Tissue Engineering Approaches for Enamel, Dentin, and Pulp Regeneration: An Update

Cytotoxicity of dilutions of bioceramic materials in stem cells of human exfoliated deciduous teeth

OBJECTIVE

Several materials have been developed to preserve pulp vitality. They should have ideal cytocompatibility characteristics to promote the activity of stem cells of human exfoliated deciduous teeth (SHED) and thus heal pulp tissue.

OBJECTIVE

To evaluate the cytotoxicity of different dilutions of bioceramic material extracts in SHED.

METHODOLOGY

SHED were immersed in αMEM + the material extract according to the following experimental groups: Group 1 (G1) -BBio membrane, Group 2 (G2) - Bio-C Repair, Group 3 (G3) - MTA Repair HP, Group 4 (G4) - TheraCal LC, and Group 5 (G5) - Biodentine. Positive and negative control groups were maintained respectively in αMEM + 10% FBS and Milli-Q Water. The methods to analyze cell viability and proliferation involved MTT and Alamar Blue assays at 24, 48, and 72H after the contact of the SHED with bioceramic extracts at 1:1 and 1:2 dilutions. Data were analyzed by the three-way ANOVA, followed by Tukey's test (p<0.05).

RESULTS

At 1:1 dilution, SHED in contact with the MTA HP Repair extract showed statistically higher cell viability than the other experimental groups and the negative control (p<0.05), except for TheraCal LC (p> 0.05). At 1:2 dilution, BBio Membrane and Bio-C showed statistically higher values in intra- and intergroup comparisons (p<0.05). BBio Membrane, Bio-C Repair, and Biodentine extracts at 1:1 dilution showed greater cytotoxicity than 1:2 dilution in all periods (p<0.05).

CONCLUSION

MTA HP Repair showed the lowest cytotoxicity even at a 1:1 dilution. At a 1:2 dilution, the SHED in contact with the BBio membrane extract showed high cell viability. Thus, the BBio membrane would be a new non-cytotoxic biomaterial for SHED. Results offer possibilities of biomaterials that can be indicated for use in clinical regenerative procedures of the dentin-pulp complex.

Correlation between tooth decay and insulin resistance in normal weight males prompts a role for myo-inositol as a regenerative factor in dentistry and oral surgery: a feasibility study

Background

In an era of precision and stratified medicine, homogeneity in population-based cohorts, stringent causative entry, and pattern analysis of datasets are key elements to investigate medical treatments. Adhering to these principles, we collected in vivo and in vitro data pointing to an insulin-sensitizing/insulin-mimetic effect of myo-inositol (MYO) relevant to cell regeneration in dentistry and oral surgery. Confirmation of this possibility was obtained by in silico analysis of the relation between in vivo and in vitro results (the so-called bed-to-benchside reverse translational approach).

Results

Fourteen subjects over the 266 screened were young adult, normal weight, euglycemic, sedentary males having normal appetite, free diet, with a regular three-times-a-day eating schedule, standard dental hygiene, and negligible malocclusion/enamel defects. Occlusal caries were detected by fluorescence videoscanning, whereas body composition and energy balance were estimated with plicometry, predictive equations, and handgrip. Statistically significant correlations (Pearson r coefficient) were found between the number of occlusal caries and anthropometric indexes predicting insulin resistance (IR) in relation to the abdominal/visceral fat mass, fat-free mass, muscular strength, and energy expenditure adjusted to the fat and muscle stores. This indicated a role for IR in affecting dentin reparative processes. Consistently, in vitro administration of MYO to HUVEC and Swiss NIH3T3 cells in concentrations corresponding to those administered in vivo to reduce IR resulted in statistically significant cell replication (ANOVA/Turkey tests), suggesting that MYO has the potential to counteract inhibitory effects of IR on dental vascular and stromal cells turnover. Finally, in in silico experiments, quantitative evaluation (WOE and information value) of a bioinformatic Clinical Outcome Pathway confirmed that in vitro trophic effects of MYO could be transferred in vivo with high predictability, providing robust credence of its efficacy for oral health.

Conclusion

Our reverse bed-to-benchside data indicate that MYO might antagonize the detrimental effects of IR on tooth decay. This provides feasibility for clinical studies on MYO as a regenerative factor in dentistry and oral surgery, including dysmetabolic/aging conditions, bone reconstruction in oral destructive/necrotic disorders, dental implants, and for empowering the efficacy of a number of tissue engineering methodologies in dentistry and oral surgery.

Tissue Regeneration on Rise: Dental Hard Tissue Regeneration and Challenges-A Narrative Review

Background

As people live longer, there is an increasing need for hard tissue regeneration and whole-tooth regeneration. Despite the advancements in the field of medicine, the field of regenerative dentistry is still challenging due to the complexity of dental hard tissues. Cross-disciplinary collaboration among material scientists, cellular biologists, and odontologists aimed at developing strategies and uncovering solutions related to dental tissue regeneration. Methodology. A search of the literature was done for pertinent research. Consistent with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) 2020 Statement, the electronic databases looked at were PubMed, Science Direct, Scopus, and Google Scholar, with the keyword search "hard dental tissue regeneration."

Results

Database analysis yielded a total of 476 articles. 222 duplicate articles have been removed in total. Articles that have no connection to the directed regeneration of hard dental tissue were disregarded. The review concluded with the inclusion of four studies that were relevant to our research objective.

Conclusion

Current molecular signaling network investigations and novel viewpoints on cellular heterogeneity have made advancements in understanding of the kinetics of dental hard tissue regeneration possible. Here, we outline the fundamentals of stem hard dental tissue maintenance, regeneration, and repair, as well as recent advancements in the field of hard tissue regeneration. These intriguing findings help establish a framework that will eventually enable basic research findings to be utilized towards oral health-improving medicines.

The Role of Photobiomodulation on Dental-Derived Stem Cells in Regenerative Dentistry: A Comprehensive Systematic Review

BACKGROUND

Photobiomodulation therapy involves exposing tissues to light sources, including light-emitting diodes or low-level lasers, which results in cellular function modulation. The molecular mechanism of this treatment is revealed, demonstrating that depending on the light settings utilized, it has the potential to elicit both stimulatory and inhibitory reactions.

OBJECTIVE

The current systematic review aimed to evaluate the impact of photobiomodulation therapy on dental stem cells and provide an evidence-based conclusion in this regard.

METHODS

This systematic review was performed and reported based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) revised guidelines. PICO(S) components were employed to define the inclusion criteria. Web of Science, Scopus, Medline as well as grey literature, and google scholar were searched up to September 2021 to retrieve relevant papers.

RESULTS

Photobiomodulation therapy showed promising effects on the proliferation, viability, and differentiation of dental stem cells. This finding was based on reviewing related articles with a low risk of bias.

CONCLUSION

Despite the positive benefits of photobiomodulation therapy on dental stem cells, the current data do not provide a definitive conclusion on the best physical parameters for enhancing cell viability, proliferation, and differentiation.

Exosome-based engineering strategies for the diagnosis and treatment of oral and maxillofacial diseases

Oral and maxillofacial diseases are one of the most prevalent diseases in the world, which not only seriously affect the health of patients' oral and maxillofacial tissues, but also bring serious economic and psychological burdens to patients. Therefore, oral and maxillofacial diseases require effective treatment. Traditional treatments have limited effects. In recent years, nature exosomes have attracted increasing attention due to their ability to diagnose and treat diseases. However, the application of nature exosomes is limited due to low yield, high impurities, lack of targeting, and high cost. Engineered exosomes can be endowed with better comprehensive therapeutic properties by modifying exosomes of parent cells or directly modifying exosomes, and biomaterial loading exosomes. Compared with natural exosomes, these engineered exosomes can achieve more effective diagnosis and treatment of oral and maxillary system diseases, and provide reference and guidance for clinical application. This paper reviews the engineering modification methods of exosomes and the application of engineered exosomes in oral and maxillofacial diseases and looks forward to future research directions.

Approaches to vital pulp therapies

Tooth decay, which leads to pulpal inflammation due to the pulp's response to bacterial components and byproducts is the most common infectious disease. The main goals of clinical management are to eliminate sources of infection, to facilitate healing by regulating inflammation indental tissue, and to replace lost tissues. A variety of novel approaches from tissue engineering based on stem cells, bioactive molecules, and extracellular matrix-like scaffold structures to therapeutic applications, or a combination of all these are present in the literature. Shortcomings of existing conventional materials for pulp capping and the novel approches aiming to preserve pulp vitality highligted the need for developing new targeted dental materials. This review looks at the novel approches for vital pulp treatments after briefly addresing the conventional vital pulp treatment as well as the regenerative and self defense capabilities of the pulp. A narrative review focusing on the current and future approaches for pulp preservation was performed after surveying the relevant papers on vital pulp therapies including pulp capping, pulpotomy, and potential approaches for facilitating dentin-pulp complex regeneration in PubMed, Medline, and Scopus databases.

Advancing Dentistry through Bioprinting: Personalization of Oral Tissues

Despite significant advancements in dental tissue restoration and the use of prostheses for addressing tooth loss, the prevailing clinical approaches remain somewhat inadequate for replicating native dental tissue characteristics. The emergence of three-dimensional (3D) bioprinting offers a promising innovation within the fields of regenerative medicine and tissue engineering. This technology offers notable precision and efficiency, thereby introducing a fresh avenue for tissue regeneration. Unlike the traditional framework encompassing scaffolds, cells, and signaling factors, 3D bioprinting constitutes a contemporary addition to the arsenal of tissue engineering tools. The ongoing shift from conventional dentistry to a more personalized paradigm, principally under the guidance of bioprinting, is poised to exert a significant influence in the foreseeable future. This systematic review undertakes the task of aggregating and analyzing insights related to the application of bioprinting in the context of regenerative dentistry. Adhering to PRISMA guidelines, an exhaustive literature survey spanning the years 2019 to 2023 was performed across prominent databases including PubMed, Scopus, Google Scholar, and ScienceDirect. The landscape of regenerative dentistry has ushered in novel prospects for dentoalveolar treatments and personalized interventions. This review expounds on contemporary accomplishments and avenues for the regeneration of pulp-dentin, bone, periodontal tissues, and gingival tissues. The progressive strides achieved in the realm of bioprinting hold the potential to not only enhance the quality of life but also to catalyze transformative shifts within the domains of medical and dental practices.

Improved Method for Dental Pulp Stem Cell Preservation and Its Underlying Cell Biological Mechanism

Dental pulp stem cells (DPSCs) are considered a valuable cell source for regenerative medicine because of their high proliferative potential, multipotency, and availability. We established a new cryopreservation method (NCM) for collecting DPSCs, in which the tissue itself is cryopreserved and DPSCs are collected after thawing. We improved the NCM and developed a new method for collecting and preserving DPSCs more efficiently. Dental pulp tissue was collected from an extracted tooth, divided into two pieces, sandwiched from above and below using cell culture inserts, and cultured. As a result, the cells in the pulp tissue migrated vertically over time and localized near the upper and lower membranes over 2-3 days. With regard to the underlying molecular mechanism, SDF1 was predominantly involved in cell migration. This improved method is valuable and enables the more efficient collection and reliable preservation of DPSCs. It has the potential to procure a large number of DPSCs stably.

Adult Mesenchymal Stem Cells from Oral Cavity and Surrounding Areas: Types and Biomedical Applications

Adult mesenchymal stem cells are those obtained from the conformation of dental structures (DMSC), such as deciduous and permanent teeth and other surrounding tissues. Background: The self-renewal and differentiation capacities of these adult stem cells allow for great clinical potential. Because DMSC are cells of ectomesenchymal origin, they reveal a high capacity for complete regeneration of dental pulp, periodontal tissue, and other biomedical applications; their differentiation into other types of cells promotes repair in muscle tissue, cardiac, pancreatic, nervous, bone, cartilage, skin, and corneal tissues, among others, with a high predictability of success. Therefore, stem and progenitor cells, with their exosomes of dental origin and surrounding areas in the oral cavity due to their plasticity, are considered a fundamental pillar in medicine and regenerative dentistry. Tissue engineering (MSCs, scaffolds, and bioactive molecules) sustains and induces its multipotent and immunomodulatory effects. It is of vital importance to guarantee the safety and efficacy of the procedures designed for patients, and for this purpose, more clinical trials are needed to increase the efficacy of several pathologies. Conclusion: From a bioethical and transcendental anthropological point of view, the human person as a unique being facilitates better clinical and personalized therapy, given the higher prevalence of dental and chronic systemic diseases.

Evaluation of the Effects of Amoxicillin on Tooth Development in Rats by Histological and Histomorphometric Study

Amoxicillin is one of the most commonly prescribed antibiotics in children. As a result, it is prescribed as the first line of defence against cutaneous, gastrointestinal, and respiratory infections. The objective of this study was to evaluate the effects of Amoxicillin on the formation of dentin and enamel during the secretory and early phases of mineralization. Regarding the materials and methods used to perform this study, 16 pregnant adult Wistar rats were equally divided into two groups. The first group did not receive the drug and was prescribed a saline solution (control group), and the other group received 250 mg/kg/day of Amoxicillin (experimental group). From the 13th gestational day until delivery, the treatment was given every day by oral gavage. After birth, the newborns also received the same treatment as their mothers from the first day until 7 or 12 days after birth. The newborns were sacrificed at 7 and 12 days postnatally, the jaws were dissected, the maxilla was taken, the samples were fixed in 10% formaldehyde solution, and the upper first molars were analyzed histologically by H & E stain and histomorphometrically by image J to examine the enamel, dentin, ameloblast and odontoblast mean thickness in both groups and each healing periods. The study's results showed that the mean enamel, as well as ameloblastic and odontoblastic layer thickness, were significantly different in the Amoxicillin 250 mg/kg group, compared to the control group. The result also revealed a non-significant group difference in the dentin thickness in both durations (P-value at day 7=0.147 and the P-value at day 12=0.054). Vacuolization of the ameloblastic and odontoblastic layers was observed in the Amoxicillin-treated group in both durations.

Propolis Controlled Delivery Systems for Oral Therapeutics in Dental Medicine: A Systematic Review

This systematic review synthesizes the existing evidence in the literature regarding the association of propolis with controlled delivery systems (DDSs) and its potential therapeutic action in dental medicine. Two independent reviewers performed a literature search up to 1 June 2023 in five databases: PubMed/Medline, Web of Science, Cochrane Library, Scopus, and Embase, to identify the eligible studies. Clinical, in situ, and in vitro studies that investigated the incorporation of propolis as the main agent in DDSs for dental medicine were included in this study. Review articles, clinical cases, theses, dissertations, conference abstracts, and studies that had no application in dentistry were excluded. A total of 2019 records were initially identified. After carefully examining 21 full-text articles, 12 in vitro studies, 4 clinical, 1 animal model, and 3 in vivo and in vitro studies were included (n = 21). Relevant data were extracted from the included studies and analyzed qualitatively. The use of propolis has been reported in cariology, endodontics, periodontics, stomatology, and dental implants. Propolis has shown non-cytotoxic, osteoinductive, antimicrobial, and anti-inflammatory properties. Moreover, propolis can be released from DDS for prolonged periods, presenting biocompatibility, safety, and potential advantage for applications in dental medicine.

Application of Biocompatible Scaffolds in Stem-Cell-Based Dental Tissue Engineering

Tissue engineering as an important field in regenerative medicine is a promising therapeutic approach to replace or regenerate injured tissues. It consists of three vital steps including the selection of suitable cells, formation of 3d scaffolds, and adding growth factors. Mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs) are mentioned as two main sources for this approach that have been used for the treatment of various types of disorders. However, the main focus of literature in the field of dental tissue engineering is on utilizing MSCs. On the other hand, biocompatible scaffolds play a notable role in this regenerative process which is mentioned to be harmless with acceptable osteoinductivity. Their ability in inhibiting inflammatory responses also makes them powerful tools. Indeed, stem cell functions should be supported by biomaterials acting as scaffolds incorporated with biological signals. Naturally derived polymeric scaffolds and synthetically engineered polymeric/ceramic scaffolds are two main types of scaffolds regarding their materials that are defined further in this review. Various strategies of tissue bioengineering can affect the regeneration of dentin-pulp complex, periodontium regeneration, and whole teeth bioengineering. In this regard, in vivo/ex vivo experimental models have been developed recently in order to perform preclinical studies of dental tissue engineering which make it more transferable to be used for clinic uses. This review summarizes dental tissue engineering through its different components. Also, strategies of tissue bioengineering and experimental models are introduced in order to provide a perspective of the potential roles of dental tissue engineering to be used for clinical aims.

Dentin regeneration based on tooth tissue engineering: A review

Missing or damaged teeth due to caries, genetic disorders, oral cancer, or infection may contribute to physical and mental impairment that reduces the quality of life. Despite major progress in dental tissue repair and those replacing missing teeth with prostheses, clinical treatments are not yet entirely satisfactory, as they do not regenerate tissues with natural teeth features. Therefore, much of the focus has centered on tissue engineering (TE) based on dental stem/progenitor cells to create bioengineered dental tissues. Many in vitro and in vivo studies have shown the use of cells in regenerating sections of a tooth or a whole tooth. Tooth tissue engineering (TTE), as a promising method for dental tissue regeneration, can form durable biological substitutes for soft and mineralized dental tissues. The cell-based TE approach, which directly seeds cells and bioactive components onto the biodegradable scaffolds, is currently the most potential method. Three essential components of this strategy are cells, scaffolds, and growth factors (GFs). This study investigates dentin regeneration after an injury such as caries using TE and stem/progenitor cell-based strategies. We begin by discussing about the biological structure of a dentin and dentinogenesis. The engineering of teeth requires knowledge of the processes that underlie the growth of an organ or tissue. Then, the three fundamental requirements for dentin regeneration, namely cell sources, GFs, and scaffolds are covered in the current study, which may ultimately lead to new insights in this field.

Metformin carbon nanodots promote odontoblastic differentiation of dental pulp stem cells by pathway of autophagy

Human dental pulp stem cells (hDPSCs) have been a focus of pulp regeneration research because of their excellent odontogenic potential and availability. Applying the odontoblastic differentiation of hDPSCs to tooth regeneration has been challenging. Metformin-based carbon nanodots (MCDs) were synthesized and characterized to investigate their effects in vitro on odontoblastic hDPSC differentiation and the underlying mechanism. MCDs were synthesized by a hydrothermal treatment method and characterized using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The biocompatibility and fluorescence properties of the MCDs in Dulbecco’s modified Eagle’s medium high-glucose culture medium and the in vitro odontogenic potential and related mechanism of the bioactive nanomaterial was explored. TEM images showed that MCDs were spherical in shape with a size of approximately 5.9 nm. MCDs showed biological safety in cell viability, apoptosis, and fluorescence labelling ability at a concentration up to 200 μg/ml in vitro. The presence of MCDs facilitated high-efficiency odontogenic differentiation of hDPSCs by promoting odontogenic gene and protein expression. Moreover, MCDs promoted odontoblastic hDPSC differentiation via autophagy. MCDs are capable of activating autophagy and enhancing the odontogenic differentiation of hDPSCs by upregulating odontoblast gene marker (DMP1, DSPP, RUNX2, and SP7) and protein (DSPP and DMP1) expression.

Tissue Engineering with Stem Cell from Human Exfoliated Deciduous Teeth (SHED) and Collagen Matrix, Regulated by Growth Factor in Regenerating the Dental Pulp

Maintaining dental pulp vitality and preventing tooth loss are two challenges in endodontic treatment. A tooth lacking a viable pulp loses its defense mechanism and regenerative ability, making it more vulnerable to severe damage and eventually necessitating extraction. The tissue engineering approach has drawn attention as an alternative therapy as it can regenerate dentin-pulp complex structures and functions. Stem cells or progenitor cells, extracellular matrix, and signaling molecules are triad components of this approach. Stem cells from human exfoliated deciduous teeth (SHED) are a promising, noninvasive source of stem cells for tissue regeneration. Not only can SHEDs regenerate dentin-pulp tissues (comprised of fibroblasts, odontoblasts, endothelial cells, and nerve cells), but SHEDs also possess immunomodulatory and immunosuppressive properties. The collagen matrix is a material of choice to provide structural and microenvironmental support for SHED-to-dentin pulp tissue differentiation. Growth factors regulate cell proliferation, migration, and differentiation into specific phenotypes via signal-transduction pathways. This review provides current concepts and applications of the tissue engineering approach, especially SHEDs, in endodontic treatment.

Determinants of Dental Pulp Stem Cell Heterogeneity

INTRODUCTION

The aim of this review is to provide a narrative review on the determinants of dental pulp stem cell (DPSC) heterogeneity that may affect the regenerative properties of these cells.

METHODS

PubMed, Scopus and Medline (Ovid) literature searches were done on human dental pulp stem cell (hDPSC) heterogeneity. The focus was on human dental pulp stem cells (hDPSCs) with a primary focus on DPSC heterogeneity.

RESULTS

DPSCs display significant heterogeneity as illustrated by the various subpopulations reported, including differences in proliferation and differentiation capabilities and the impact of various intrinsic and extrinsic factors.

CONCLUSIONS

The lack of consistent and reliable results in the clinical setting may be due to the heterogeneous nature of DPSC populations. Standardization in isolation techniques and in criteria to characterize DPSCs should lead to less variability in results reported and improve comparison of findings between studies. Single-cell RNA sequencing holds promise in elucidating DPSC heterogeneity and may contribute to the establishment of standardized techniques.

Epiprofin Transcriptional Activation Promotes Ameloblast Induction From Mouse Induced Pluripotent Stem Cells via the BMP-Smad Signaling Axis

The transcriptional regulation of induced pluripotent stem cells (iPSCs) holds promise for their directed differentiation into ameloblasts, which are usually lost after tooth eruption. Ameloblast differentiation is regulated by multiple signaling molecules, including bone morphogenetic proteins (BMPs). Epiprofin (Epfn), a transcription factor, is expressed in the dental epithelium, and epithelial Epfn overexpression results in ectopic ameloblast differentiation and enamel formation in mouse incisor, a striking phenotype resembling that of mice with deletion of follistatin (a BMP inhibitor). However, it remains unknown whether and how Epfn transcriptional activation promotes ameloblast induction from mouse iPSCs. Here, we generated doxycycline-inducible Epfn-expressing mouse iPSCs (Epfn-iPSCs). Ameloblasts, which are characterized by positive staining for keratin 14 and amelogenin and alizarin red S staining, were successfully derived from Epfn-iPSCs based on a stage-specific induction protocol, which involved the induction of the surface ectoderm, dental epithelial cells, and ameloblasts at stages 1, 2, and 3, respectively. Epfn activation by doxycycline at stages 2 and/or 3 decreased cell proliferation and promoted ameloblast differentiation, along with the upregulation of p-Smad1/5/8, a key regulator of the BMP-Smad signaling pathway. Gene analysis of the BMP-Smad signaling pathway-associated molecules revealed that Epfn activation decreased follistatin expression at stage 2, but increased BMP2/4/7 expression at stage 3. Perturbations in the ameloblast differentiation process were observed when the BMP-Smad signaling pathway was inhibited by a BMP receptor inhibitor (LDN-193189). Simultaneous LDN-193189 treatment and Epfn activation largely reversed the perturbations in ameloblast induction, with partial recovery of p-Smad1/5/8 expression, suggesting that Epfn activation promotes ameloblast induction from mouse iPSCs partially by upregulating BMP-Smad activity. These results reveal the potential regulatory networks between Epfn and the BMP-Smad pathway and suggest that Epfn is a promising target for inducing the differentiation of ameloblasts, which can be used in enamel and tooth regeneration.

Clinical Potential of Dental Pulp Stem Cells in Pulp Regeneration: Current Endodontic Progress and Future Perspectives

Dental caries is a common disease that not only destroys the rigid structure of the teeth but also causes pulp necrosis in severe cases. Once pulp necrosis has occurred, the most common treatment is to remove the damaged pulp tissue, leading to a loss of tooth vitality and increased tooth fragility. Dental pulp stem cells (DPSCs) isolated from pulp tissue exhibit mesenchymal stem cell-like characteristics and are considered ideal candidates for regenerating damaged dental pulp tissue owing to their multipotency, high proliferation rate, and viability after cryopreservation. Importantly, DPSCs do not elicit an allogeneic immune response because they are non-immunogenic and exhibit potent immunosuppressive properties. Here, we provide an up-to-date review of the clinical applicability and potential of DPSCs, as well as emerging trends in the regeneration of damaged pulp tissue. In addition, we suggest the possibility of using DPSCs as a resource for allogeneic transplantation and provide a perspective for their clinical application in pulp regeneration.

Future horizons: embedding the evolving science of regenerative dentistry in a modern, sustainable dental curriculum

Regenerative dentistry is an emerging field promising to revolutionise the way we approach and perform clinical therapies. This multidisciplinary field, integrating cellular biology, material science and tissue engineering, aims to restore and maintain biological vitality unlike conventional dental therapies, providing a new approach in achieving sustainability within dentistry. Although this emerging field in dentistry seems futuristic and a distant reality, it is closer than we perceive it, as rapid scientific advances contribute to novel technologies. In this opinion piece we share our views on the emerging field and the need of embedding the scientific knowledge and sustainability within the dental curriculum. We critically discuss challenges and quests ahead of our dental profession facing the future.

Mineral-induced bubbling effect and biomineralization as strategies to create highly porous and bioactive scaffolds for dentin tissue engineering

The objective of the study was to assess the biological and mechanical characteristics of chitosan-based scaffolds enriched by mineral phases and biomineralized in simulated body fluid (SBF) as a possible biomaterial for dentin regeneration. Thus, porous chitosan scaffolds were prepared by the mineral-induced bubbling-effect technique and subjected to biomineralization to create biomimetic scaffolds for dentin tissue engineering. Suspensions containing calcium hydroxide, nanohydroxyapatite, or β-tricalcium phosphate were added to the chitosan (CH) solution and subjected to gradual freezing and freeze-drying to obtain CHCa, CHnHA, and CHβTCP porous scaffolds, respectively, by the bubbling effect. Then, scaffolds were incubated in SBF for 5 days at 37°C, under constant stirring, to promote calcium-phosphate (CaP) biomineralization. Scanning electron microscopy revealed increased pore size and porosity degree on mineral-containing scaffolds, with CHCa and CHnHA presenting as round, well-distributed, and with an interconnected pore network. Nevertheless, incubation in SBF disrupted the porous architecture, except for CHCa_SBF , leading to the deposition of CaP coverage, confirmed by Fourier Transform Infrared Spectroscopy analyses. All mineral-containing and SBF-treated formulations presented controlled degradation profiles and released calcium throughout 28 days. When human dental pulp cells (HDPCs) were seeded onto scaffold structures, the porous and interconnected architecture of CHCa, CHnHA, and CHCa_SBF allowed cells to infiltrate and spread throughout the scaffold structure, whereas in other formulations cells were dispersed or agglomerated. It was possible to determine a positive effect on cell proliferation and odontogenic differentiation for mineral-containing formulations, intensely improved by biomineralization. A significant increase in mineralized matrix deposition (by 8.4 to 18.9 times) was observed for CHCa_SBF , CHnHA_SBF , and CHβTCP_SBF in comparison with plain CH. The bioactive effect on odontoblastic marker expression (ALP activity and mineralized matrix) was also observed for HDPCs continuously cultivated with conditioned medium obtained from scaffolds. Therefore, biomineralization of chitosan scaffolds containing different mineral phases was responsible for increasing the capacity for mineralized matrix deposition by pulpal cells, with potential for use in dentin tissue engineering.

Progress and perspectives on cell-free regenerative endodontic therapy

Although teeth with pulpitis/apical periodontitis are saved after successful endodontic therapy, they are devitalized and susceptible to reinfections and fractures. The development of biology-based approaches for dental pulp regeneration or repair is possible today because of recent advances in tissue engineering and biomaterials. Cell-free regenerative endodontic therapy offers a promising strategy for the treatment of necrotic immature permanent teeth in children and adolescents. However, studies are underway to determine whether this procedure can be applied to mature teeth.

Salidroside promotes the osteogenic and odontogenic differentiation of human dental pulp stem cells through the BMP signaling pathway

Regenerative endodontics, as an alternative approach, aims to regenerate dental pulp-like tissues and is garnering the attention of clinical dentists. This is due to its reported biological benefits for dental therapeutics. Stem cells and their microenvironment serve an important role in the process of pulp regeneration. Regulation of the stem cell microenvironment and the directed differentiation of stem cells is becoming a topic of intensive research. Salidroside (SAL) is extracted from the root of Rhodiola rosea and it has been reported that SAL exerts antiaging, neuroprotective, hepatoprotective, cardioprotective and anticancer effects. However, the ability of SAL to regulate the osteo/odontogenic differentiation of hDPSCs remains to be elucidated. In the present study, the effect of SAL on the proliferation and osteogenic/odontogenic differentiation of human dental pulp stem cells (hDPSCs) was investigated. This was achieved by performing CCK-8 ARS staining assay, reverse transcription-quantitative PCR to detect mRNA of ALP, OSX, RUNX2, OCN, DSPP and BSP, western blotting to detect the protein of MAPK, Smad1/5/8, OSX, RUNX2, BSP and GAPDH and immunofluorescence assays to detect DSPP. The results indicated that SAL promoted the cell viability and the osteogenic/odontogenic differentiation of hDPSCs whilst increasing the expression of genes associated with osteogenic/odontogenic differentiation by ARS staining assay. In addition, SAL promoted osteogenic and odontogenic differentiation by activating the phosphorylation of Smad1/5/8. Collectively, these findings suggest that SAL promoted the osteogenic and odontogenic differentiation of hDPSCs activating the BMP signaling pathway.

Fabrication of Vascularized DPSC Constructs for Efficient Pulp Regeneration

Dental pulp regeneration is a promising approach to restore the vitality of necrotic teeth. We have previously reported the fabrication of scaffold-free cell constructs containing only dental pulp stem cells (DPSCs) and their ability to form pulp-like tissue in the pulpless tooth. However, the DPSC construct could not build pulp-like tissue with a full root length because it is difficult to induce blood vessels from a small root canal foramen. Therefore, we hypothesized that vascular structure could be preformed in the DPSC construct by employing endothelial differentiation capability of DPSCs, and vascularized constructs might facilitate dental pulp regeneration in the pulpless tooth. In this study, vascularized DPSC constructs were fabricated by inducing endothelial differentiation, and then we investigated the behavior of differentiated DPSCs, the internal structure of cell constructs, and their pulp regenerative ability in vivo. We observed that DPSCs positive for CD31 and von Willebrand factor were localized at the outer layer of constructs and formed a reticulated lumen structure. The cells constituting the outer layer of the construct expressed endothelial differentiation markers at higher levels than cells in the inner part. These results indicated that DPSCs in the outer layer differentiated into endothelial cells and formed vascular-like structures in the cell construct. Next, a vascularized DPSC construct was transplanted into the human pulpless tooth that was implanted into immunodeficient mice in the subcutaneous space. After 6 wk of implantation, the vascularized construct formed pulp-like tissues with higher density of human CD31-positive blood vessels when compared with specimens implanted with a DPSC construct without prevascularization. These results suggest that the vascular structure formed in the DPSC construct facilitated the blood supply and enhanced pulp regeneration. This study demonstrates that a vascularized DPSC construct is a prospective biomaterial as an implant for novel dental pulp regeneration.

Can Cultured Meat Be an Alternative to Farm Animal Production for a Sustainable and Healthier Lifestyle?

Producing animal proteins requires large areas of agricultural land and is a major source of greenhouse gases. Cellular agriculture, especially cultured meat, could be a potential alternative for the environment and human health. It enables meat and other agricultural products to be grown from cells in a bioreactor without being taken from farm animals. This paper aims at an interdisciplinary review of literature focusing on potential benefits and risks associated with cultured meat. To achieve this goal, several international databases and governmental projects were thoroughly analyzed using keywords and phrases with specialty terms. This is a growing scientific domain, which has generated a series of debates regarding its potential effects. On the one hand the potential of beneficial effects is the reduction of agricultural land usage, pollution and the improvement of human health. Other authors question if cultured meat could be a sustainable alternative for reducing gas emissions. Interestingly, the energy used for cultured meat could be higher, due to the replacement of some biological functions, by technological processes. For potential effects to turn into results, a realistic understanding of the technology involved and more experimental studies are required.

Cell-Based Transplantation versus Cell Homing Approaches for Pulp-Dentin Complex Regeneration

Regenerative dentistry has paved the way for a new era for the replacement of damaged dental tissues. Whether the causative factor is dental caries, trauma, or chemical insult, the loss of the pulp vitality constitutes one of the major health problems worldwide. Two regenerative therapies were introduced for a fully functional pulp-dentin complex regeneration, namely, cell-based (cell transplantation) and cell homing (through revascularization or homing by injection of stem cells in situ or intravenously) therapies, with each demonstrating advantages as well as drawbacks, especially in clinical application. The present review is aimed at elaborating on these two techniques in the treatment of irreversibly inflamed or necrotic pulp, which is aimed at regenerating a fully functional pulp-dentin complex.

Enamel matrix derivative (EMD) enhances the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs)

To investigate the EMD's capacity in BMSCs osteogenic differentiation. In vivo and in vitro, BMSCs were treated with EMD, scanning electron microscopy, and Alizarin Red staining were used to detect the changes in the osteogenic ability of BMSCs, and the proliferation ability of BMSCs was evaluated by CCK8. In addition, by adding xav939, a typical inhibitor of Wnt/β-catenin signaling pathway, the regulatory function of Wnt/β-catenin signaling was clarified. The results showed that EMD promote cell proliferation and 25 μg/ml EMD had the most significant effect. Cells inducing osteogenesis for 2 and 3 even 4 weeks, the cell staining is deeper in EMD treated group than that of the control (P < 0.05) by alizarin Red staining, suggesting more mineralization of BMSCs. In vivo implanting the titanium plate wrapped with 25 μg/ml EMD treated-BMSC film into nude mice for 8 weeks, more nodules were formed on the surface of the titanium plate than that the control (P < 0.05). HE showed that there is a little blue-violet immature bone-like tissue block. Besides, the expression of RUNX Family Transcription Factor 2 (Runx2), Osterix, Osteocalcin (OCN), collagen I (COLI), alkaline phosphatase (ALP) and β-catenin were inhibited in xav939 group (P < 0.05); Inversely, all were activated in EMD group (P < 0.05). In conclusion, EMD promoted the proliferation and osteogenic differentiation of BMSCs. EMD's function on BMSCs might be associated with the Wnt/β-catenin signaling pathway.

Wnt Signalling in Regenerative Dentistry

Teeth are complex structures where a soft dental pulp tissue is enriched with nerves, vasculature and connective tissue and encased by the cushioning effect of dentin and the protection of a hard enamel in the crown and cementum in the root. Injuries such as trauma or caries can jeopardise these layers of protection and result in pulp exposure, inflammation and infection. Provision of most suitable materials for tooth repair upon injury has been the motivation of dentistry for many decades. Wnt signalling, an evolutionarily conserved pathway, plays key roles during pre- and post-natal development of many organs including the tooth. Mutations in the components of this pathway gives rise to various types of developmental tooth anomalies. Wnt signalling is also fundamental in the response of odontoblasts to injury and repair processes. The complexity of tooth structure has resulted in diverse studies looking at specific compartments or cell types of this organ. This review looks at the current advances in the field of tooth development and regeneration. The objective of the present review is to provide an updated vision on dental biomaterials research, focusing on their biological properties and interactions to act as evidence for their potential use in vital pulp treatment procedures. We discuss the outstanding questions and future directions to make this knowledge more translatable to the clinics.

The Emerging Role of Stem Cells in Regenerative Dentistry

Progress of modern dentistry is accelerating at a spectacular speed in the scientific, technological and clinical areas. Practical examples are the advancement in the digital field, which has guaranteed an average level of prosthetic practices for all patients, as well as other scientific developments, including research on stem cell biology. Given their plasticity, defined as the ability to differentiate into specific cell lineages with a capacity of almost unlimited self-renewal and release of trophic/immunomodulatory factors, stem cells have gained significant scientific and commercial interest in the last 15 years. Stem cells that can be isolated from various tissues of the oral cavity have emerged as attractive sources for bone and dental regeneration, mainly due to their ease of accessibility. This review will present the current understanding of emerging conceptual and technological issues of the use of stem cells to treat bone and dental loss defects. In particular, we will focus on the clinical application of stem cells, either directly isolated from oral sources or in vitro reprogrammed from somatic cells (induced pluripotent stem cells). Research aimed at further unraveling stem cell plasticity will allow to identify optimal stem cell sources and characteristics, to develop novel regenerative tools in dentistry.

Stage-Specific Role of Amelx Activation in Stepwise Ameloblast Induction from Mouse Induced Pluripotent Stem Cells

Amelogenin comprises ~90% of enamel proteins; however, the involvement of Amelx transcriptional activation in regulating ameloblast differentiation from induced pluripotent stem cells (iPSCs) remains unknown. In this study, we generated doxycycline-inducible Amelx-expressing mouse iPSCs (Amelx-iPSCs). We then established a three-stage ameloblast induction strategy from Amelx-iPSCs, including induction of surface ectoderm (stage 1), dental epithelial cells (DECs; stage 2), and ameloblast lineage (stage 3) in sequence, by manipulating several signaling molecules. We found that adjunctive use of lithium chloride (LiCl) in addition to bone morphogenetic protein 4 and retinoic acid promoted concentration-dependent differentiation of DECs. The resulting cells had a cobblestone appearance and keratin14 positivity. Attenuation of LiCl at stage 3 together with transforming growth factor β1 and epidermal growth factor resulted in an ameloblast lineage with elongated cell morphology, positivity for ameloblast markers, and calcium deposition. Although stage-specific activation of Amelx did not produce noticeable phenotypic changes in ameloblast differentiation, Amelx activation at stage 3 significantly enhanced cell adhesion as well as decreased proliferation and migration. These results suggest that the combination of inducible Amelx transcription and stage-specific ameloblast induction for iPSCs represents a powerful tool to highlight underlying mechanisms in ameloblast differentiation and function in association with Amelx expression.

Hard Dental Tissues Regeneration-Approaches and Challenges

With the development of the modern concept of tissue engineering approach and the discovery of the potential of stem cells in dentistry, the regeneration of hard dental tissues has become a reality and a priority of modern dentistry. The present review reports the recent advances on stem-cell based regeneration strategies for hard dental tissues and analyze the feasibility of stem cells and of growth factors in scaffolds-based or scaffold-free approaches in inducing the regeneration of either the whole tooth or only of its component structures.

Effects of Physical Stimulation in the Field of Oral Health

Physical stimulation has been widely used in clinical medicine and healthcare due to its noninvasiveness. The main applications of physical stimulation in the oral cavity include laser, ultrasound, magnetic field, and vibration, which have photothermal, cavitation, magnetocaloric, and mechanical effects, respectively. In addition, the above four stimulations with their unique biological effects, which can play a role at the gene, protein, and cell levels, can provide new methods for the treatment and prevention of common oral diseases. These four physical stimulations have been used as important auxiliary treatment methods in the field of orthodontics, implants, periodontal, dental pulp, maxillofacial surgery, and oral mucosa. This paper systematically describes the application of physical stimulation as a therapeutic method in the field of stomatology to provide guidance for clinicians. In addition, some applications of physical stimulation in specific directions are still at the research stage, and the specific mechanism has not been fully elucidated. To encourage further research on the oral applications of physical stimulation, we elaborate the research results and development history of various physical stimuli in the field of oral health.

Scaffold-based developmental tissue engineering strategies for ectodermal organ regeneration

Tissue engineering (TE) is a multidisciplinary research field aiming at the regeneration, restoration, or replacement of damaged tissues and organs. Classical TE approaches combine scaffolds, cells and soluble factors to fabricate constructs mimicking the native tissue to be regenerated. However, to date, limited success in clinical translations has been achieved by classical TE approaches, because of the lack of satisfactory biomorphological and biofunctional features of the obtained constructs. Developmental TE has emerged as a novel TE paradigm to obtain tissues and organs with correct biomorphology and biofunctionality by mimicking the morphogenetic processes leading to the tissue/organ generation in the embryo. Ectodermal appendages, for instance, develop in vivo by sequential interactions between epithelium and mesenchyme, in a process known as secondary induction. A fine artificial replication of these complex interactions can potentially lead to the fabrication of the tissues/organs to be regenerated. Successful developmental TE applications have been reported, in vitro and in vivo, for ectodermal appendages such as teeth, hair follicles and glands. Developmental TE strategies require an accurate selection of cell sources, scaffolds and cell culture configurations to allow for the correct replication of the in vivo morphogenetic cues. Herein, we describe and discuss the emergence of this TE paradigm by reviewing the achievements obtained so far in developmental TE 3D scaffolds for teeth, hair follicles, and salivary and lacrimal glands, with particular focus on the selection of biomaterials and cell culture configurations.

Characterization of Dental Pulp Stem Cell Responses to Functional Biomaterials Including Mineralized Trioxide Aggregates

INTRODUCTION

Many studies in stem cell biology have demonstrated that dental pulp stem cells (DPSC) may be highly proliferative and capable of pluripotent differentiation into many different tissue types. Recent advances in stem cell research have outlined methods for directing in vitro or in vivo growth, viability, and proliferation, as well as differentiation of DPSC-although much remains to be discovered. Based upon this information, the primary objective of this study was to understand the functional biomaterials needed to more effectively direct DPSC viability, growth, and proliferation.

METHODS

Using an approved protocol, previously collected and isolated samples of DPSC from an existing repository were used. Previously established stem cell biomarkers (Sox-2, Oct-4, NANOG) from each isolate were correlated with their proliferation rates or doubling times to categorize them into rapid, intermediate, or slow-dividing multipotent DPSC. Growth factors and other functional dental biomaterials were subsequently tested to evaluate DPSC responses in proliferation, viability, and morphology.

RESULTS

Differential responses were observed among DPSC isolates to growth factors, including vascular endothelial growth factor (VEGF) and bone morphogenic protein (BMP-2), and functional biomaterials such as mineralized trioxide aggregates (MTA). The responsiveness of DPSC isolates did not correlate with any single factor but rather with a combination of proliferation rate and biomarker expression.

CONCLUSIONS

These data strongly suggest that some, but not all, DPSC isolates are capable of a robust and significant in vitro response to differentiation stimuli, although this response is not universal. Although some biomarkers and phenotypes that distinguish and characterize these DPSC isolates may facilitate the ability to predict growth, viability, and differentiation potential, more research is needed to determine the other intrinsic and extrinsic factors that may contribute to and modulate these DPSC responses to these functional biomaterials for biotechnology and bioengineering applications.

Different Approaches to the Regeneration of Dental Tissues in Regenerative Endodontics

(1) Background: The regenerative procedure has established a new approach to root canal therapy, to preserve the vital pulp of the tooth. This present review aimed to describe and sum up the different approaches to regenerative endodontic treatment conducted in the last 10 years; (2) Methods: A literature search was performed in the PubMed and Cochrane Library electronic databases, supplemented by a manual search. The search strategy included the following terms: “regenerative endodontic protocol”, “regenerative endodontic treatment”, and “regenerative endodontics” combined with “pulp revascularization”. Only studies on humans, published in the last 10 years and written in English were included; (3) Results: Three hundred and eighty-six potentially significant articles were identified. After exclusion of duplicates, and meticulous analysis, 36 case reports were selected; (4) Conclusions: The pulp revascularization procedure may bring a favorable outcome, however, the prognosis of regenerative endodontics (RET) is unpredictable. Permanent immature teeth showed greater potential for positive outcomes after the regenerative procedure. Further controlled clinical studies are required to fully understand the process of the dentin–pulp complex regeneration, and the predictability of the procedure.

Hydrogels and Dentin-Pulp Complex Regeneration: From the Benchtop to Clinical Translation

Dentin-pulp complex is a term which refers to the dental pulp (DP) surrounded by dentin along its peripheries. Dentin and dental pulp are highly specialized tissues, which can be affected by various insults, primarily by dental caries. Regeneration of the dentin-pulp complex is of paramount importance to regain tooth vitality. The regenerative endodontic procedure (REP) is a relatively current approach, which aims to regenerate the dentin-pulp complex through stimulating the differentiation of resident or transplanted stem/progenitor cells. Hydrogel-based scaffolds are a unique category of three dimensional polymeric networks with high water content. They are hydrophilic, biocompatible, with tunable degradation patterns and mechanical properties, in addition to the ability to be loaded with various bioactive molecules. Furthermore, hydrogels have a considerable degree of flexibility and elasticity, mimicking the cell extracellular matrix (ECM), particularly that of the DP. The current review presents how for dentin-pulp complex regeneration, the application of injectable hydrogels combined with stem/progenitor cells could represent a promising approach. According to the source of the polymeric chain forming the hydrogel, they can be classified into natural, synthetic or hybrid hydrogels, combining natural and synthetic ones. Natural polymers are bioactive, highly biocompatible, and biodegradable by naturally occurring enzymes or via hydrolysis. On the other hand, synthetic polymers offer tunable mechanical properties, thermostability and durability as compared to natural hydrogels. Hybrid hydrogels combine the benefits of synthetic and natural polymers. Hydrogels can be biofunctionalized with cell-binding sequences as arginine-glycine-aspartic acid (RGD), can be used for local delivery of bioactive molecules and cellularized with stem cells for dentin-pulp regeneration. Formulating a hydrogel scaffold material fulfilling the required criteria in regenerative endodontics is still an area of active research, which shows promising potential for replacing conventional endodontic treatments in the near future.

Dental pulp stem cells response on the nanotopography of scaffold to regenerate dentin-pulp complex tissue

The study of regenerative dentistry receives a fast growing interest. The potential ability of the dentin-pulp complex to regenerate is both promising and perplexing. To answer the challenging nature of the dental environment, scientists have developed various combinations of biomaterial scaffolds, stem cells, and incorporation of several growth factors. One of the crucial elements of this tissue engineering plan is the selection and fabrication of scaffolds. However, further findings suggest that cell behavior hugely depends on mechanical signaling. Nanotopography modifies scaffolds to alter cell migration and differentiation. However, to the best of the author's knowledge, there are very few studies addressing the correlation between nanotopography and dentin-pulp complex regeneration. Therefore, this article presents a comprehensive review of these studies and suggests a direction for future developments, particularly in the incorporation of nanotopography design for dentin-pulp complex regeneration.

Chitosan-Based Biomimetically Mineralized Composite Materials in Human Hard Tissue Repair

Chitosan is a natural, biodegradable cationic polysaccharide, which has a similar chemical structure and similar biological behaviors to the components of the extracellular matrix in the biomineralization process of teeth or bone. Its excellent biocompatibility, biodegradability, and polyelectrolyte action make it a suitable organic template, which, combined with biomimetic mineralization technology, can be used to develop organic-inorganic composite materials for hard tissue repair. In recent years, various chitosan-based biomimetic organic-inorganic composite materials have been applied in the field of bone tissue engineering and enamel or dentin biomimetic repair in different forms (hydrogels, fibers, porous scaffolds, microspheres, etc.), and the inorganic components of the composites are usually biogenic minerals, such as hydroxyapatite, other calcium phosphate phases, or silica. These composites have good mechanical properties, biocompatibility, bioactivity, osteogenic potential, and other biological properties and are thus considered as promising novel materials for repairing the defects of hard tissue. This review is mainly focused on the properties and preparations of biomimetically mineralized composite materials using chitosan as an organic template, and the current application of various chitosan-based biomimetically mineralized composite materials in bone tissue engineering and dental hard tissue repair is summarized.

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.

circRNA Expression Profile in Dental Pulp Stem Cells during Odontogenic Differentiation

Introduction

Odontogenic differentiation of human dental pulp stem cells (hDPSCs) is a key step of pulp regeneration. Recent studies showed that circular RNAs (circRNAs) have many biological functions and that competing endogenous RNA (ceRNA) is their most common mechanism of action. However, the role of circRNAs in hDPSCs during odontogenesis is still unclear.

Methods

Isolated hDPSCs were cultured in essential and odontogenic medium. Total RNA was extracted after 14 days of culture, and then, microarray analysis was performed to measure the differential expressions of circRNAs. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was then performed to validate the microarray results. Based on microarray data from this study and available in the database, a ceRNA network was constructed to investigate the potential function of circRNAs during odontogenesis. In addition, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to investigate the potential correlation between signaling pathways and circRNAs. In addition, qRT-PCR and Western blot analysis were used to explore the function of hsa_circRNA_104101.

Results

We found 43 upregulated circRNAs and 144 downregulated circRNAs during the odontogenic differentiation process (fold change > 1.5 and <-1.5, respectively; P < 0.05). qRT-PCR results were in agreement with the microarray results. Bioinformatic analysis revealed that the Wnt signaling pathway and the TGF-β signaling pathway, as well as the other pathways associated with odontogenic differentiation, were correlated to the differentially expressed circRNAs. hsa_circRNA_104101 was proved to promote the odontogenic differentiation of hDPSCs.

Conclusion

This study reported 187 circRNAs that were differentially expressed in hDPSCs during odontogenic differentiation. Bioinformatic analysis of the expression data suggested that circRNA-miRNA-mRNA networks might act as a crucial mechanism for hDPSC odontogenic differentiation, providing a theoretical foundation for the study of pulp regeneration regulation by circRNAs.

Mesenchymal Stem/Progenitor Cells: The Prospect of Human Clinical Translation

Mesenchymal stem/progenitor cells (MSCs) are key players in regenerative medicine, relying principally on their differentiation/regeneration potential, immunomodulatory properties, paracrine effects, and potent homing ability with minimal if any ethical concerns. Even though multiple preclinical and clinical studies have demonstrated remarkable properties for MSCs, the clinical applicability of MSC-based therapies is still questionable. Several challenges exist that critically hinder a successful clinical translation of MSC-based therapies, including but not limited to heterogeneity of their populations, variability in their quality and quantity, donor-related factors, discrepancies in protocols for isolation, in vitro expansion and premodification, and variability in methods of cell delivery, dosing, and cell homing. Alterations of MSC viability, proliferation, properties, and/or function are also affected by various drugs and chemicals. Moreover, significant safety concerns exist due to possible teratogenic/neoplastic potential and transmission of infectious diseases. Through the current review, we aim to highlight the major challenges facing MSCs' human clinical translation and shed light on the undergoing strategies to overcome them.

Emerging role of exosomes in craniofacial and dental applications

Exosomes, a specific subgroup of extracellular vesicles that are secreted by cells, have been recognized as important mediators of intercellular communication. They participate in a diverse range of physiological and pathological processes. Given the capability of exosomes to carry molecular cargos and transfer bioactive components, exosome-based disease diagnosis and therapeutics have been extensively studied over the past few decades. Herein, we highlight the emerging applications of exosomes as biomarkers and therapeutic agents in the craniofacial and dental field. Moreover, we discuss the current challenges and future perspectives of exosomes in clinical applications.

The combined application of rat bone marrow mesenchymal stem cells and bioceramic materials in the regeneration of dental pulp-like tissues

This study aims to observe the effects of the combined application of rat bone marrow mesenchymal stem cells (rBMSCs) and a bioceramic material on pulp-like tissue formation. Rat incisor root fragments without pulp tissues were prepared and filled with a collagen scaffold seeded with rBMSCs, while one side of the root segment was covered by a bioceramic material (iRoot BP). After they were cultured for 12 hours, the root fragments were implanted subcutaneously for 3 months. Hematoxylin and eosin (HE) staining was applied to observe the biocompatibility and the formation of pulp-like tissues. The incisor root fragments were divided into three parts (BP1/3, M1/3, and D1/3) to analyze the areas and the number of new vessels. Immunohistochemical staining of the neuroendocrine marker PGP9.5, the dentin sialophosphoprotein (DSPP), and the vascular endothelial growth factor (VEGF) was applied to observe the formation of the pulp-like tissues. Root fragments filled with only the collagen scaffold were used as a control. Three months after the implantation, the root fragments were collected, and they were surrounded by a transparent tissue membrane with a good blood supply. The root fragment cavity was filled with pink vascularized pulp-like tissue. According to the HE results, iRoot BP had good biocompatibility with the new pulp-like tissues and a few infiltrating inflammatory cells. Increases in the number and area of the new blood vessels were observed in BP1/3 compared with the other two parts. The PGP9.5 and DSPP expressions showed that the newly formed tissues were similar to normal pulp tissues. iRoot BP has good biocompatibility and increases the number and area of new blood vessels. The combined application of stem cells and bioceramic materials may be a better method for pulp revascularization.