Stem/progenitor cell-mediated pulpal tissue regeneration: a systematic review and meta-analysis

Toll-like receptor expression profile of stem/progenitor cells from human exfoliated deciduous teeth

BACKGROUND

Stem/progenitor cells from human exfoliated deciduous teeth (SHED) show remarkable pluripotent, regenerative, and immunological capacities. During in vivo regenerative processes, there could be the presence of SHED in the surrounding inflammatory microenvironment, through toll-like receptors (TLRs).

AIM

The aim of this paper was to present a characteristic TLR expression profile on SHED for the first time.

DESIGN

Cells were harvested from extracted primary teeth (n = 10), anti-STRO-1 immunomagnetically sorted and cultivated, through colony-forming units (CFUs). SHED were examined for mesenchymal stem/progenitor cell traits, including the expression of clusters of differentiation (CDs) 14, 34, 45, 73, 90, 105, and 146, and their multilineage differentiation aptitude. TLRs 1-10 expression was investigated for SHED in uninflamed and inflamed (25 ng/mL IL-1β, 103 U/mL IFN-γ, 50 ng/mL TNF-α, and 3 × 103  U/mL IFN-α; SHED-i) microenvironmental conditions.

RESULTS

SHED were negative for CDs 14, 34, and 45, but were positive for CDs 73, 90, 105, and 146, and demonstrated characteristic multilineage differentiation. In an uninflamed microenvironment, SHED expressed TLRs 1, 2, 3, 4, 6, 8, 9, and 10. The inflammatory microenvironment downregulated TLR7 significantly on gene level and upregulated TLR8 on gene and protein levels (p < .05; Wilcoxon signed-rank test).

CONCLUSION

There appears to be a unique TLR expression profile on SHED, which could modulate their immunological and regenerative abilities in oral tissue engineering approaches.

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.

Dental Pulp Stem Cell Heterogeneity: Finding Superior Quality "Needles" in a Dental Pulpal "Haystack" for Regenerative Medicine-Based Applications

Human dental pulp stem/stromal cells (hDPSCs) derived from the permanent secondary dentition are recognised to possess certain advantageous traits, which support their potential use as a viable source of mesenchymal stem/stromal cells (MSCs) for regenerative medicine-based applications. However, the well-established heterogeneous nature of hDPSC subpopulations, coupled with their limited numbers within dental pulp tissues, has impeded our understanding of hDPSC biology and the translation of sufficient quantities of these cells from laboratory research, through successful therapy development and clinical applications. This article reviews our current understanding of hDPSC biology and the evidence underpinning the molecular basis of their heterogeneity, which may be exploited to distinguish individual subpopulations with specific or superior characteristics for regenerative medicine applications. Pertinent unanswered questions which still remain, regarding the developmental origins, hierarchical organisation, and stem cell niche locations of hDPSC subpopulations and their roles in hDPSC heterogeneity and functions, will further be explored. Ultimately, a greater understanding of how key features, such as specific cell surface, senescence and other relevant genes, and protein and metabolic markers, delineate between hDPSC subpopulations with contrasting stemness, proliferative, multipotency, immunomodulatory, anti-inflammatory, and other relevant properties is required. Such knowledge advancements will undoubtedly lead to the development of novel screening, isolation, and purification strategies, permitting the routine and effective identification, enrichment, and expansion of more desirable hDPSC subpopulations for regenerative medicine-based applications. Furthermore, such innovative measures could lead to improved cell expansion, manufacture, and banking procedures, thereby supporting the translational development of hDPSC-based therapies in the future.

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.

Low-Intensity Pulsed Ultrasound as a Potential Adjuvant Therapy to Promote Spinal Fusion: Systematic Review and Meta-analysis of the Available Data

Despite extensive research, nonunion continues to affect a nontrivial proportion of patients undergoing spinal fusion. Recently, preclinical studies have suggested that low-intensity pulsed ultrasound (LIPUS) may increase rates of spinal fusion. In this study, we summarized the available in vivo literature evaluating the effect of LIPUS on spinal fusion and performed a meta-analysis of the available data to estimate the degree to which LIPUS may mediate higher fusion rates. Across 13 preclinical studies, LIPUS was associated with a 9-fold increase in the odds of successful spinal fusion. Future studies are necessary to establish the benefit of LIPUS on spinal fusion in clinical populations.

Effect of Polymeric Matrix Stiffness on Osteogenic Differentiation of Mesenchymal Stem/Progenitor Cells: Concise Review

Mesenchymal stem/progenitor cells (MSCs) have a multi-differentiation potential into specialized cell types, with remarkable regenerative and therapeutic results. Several factors could trigger the differentiation of MSCs into specific lineages, among them the biophysical and chemical characteristics of the extracellular matrix (ECM), including its stiffness, composition, topography, and mechanical properties. MSCs can sense and assess the stiffness of extracellular substrates through the process of mechanotransduction. Through this process, the extracellular matrix can govern and direct MSCs' lineage commitment through complex intracellular pathways. Hence, various biomimetic natural and synthetic polymeric matrices of tunable stiffness were developed and further investigated to mimic the MSCs' native tissues. Customizing scaffold materials to mimic cells' natural environment is of utmost importance during the process of tissue engineering. This review aims to highlight the regulatory role of matrix stiffness in directing the osteogenic differentiation of MSCs, addressing how MSCs sense and respond to their ECM, in addition to listing different polymeric biomaterials and methods used to alter their stiffness to dictate MSCs' differentiation towards the osteogenic lineage.

Multipotent stem cells from apical pulp of human deciduous teeth with immature apex

Isolation of high-quality human postnatal stem cells from accessible sources is an important goal for dental tissue engineering. Stem cells from developing organs are a better cell source but are hard to obtain. With extensive caries that are difficult to restore, the extracted deciduous tooth with an immature apex is a developing organ for investigation. In the present study, a cell population from the tip of apical pulp of human deciduous teeth with an immature apex was isolated and termed apical pulp-derived cells of deciduous teeth (De-APDCs). De-APDCs expressed STRO-1, CD44, CD90 and CD105 but not CD34 or CD45. Furthermore, De-APDCs demonstrated a significantly higher clonogenic and proliferative ability and osteo/dentinogenic differentiation capacity than dental pulp cells from exfoliated deciduous teeth (De-DPCs) (P < 0.05). Differentiation potential toward adipogenic, neurogenic and chondrogenic lineages was also observed in induced De-APDCs. In addition, after De-APDCs were seeded into hydroxyapatite/tricalcium phosphate (HA/TCP) scaffolds and transplanted into nude mice, they were able to regenerate dentin/pulp-like structures aligned with human odontoblast-like cells. In conclusion, De-APDCs, which are derived from a developing tissue, represent an accessible and prospective cell source for tooth regeneration.

A Cell-Based Approach to Dental Pulp Regeneration Using Mesenchymal Stem Cells: A Scoping Review

Despite the recent explosion of investigations on dental pulp regeneration using various tissue engineering strategies, the translation of the findings from such studies into therapeutic applications has not been properly achieved. The purpose of this scoping review was to systematically review the efficacy of mesenchymal stem cell transplantation for dental pulp regeneration. A literature search was conducted using five electronic databases from their inception to January 2021 and supplemented by hand searches. A total of 17 studies, including two clinical trials and 15 animal studies using orthotopic pulp regeneration models, were included for the review. The risk of bias for the individual studies was assessed. This scoping review demonstrated that the regeneration of vascularized pulp-like tissue was achieved using the stem cell transplantation strategy in animal models. Autologous cell transplantation in two clinical studies also successfully regenerated vascularized vital tissue. Dental pulp stem cell subpopulations, such as mobilized dental pulp stem cells, injectable scaffolds such as atelocollagen, and a granulocyte-colony forming factor, were the most commonly used for pulp regeneration. The overall risk of bias was unclear for animal studies and was moderate or judged to raise some concerns for clinical studies. More high-quality clinical studies are needed to further determine the safety and efficacy of the stem cell transplantation strategy for dental pulp regeneration.

Regenerative Endodontic Procedures: An Umbrella Review

The Regenerative Endodontic Procedure (REP) is a biologically based method in which a damaged pulp-dentin complex is replaced by a new vital tissue. This umbrella review aimed to critically assess the available systematic reviews (SRs) on REP. An electronic database search was conducted (PubMed-Medline, CENTRAL, Scielo, Web of Science, and LILACS) until December 2020. Studies were included if they were an SR on REP. The Risk of Bias (RoB) of SRs was analyzed using the Measurement Tool to Assess SRs criteria 2 (AMSTAR2). The primary outcome was the methodological quality in each specific section of REP protocols and outcomes. From 403 entries, 29 SRs were included. Regarding the methodological quality, ten studies were of critically low, three of low, fourteen of moderate, and two were rated as high quality. The quality of evidence produced by the available SRs was not favorable. Future high standard SRs and well-designed clinical trials are warranted to better elucidate the clinical protocols and outcomes of REP.

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.

Dentin-Pulp Tissue Regeneration Approaches in Dentistry: An Overview and Current Trends

Conventional treatment approaches in irreversible pulpitis and apical periodontitis include the disinfection of the pulp space followed by filling with various materials, which is commonly known as the root canal treatment. Disadvantages including the loss of tooth vitality and defense mechanism against carious lesions, susceptibility to fractures, discoloration and microleakage led to the development of regenerative therapies for the dentin pulp-complex. The goal of dentin-pulp tissue regeneration is to reestablish the physiological pulp function such as pulp sensibility, pulp repair capability by mineralization and pulp immunity. Recent dentin-pulp tissue regeneration approaches can be divided into cell homing and cell transplantation. Cell based approaches include a suitable scaffold for the delivery of potent stem cells with or without bioactive molecules into the root canal system while cell homing is based on the recruitment of host endogenous stem cells from the resident tissue including periapical region or dental pulp. This review discusses the recent treatment modalities in dentin-pulp tissue regeneration through tissue engineering and current challenges and trends in this field of research.

Preclinical and Clinical Applications of Biomaterials in the Enhancement of Wound Healing in Oral Surgery: An Overview of the Available Reviews

Oral surgery has undergone dramatic developments in recent years due to the use of biomaterials. The aim of the present review is to provide a general overview of the current biomaterials used in oral surgery and to comprehensively outline their impact on post-operative wound healing. A search in Medline was performed, including hand searching. Combinations of searching terms and several criteria were applied for study identification, selection, and inclusion. The literature was searched for reviews published up to July 2020. Reviews evaluating the clinical and histological effects of biomaterials on post-operative wound healing in oral surgical procedures were included. Review selection was performed by two independent reviewers. Disagreements were resolved by a third reviewer, and 41 reviews were included in the final selection. The selected papers covered a wide range of biomaterials such as stem cells, bone grafts, and growth factors. Bioengineering and biomaterials development represent one of the most promising perspectives for the future of oral surgery. In particular, stem cells and growth factors are polarizing the focus of this ever-evolving field, continuously improving standard surgical techniques, and granting access to new approaches.

RGD- and VEGF-Mimetic Peptide Epitope-Functionalized Self-Assembling Peptide Hydrogels Promote Dentin-Pulp Complex Regeneration

INTRODUCTION

Cell-based tissue engineering is a promising method for dentin-pulp complex (DPC) regeneration. The challenges associated with DPC regeneration include the generation of a suitable microenvironment that facilitates the complete odontogenic differentiation of dental pulp stem cells (DPSCs) and the rapid induction of angiogenesis. Thus, the survival and subsequent differentiation of DPSCs are limited. Extracellular matrix (ECM)-like biomimetic hydrogels composed of self-assembling peptides (SAPs) were developed to provide an appropriate microenvironment for DPSCs. For functional DPC regeneration, the most important considerations are to provide an environment that promotes the adequate attachment of DPSCs and rapid vascularization of the regenerating pulp. Morphogenic signals in the form of growth factors (GFs) have been incorporated into SAPs to promote productive DPSC behaviors. However, the use of GFs has several drawbacks. We envision using a scaffold with SAPs coupled with long-term factors to increase DPSC attachment and vascularization as a method to address this challenge.

METHODS

In this study, we developed synthetic material for an SAP-based scaffold with RGD- and vascular endothelial growth factor (VEGF)-mimetic peptide epitopes with the dual functions of dentin and pulp regeneration. DPSCs and human umbilical vein endothelial cells (HUVECs) were used to evaluate the biological effects of SAP-based scaffolds. Furthermore, the pulpotomized molar rat model was employed to test the reparative and regenerative effects of SAP-based scaffolds.

RESULTS

This scaffold simultaneously presented RGD- and VEGF-mimetic peptide epitopes and provided a 3D microenvironment for DPSCs. DPSCs grown on this composite scaffold exhibited significantly improved survival and angiogenic and odontogenic differentiation in the multifunctionalized group in vitro. Histological and functional evaluations of a partially pulpotomized rat model revealed that the multifunctionalized scaffold was superior to other options with respect to stimulating pulp recovery and dentin regeneration in vivo.

CONCLUSION

Based on our data obtained with the functionalized SAP scaffold, a 3D microenvironment that supports stem cell adhesion and angiogenesis was generated that has great potential for dental pulp tissue engineering and regeneration.

Allogeneic Cellular Therapy in a Mature Tooth with Apical Periodontitis and Accidental Root Perforation: A Case Report

INTRODUCTION

Cell therapy in regenerative endodontics introduces an alternative option to classic treatment strategies for complex endodontic cases. The aim of this case report was to describe cell-based therapy using allogeneic umbilical cord mesenchymal stem cells (UC-MSCs) encapsulated in a bioscaffold for a complex case of a mature permanent tooth with apical periodontitis and accidental root perforation.

METHODS

A healthy 19-year-old man undergoing orthodontic treatment was referred for endodontic treatment in tooth #7; he was diagnosed with apical periodontitis during a previously initiated treatment associated with accidental perforation of the radicular cervical third. The root perforation was sealed with glass ionomer and composite resin, and the root canal was instrumented, disinfected, and dressed with calcium hydroxide. After 3 weeks, allogeneic UC-MSCs were encapsulated in platelet-poor plasma and then implanted into the root canal, and Biodentine (Septodont, Saint-Maur-des-Fosses, France) was placed below the cementoenamel junction. Finally, the tooth was restored with composite resin.

RESULTS

Follow-up examinations were performed 6 months and 1 year later. The examinations included periapical radiography, cone-beam computed tomographic imaging, and sensitivity and vitality tests. Radiographic and cone-beam computed tomographic images indicated remission of the apical lesion. Clinical evaluations revealed normal responses to percussion and palpation tests; the tooth was responsive to the electric pulp test, and the vitality test indicated low blood perfusion units.

CONCLUSIONS

This case report reveals the potential use of allogeneic cellular therapy using encapsulated UC-MSCS in a platelet-poor plasma scaffold for a complex case of a permanent tooth with apical periodontitis and root perforation.

Cell-Based Regenerative Endodontics for Treatment of Periapical Lesions: A Randomized, Controlled Phase I/II Clinical Trial

A randomized controlled phase I/II clinical trial was designed to evaluate the safety and efficacy of encapsulated human umbilical cord mesenchymal stem cells in a plasma-derived biomaterial for regenerative endodontic procedures (REPs) in mature permanent teeth with apical lesions. The trial included 36 patients with mature incisors, canines, or mandibular premolars showing pulp necrosis and apical periodontitis. Patients were randomly and equally allocated between experimental (REP) or conventional root canal treatment (ENDO) groups. On the first visit, cavity access and mechanical preparation of the root canal were performed. Calcium hydroxide medication was used, and the cavity was sealed. Three weeks later, patients were treated following their assigned protocol of ENDO or REP. Clinical follow-up examinations were performed at 6 and 12 mo. Categorical variables were evaluated by Fisher's exact test. Quantitative variables were compared using the Mann-Whitney test. The evolution over time of the percentage of perfusion units and the dimensions of lesion and cortical compromise were explored. After the 12-mo follow-up, no adverse events were reported, and the patients showed 100% clinical efficacy in both groups. Interestingly, in the REP group, the perfusion unit percentage measured by laser Doppler flowmetry revealed an increase from 60.6% to 78.1% between baseline and 12-mo follow-up. Sensitivity tests revealed an increase of the positive pulp response in the REP group at 12-mo follow-up (from 6% to 56% on the cold test, from 0% to 28% on the hot test, and from 17% to 50% on the electrical test). We present the first clinical safety and efficacy evidence of the endodontic use of allogenic umbilical cord mesenchymal stem cells encapsulated in a plasma-derived biomaterial. The innovative approach, based on biological principles that promote dentin-pulp regeneration, presents a promising alternative for the treatment of periapical pathology (ClinicalTrials.gov NCT03102879).

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

Stem/progenitor cells are undifferentiated cells characterized by their exclusive ability for self-renewal and multilineage differentiation potential. In recent years, researchers and investigations explored the prospect of employing stem/progenitor cell therapy in regenerative medicine, especially stem/progenitor cells originating from the oral tissues. In this context, the regeneration of the lost dental tissues including enamel, dentin, and the dental pulp are pivotal targets for stem/progenitor cell therapy. The present review elaborates on the different sources of stem/progenitor cells and their potential clinical applications to regenerate enamel, dentin, and the dental pulpal tissues.