveness. Based on the significant use of natural scaffolds for tissue regeneration and bioengineering strategies, this review focuses on recent and ongoing efforts to engineer whole organs, such as the tooth, featuring natural extracellular matrix molecules.

In vitro cellular responses to scaffolds containing two microencapulated growth factors

Growth factors play an important role in the complex cascade of tissue events in periodontal regeneration, although optimal methods of delivery remain to be identified. We hypothesize that multiple delivery of growth factors, particularly via a microparticle-containing scaffold, will enhance cellular events leading to periodontal regeneration. In this study, cellular responses of periodontal ligament fibroblasts (PDLFs) in scaffolds containing microparticles (MPs) loaded with either bone morphogenetic protein (BMP)-2, insulin-like growth factor (IGF)-1, or a mixture of both MPs were evaluated, and the dual-MP-containing scaffold exhibited the release of different proteins in a sustained and independent fashion. When PDLF-seeded scaffolds were cultured in a flow perfusion bioreactor, cell metabolism and proliferation of PDLFs were significantly increased within 3 days in all IGF-1-containing scaffolds compared with those in groups lacking IGF-1 and particulate delivery enhanced these effects between 3 and 7 days. The dual-MP-containing group showed the most positive results. Both the BMP-2-in-MP and IGF-1-in-MP groups showed greater effects of alkaline phosphatase activity, more osteocalcin and osteopontin production, and more calcium deposition compared with matched GF-adsorbed groups. All osteoblastic markers were at their highest in the dual-MP-containing group at all detected time points. The combined results suggest that our dual-MP-containing scaffold can be used as a cell vehicle to positively affect cell behavior, thus exhibiting the potential to be a candidate scaffold for future periodontal tissue engineering.

A curriculum vitae of teeth: evolution, generation, regeneration

The ancestor of recent vertebrate teeth was a tooth-like structure on the outer body surface of jawless fishes. Over the course of 500,000,000 years of evolution, many of those structures migrated into the mouth cavity. In addition, the total number of teeth per dentition generally decreased and teeth morphological complexity increased. Teeth form mainly on the jaws within the mouth cavity through mutual, delicate interactions between dental epithelium and oral ectomesenchyme. These interactions involve spatially restricted expression of several, teeth-related genes and the secretion of various transcription and signaling factors. Congenital disturbances in tooth formation, acquired dental diseases and odontogenic tumors affect millions of people and rank human oral pathology as the second most frequent clinical problem. On the basis of substantial experimental evidence and advances in bioengineering, many scientists strongly believe that a deep knowledge of the evolutionary relationships and the cellular and molecular mechanisms regulating the morphogenesis of a given tooth in its natural position, in vivo, will be useful in the near future to prevent and treat teeth pathologies and malformations and for in vitro and in vivo teeth tissue regeneration.

Dental pulp stem cells: what, where, how?

INTRODUCTION

It is now accepted that progenitor/stem cells reside within the post-natal dental pulp. Studies have identified several niches of multipotent mesenchymal progenitor cells, known as dental pulp stem cells, which have a high proliferative potential for self-renewal. These progenitor stem cells are now recognized as being vital to the dentine regeneration process following injury. Understanding the nature of these progenitor/stem cell populations in the pulp is important in determining their potentialities and development of isolation or recruitment strategies for use in regeneration and tissue engineering. Characterization of these cells, and determination of their potentialities in terms of specificity of regenerative response, may help direct new clinical treatment modalities. Such novel treatments may involve controlled direct recruitment of the cells in situ and possible seeding of stem cells at sites of injury for regeneration or use of the stem cells with appropriate scaffolds for tissue engineering solutions. Such approaches may provide an innovative and novel biologically based new generation of clinical materials and/or treatments for dental disease.

AIM

This study aimed to review the body of knowledge relating to stem cells and to consider the possibility of these cell populations, and related technology, in future clinical applications.