Bio-Root and Implant-Based Restoration as a Tooth Replacement Alternative

Recent adavances of functional modules for tooth regeneration

Dental diseases, such as dental caries and periodontal disorders, constitute a major global health challenge, affecting millions worldwide and often resulting in tooth loss. Traditional dental treatments, though beneficial, typically cannot fully restore the natural functions and structures of teeth. This limitation has prompted growing interest in innovative strategies for tooth regeneration methods. Among these, the use of dental stem cells to generate functional tooth modules represents an emerging and promising approach in dental tissue engineering. These modules aim to closely replicate the intricate morphology and essential physiological functions of dental tissues. Recent advancements in regenerative research have not only enhanced the assembly techniques for these modules but also highlighted their therapeutic potential in addressing various dental diseases. In this review, we discuss the latest progress in the construction of functional tooth modules, especially on regenerating dental pulp, periodontal tissue, and tooth roots.

Enhancing clinical safety in bioengineered-root regeneration: The use of animal component-free medium

Background

Most studies used animal serum-containing medium for bioengineered-root regeneration, but ethical and safety issues raised by animal serum are a potentially significant risk for clinical use. Thus, this study aimed to find a safer method for bioengineered-root regeneration.

Methods

The biological properties of human dental pulp stem cells (hDPSCs) cultured in animal component-free (ACF) medium or serum-containing medium (5%, 10% serum-containing medium, SCM) were compared in vitro. hDPSCs were cultured in a three-dimensional (3D) environment with human-treated dentin matrix (hTDM). The capacity for odontogenesis was compared using quantitative real-time PCR (qPCR) and Western blot. Subsequently, the hDPSCs/hTDM complexes were transplanted into nude mice subcutaneously. Histological staining was then used to verify the regeneration effect in vivo.

Results

ACF medium promoted the migration of hDPSCs, but slightly inhibited the proliferation of hDPSCs in the first three days of culture compared to SCM. However, it had no significant effect on cell aging and apoptosis. After 7 days of 3D culture in ACF medium with hTDM, qPCR showed that DMP1, DSPP, OCN, RUNX2, and β-tubulin III were highly expressed in hDPSCs. In addition, 3D cultured hDPSCs/hTDM complexes in ACF medium regenerated dentin, pulp, and periodontal ligament-like tissues similar to SCM groups in vivo.

Conclusion

ACF medium was proved to be an alternative medium for bioengineered-root regeneration. The strategy of using ACF medium to regenerate bioengineered-root can improve clinical safety for tooth tissue engineering.

Research and development of microenvironment's influence on stem cells from the apical papilla - construction of novel research microdevices: tooth-on-a-chip

Stem cells are crucial in tissue engineering, and their microenvironment greatly influences their behavior. Among the various dental stem cell types, stem cells from the apical papilla (SCAPs) have shown great potential for regenerating the pulp-dentin complex. Microenvironmental cues that affect SCAPs include physical and biochemical factors. To research optimal pulp-dentin complex regeneration, researchers have developed several models of controlled biomimetic microenvironments, ranging from in vivo animal models to in vitro models, including two-dimensional cultures and three-dimensional devices. Among these models, the most powerful tool is a microfluidic microdevice, a tooth-on-a-chip with high spatial resolution of microstructures and precise microenvironment control. In this review, we start with the SCAP microenvironment in the regeneration of pulp-dentin complexes and discuss research models and studies related to the biological process.

Stem cells in regenerative dentistry: Current understanding and future directions

BACKGROUND

Regenerative dentistry aims to enhance the structure and function of oral tissues and organs. Modern tissue engineering harnesses cell and gene-based therapies to advance traditional treatment approaches. Studies have demonstrated the potential of mesenchymal stem cells (MSCs) in regenerative dentistry, with some progressing to clinical trials. This review comprehensively examines animal studies that have utilized MSCs for various therapeutic applications. Additionally, it seeks to bridge the gap between related findings and the practical implementation of MSC therapies, offering insights into the challenges and translational aspects involved in transitioning from preclinical research to clinical applications.

HIGHLIGHTS

To achieve this objective, we have focused on the protocols and achievements related to pulp-dentin, alveolar bone, and periodontal regeneration using dental-derived MSCs in both animal and clinical studies. Various types of MSCs, including dental-derived cells, bone-marrow stem cells, and umbilical cord stem cells, have been employed in root canals, periodontal defects, socket preservation, and sinus lift procedures. Results of such include significant hard tissue reconstruction, functional pulp regeneration, root elongation, periodontal ligament formation, and cementum deposition. However, cell-based treatments for tooth and periodontium regeneration are still in early stages. The increasing demand for stem cell therapies in personalized medicine underscores the need for scientists and responsible organizations to develop standardized treatment protocols that adhere to good manufacturing practices, ensuring high reproducibility, safety, and cost-efficiency.

CONCLUSION

Cell therapy in regenerative dentistry represents a growing industry with substantial benefits and unique challenges as it strives to establish sustainable, long-term, and effective oral tissue regeneration solutions.

METTL3-mediated pre-miR-665/DLX3 m6A methylation facilitates the committed differentiation of stem cells from apical papilla

Methyltransferase-like 3 (METTL3) is a crucial element of N6-methyladenosine (m6A) modifications and has been extensively studied for its involvement in diverse biological and pathological processes. In this study, we explored how METTL3 affects the differentiation of stem cells from the apical papilla (SCAPs) into odonto/osteoblastic lineages through gain- and loss-of-function experiments. The m6A modification levels were assessed using m6A dot blot and activity quantification experiments. In addition, we employed Me-RIP microarray experiments to identify specific targets modified by METTL3. Furthermore, we elucidated the molecular mechanism underlying METTL3 function through dual-luciferase reporter gene experiments and rescue experiments. Our findings indicated that METTL3+/- mice exhibited significant root dysplasia and increased bone loss. The m6A level and odonto/osteoblastic differentiation capacity were affected by the overexpression or inhibition of METTL3. This effect was attributed to the acceleration of pre-miR-665 degradation by METTL3-mediated m6A methylation in cooperation with the "reader" protein YTHDF2. Additionally, the targeting of distal-less homeobox 3 (DLX3) by miR-665 and the potential direct regulation of DLX3 expression by METTL3, mediated by the "reader" protein YTHDF1, were demonstrated. Overall, the METTL3/pre-miR-665/DLX3 pathway might provide a new target for SCAP-based tooth root/maxillofacial bone tissue regeneration.

Personalized 3D-Printed Scaffolds with Multiple Bioactivities for Bioroot Regeneration

Recent advances in 3D printing offer a prospective avenue for producing transplantable human tissues with complex geometries; however, the appropriate 3D-printed scaffolds possessing the biological compatibility for tooth regeneration remain unidentified. This study proposes a personalized scaffold of multiple bioactivities, including induction of stem cell proliferation and differentiation, biomimetic mineralization, and angiogenesis. A brand-new bioink system comprising a biocompatible and biodegradable polymer is developed and reinforced with extracellular matrix generated from dentin tissue (treated dentin matrix, TDM). Adding TDM optimizes physical properties including microstructure, hydrophilicity, and mechanical strength of the scaffolds. Proteomics analysis reveals that the released proteins of the 3D-printed TDM scaffolds relate to multiple biological processes and interact closely with each other. Additionally, 3D-printed TDM scaffolds establish a favorable microenvironment for cell attachment, proliferation, and differentiation in vitro. The 3D-printed TDM scaffolds are proangiogenic and facilitate whole-thickness vascularization of the graft in a subcutaneous model. Notably, the personalized TDM scaffold combined with dental follicle cells mimics the anatomy and physiology of the native tooth root three months after in situ transplantation in beagles. The remarkable in vitro and in vivo outcomes suggest that the 3D-printed TDM scaffolds have multiple bioactivities and immense clinical potential for tooth-loss therapy.

BMP signaling in the development and regeneration of tooth roots: from mechanisms to applications

Short root anomaly (SRA), along with caries, periodontitis, and trauma, can cause tooth loss, affecting the physical and mental health of patients. Dental implants have become widely utilized for tooth restoration; however, they exhibit certain limitations compared to natural tooth roots. Tissue engineering-mediated root regeneration offers a strategy to sustain a tooth with a physiologically more natural function by regenerating the bioengineered tooth root (bio-root) based on the bionic principle. While the process of tooth root development has been reported in previous studies, the specific molecular mechanisms remain unclear. The Bone Morphogenetic Proteins (BMPs) family is an essential factor regulating cellular activities and is involved in almost all tissue development. Recent studies have focused on exploring the mechanism of BMP signaling in tooth root development by using transgenic animal models and developing better tissue engineering strategies for bio-root regeneration. This article reviews the unique roles of BMP signaling in tooth root development and regeneration.

The Role of Gli1+ Mesenchymal Stem Cells in Osteogenesis of Craniofacial Bone

Glioma-associated oncogene homolog 1 (Gli1) is a transcriptional activator of hedgehog (Hh) signaling that regulates target gene expression and several cellular biological processes. Cell lineage tracing techniques have highlighted Gli1 as an ideal marker for mesenchymal stem cells (MSCs) in vivo. Gli1+ MSCs are critical for the osteogenesis of the craniofacial bone; however, the regulatory mechanism by which Gli1+ MSCs mediate the bone development and tissue regeneration of craniofacial bone has not been systematically outlined. This review comprehensively elucidates the specific roles of Gli1+ MSCs in craniofacial bone osteogenesis. In addition to governing craniofacial bone development, Gli1+ MSCs are associated with the tissue repair of craniofacial bone under pathological conditions. Gli1+ MSCs promote intramembranous and endochondral ossification of the craniofacial bones, and assist the osteogenesis of the craniofacial bone by improving angiopoiesis. This review summarizes the novel role of Gli1+ MSCs in bone development and tissue repair in craniofacial bones, which offers new insights into bone regeneration therapy.

Mesenchymal condensation in tooth development and regeneration: a focus on translational aspects of organogenesis

The teeth are vertebrate-specific, highly specialized organs performing fundamental functions of mastication and speech, the maintenance of which is crucial for orofacial homeostasis and is further linked to systemic health and human psychosocial well-being. However, with limited ability for self-repair, the teeth can often be impaired by traumatic, inflammatory, and progressive insults, leading to high prevalence of tooth loss and defects worldwide. Regenerative medicine holds the promise to achieve physiological restoration of lost or damaged organs, and in particular an evolving framework of developmental engineering has pioneered functional tooth regeneration by harnessing the odontogenic program. As a key event of tooth morphogenesis, mesenchymal condensation dictates dental tissue formation and patterning through cellular self-organization and signaling interaction with the epithelium, which provides a representative to decipher organogenetic mechanisms and can be leveraged for regenerative purposes. In this review, we summarize how mesenchymal condensation spatiotemporally assembles from dental stem cells (DSCs) and sequentially mediates tooth development. We highlight condensation-mimetic engineering efforts and mechanisms based on ex vivo aggregation of DSCs, which have achieved functionally robust and physiologically relevant tooth regeneration after implantation in animals and in humans. The discussion of this aspect will add to the knowledge of development-inspired tissue engineering strategies and will offer benefits to propel clinical organ regeneration.

Biofabrication of engineered dento-alveolar tissue

Oral health is essential for a good overall health. Dento-alveolar conditions have a high prevalence, ranging from tooth decay periodontitis to alveolar bone resorption. However, oral tissues exhibit a limited regenerative capacity, and full recovery is challenging. Therefore, regenerative therapies for dento-alveolar tissue (e.g., alveolar bone, periodontal membrane, dentin-pulp complex) have gained much attention, and novel approaches have been proposed in recent decades. This review focuses on the cells, biomaterials and the biofabrication methods used to develop therapies for tooth root bioengineering. Examples of the techniques covered are the multitude of additive manufacturing techniques and bioprinting approaches used to create scaffolds or tissue constructs. Furthermore, biomaterials and stem cells utilized during biofabrication will also be described for different target tissues. As these new therapies gradually become a reality in the lab, the translation to the clinic is still minute, with a further need to overcome multiple challenges and broaden the clinical application of these alternatives.

Apical Papilla Regulates Dental Follicle Fate via the OGN-Hh Pathway

Root apical complex, including Hertwig's epithelial root sheath, apical papilla, and dental follicle (DF), is the germinal center of root development, wherein the DF constantly develops into periodontal tissue. However, whether DF development is regulated by the adjacent apical papilla remains largely unknown. In this study, we employed a transwell coculture system and found that stem cells from the apical papilla (SCAPs) inhibit the differentiation and maintain the stemness of dental follicle stem cells (DFSCs). Meanwhile, partial SCAP differentiation markers were upregulated after DFSC coculture. High-throughput RNA sequencing revealed that the Hedgehog (Hh) pathway was significantly downregulated in DFSCs cocultured with SCAPs. Upregulation or downregulation of the Hh pathway can respectively activate or inhibit the multidirectional differentiation of DFSCs. Osteoglycin (OGN) (previously known as mimecan) is highly expressed in the dental papilla, similarly to Hh pathway factors. By secreting OGN, SCAP regulated the stemness and multidirectional differentiation of DFSCs via the OGN-Hh pathway. Finally, Ogn^-/- mice were established using the CRISPR/Cas9 system. We found that the root length growth rate was accelerated during root development from PN0 to PN30 in Ogn^-/- mice. Moreover, the hard tissues (including dentin and cementum) of the root in Ogn^-/- mice were thicker than those in wild-type mice. These phenotypes were likely due to Hh pathway activation and the increased cell proliferation and differentiation in both the apical papilla and DF. The current work elucidates the molecular regulation of early periodontal tissue development, providing a theoretical basis for future research on tooth root biology and periodontal tissue regeneration.

Current Understanding of the Regulatory Mechanism of Tooth Root Development and Future Perspectives

Background

The purpose of this review article is to understand tooth root development and its regulation through evolution and epigenetics as well as future implications involving root regeneration and tissue engineering.

Types of Studies Reviewed

we performed a comprehensive PubMed search to review all published studies related to the molecular regulation of tooth root development and regeneration until August 2022. Articles selected include original research studies and reviews.

Results

Epigenetic regulation strongly influences dental tooth root patterning and development. One study highlights how genes such as Ezh2 and Arid1a are crucial components in the development of tooth root furcation patterning. Another study shows that loss of Arid1a ultimately leads to shortened root morphology. Furthermore, researchers are utilizing information about root development and stem cells to find alternative treatments in replacing missing teeth through a stem cell-mediated bioengineered tooth root (bio-root).

Practical Implications

Dentistry values preserving natural tooth morphology. Presently, implants are the best treatment for replacing missing teeth, but alternative future treatments might include tissue engineering/bio-root regeneration to restore our dentition.

Effectiveness of biomechanically stable pergola-like additively manufactured scaffold for extraskeletal vertical bone augmentation

Objective: Extraskeletal vertical bone augmentation in oral implant surgery requires extraosseous regeneration beyond the anatomical contour of the alveolar bone. It is necessary to find a better technical/clinical solution to solve the dilemma of vertical bone augmentation. 3D-printed scaffolds are all oriented to general bone defect repair, but special bone augmentation design still needs improvement.

Methods: This study aimed to develop a structural pergola-like scaffold to be loaded with stem cells from the apical papilla (SCAPs), bone morphogenetic protein 9 (BMP9) and vascular endothelial growth factor (VEGF) to verify its bone augmentation ability even under insufficient blood flow supply. Scaffold biomechanical and fluid flow optimization design by finite element analysis (FEA) and computational fluid dynamics (CFD) was performed on pergola-like additive-manufactured scaffolds with various porosity and pore size distributions. The scaffold geometrical configuration showing better biomechanical and fluid dynamics properties was chosen to co-culture for 2 months in subcutaneously into nude mice, with different SCAPs, BMP9, and (or) VEGF combinations. Finally, the samples were removed for Micro-CT and histological analysis.

Results: Micro-CT and histological analysis of the explanted scaffolds showed new bone formation in the “Scaffold + SCAPs + BMP9” and the “Scaffold + SCAPs + BMP9 + VEGF” groups where the VEGF addition did not significantly improve osteogenesis. No new bone formation was observed either for the “Blank Scaffold” and the “Scaffold + SCAPs + GFP” group. The results of this study indicate that BMP9 can effectively promote the osteogenic differentiation of SCAPs.

Conclusion: The pergola-like scaffold can be used as an effective carrier and support device for new bone regeneration and mineralization in bone tissue engineering, and can play a crucial role in obtaining considerable vertical bone augmentation even under poor blood supply.

Residual periodontal ligament in the extraction socket promotes the dentin regeneration potential of DPSCs in the rabbit jaw

BACKGROUND

Because of the low regeneration efficiency and unclear underlying molecular mechanism, tooth regeneration applications are limited. In this study, we explored the influence of residual periodontal ligament on the dentin regeneration potential of dental pulp stem cells (DPSCs) in the jaw.

METHODS

To establish a tooth regeneration model, the incisors of New Zealand white rabbits were extracted while preserving residual periodontal ligament, followed by the implantation of DPSCs. After 3 months, micro-computed tomography (micro-CT), stereomicroscopy and scanning electron microscopy (SEM) were used to observe the volume, morphology and microstructure of regenerated tissue. Histological staining and immunostaining analyses were used to observe the morphological characteristics and expression of the dentin-specific proteins DMP1 and DSPP. To explore the mechanism, DPSCs and periodontal ligament stem cells (PDLSCs) were cocultured in vitro, and RNA was collected from the DPSCs for RNA-seq and bioinformatic analysis.

RESULTS

The results of micro-CT and stereomicroscopy showed that the number of sites with regeneration and the volume of regenerated tissue in the DPSCs/PDL group (6/8, 1.07 ± 0.93 cm³) were larger than those in the DPSCs group (3/8, 0.23 ± 0.41 cm³). The results of SEM showed that the regenerated dentin-like tissue in the DPSCs and DPSCs/PDL groups contained dentin tubules. Haematoxylin and eosin staining and immunohistochemical staining indicated that compared with the DPSCs group, the DPSCs/PDL group showed more regular regenerated tissue and higher expression levels of the dentin-specific proteins DMP1 and DSPP (DMP1: P = 0.02, DSPP: P = 0.01). RNA-seq showed that the coculture of DPSCs with PDLSCs resulted in the DPSCs differentially expressing 427 mRNAs (285 upregulated and 142 downregulated), 41 lncRNAs (26 upregulated and 15 downregulated), 411 circRNAs (224 upregulated and 187 downregulated), and 19 miRNAs (13 upregulated and 5 downregulated). Bioinformatic analysis revealed related Gene Ontology function and signalling pathways, including extracellular matrix (ECM), tumour necrosis factor (TNF) signalling and chemokine signalling pathways.

CONCLUSIONS

Residual periodontal ligament in the extraction socket promotes the dentin regeneration potential of DPSCs in the jaw. RNA-seq and bioinformatic analysis revealed that ECM, TNF signalling and chemokine signalling pathways may represent the key factors and signalling pathways.

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.

A Review of In Vivo and Clinical Studies Applying Scaffolds and Cell Sheet Technology for Periodontal Ligament Regeneration

Different approaches to develop engineered scaffolds for periodontal tissues regeneration have been proposed. In this review, innovations in stem cell technology and scaffolds engineering focused primarily on Periodontal Ligament (PDL) regeneration are discussed and analyzed based on results from pre-clinical in vivo studies and clinical trials. Most of those developments include the use of polymeric materials with different patterning and surface nanotopography and printing of complex and sophisticated multiphasic composite scaffolds with different compartments to accomodate for the different periodontal tissues' architecture. Despite the increased effort in producing these scaffolds and their undoubtable efficiency to guide and support tissue regeneration, appropriate source of cells is also needed to provide new tissue formation and various biological and mechanochemical cues from the Extraccellular Matrix (ECM) to provide biophysical stimuli for cell growth and differentiation. Cell sheet engineering is a novel promising technique that allows obtaining cells in a sheet format while preserving ECM components. The right combination of those factors has not been discovered yet and efforts are still needed to ameliorate regenerative outcomes towards the functional organisation of the developed tissues.

Whole Tooth Regeneration: Can Animal Studies be Translated into Clinical Application?

Tooth loss leads to several oral problems and although a large number of treatments have been proposed to rehabilitate partially or totally edentulous patients, none of them is based on replacement of a missing tooth by a new natural whole tooth. In the field of tissue engineering, some animal models have been developed to regenerate a natural tooth in the oral cavity. This review shows the state of the art in whole tooth regeneration based on data from in vivo studies. A systematic scoping review was conducted to evaluate studies that described whole-tooth regeneration and eruption in the oral cavity. The data demonstrated that over 100 animals were used in experimental studies and all of them received implants of tooth germs constructed by bioengineering processes. Mini pigs and pigs were used in four studies followed by mice (n = 1) and dog (n = 1). Over 58 (44%) animals showed whole tooth eruption around 3.5 months after tooth germ implantation (1 to 13.5 months). Most of specimens revealed the presence of odontoblasts, dentin, dentinal tubules, dental pulp, root analogue, cementum, blood vessels, and alveolar bone. It could be concluded that in vivo whole tooth regeneration was proved to be possible, but the challenge to overcome translational barriers and test these approaches in humans still remains. Impact Statement Advances in tissue engineering have led to the development of new methods to regenerate and replace tissues and organs, including teeth. Tooth regeneration is the main goal for the replacement of tooth loss and therefore current evidence showed that tissue engineering might provide this treatment in future.

Magnetism in Dentistry: Review and Future Perspectives

Tissue engineering or tissue reconstruction/repair/regeneration may be considered as a guiding strategy in oral and maxillofacial surgery, as well as in endodontics, orthodontics, periodontics, and daily clinical practice. A wide range of techniques has been developed over the past years, from tissue grafts to the more recent and innovative regenerative procedures. Continuous research in the field of natural and artificial materials and biomaterials, as well as in advanced scaffold design strategies has been carried out. The focus has also been on various growth factors involved in dental tissue repair or reconstruction. Benefiting from the recent literature, this review paper illustrates current innovative strategies and technological approaches in oral and maxillofacial tissue engineering, trying to offer some information regarding the available scientific data and practical applications. After introducing tissue engineering aspects, an overview on additive manufacturing technologies will be provided, with a focus on the applications of superparamagnetic iron oxide nanoparticles in the biomedical field. The potential applications of magnetic fields and magnetic devices on the acceleration of orthodontic tooth movement will be analysed.

miR-6807-5p Inhibited the Odontogenic Differentiation of Human Dental Pulp Stem Cells Through Directly Targeting METTL7A

Background: Tooth tissue regeneration mediated by mesenchymal stem cells (MSCs) has become the most ideal treatment. Although the known regulatory mechanism and some achievements have been discovered, directional differentiation cannot effectively induce regeneration of tooth tissue. In this study, we intended to explore the function and mechanism of miR-6807-5p and its target gene METTL7A in odontogenic differentiation.

Methods: In this study, human dental pulp stem cells (DPSCs) were used. Alkaline phosphatase (ALP), Alizarin red staining (ARS), and calcium ion quantification were used to detect the odontogenic differentiation of miR-6807-5p and METTL7A. Real-time RT-PCR, western blot, dual-luciferase reporter assay, and pull-down assay with biotinylated miRNA were used to confirm that METTL7A was the downstream gene of miR-6807-5p. Protein mass spectrometry and co-immunoprecipitation (Co-IP) were used to detect that SNRNP200 was the co-binding protein of METTL7A.

Results: After mineralized induction, the odontogenic differentiation was enhanced in the miR-6807-5p-knockdown group and weakened in the miR-6807-5p-overexpressed group compared with the control group. METTL7A was the downstream target of miR-6807-5p. After mineralized induction, the odontogenic differentiation was weakened in the METTL7A-knockdown group and enhanced in the METTL7A-overexpressed group compared with the control group. SNRNP200 was the co-binding protein of METTL7A. The knockdown of SNRNP200 inhibited the odontogenic differentiation of DPSCs.

Conclusion: This study verified that miR-6807-5p inhibited the odontogenic differentiation of DPSCs. The binding site of miR-6807-5p was the 3′UTR region of METTL7A, which was silenced by miR-6807-5p. METTL7A promoted the odontogenic differentiation of DPSCs. SNRNP200, a co-binding protein of METTL7A, promoted the odontogenic differentiation of DPSCs.

Characteristics of Large Animal Models for Current Cell-Based Oral Tissue Regeneration

The recent advances in the field of cell-based therapeutics open promising perspectives for oral tissue regeneration. The development of large animal models, which overcome the limits of the rodent models and allow to emulate clinical situations, is crucial for the validation of regenerative strategies to move toward clinical application. Currently, porcine, canine, and ovine models are mainly developed for oral regeneration and their specific characteristics have an impact on the outcomes of the studies. Thus, this systematic review investigates the application of porcine, canine, and ovine models in present cell-based oral regeneration, according to the species characteristics and the targeted tissue to regenerate. A customized search of PubMed, EMBASE, Scopus, and Web of Science databases from January 2015 to March 2020 was conducted. Relevant articles about cell-based oral tissues engineering in porcine, canine, and ovine models were evaluated. Among the evaluated articles, 58 relevant studies about cell-based oral regeneration in porcine, canine, and ovine models matched the eligibility criteria and were selected for full analysis. Porcine models, the most similar species with humans, were mostly used for bone and periodontium regeneration; tooth regeneration was reported only in pig, except for one study in dog. Canine models were the most transversal models, successfully involved for all oral tissue regeneration and notably in implantology. However, differences with humans and ethical concerns affect the use of these models. Ovine models, alternative to porcine and canine ones, were mainly used for bone and, scarcely, periodontium regeneration. The anatomy and physiology of these animals restrain their involvement. If consistency was found in defect specificities and cell trends among different species animal models of bone, dentin-pulp complex, or tooth regeneration, variability appeared in periodontium. Regeneration assessment methods were more elaborate in porcines and canines than in ovines. Risk of bias was low for selection, attrition and reporting, but unclear for performance and detection. Overall, if none of the large animal models can be considered an ideal one, they are of deemed importance for oral cell-based tissue engineering and researchers should consider their relevance to establish favorable conditions for a given preclinical cell-based therapeutics.

Dental tissue-derived stem cell sheet biotechnology for periodontal tissue regeneration: A systematic review

OBJECTIVE

This study aimed to conduct a systematic review of the use of a cell sheet formed by mesenchymal stem cells derived from dental tissues (ddMSCs) for periodontal tissue regeneration in animal models in comparison with any other type of regenerative treatment.

DESIGN

PubMed and Scopus databases were searched for relevant studies up to December 2020. The review was conducted based on the Preferred Reporting Items for Systematic Reviews and Meta-analysis guidelines.

RESULTS

Of the 1542 potentially relevant articles initially identified, 33 fulfilled the eligibility criteria and were considered for this review. Even with a wide variety of selected study methods, the periodontal tissue was always regenerated; this indicates the potential for the use of these cell sheets in the future of periodontics. However, this regeneration process is not always complete.

CONCLUSION

Despite the implantation, ddMSCs sheets have a great potential to be used in the regeneration of periodontal tissue. More in vivo studies should be conducted using standardized techniques for cell sheet implantation to obtain more robust evidence of the relevance of using this modality of cell therapy for periodontal tissue regeneration.

Advanced Biomaterials and Techniques for Oral Tissue Engineering and Regeneration-A Review

The reconstruction or repair of oral and maxillofacial functionalities and aesthetics is a priority for patients affected by tooth loss, congenital defects, trauma deformities, or various dental diseases. Therefore, in dental medicine, tissue reconstruction represents a major interest in oral and maxillofacial surgery, periodontics, orthodontics, endodontics, and even daily clinical practice. The current clinical approaches involve a vast array of techniques ranging from the traditional use of tissue grafts to the most innovative regenerative procedures, such as tissue engineering. In recent decades, a wide range of both artificial and natural biomaterials and scaffolds, genes, stem cells isolated from the mouth area (dental follicle, deciduous teeth, periodontal ligament, dental pulp, salivary glands, and adipose tissue), and various growth factors have been tested in tissue engineering approaches in dentistry, with many being proven successful. However, to fully eliminate the problems of traditional bone and tissue reconstruction in dentistry, continuous research is needed. Based on a recent literature review, this paper creates a picture of current innovative strategies applying dental stem cells for tissue regeneration in different dental fields and maxillofacial surgery, and offers detailed information regarding the available scientific data and practical applications.

Hybrid chitosan/gelatin/nanohydroxyapatite scaffolds promote odontogenic differentiation of dental pulp stem cells and in vitro biomineralization

OBJECTIVE

Hybrid chitosan/gelatin/nanohydroxyapatite (CS/Gel/nHA) scaffolds have attracted considerable interest in tissue engineering (TE) of mineralized tissues. The present study aimed to investigate the potential of CS/Gel/nHA scaffolds loaded with dental pulp stem cells (DPSCs) to induce odontogenic differentiation and in vitro biomineralization.

METHODS

CS/Gel/nHA scaffolds were synthesized by freeze-drying, seeded with DPSCs, and characterized with flow cytometry. Scanning Electron Microscopy (SEM), live/dead staining, and MTT assays were used to evaluate cell morphology and viability; real-time PCR for odontogenesis-related gene expression analysis; SEM-EDS (Energy Dispersive X-ray spectroscopy), and X-ray Diffraction analysis (XRD) for structural and chemical characterization of the mineralized constructs, respectively.

RESULTS

CS/Gel/nHA scaffolds supported viability and proliferation of DPSCs over 14 days in culture. Gene expression patterns indicated pronounced odontogenic shift of DPSCs, evidenced by upregulation of DSPP, BMP-2, ALP, and the transcription factors RunX2 and Osterix. SEM-EDS showed the production of a nanocrystalline mineralized matrix inside the cell-based and - to a lesser extent - the cell-free constructs, with a time-dependent production of net-like nanocrystals (appr. 25-30nm in diameter). XRD analysis gave the crystallite size (D=50nm) but could not distinguish between the initially incorporated and the biologically produced nHA.

SIGNIFICANCE

This is the first study validating the potential of CS/Gel/nHA scaffolds to support viability and proliferation of DPSCs, and to provide a biomimetic microenvironment favoring odontogenic differentiation and in vitro biomineralization without the addition of any inductive factors, including dexamethasone and/or growth/morphogenetic factors. These results reveal a promising strategy towards TE of mineralized dental tissues.

SFRP2 enhances dental pulp stem cell-mediated dentin regeneration in rabbit jaw

OBJECTIVES

Dental tissue-derived mesenchymal stem cell (MSC)-mediated tooth regeneration may be a useful therapeutic tool for repairing tooth loss. However, the low success rate of tooth regeneration restricts its clinical application. Identifying key factors for enhancing dentinogenesis in MSCs is crucial for promoting tooth regeneration.

MATERIALS AND METHODS

Human dental pulp stem cells (DPSCs) were transfected with retrovirus to obtain SFRP2-over-expressing DPSCs. Alkaline phosphatase (ALP) activity assay, Alizarin red staining, quantitative analysis of calcium, and dentinogenesis-related genes were detected. Additionally, transplantation in a rabbit tooth extraction model was used to explore the role of SFRP2 in dentin regeneration.

RESULTS

We found SFRP2 over-expression greatly enhanced ALP activity, and mineralization in DPSCs. Real-time RT-PCR revealed SFRP2 over-expression promoted the expressions of OSX, RUNX2, DSPP, DMP1, and BSP. Moreover, Micro CT analysis showed high-density calcification occurred to a much higher extent in SFRP2 over-expressing group compared to control group in vivo. Additionally, HE staining, immmunohistochemistry staining, and scanning electron microscopy results showed much more dentin-like tissue formed in SFRP2 over-expressing group compared to control group.

CONCLUSIONS

Our findings revealed SFRP2 is an important regulator that enhances the dentinogenesis of DPSCs and dentin regeneration in the jaw, which may have clinical applications.

Prospects of Advanced Therapy Medicinal Products-Based Therapies in Regenerative Dentistry: Current Status, Comparison with Global Trends in Medicine, and Future Perspectives

INTRODUCTION

Regenerative medicine offers innovative approaches to restore damaged tissues on the basis of tissue engineering (TE). Although research on advanced therapy medicinal products (ATMPs) has been very active in recent years, the number of licensed products remains surprisingly low and restricted to the treatment of severe, incurable diseases.

METHODS

This paper provides a critical review of current literature on the regulatory, clinical, and commercial status of ATMP-based therapies in the EU and worldwide and the hurdles to overcome for their broader application in Regenerative Dentistry.

RESULTS

Competent authorities have focused on developing regulatory pathways to address unmet patient needs. Oncology represents the dominating field, followed by cardiovascular, musculoskeletal, neurodegenerative, immunologic, and inherited diseases. Yet, the status remains in early development, and scientific, regulatory, and cost-effectiveness issues impose considerable hurdles toward marketing authorization, technology adoption, and patient accessibility. In this context, although regenerative dentistry has achieved breakthrough innovations in TE of several dental/oral tissues in preclinical models, it has hardly harnessed research progress to integrate innovative regenerative treatments into clinical practice.

CONCLUSION

Global demographic changes, which demonstrate a steady increase of the aging population, highlight the societal need for the application of ATMP-based therapies in the treatment of noncommunicable diseases (NCDs). Although oral diseases, as an integral part of NCDs, are not life-threatening and largely preventable, they sustain high prevalence, with severe burden on economy and quality of life. In this perspective, the urgent request to ultimately translate draining research in dental TE conducted during the last decades into innovative treatments brought safely and cost-effectively into society at large still holds the stage. This review provides an overview of the regulatory, clinical, and commercial status of ATMP-based therapies in the European Union and worldwide and the hurdles to overcome for their broader application in regenerative dentistry.

Bone regeneration capacities of alveolar bone mesenchymal stem cells sheet in rabbit calvarial bone defect

Mesenchymal stem cells sheets have been verified as a promising non-scaffold strategy for bone regeneration. Alveolar bone marrow mesenchymal stem cells, derived from neural crest, have the character of easily obtained and strong multi-differential potential. However, the bone regenerative features of alveolar bone marrow mesenchymal stem cells sheets in the craniofacial region remain unclear. The purpose of the present study was to compare the osteogenic differentiation and bone defect repairment characteristics of bone marrow mesenchymal stem cells sheets derived from alveolar bone (alveolar bone marrow mesenchymal stem cells) and iliac bone (Lon-bone marrow mesenchymal stem cells) in vitro and in vivo. Histology character, osteogenic differentiation, and osteogenic gene expression of human alveolar bone marrow mesenchymal stem cells and Lon-bone marrow mesenchymal stem cells were compared in vitro. The cell sheets were implanted in rabbit calvarial defects to evaluate tissue regeneration characteristics. Integrated bioinformatics analysis was used to reveal the specific gene and pathways expression profile of alveolar bone marrow mesenchymal stem cells. Our results showed that alveolar bone marrow mesenchymal stem cells had higher osteogenic differentiation than Lon-bone marrow mesenchymal stem cells. Although no obvious differences were found in the histological structure, fibronectin and integrin β1 expression between them, alveolar-bone marrow mesenchymal stem cells sheet exhibited higher mineral deposition and expression levels of osteogenic marker genes. After being transplanted in the rabbit calvarial defects area, the results showed that greater bone volume and trabecular thickness regeneration were found in bone marrow mesenchymal stem cells sheet group compared to Lon-bone marrow mesenchymal stem cells group at both 4 weeks and 8 weeks. Finally, datasets of bone marrow mesenchymal stem cells versus Lon-bone marrow mesenchymal stem cells, and periodontal ligament mesenchymal stem cells (another neural crest derived mesenchymal stem cells) versus umbilical cord mesenchymal stem cells were analyzed. Total 71 differential genes were identified by overlap between the 2 datasets. Homeobox genes, such as LHX8, MKX, PAX9, MSX, and HOX, were identified as the most significantly changed and would be potential specific genes in neural crest mesenchymal stem cells. In conclusion, the Al-bone marrow mesenchymal stem cells sheet-based tissue regeneration appears to be a promising strategy for craniofacial defect repair in future clinical applications.

Tooth Formation: Are the Hardest Tissues of Human Body Hard to Regenerate?

With increasing life expectancy, demands for dental tissue and whole-tooth regeneration are becoming more significant. Despite great progress in medicine, including regenerative therapies, the complex structure of dental tissues introduces several challenges to the field of regenerative dentistry. Interdisciplinary efforts from cellular biologists, material scientists, and clinical odontologists are being made to establish strategies and find the solutions for dental tissue regeneration and/or whole-tooth regeneration. In recent years, many significant discoveries were done regarding signaling pathways and factors shaping calcified tissue genesis, including those of tooth. Novel biocompatible scaffolds and polymer-based drug release systems are under development and may soon result in clinically applicable biomaterials with the potential to modulate signaling cascades involved in dental tissue genesis and regeneration. Approaches for whole-tooth regeneration utilizing adult stem cells, induced pluripotent stem cells, or tooth germ cells transplantation are emerging as promising alternatives to overcome existing in vitro tissue generation hurdles. In this interdisciplinary review, most recent advances in cellular signaling guiding dental tissue genesis, novel functionalized scaffolds and drug release material, various odontogenic cell sources, and methods for tooth regeneration are discussed thus providing a multi-faceted, up-to-date, and illustrative overview on the tooth regeneration matter, alongside hints for future directions in the challenging field of regenerative dentistry.

Dental stem cells in tooth repair: A systematic review

Background: Dental stem cells (DSCs) are self-renewable teeth cells, which help maintain or develop oral tissues. These cells can differentiate into odontoblasts, adipocytes, cementoblast-like cells, osteoblasts, or chondroblasts and form dentin/pulp. This systematic review aimed to summarize the current evidence regarding the role of these cells in dental pulp regeneration. Methods: We searched the following databases: PubMed, Cochrane Library, MEDLINE, SCOPUS, ScienceDirect, and Web of Science using relevant keywords. Case reports and non-English studies were excluded. We included all studies using dental stem cells in tooth repair whether in vivo or in vitro studies. Results: Dental pulp stem cell (DPSCs) is the most common type of cell. Most stem cells are incorporated and implanted into the root canals in different scaffold forms. Some experiments combine growth factors such as TDM, BMP, and G-CSF with stem cells to improve the results. The transplant of DPSCs and stem cells from apical papilla (SCAPs) was found to be associated with pulp-like recovery, efficient revascularization, enhanced chondrogenesis, and direct vascular supply of regenerated tissue. Conclusion: The current evidence suggests that DPSCs, stem cells from human exfoliated deciduous teeth, and SCAPs are capable of providing sufficient pulp regeneration and vascularization. For the development of the dental repair field, it is important to screen for more effective stem cells, dentine releasing therapies, good biomimicry scaffolds, and good histological markers.

Periodontal regenerative medicine using mesenchymal stem cells and biomaterials: A systematic review of pre-clinical studies

The aim of the systematic review was to analyze the use of mesenchymal stem cells (MSC) and biomaterial for periodontal regeneration from preclinical animal models and human. Electronic databases were searched and additional hand-search in leading journals was performed. The research strategy was achieved according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The including criteria were as follows: MSC, biomaterial, in vivo studies, with histologic and radiologic analysis and written in English. The risk of bias was assessed for individual studies. A total of 50 articles were selected and investigated in the systematic review. These results indicate that MSC and scaffold provide beneficial effects on periodontal regeneration, with no adverse effects of such interventions. Future studies need to identify the suitable association of MSC and biomaterial and to characterize the type of new cementum and the organization of the periodontal ligament fiber regeneration.

Regeneration characteristics of different dental derived stem cell sheets

BACKGROUND

Although cell sheets have gained much interest as a non-scaffold strategy for tissue regeneration, the regenerative features of different cell sheets remain unclear.

OBJECTIVE

In this study, we aimed to compare the regeneration characteristics of cell sheets derived from dental pulp stem cells (DPSCs), periodontal ligament stem cells (PDLSCs) and stem cells of the apical papilla (SCAPs).

METHODS

Dental pulp stem cells, PDLSCs and SCAPs from the same individual were acquired and induced to form sheets using 20 μg/mL vitamin C. Immunofluorescence staining was used to detect the expression of collagen I, fibronectin, integrin β1 and vimentin. Real-time PCR was used to determine NANOG, OCT4, SOX2 and TERT gene expression. The cell sheets with hydroxyapatite/tricalcium phosphate were transplanted into nude mice subcutaneously to evaluate tissue regeneration characteristics.

RESULTS

No obvious differences were found in the histological structure and extracellular matrix protein expression between DPSC, PDLSC and SCAP sheets. Dental pulp stem cell sheet showed higher expression of OCT4 and TERT than PDLSC and SCAP sheets. All three cell sheets displayed the ability of mineral tissue formation and highly expressed periostin. The tissue derived from DPSC sheet showed higher CD31 expression and porous fibres compared with that from the others. The tissue fibres formed from PDLSC sheet were directionally arranged, while the tissue derived from SCAP sheet showed highest mineral tissue formation.

CONCLUSION

Although in vitro DPSC, PDLSC and SCAP cell sheets have similar characteristics, their regenerative characteristics in vivo are different, with each showing potential application for regeneration of different tissues.

Guided Nitinol-Retained (Smileloc) Single-Tooth Dental Restorations

Nitinol metal alloy that changes shape according to temperature has been in clinical use at select clinics worldwide for the past 2 years and is now released for general use. The Smileloc Abutment and nitinol sleeve enable "cementless," "screwless," crown fastening that saves time and cost with the prospect of replacement of much of the present, sometimes troublesome, anthropic, soon to be anachronistic, technology.

Stem cells from human exfoliated deciduous teeth as an alternative cell source in bio-root regeneration

A stem cell-mediated bioengineered tooth root (bio-root) has proven to be a prospective tool for the treatment of tooth loss. As shown in our previous studies, dental follicle cells (DFCs) are suitable seeding cells for the construction of bio-roots. However, the DFCs which can only be obtained from unerupted tooth germ are restricted. Stem cells from human exfoliated deciduous teeth (SHEDs), which are harvested much more easily through a minimally invasive procedure, may be used as an alternative seeding cell. In this case, we compared the odontogenic characteristics of DFCs and SHEDs in bio-root regeneration. Methods: The biological characteristics of SHEDs and DFCs were determined in vitro. The cells were then induced to secrete abundant extracellular matrix (ECM) and form macroscopic cell sheets. We combined the cell sheets with treated dentin matrix (TDM) for subcutaneous transplantation into nude mice and orthotopic jaw bone implantation in Sprague-Dawley rats to further verify their regenerative potential. Results: DFCs exhibited a higher proliferation rate and stronger osteogenesis and adipogenesis capacities, while SHEDs displayed increased migration ability and excellent neurogenic potential. Both dental follicle cell sheets (DFCSs) and sheets of stem cells from human exfoliated deciduous teeth (SHEDSs) expressed not only ECM proteins but also osteogenic and odontogenic proteins. Importantly, similar to DFCSs/TDM, SHEDSs/TDM also successfully achieved the in vivo regeneration of the periodontal tissues, which consist of periodontal ligament fibers, blood vessels and new born alveolar bone. Conclusions: Both SHEDs and DFCs possessed a similar odontogenic differentiation capacity in vivo, and SHEDs were regarded as a prospective seeding cell for use in bio-root regeneration in the future.

Stem-Cell Therapy Advances in China

Stem-cell therapy is a promising method for treating patients with a wide range of diseases and injuries. Increasing government funding of scientific research has promoted rapid developments in stem-cell research in China, as evidenced by the substantial increase in the number and quality of publications in the past 5 years. Multiple high-quality studies have been performed in China that concern cell reprogramming, stem-cell homeostasis, gene modifications, and immunomodulation. The number of translation studies, including basic and preclinical investigations, has also increased. Around 100 stem-cell banks have been established in China, 10 stem-cell drugs are currently in the approval process, and >400 stem cell-based clinical trials are currently registered in China. With continued state funding, advanced biotechnical support, and the development of regulatory standards for the clinical application of stem cells, further innovations are expected that will lead to a boom in stem-cell therapies. This review highlights recent achievements in stem-cell research in China and discusses future prospects.

The role of stem cell therapy in regeneration of dentine-pulp complex: a systematic review

Infection of the dental pulp will result in inflammation and eventually tissue necrosis which is treated conventionally by pulpectomy and root canal treatment. Advances in regenerative medicine and tissue engineering along with the introduction of new sources of stem cells have led to the possibility of pulp tissue regeneration. This systematic review analyzes animal studies published since 2010 to determine the ability of stem cell therapy to regenerate the dentine-pulp complex (DPC) and the success of clinical protocols. In vitro and human clinical studies are excluded and only the experimental studies on animal models were included. Dental pulp stem cells constitute the most commonly used cell type. The majority of stem cells are incorporated into various types of scaffold and implanted into root canals. Some of the studies combine growth factors with stem cells in an attempt to improve the outcome. Studies of ectopic transplantation using small animal models are simple and non-systematic evaluation techniques. Stem cell concentrations have not been so far reported; therefore, the translational value of such animal studies remains questionable. Though all types of stem cells appear capable of regenerating a dentine-pulp complex, still several factors have been considered in selecting the cell type. Co-administrative factors are essential for inducing the systemic migration of stem cells, and their vascularization and differentiation into odontoblast-like cells. Scaffolds provide a biodegradable structure able to control the release of growth factors. To identify problems and reduce costs, novel strategies should be initially tested in subcutaneous or renal capsule implantation followed by root canal models to confirm results.

Dental Mesenchymal Stem Cell-Based Translational Regenerative Dentistry: From Artificial to Biological Replacement

Dentistry is a continuously changing field that has witnessed much advancement in the past century. Prosthodontics is that branch of dentistry that deals with replacing missing teeth using either fixed or removable appliances in an attempt to simulate natural tooth function. Although such "replacement therapies" appear to be easy and economic they fall short of ever coming close to their natural counterparts. Complications that arise often lead to failures and frequent repairs of such devices which seldom allow true physiological function of dental and oral-maxillofacial tissues. Such factors can critically affect the quality of life of an individual. The market for dental implants is continuously growing with huge economic revenues. Unfortunately, such treatments are again associated with frequent problems such as peri-implantitis resulting in an eventual loss or replacement of implants. This is particularly influential for patients having co-morbid diseases such as diabetes or osteoporosis and in association with smoking and other conditions that undoubtedly affect the final treatment outcome. The advent of tissue engineering and regenerative medicine therapies along with the enormous strides taken in their associated interdisciplinary fields such as stem cell therapy, biomaterial development, and others may open arenas to enhancing tissue regeneration via designing and construction of patient-specific biological and/or biomimetic substitutes. This review will overview current strategies in regenerative dentistry while overviewing key roles of dental mesenchymal stem cells particularly those of the dental pulp, until paving the way to precision/translational regenerative medicine therapies for future clinical use.

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.

MicroRNA-214 Suppresses Osteogenic Differentiation of Human Periodontal Ligament Stem Cells by Targeting ATF4

Periodontitis is the main cause of adult tooth loss. Stem cell-based tissue engineering has become a promising therapy for periodontitis treatment. To date, human periodontal ligament stem cells (hPDLSCs) have been shown to be a favorable source for tissue engineering, but modulatory mechanisms of hPDLSCs remain unclear. Approximately 60% of mammalian genes are the targets of over 2000 miRNAs in multiple human cell types, and miRNAs are able to influence various biological processes in the human body, including bone formation. In this study, we found that after osteogenic induction, miR-214 was significantly decreased in hPDLSCs; therefore, we examined the effects of miR-214 on osteogenic differentiation. Computational miRNA target prediction analyses and luciferase reporter assays revealed that activating transcription factor 4 (ATF4) is a direct target of miR-214. We prepared cells overexpressing miR-214 and found that miR-214 negatively regulates osteogenic differentiation of hPDLSCs. For the target of miR-214, ATF4 protein expression level was decreased after induction. In conclusion, we found that miR-214-ATF4 axis is a novel pathway for regulating hPDLSC osteogenic differentiation.

Cellular and molecular mechanisms of tooth root development

The tooth root is an integral, functionally important part of our dentition. The formation of a functional root depends on epithelial-mesenchymal interactions and integration of the root with the jaw bone, blood supply and nerve innervations. The root development process therefore offers an attractive model for investigating organogenesis. Understanding how roots develop and how they can be bioengineered is also of great interest in the field of regenerative medicine. Here, we discuss recent advances in understanding the cellular and molecular mechanisms underlying tooth root formation. We review the function of cellular structure and components such as Hertwig's epithelial root sheath, cranial neural crest cells and stem cells residing in developing and adult teeth. We also highlight how complex signaling networks together with multiple transcription factors mediate tissue-tissue interactions that guide root development. Finally, we discuss the possible role of stem cells in establishing the crown-to-root transition, and provide an overview of root malformations and diseases in humans.

The Angiogenic Potential of DPSCs and SCAPs in an In Vivo Model of Dental Pulp Regeneration

Adequate vascularization, a restricting factor for the survival of engineered tissues, is often promoted by the addition of stem cells or the appropriate angiogenic growth factors. In this study, human dental pulp stem cells (DPSCs) and stem cells from the apical papilla (SCAPs) were applied in an in vivo model of dental pulp regeneration in order to compare their regenerative potential and confirm their previously demonstrated paracrine angiogenic properties. 3D-printed hydroxyapatite scaffolds containing DPSCs and/or SCAPs were subcutaneously transplanted into immunocompromised mice. After twelve weeks, histological and ultrastructural analysis demonstrated the regeneration of vascularized pulp-like tissue as well as mineralized tissue formation in all stem cell constructs. Despite the secretion of vascular endothelial growth factor in vitro, the stem cell constructs did not display a higher vascularization rate in comparison to control conditions. Similar results were found after eight weeks, which suggests both osteogenic/odontogenic differentiation of the transplanted stem cells and the promotion of angiogenesis in this particular setting. In conclusion, this is the first study to demonstrate the successful formation of vascularized pulp-like tissue in 3D-printed scaffolds containing dental stem cells, emphasizing the promising role of this approach in dental tissue engineering.

Stem cell-based tooth and periodontal regeneration

Currently regeneration of tooth and periodontal damage still remains great challenge. Stem cell-based tissue engineering raised novel therapeutic strategies for tooth and periodontal repair. Stem cells for tooth and periodontal regeneration include dental pulp stem cells (DPSCs), periodontal ligament stem cells (PDLSCs), stem cells from the dental apical papilla (SCAPs), and stem cells from human exfoliated deciduous teeth (SHEDs), dental follicle stem cells (DFSCs), dental epithelial stem cells (DESCs), bone marrow mesenchymal stem cells (BMMSCs), adipose-derived stem cells (ADSCs), embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). To date, substantial advances have been made in stem cell-based tooth and periodontal regeneration, including dentin-pulp, whole tooth, bioroot and periodontal regeneration. Translational investigations have been performed such as dental stem cell banking and clinical trials. In this review, we present strategies for stem cell-based tissue engineering for tooth and periodontal repair, and the translational studies.

Xenogeneic Bio-Root Prompts the Constructive Process Characterized by Macrophage Phenotype Polarization in Rodents and Nonhuman Primates

Tissue or organ regeneration using xenogeneic matrices is a promising approach to address the shortage of donor matrices for allotransplantation. Success of such approach has been demonstrated to correlate with macrophage-mediated fibrotic homeostasis and tissue remodeling. The previous studies have demonstrated that treated dentin matrix (TDM) could be a suitable bioactive substrate for allogeneic tooth root regeneration. This study constructed xenogeneic bioengineered tooth root (bio-root) via a combination of porcine TDM (pTDM) with allogeneic dental follicle cells (DFCs). Macrophage phenotypes are used to evaluate the remodeling process of xenogeneic bio-roots in vitro and in vivo. pTDM can facilitate odontoblast differentiation of human derived DFCs. Xenogeneic bio-roots in rat subcutaneous tissue prompt constructive response via M1 macrophage infiltration during early postimplantation stages and increase restorative M2 phenotype at later stages. After implantation of bio-roots into jaws of rhesus monkeys for six months, periodontal ligament-like fibers accompanied by macrophage polarization are observed, which are positive for COL-1, Periostin, βIII-tubulin and display such structures as fibroblasts and blood vessels. The reconstructed bio-root possesses biomechanical properties for the dissipation of masticatory forces. These results support that xenogeneic bio-root could maintain fibrotic homeostasis during remodeling process and highlight the potential application of xenogeneic matrices in regenerative medicine.

Therapeutic potential of dental stem cells

Stem cell biology has become an important field in regenerative medicine and tissue engineering therapy since the discovery and characterization of mesenchymal stem cells. Stem cell populations have also been isolated from human dental tissues, including dental pulp stem cells, stem cells from human exfoliated deciduous teeth, stem cells from apical papilla, dental follicle progenitor cells, and periodontal ligament stem cells. Dental stem cells are relatively easily obtainable and exhibit high plasticity and multipotential capabilities. The dental stem cells represent a gold standard for neural-crest-derived bone reconstruction in humans and can be used for the repair of body defects in low-risk autologous therapeutic strategies. The bioengineering technologies developed for tooth regeneration will make substantial contributions to understand the developmental process and will encourage future organ replacement by regenerative therapies in a wide variety of organs such as the liver, kidney, and heart. The concept of developing tooth banking and preservation of dental stem cells is promising. Further research in the area has the potential to herald a new dawn in effective treatment of notoriously difficult diseases which could prove highly beneficial to mankind in the long run.

Progress in Bioengineered Whole Tooth Research: From Bench to Dental Patient Chair

Tooth loss is a significant health issue that affects the physiological and social aspects of everyday life. Missing teeth impair simple tasks of chewing and speaking, and can also contribute to reduced self-confidence. An emerging and exciting area of regenerative medicine based dental research focuses on the formation of bioengineered whole tooth replacement therapies that can provide both the function and sensory responsiveness of natural teeth. This area of research aims to enhance the quality of dental and oral health for those suffering from tooth loss. Current approaches use a combination of dental progenitor cells, scaffolds and growth factors to create biologically based replacement teeth to serve as improved alternatives to currently used artificial dental prosthetics. This article is an overview of current progress, challenges, and future clinical applications of bioengineered whole teeth.