Dental stem cells in tooth repair: A systematic review

Introduction

Regenerative dentistry is designed to recover dental anatomy and function. Regenerative endodontics procedures (REPs) of a damaged tooth are a series of biological processes aimed to restore the dental pulp's physiological functions, cure periapical lesions, and substitute pulp-dentin complex cells and dentin^1,2. Three components are involved in these techniques: stem cells, growth and bio-materials, which are often known as scaffolds or templates³

The dental pulp consists of nerves, blood vessels and connective tissue to maintain teeth's integrity. The nerves of the pulp can mediate pain, blood flow control, recruit immunocompetent cells, and act as a mesenchymal stem cells (MSCs) niche⁴. Loss of tooth pulp stops the development of permanent root teeth that can weaken the periodontal connection and lead to teeth loss. Recent animal studies indicate that vascular dental pulp can be regenerated by cell-based therapy⁵.

Dental stem cells (DSCs) are self-renewable teeth cells, which help maintain or develop oral tissues⁶. In the literature, there are various types of dental adult stem cells, such as dental pulp stem cells (DPSCs), stem cells from human exfoliated deciduous teeth (SHEDs), periodontal ligament stem cells or stem cells of the developing root apical papilla (SCAPs), dental follicle stem cells (DFSCs), and dental MSCs (DMSCs)^7,8. Such cells can differentiate into dentine/pulp, odontoblast, adipocyte, cementblast-like, osteoblast, and chondroblast cells. DSC regenerative potential is explained through both natural and experimental conditions^9,10. Differentiated dentinoblasts, also called secondary odontoblasts, produce new dentine in response to dental cell injury. This regenerative process is called reparative tertiary dentinogenesis¹¹. This process of dentinogenesis was suggested to be used in the recruitment of endogenous DSCs. Most recent animal studies have investigated the role of DSCs in the regeneration of dental pulp tissues.

Bakhtiar et al.¹² conducted a systematic review on 47 studies that investigate the role of stem cell therapy in regeneration of dentine‑pulp complex; the current systematic review aimed to update this previous systematic review, presenting 57 articles, and summarizes the current evidence regarding the efficacy of dental stem cells in dental pulp regeneration in animal models.

Methods

We report this manuscript following the preferred reporting items systematic reviews and meta-analysis (PRISMA statement) guideline¹³. All methods used in this review were conducted in strict accordance with the Cochrane Handbook for Systematic Reviews of Interventions¹⁴.

Results

Search strategy results

The electronic search retrieved 4433 unique articles. After removing duplications, 2780 articles were enrolled in the title/abstract screening. This led to the retrieval and screening of 327 full-text articles for eligibility. Studies that were not eligible with our criteria were excluded. In total 57 articles were included in the qualitative synthesis. A flow diagram of the selection process is shown in Figure 1. A summary of characteristics, models, and populations of the included studies and their key outcomes are shown in Table 1. Variation of the extracted data is reported in Table 2.

Figure 1. PRISMA flow diagram of article selection in this systematic review.

Table 1. Summary of included studies.

This table was adapted from a previous systematic review with written permission from the authors and under a Creative Commons Attribution 4.0 International License¹².

Cell type	Animal model	Dose & dosage	Route of administration	Co-administrative factors	TERM approach	Time point	Main results	Reference
DPSC	Rat	Not declared	Allogenic transplantation Into renal capsule	NA	AGS	2 weeks	Inflamed DPSC has more tendency to osteogenesis rather than dentinogenesis	Wang et al. (2013)15
	Mice	5 × 106 cells/ml	Transplantation into subrenal capsule	NA	PLLA/(HA,TCP & CDHA)	5 weeks	PLLA/TCP superiority for tooth tissue regeneration	Zheng et al. (2011)16
	Mice	1 × 106 cells	Xenograft subcutaneous tooth slice	NA	collagen TE	4 weeks	Similar regeneration of MDPSCs from young and aged donors	Horibe et al. (2014)27
	Mice	256,000/190 μL	Xenograft subcutaneous tooth slice	Nephronblastoma overexpressed	3D micro tissue Spheroids	4 weeks	Vascular and pulp like tissue regeneration	Dissanayaka et al. (2014)38
	Mice	1 × 106 cells	Xenograft subcutaneous Transplantation	NA	Porous PLGA	4 weeks	Promotion of dentinogenesis and odontoblastic differentiation	Wang et al. (2014)40
	Mice	5 × 103 cells/well	Xenograft subcutaneous Transplantation	Plasmid vectors encoding BMP-7	NA	8 weeks	Maintained MSC characteristics after implantation (DPSC > PDLSC)	Lei et al. (2014)41
	Mice	1.0 × 106 cells/mL	Xenograft subcutaneous Implantation	NA	Chitosan/collagen	4 weeks	Odontoblast-like phenotype Differentiation	Yang et al. (2012)42
	Mice	2.0 × 106 cells	Xenograft subcutaneous Implantation	NA	Fibrin gel CBB	8 weeks	Capability of mineralization (SHEDs > DPSCs) and CT formation (SHEDs < DPSCs)	Wang et al. (2012)43
	Mice	3 × 106 cells/mL	Xenogenic subcutaneous Transplantation	NA	HA/TCP Cell sheets/ powdery	12 weeks	PL enhances the and layer of odontoblast-like cell formation	Chen et al. (2012)44
	Mice	5 × 106 cells	Xenogenic subcutaneous transplantation	NA	CBB particles	6 weeks	Regular dentin–pulp complex and columnar odontoblast-like cells generation	Wang et al. (2011)45
	Mice	106 cells	Xenograft subcutaneous Transplantation	NA	NF-PLLA	8 weeks	Enhanced odontogenic differentiation of human DPSCs and mineralization in NF-PLLA	Wang et al.(2011)17
	Mice	1 × 107 cells	Xenograft subcutaneous Transplantation	pre ameloblast-CM	HA/TCP ceramic powder	6–12 weeks	Dentin deposition with palisaded odontoblast-like cells formation	Oh et al. (2015)18
	Mice	1 × 106 cells/100μL	Xenograft subcutaneous in dentin cylinder transplantation	VEGF, TGFb1, FGF2	Laden peptide Hydrogel	6 weeks	Generation of odontoblasts-like phenotypes, vascularization	Galler et al. (2011)19
	Mice	4 × 106 cells	Xenograft subcutaneous Transplantation	NA	HA and TCP Powder	8 weeks	DPSCs from inflamed pulp formed pulp/dentin complexes in lesser extent than DPSCs–NPs	Alongi et al. (2010)20
	Mice	1 × 106 cells	Xenograft subcutaneous Transplantation	BMP-7 + dexamethasone	NF-PLLA	8 weeks	More organized odontoblast like cells formation	Wang et al. (2010)21
	Pig	2 × 106 Cells	Allogeneic direct implantation into socket	Vitamin C	PDLSC sheet + HA/TCP/ DPSC	24 weeks	Generation of bio-root with normal pulp and dentin-like matrix and natural biomechanical structure in low rate.	Gao et al. (2016)22
	Pig	3 × 106 cells	Autologous root fragment transplantation into jawbone	NA	Collagen PLGA	6–10 weeks	Formation of continuous polarized & non-polarized cell along the canal wall	Kodonas et al. (2012)23
DPSC	Rabbit	5 × 106 cells/ml	Autologous transplantation into the extracted socket	BMP-2	Collagen gel	12 weeks	Similar tooth structure by different stem cells close to a normal living tooth	Hung et al. (2011)24
	Rat	8 × 106 cells	Xenograft intracanal Transplantation	Hypoxic treatment	PLLA Nanofibrous spongy microsphere	4 weeks	Enhanced vascularization	Kuang et al. (2016)25
	Dog	1 × 104 cell/cm2	Autologous interacanal Transplantation	G-CSF	Atelocollagen	13–26 weeks	Normal pulp-like tissue and apical secondary dentin formation	Iohara et al. (2018)26
	Dog	2 × 104 cells/100 mL	Autologous interacanal Transplantation	G-CSF	Drug approved collagen	2, 4, 9, 26 weeks	Regeneration of vascularized pulp tissue, dentin deposition along dentin wall and dense nerve plexus	Nakashima and Iohara (2014)28
	Dog	1 × 106 cells/ml	Autologous interacanal Transplantation	G-CSF	Atelocollagen	2–17 weeks	Pulp-like tissue regeneration 60% apically, dentin & nerve formation	Iohara et al. (2014)29
	Dog	1 × 106 cell per ml	Autologous intracanal Transplantation	G-CSF	Clinical-graded atelocollagen	2, 4, 9, 26 weeks	Over 90% pulp-like tissue regeneration, dentin & dense nerve plexus Formation	Iohara et al. (2013)30
	Beagles	2.0 × 107 cells	Autologous transplantation into the pulp canal	NA	Gel foam	24 Week	Generation of pulp-like tissues	Wang et al. (2013)15
	Mice	5 ×105 cells	Allogenic subcutaneous implantation	Costal chondrocytes/ FGF9 protein	Collagen/PGA	4–8 weeks	Enhance chondrogenesis and partially inhibit ossification in engineered cartilage	Dai et al. (2012)31
	Mice	2×105 cells	Subcutaneous implantation in mouse of human cells	ND/NA	TCP	8 weeks	DPSC regulates dentin development and regeneration	Zhou et al. (2015)32
	Mice	1×106 cells/mL	Subcutaneous implantation in mouse of treated human tooth root	PuraMatrix/MTA	3D microtissue Spheroids	4 weeks	DPSC exhibited vascularized pulp-like tissue with patches of osteo-dentin after transplantation	Dissanayaka et al (2015)33
	Mice	NA	Subcutaneous implantation in mouse of human tooth root and REP	Growth factor	Alginate	6 weeks	Enhance chondrogenesis	Schmalz et al. (2016)37
	Mice	1 × 106 cells in each	Xenograft subcutaneous Implantation	TDM	Collagen TE	4 weeks	Angiogenesis, neurogenesis and pulp regeneration induction	Ishizaka et al. (2013)34
	Dog	1 × 106 cells in each	Autologous intracanal Transplantation	SDF-1	Collagen TE	2, 4, 13 week	Full length pulp-like tissue formation, odontoblastic lining & tubular dentin along dental wall	Iohara et al. (2011)35
	Rat	NA	Femur and autologous implantation of rat tooth chambers	FGF2/VEGF/PDGF	Collagen/gelatin	4,8 weeks	Successful revascularization and tissue regeneration with direct vascular supply	Srisuwan et al. (2013)36
	Mice	1 × 105 cells	Subcutaneous implantation in mouse of human tooth root	GCSF	Collagen	6 weeks	MDPSCs accelerated vasculo- genesis in an ischemic hindlimb model and augmented regenerated pulp tissue	Murakami et al (2013)39
SCAP	Rat	1 × 106 cells	Xenograft Transplantation Into renal capsules	NA	SCAP pellets /root segment	8 weeks	MTA regulates dentinogenesis of SCAPs	Yan et al. (2014)49
	Rat	1 × 106 cells	Xenograft root fragment transplantation into renal capsule	Different concentration of KH2PO4 (M2 > M1)	Root segments containing SCAP pellets/AGS	2 weeks	More mineralized tissues generation &, higher osteo /odontoblast differentiation in supplemented khpo4 medium	Wang et al. (2013)15
	Mice	2 × 104 cells/well	Subcutaneous	VEGF	Poly dioxanone Fiber	3 weeks	Blood vessel formation Negligible inflammation	Yadlapati et al. (2017)50
	Mice	1 × 107 cell/100 mg Powder	Xenograft Subcutaneous Transplantation	rhPAI-1	HA/TCP ceramic powder fibrin gel	12 weeks	Dentin formation odontoblast presses inserted to dental tubules	Jin and Choung (2016)51
SCAP	Mice	3 × 106 cells	Xenograft Subcutaneous injection	BMP-2	PLLA, NF-MS + PLGA, MS	4, 8 weeks	Mineralized tissue with embedded cells resembling osteodentin excellent microenvironment for SCAP to regenerate dentin tissue	Wang et al. (2016)47
	Mice	2x104 cells/ well	Subcutaneous implantation	Nuclear Factor I-C (NFIC)	WNT3A/BMP9	5 weeks	SCAPs may promote osteo/ odontoblastic differentiation	Zhang et al (2015)48
	Mice	107 cells/mL	Xenograft Subcutaneous root fragment transplantation	NA	PLG	21–28 weeks	Fulfilling vascularization, continuous dentin-like tissue deposition	Huang et al. (2010)46
	Mice	NR	Xenograft Subcutaneous transplantation	NA	HA/TCP hydrogel	8, 12 weeks	Function of vascularized pulp- like tissue	Hilkens et al. (2017)52
SHED	Mice	4 × 106 cells	Xenograft subcutaneous transplantation	NA	HA/TCP	8 weeks	Mineralization & DPC generation equally in SHED Fresh and SHED-Cryo	Ma et al. (2012)58
	Mice	2.0 × 106 cells	Xenograft subcutaneous Transplantation	NA	Fibrin gel CBB	8 weeks	Capability of mineralization SHEDs > DPSCs CT formation SHEDs < DPSCs	Wang et al. (2012)43
	Mice	3 × 106 cells	Xenograft subcutaneous transplantation	NA	macroporous biphasic calcium phosphate	9 weeks	Hard tissue formation (o-SHED > e-SHED) quality of hard tissue (o-SHED = e-SHED)	Jeon et al. (2014)59
	Mice	5 × 104 cells	Subcutaneous implantation in mouse of treated human tooth slice	ND/NA	PLLA	NA	SHED express markers of odontoblastic differentiation (DSPP, DMP-1, MEPE)	Casagrande et al. (2010)60
BMSC	Mice	1 × 106 cells	Allograft Transplantation Into renal capsules	NA	Lyophilized hydrogel	2 week	Local mineralization production of dentin-like tissue	Hashmi et al. (2017)61
	Rat	5 × 106 cells	Allogenic Dentin slice Transplantation into renal capsule	Dentin slice	Dentin slices	6 weeks	Polarized cells penetrating into dentin wall	Lei et al. (2013)62
	Mice	1 × 107 cells/ml	Xenograft subcutaneous cell-transplantation	SDF-1	Collagen	3 weeks	Participation of systemic BMSC in intracanal dental-pulp-like tissue regeneration	Zhang et al. (2015)63
	Dog	5 × 105 cells	Autologous interacanal Transplantation	G-CSF	Atelocollagen	2 weeks	Potential pulp regeneration in MADSC & MBMSC but in less volume	Murakami et al. (2015)64
DFSC	Pig	1 × 106 cells	Direct implantation into socket	APES/TDM/DPEM	APES/TDM/DPEM	12 weeks	Generation of uniform pulp-like tissue, predentin matrix formation	Chen et al. (2015)53
	Mice	1 × 107 cells/mL	Allograft subcutaneous Transplantation	TDM	TDM	6 weeks	Similar dentin-like tissue Formation	Chen et al (2015)54
	Mice	5 × 104 Cells/ scaffold	Xenograft subcutaneous Transplantation	TDM	TDM	8 Weeks	The structure of dentin tissues generated by DFCs was more complete	Tian et al. (2015)55
DFSC	Mice	1 × 104 cells	Xenograft subcutaneous Transplantation	dentin matrix	Human TDM and CDM	8 Weeks	More mechanical properties dentinogenic protein release by CDM	Jiao et al. (2014)56
	Mice	5 × 104 cells in each	Xenograft subcutaneous Implantation	TDM	TDM	8 Weeks	Formation of pulpdentin/ cementum/periodontium-like tissues	Guo et al. (2013)57
	Mice	1 × 106 cells/mL	Xenograft subcutaneous Implantation	TDM	TDM	8 Weeks	New dentin-pulp like tissues and cementum-periodontal complexes	Yang et al. (2012)42
PDLSC	Mice	3 × 104 cells/dish	Xenograft subcutaneous Transplantat	NA	NA	8 Weeks	Maintained MSC characteristics after implantation (DPSC > PDLSC)	Lei et al. (2014)41
	Mice	5 × 104 Cells/ scaffold	Xenograft subcutaneous Transplantat	TDM	TDM	8 Weeks	The structure of dentin tissues generated by DFCs was more complete	Tian et al. (2015)55
	Pig	2 × 105 Cells	Allogeneic direct implantation into socket	Vitamin C	PDLSC sheet + HA/TCP/ DPSC	24 weeks	Generation of bio-root with normal pulp and dentin-like matrix and natural biomechanical structure in low rate.	Gao et al. (2016)22
ADSC	Rabbit	5 × 106 cells/ml	Autologous transplantation into the extracted socket	BMP-2	Collagen gel	12 weeks	Similar tooth structure by different stem cells close to a Normal living tooth	Hung et al. (2011)24
RPSC	Rat	106 cells each	Allogeneic transplantation into the renalcapsules	NA	AGS	2 weeks	Typical dentinogenesis by iRPSC, bone-like tissues by mRPSC	Lei et al. (2011)66
Mesenchymal	Mice	2 × 105 cells	Rat to mice Transplantation intorenal capsule	hBMP4 hBMP7	PLGA	8 weeks	Enamel and dentin-like tissues generation in two integrated layers with amelogenin expression and amelo blastin	Jiang et al. (2014)67
UCMSC	Mice	5 × 104 cells/well	Xenograft subcutaneous Transplantat	hTDM	TDM	8 Weeks	Formation of layers of cells and calcifications	Chen et al. (2015)68
Human DP Progenitors	Mice	106 cells/50 μl	Xenograft subcutaneous Implantation	Stem cell factor (SCF)	Collagen sponge	4 weeks	Induction of cell homing, angiogenesis, and tissue remodeling	Pan et al. (2013)69
Dermal multi potent cells	Mice	2.0 × 106 cells	Xenograft subcutaneous transplantation	Embryonic and neonatal TGC-CM	Fibrin gel	4 weeks	Bone like structure formation from embryonic TGC-CM	Huo et al. (2010)70
DBCs	Porcine	1 × 107 cells	Autotransplantation into swine’s original alveolar socket	GCHT	Gelatin- chrondroitinhyaluronan- tricopolymer	36 weeks	Successful rate of tooth regeneration from DBCs/GCHT scaffolds’ was about 33.3%	Kuo et al. (2007)71
NA	Beagles	NA	Cell homing	SDF-1α	Silk/Fibroin	12 weeks	Pulp tissue generation andmineralization along dentinal wall	Yang et al. (2015)72

BC, blood clot; bFGF, basic fibroblast growth factor; BMP, bone morphogenetic protein; BMSC, bone marrow mesenchyme stem cell; CC, costal chondrocyte; CDHA, calcium carbonate hydroxyapatite; CNCC, cranial neural crest cell; CXCL14, chemokine (CXC motif) ligand-14; DFSC, dental follicle stem cell; DPSC, dental pulp stem cell; FGF, fibroblast growth factor; GCSF, granulocyte colony-stimulating factor; GF, growth factors; HA, hydroxyapatite; iPS, induced pluripotent stem cell; MCP1, monocyte chemoattractant protein-1; MSC, mesenchymal stem cell; MTA, mineral trioxide aggregate; NA, not exogenously added; ND, not determined; NGF, nerve growth factor; PCL, polycaprolactone; PGA, polyglycolic acid; PGDF, platelet-derived growth factor; PLGA, polylactic-co-glycolic acid; PLLA, poly-L-lactic acid; PRF, platelet-rich fibrin; PRP, platelet-rich plasma; REP, regenerative endodontic procedure; SCAP, stem cell of the apical papilla; SHED, stem cell from human exfoliated deciduous teeth; TCP, tricalcium phosphate; TDM, treated dentin matrix; TGF, transforming growth factor; VEGF, vascular endothelial growth factor; DBCs, dental bud cells

Table 2. Variations of extracted data from reviewed articles.

Variables		Number of studies (%)*
Cell type	DPSCs	31 (46)
	SCAP	8 (12)
	DFSC	6 (9)
	BMSC	4 (6)
	SHED	4 (6)
	PDLSC	3 (4.4)
	ADSC	1 (1.5)
	Other	7 (10.4)
Scaffold	Collagen	15 (22.3)
	TDM	9 (13.4)
	HA/TCP	10 (15)
	PLLA	6 (9)
	PLGA	4 (6)
	Atelocollagen	4 (6)
	Fibrin gel	8 (12)
	CBB	3 (4.4)
	Silk fibroin	1 (1.5)
	Other	3 (4.4)
Growth factors	TDM	9 (13.4)
	BMP	5 (7.4)
	G-CSF	5 (7.4)
	SDF-1	3 (4.4)
	VEGF	3 (4.4)
	b-FGF	3 (4.4)
	Other	35 (52.2)
Transplantation site	Subcutaneous	40 (59.7)
	Inter canal	4 (6)
	Renal capsule	8 (12)
	Into socket	3 (4.4)
	Other	8 (12)
Animals	Mice	44 (65.6)
	Rat	7 (10.4)
	Pig	4 (6)
	Dog	7 (10.4)
	Rabbit	2 (2.9)
	Beagles	2 (2.9)

*The number of included studies is 57 studies; however, the number of trials is 67 trials. Therefore, each study may include one or more types of cells.

BC, blood clot; bFGF, basic fibroblast growth factor; BMP, bone morphogenetic protein; BMSC, bone marrow mesenchyme stem cell; CC, costal chondrocyte; CDHA, calcium carbonate hydroxyapatite; CNCC, cranial neural crest cell; CXCL14, chemokine (CXC motif) ligand-14; DFSC, dental follicle stem cell; DPSC, dental pulp stem cell; FGF, fibroblast growth factor; GCSF, granulocyte colony-stimulating factor; GF, growth factors; HA, hydroxyapatite; iPS, induced pluripotent stem cell; MCP1, monocyte chemoattractant protein-1; MSC, mesenchymal stem cell; MTA, mineral trioxide aggregate; NA, not exogenously added; ND, not determined; NGF, nerve growth factor; PCL, polycaprolactone; PGA, polyglycolic acid; PGDF, platelet-derived growth factor; PLGA, polylactic-co-glycolic acid; PLLA, poly-L-lactic acid; PRF, platelet-rich fibrin; PRP, platelet-rich plasma; REP, regenerative endodontic procedure; SCAP, stem cell of the apical papilla; SHED, stem cell from human exfoliated deciduous teeth; TCP, tricalcium phosphate; TDM, treated dentin matrix; TGF, transforming growth factor; VEGF, vascular endothelial growth factor.

Discussion

This is the largest and most updated systematic review aiming to investigate the role of DSCs in tooth repair. We found that multiple DSCs have a potent role in tissue regeneration and vascularization of dental pulp-like tissues^{54,56,58,61,66,70,72}. Most of the included research assessed the 4–8 week dentine-pulp regeneration following transplant^57,67,69,70. These studies used the ectopic models of dentine pulp-complex. A few studies used long-term evaluation of up to 36 weeks after surgery⁷¹. However, there are some studies that had multiple time points for evaluation.

Like other tissues, three primary components are required to regenerate a necrotic pulp: 1) vital root canal cells, which can distinguish into normal pulp cells, 2) morphogenic and growth factors to activate and encourage cell distinction, and 3) a matrix that ensures an environment that maintains their vitality and growth and supports cells in a mechanical way^58,59,61,62.

Growth factors, drugs, bioactive products, glycosaminoglycans and other small molecules and motifs of peptide are considered promotive healing factors that can be used for stem cells and matrix to improve the effectiveness of stem cell therapy for dentine-pulp regeneration and biodegradation. Growth factors have a short half-life; therefore, degradable materials are required to control their release^47,48,73.

Recent studies for dentine pulp regeneration have been done in various types of stem cells from various sources in body. DPSCs are the preferred cells in the majority of these studies and have demonstrated their capacity to regenerate the complex dentine^{15,22,25,46,65}. Although the great tendency for dentine-pulp complex regeneration, SCAP and SHED were rarely administered^44,45. DPSCs and SHEDs were evaluated with adequate or partly successful histological outcomes in various REP research. DPSC, collagen or polylactic/glycol and scarce factors with or without growth factors are optimized when compared to REPs with growth factors but without amplified stem cells^19,20. Several dentin therapies demonstrate further excellent outcomes, which should be followed by platelet-rich plasma/platelet-rich fibrin (PRP/PRF) or collagen gels in REPs and improved biomimicry to maintain various levels of the variables that release oral stem cell niche formation. Recently, cell survival of stem cells is much easier than in the past due to the appropriate interaction with dentine-released factors^21,23. Thus, screening for more appropriate stem cells, dentine releasing treatments, scaffolds with good biomimicry and good histological markers is an exciting activity for future REP improvements.

Besides dental sources, non-dental cells, such as the MSCs derived from bone marrow and adipose stem cells, are able to regenerate the pulp tissue.

Generally, our study showed that adult stem cells appear to be able to regenerate dentine-pulp complexes; therefore, the criteria of selection should be considered the most cost-effective and cheapest, particularly when the main obstacle is the expense^28,32,35. Moreover, our findings demonstrated that the human body is a wealthy source of stem cells; therefore, the third molars or any orthodontic tooth originated from a human body are excellent sources of stem cells. As regards cells circulating, these cells migrate to sites and engage in a recovery process in the presence of chemotactic gradients, as their capacity for root canal migration was shown³³.

This study showed two limitations; 1) we could not conduct a meta-analysis due to insufficient data; and 2) we failed to find a suitable tool to assess the quality of included studies and risk of bias.

In conclusion, the current evidence suggests that the DPSCs, SHEDs, and SCAPs are capable of providing a sufficient pulp regeneration and vascularization. Nevertheless, the efficacy of stem cell transplantation in therapy locations and their cost may be obstacles to their clinical use. Scaffolds and biomaterials provide a useful strategy for stronger incorporation of stem cells and development factors together with monitored regeneration rates. Hence, we suggest future studies to concentrate on offering definite guidance on appropriate and preferable biomaterial characteristics for use in regenerative endodontics.

Data availability