Exploring the potential of stem cells from the apical papilla (SCAPs) in regenerative medicine: advantages, applications, challenges and opportunities

Abstract

Stem cells from the apical papilla (SCAPs) represent a unique population of mesenchymal stem cells (MSCs) located in the apical papilla of immature permanent teeth. These cells exhibit essential MSC characteristics, including specific marker expression, self-renewal, proliferation, migration, multipotent differentiation, and immunosuppressive properties. Additionally, SCAPs secrete bioactive factors that promote tissue regeneration, making them promising candidates for stem cell-based therapies. Their regenerative potential encompasses diverse applications in dentistry, bone repair, neural regeneration, and vascular engineering, thereby positioning SCAPs as a versatile tool in regenerative medicine. However, challenges such as phenotypic instability during long-term culture and inconsistent regenerative outcomes impede their clinical translation. Addressing these challenges is crucial for advancing the clinical application of SCAPs. This review examines the advantages and therapeutic applications of SCAPs, identifies barriers to their clinical implementation, and highlights opportunities for optimizing their efficacy. By synthesizing current knowledge and proposing future research directions, this work aims to facilitate the development of SCAP-based strategies for tissue repair, bridging the gap between laboratory research and clinical practice.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-025-04705-8.

Introduction

Regenerative medicine aims to restore tissue function through biotechnology, integrating stem cell research and materials engineering [1]. This field employs two approaches to achieve regenerative therapeutic effects [2]: endogenous regeneration, enhancing the body’s innate repair mechanisms; and exogenous regeneration, implanting bioengineered organs for seamless integration (Fig. 1).

Fig. 1.

Two methods of tissue regeneration, as exemplified by pulp regeneration. Reproduced with permission [2]. Copyright © 2021 Liang et al. A Dental pulp regeneration with endogenous stem cells. B Dental pulp regeneration with exogenous stem cells

Mesenchymal stem cells (MSCs), with their multi-lineage differentiation capacity, are key drivers of these strategies [3]. Stem cells from apical papilla (SCAPs), a neural crest-derived MSC population first isolated from immature permanent teeth [4], exhibit exceptional self-renewal, proliferative potential, and immunomodulatory properties [5]. Residing in tooth root apices, they continuously differentiate into odontoblasts to promote root development [6].

Critically, SCAPs’ developmental origin suggests greater plasticity than other dental stem cells. However, their potential application in regenerative medicine, along with associated challenges and strategies, remains underexplored. While numerous reviews focus on SCAPs in regenerative dentistry, there is limited information on their benefits and applications in broader regenerative medicine. Additionally, reviews addressing the drawbacks and strategies for SCAPs application in regenerative medicine are scarce, and specific challenges in clinical translation are not adequately addressed. Therefore, this review aims to explore the potential of SCAPs in regenerative medicine by summarizing therapeutic applications, discussing challenges and strategies, and identifying opportunities for future research.

The role of SCAPs in regenerative medicine

Isolation and characterization of SCAPs

As Fig. 2 shows, SCAPs are readily obtainable from the root apex of extracted young permanent teeth, which are typically considered clinical “waste tissue”. SCAPs are characterized by specific surface and intracellular molecule expression (Table 1). Table 2 compares the phenotypic markers of SCAPs with other dental stem cells, such as dental pulp stem cells (DPSCs), stem cells from human exfoliated deciduous teeth (SHEDs), dental follicle progenitor cells (DFPCs), and periodontal ligament stem cells (PDLSCs), highlighting distinctions among them.

Fig. 2.

Isolation and characterization of SCAPs. A SCAPs were extracted and isolated from apical papilla form young permanent tooth with an open apex. Reproduced with permission [14]. Copyright © 2011 Bakopoulou et al. B Typical surface marker expression of SCAPs. SCAPs express mesenchymal stem cell markers CD44, CD90, and CD105 but do not express the hematopoietic marker CD45. Reproduced with permission [15]. Copyright © 2021 Damrongsri et al. C Microscopic observation of SCAPs. Reproduced with permission [15]. Copyright © 2021 Damrongsri et al. D Apical papilla cells express characteristic MSC markers. Reproduced with permission [16]. Copyright © 2013 Ruparal et al

Table 1.

Marker expression in SCAPs [5]

Positive markers	CD13, CD24, CD29, CD44, CD49, CD51, CD56, CD61, CD73, CD90, CD105, CD106, CD146, CD166, STRO-1, Oct3/4, Sox2, Nanog, Notch3, vimentin, survivin
Negative markers	CD14, CD18, CD34, CD45, CD117, CD150

Table 2.

Comparison of in vitro phenotypes of SCAPs to other dental stem cells [7]

Marker		SCAPs	DPSCs	SHEDs	DFPCs	PDLSCs
Embryonic stem cell markers	Oct-4	+	+	+	-	+
	Nanog	-	+	+	-	-
Mesenchymal markers	CD73	+	+	+	+	+
	CD90	+	+	+	+	+
	CD105	+	+	+	+	+
	CD106	+	-	-	-	-
	CD166	+	+	+	+	+
Stem cell markers	SSEA-4	+	+	+	+	-
	CD9	+	+	-	+	+
	CD13	+	+	-	+	+
	CD146	+	+	+	+	+
	Nestin	+	+	+	+	+
	Notch1	-	-	-	+	-
	STRO-1	+	+	+	+	+
	CD44	+	+	+	+	+
	CD24	+	-	-	+	-
	CD29	+	+	-	+	+
Hematopoietic markers	CD34	-	-	-	-	-
	CD45	-	-	-	-	-
	CD80	+	-	-	-	-
	CD86	+	-	-	-	-

(+: positive express marker; -: negative express marker)

SCAPs exhibit a characteristic surface marker profile that distinguishes them from hematopoietic lineages: these cells lack CD14, CD18, CD34, CD45, CD117, and CD150 expression [8]. Critically, CD24 serves as a defining marker for SCAPs [9]. Although expressed at low levels (3.2–15%) and absent in other MSCs (e.g., DPSCs) [10–12], CD24 is strongly associated with an undifferentiated state and high cellular stemness. Its expression inversely correlates with alkaline phosphatase (ALP) activity, declining as ALP rises during osteoblastic differentiation [11, 12]. Notably, Zhang et al. observed complete loss of CD24 by passage 10 [13], suggesting progressive attenuation of stemness with serial passaging.

Multilineage differentiation potential of SCAPs

SCAPs are highly favored in regenerative medicine due to their remarkable capacity to differentiate into multiple lineages [5, 17–23] (Fig. 3). SCAPs can differentiate into osteoblasts and odontoblasts. When cultured in an osteo/odontogenic medium with L-ascorbate-2-phosphate, dexamethasone, and β-glycerophosphate, SCAPs express specific markers like ALP, runt-related transcription factor 2, osteocalcin, dentin sialophosphoprotein, bone sialoprotein, and dentin matrix protein 1 [24]. Additionally, SCAPs show significant potential for chondrogenesis, expressing key chondrogenic markers like collagen type II(Col2), collagen type V, and sex-determining region Y-box 9(Sox9) during cartilage differentiation [25].

Fig. 3.

The multilineage differentiation potential and clinical application of SCAPs and SCAPs-Exos. A SCAPs demonstrate potential for differentiation into osteogenic, odontogenic, adipogenic, chondrogenic, neurogenic, and angiogenic lineage. Reproduced with permission [25–27]. Copyright © 2020 Yang et al.;2011 Bakopoulou et al.; 2016 Yuan et al. B Von Kossa staining assay with and without SCAPs. SCAPs group exhibited larger and darker stained areas, indicating increased new bone formation. Reproduced with permission [17]. Copyright © 2023 Yang et al. C Macroscopic assessment of blood vessel ingrowth after 12 weeks of SCAPs transplantation. Reproduced with permission [28]. Copyright © 2017 Petra Hilkens et al. D Matrigel plug images reveal increased new blood vessel formation in the SCAP-Exos group compared to the control. Reproduced with permission [20]. Copyright © 2021 Liu et al

SCAPs facilitate angiogenesis by secreting growth factors like Angiopoietin-1 and vascular endothelial growth factor(VEGF) [29]. During embryonic development, SCAPs enhance angiogenesis by downregulating KISS1 metastasis suppressor expression, inhibiting the MAPK/ERK(mitogen-activated protein kinase/extracellular signal-regulated kinase) signaling pathway, and promoting the proliferation and migration of vascular smooth muscle cells [30]. These insights reveal SCAP’s multifaceted role in angiogenesis and suggest new avenues for vascular regeneration therapies. Notably, SCAPs can express neural markers without neurogenic stimuli, hinting at a potential neural crest origin [8]. Upon stimulation, SCAPs express a wider range of neural markers, such as βIII-tubulin, GFAP, GAD, and nestin [31]. These findings indicate that SCAPs could be particularly suitable for treating neurodegenerative diseases.

SCAPs possess adipogenic differentiation ability, though to a lesser extent than other MSC populations [29]. Several approaches, such as overexpressing secreted frizzled-related protein 2 [32], upregulating CD24 [33], and genetically ablating the histone demethylase KDM2A [11], have been reported to enhance the adipogenic differentiation potential of SCAPs.

Secretome and exosomes of SCAPs

To compensate for deficiencies in essential growth factors, cells can autonomously synthesize and secrete these molecules through their secretome, thereby maintaining regulatory control over cellular functions. The SCAP secretome has been comprehensively characterized [34], compassing angiogenic, immunomodulatory, and antiapoptotic factors, along with chemokines, neurotrophic factors, extracellular matrix components, and other proteins. This secretome is crucial in regenerative medicine, offering therapeutic potential for conditions such as traumatic brain injuries, chronic wounds, and bone defects [34–36]. Compared to bone marrow-derived MSCs, SCAPs exhibit significantly higher secretion of chemokines, neurotrophins, and proteins [34].

Exosomes, containing RNA, proteins, lipids, and metabolites, have emerged as key regulators of fundamental biological processes and play crucial roles in regenerative medicine. They not only replicate the effects of their parent cells but also offer several advantages, such as high drug-loading capacity, low immunogenicity, excellent biocompatibility, and minimal side effects [37]. Exosomes derived from SCAPs (SCAPs-Exos) show significant potential for tissue regeneration [38]. Zhuang et al. demonstrated that SCAPs-Exos enhance dentinogenesis in BMMSCs both in vitro and in vivo, indicating their promise as a therapeutic approach for regenerating the dentin-pulp complex [39]. Injecting SCAPs-Exos into critical-size defects in the palatal gingival complex of mice resulted in notable improvements in angiogenesis and soft tissue regeneration (Fig. 3D) [19, 20, 23, 40]. These enhancements are attributed to SCAPs-Exos’ ability to promote filopodium formation, migration, and cytoskeletal reorganization in endothelial cells through the delivery of exosomal factors [41].

Therapeutic applications of SCAPs in regenerative medicine

Dentin-pulp complex regeneration

As shown in Fig. 4, common dental conditions such as caries and accidental trauma can lead to pulp infection, ultimately resulting in pulp necrosis [42]. Dentin-pulp regeneration aims to restore damaged dental pulp, with success evaluated through histological and clinical criteria. Histologically, the reconstruction of the dentin-pulp complex via angiogenesis and neurogenesis facilitates cervical and apical dentin formation. Clinically, successful regeneration is marked by symptom resolution, functional restoration, and an increase in root wall thickness or length. Achieving these objectives relies on the application of stem cells. SCAPs, with high proliferation and multilineage differentiation potential, are promising stem cell resource for dentin-pulp regeneration. In 2006, Sonoyama et al. first demonstrated this by generating dentin in mice and swine using SCAPs with hydroxyapatite/tricalcium phosphate scaffolds [4], a finding validated by subsequent studies [43–47].

Fig. 4.

Histological and clinical goals of pulp regeneration dental pulp damage, caused by caries, trauma, or iatrogenic factors, require regeneration defined by histological and clinical criteria. Histological success relies on dentin-pulp complex reconstruction via angiogenesis and neurogenesis, leading to cervical and apical dentin formation. Clinically, success is marked by symptom resolution (pain, bone resorption), restored function, and increased root wall thickness or length. Reproduced with permission [42]. Copyright © 2021 Xie et al

Current research aims to enhance SCAPs’ efficacy in dentin-pulp regeneration and elucidate underlying molecular mechanisms. Liang et al. discovered that lysine demethylase 4D, along with ribosomal protein S5, boosts the osteogenic/odontogenic differentiation and migration potential of SCAPs [48]. Xiao et al. identified stromal-derived factor-1α(SDF-1α) as a crucial factor in promoting SCAP migration, and found that the SDF-1α/C-X-C chemokine receptor type 4(CXCR4) signaling pathway is vital for bone morphogenetic protein (BMP)-2-induced odontogenic differentiation [49]. Wang et al. pinpointed protein arginine methyltransferase 6 as a key target for SCAP-mediated bone and tooth tissue regeneration [50]. These insights could inform novel strategies for dentin-pulp regeneration.

Originating from the neural crest, SCAPs naturally express neural markers without neurogenic induction [8], suggesting a significant capacity for neural tissue differentiation. Treatment with VEGF and nerve growth factors has demonstrated the promising dentinogenic and neurogenic potential of SCAPs [51]. Building on this, researchers are exploring strategies to enhance SCAPs’ neurogenic differentiation. Mohammed et al. found that spheres formed by iSCAPs interacting with SCAPs and human umbilical vein endothelial cells (HUVECs) can promote both vasculogenesis and neurogenesis [21]. Liu et al. showed that an electroconductive scaffold significantly enhances the neuronal differentiation of SCAPs [52].

However, regenerative dentistry are often unpredictable and primarily limited to immature teeth. Mature teeth, with single apical blood supply, pose challenges for pulp regeneration. Angiogenesis plays a critical role in dental pulp regeneration by facilitating the development of new capillary network from granulation tissue, which is essential for resolving chronic inflammation [53–55]. Angiogenesis is critical for pulp regeneration, where SCAPs exhibit superior angiogenic potential versus other oral-derived MSCs [56], further enhanced by stress microenvironments [57]. However, challenging microenvironment of root canal poses significant obstacles to SCAP differentiation and vascularization [28]. Strategies to boost SCAP angiogenic capacity include constructing functionalized scaffolds [58, 59], coculturing with specific bioactive materials [60], and regulating specific gene expression [61]. For instance, EphrinB2, a transmembrane ligand of EphB receptor tyrosine kinases expressed in arteries, can stabilize vessel-like structures formed by coculturing SCAPs with HUVECs [27]. Coculturing these cells under hypoxic conditions also facilitates the formation of endothelial tubules and capillary networks, as noted by Nam et al. [62]. Additionally, VEGF-loaded fibers offer a promising strategy to enhance SCAP angiogenesis and promote new tissue formation during endodontic procedures [63].

Pulp revascularization

Pulp revascularization is an innovative endodontic procedure designed to regenerate dental pulp and promote root development in teeth with necrotic pulp and immature apices [64]. SCAPs are crucial to this process. During pulp revascularization, a blood clot serves as a biological scaffold [65, 66]. SCAPs migrate to the scaffold, proliferate, and differentiate into various cell types, including odontoblast-like cells, contributing to dentin formation and the regeneration of pulp-like tissue [67].

While both pulp revascularization and pulp regeneration aim to restore tooth vitality, their approaches, outcomes, and the role of SCAPs differ significantly. Pulp revascularization involves disinfecting the root canal, creating a blood clot scaffold, and sealing the tooth crown to foster a protective environment for new tissue growth. The primary goal is to re-establish vascularity within the root canal, potentially leading to new tissue formation, though not necessarily normal pulp tissue [64, 67]. In this process, SCAPs are the main stem cell source, migrating from apical papilla tissues root canals, which is known as “cell homing”. In contrast, pulp regeneration is a more comprehensive approach aimed at regenerating the entire dentin-pulp complex. It utilizes stem cells, growth factors, and scaffolds to regenerate fully functional pulp tissue, including vascular and neural components, closely mimicking natural pulp tissue [2]. In pulp regeneration, SCAPs contribute to new tissue construction not only through homing from the treated tooth’s apex but also by being harvested from the apical papilla of other teeth. These cells are cultured and expanded in vitro before transplantation into the pulp chamber [68].

Periodontal tissue regeneration

Periodontitis, a prevalent chronic inflammatory disorder of periodontal tissues, represents a leading cause of tooth loss and irreversible damage to tooth-supporting structures. While conventional therapeutic approaches effectively control microbial infection, they demonstrate limited capacity to reconstruct the native architecture and biological function of periodontal tissues. Thus, periodontal regeneration represents a promising therapeutic alternative. SCAPs, PDLSCs, and DPSCs are regarded as promising seed cells for facilitating periodontal regeneration [5, 69–71]. SCAPs exhibit higher proliferation rates, greater mineralization capacity, and stronger osteogenic differentiation potential compared to PDLSCs and DPSCs. Ebadi et al. [72] extracted SCAPs from the root apex of human third molars and differentiated them into cementoblasts successfully. Li et al. [73] investigated the impact of SCAPs on periodontal tissue regeneration in swine through local injection. Twelve weeks post-injection, clinical assessments, CT scans, and histopathological analyses demonstrated significant improvements in periodontal regeneration attributed to SCAPs. Further research [74] demonstrated SCAPs’ potential for periodontal regeneration. In a minipig periodontitis model, injection of SFRP2-overexpressing SCAPs into damaged sites significantly reduced gingival inflammation, and regenerated bone, periodontal ligament, and cementum, which suggests that SFRP2 may serve as a key therapeutic target for future periodontal tissue regeneration. These studies underscore the potential of SCAPs as an alternative stem cell source for periodontal tissue regeneration.

Bone regeneration

Bone deficiencies resulting from oncological resections, traumatic injuries, or pathological conditions are intimately linked with significant functional impairments [75]. Autologous bone grafting is commonly used to repair compromised osseous structures, yet it faces limitations such as restricted blood supply, limited volume, and difficulty conforming to complex anatomical geometries. As an alternative, cellular and biomaterial complexes have emerged as a promising approach for restoring defective bone tissue [76, 77]. So far, the osteogenic capacity of SCAPs has been extensively validated [45, 78]. However, further study is required to determine the effectiveness of SCAPs in promoting osteogenic differentiation. Deng et al. found that PDGFBB (Platelet-Derived Growth Factor Subunit B) gene-modified SCAPs can improve bone formation in calvarial defects [79]. Touya et al. developed a novel tricalcium silicate-based ink with SCAPs for bone regeneration, which utilized laser-assisted bioprinting with promising results in both in vitro and in vivo experiments [80]. The pergola-like scaffold can also serve as an efficient carrier and supportive device for promoting bone regeneration and mineralization in bone tissue engineering. It plays a critical role in achieving vertical bone augmentation, even in situations with limited blood supply [17]. Overall, these studies highlight the potential of SCAP transplantation as a treatment for bone defects, though further research is essential for clinical application.

Neural regeneration

Co-culturing dental stem cells with trigeminal sensory neurons enhances ATP-induced inward current density, positively influencing sensory nerve activity and cold-sensitive ion channels [81]. SCAPs demonstrate higher proliferation rates and express key stem cell markers, outperforming DPSCs in BrdU uptake, cell doubling, tissue regeneration, and the number of STRO-1-positive cells [82]. Therefore, SCAPs could serve as a potential cell source for treating nerve injuries. In a 3D organotypic culture, SCAPs generate nerve-like tissue containing axons and myelin structures in vitro [83]. Transplanted SCAPs can protect spinal cord neurons and promote functional recovery following spinal cord injury [84], as well as enhance axon regeneration and exert neuroprotective effects on dorsal root ganglia neurons in a rat sciatic nerve injury model [85]. Additionally, SCAPs expedite spinal cord injury healing by reducing tumor necrosis factor-α(TNF-α) levels and promoting oligodendrocyte progenitor cell differentiation [86]. Previous studies indicated that SCAPs have the ability to secrete neurotrophic factors, including nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, and activin-A [87–89]. These findings highlight the therapeutic potential of SCAPs in neural regeneration.

Recent research has explored optimizing SCAPs for neural repair. Koh et al. [90] demonstrated that small molecules induce SCAPs into neural progenitor cells within three days, followed by neuron-like differentiation. Tubular sheets constructed from these cells, when transplanted into rat sciatic nerve injury models, significantly improved sciatic functional index and preserved gastrocnemius mass. However, despite SCAP survival and partial functional restoration, poor integration with host tissue hindered nerve fiber pathways, potentially limiting long-term outcomes. Basabrain et al. [21, 91, 92] systematically investigated spheroid culture’s impact on SCAP neurogenic potential. Culturing SCAPs in micromolded scaffolds revealed a transition from fibroblast-like to neuron-like morphology during migration [91]. Neural differentiation experiments showed SCAP spheroids formed longer, more abundant neurites than monolayer cultures, indicating enhanced neurogenic capacity [21]. Subsequent co-culture of induced SCAP spheroids with SCAPs and HUVECs revealed coordinated neural-endothelial cell migration, forming neurovascular structures—a promising approach for functional tissue regeneration [21]. Zhang et al. [93] identified the role of Mixed lineage leukemia 1 (MLL1) in SCAP neurogenic differentiation. MLL1 interacts with WD repeat domain 5 (WDR5) to suppress hairy and enhancer of split 1 (HES1) expression, modulating neurogenic potential. This study first established the MLL1-WDR5-HES1 negative regulatory axis in SCAP neurogenesis, showing that MLL1 knockdown enhances neurogenic differentiation and promotes spinal cord injury repair, offering a novel therapeutic target.

Vascular regeneration

The formation and regeneration of physiological tissues necessitates vascular network reestablishment [89]. Notably, stem cells across diverse niches consistently localize to vascular-rich regions [29], suggesting an inherent, predictable role in promoting angiogenesis during microenvironment restoration [94]. Hilkens et al. [28] demonstrated SCAPs express pro-angiogenic factors (VEGF, fibroblast growth factor 2, angiopoietin-1) and exhibit potent vascular regenerative capabilities in vitro and in vivo (Fig. 4C). Complementing this, Yi et al. [95] induced SCAPs over 8 days to adopt an endothelial-like phenotype, evidenced by tubular structure formation, acetylated low-density lipoprotein uptake, and nitric oxide production. These cells further formed functional, host-anastomosed blood vessels in murine matrigel plugs, confirming SCAPs’ intrinsic angiogenic potential. Moreover, SCAPs synergize with HUVECs to enhance vascular stability, particularly under hypoxia [96]. Liu et al. [19] revealed hypoxia-primed SCAPs-Exos that are efficiently internalized by HUVECs, boosting their proliferation, migration, and tube formation. SCAPs-Exos alone exerted strong pro-angiogenic effects, accelerating angiogenesis and tissue regeneration in murine palatal defects (Fig. 4D) [20]. However, compared to non-oral stem cells like BMSCs, which generate more mature vasculature, SCAPs exhibit limitations in producing stable vascularized tissues, potentially restricting their utility for ischemic therapies [97]. Thus, while SCAPs’ angiogenic properties are well-established, strategies to enhance their vascular maturation remain critical for extending applications beyond dentistry.

Potential applications in other tissue types

Retina, as a part of the central nervous system, consists of six types of neural cells (rods, cones, retinal ganglion cells, bipolar cells, horizontal cells, and amacrine cells) and three types of glial cells (astrocytes, microglia, and Müller cells). These cells reside on top of retinal pigment epithelium. Unfortunately, human retina has limited regenerative capacity due to reduced production of neurotrophic growth factors and increased inhibitory molecules against axon growth [98]. Retinal diseases impact different layers of retina, leading to loss of neurons and their connections. SCAPs can be a good source for retinal regeneration. To assess retinal differentiation, Karamali et al. conducted a study comparing co-cultured human pluripotent stem cells (hPSCs) and SCAPs on matrigel, as well as hPSCs cultured alone [99]. The results showed in co-culture system, SCAPs significantly enhanced neural differentiation of hPSCs. The induced hPSCs co-cultured with SCAPs exhibited significant expression of eye-associated markers, including paired box protein 6(PAX6), retinal homeobox(RAX), SIX homeobox 3(SIX3), and LIM Homeobox 2, and demonstrated five-fold retinal pigmented epithelium colonies. Additionally, the neural tube-like structures formed in the presence of SCAPs expressed markers associated with retinal progenitor cells, such as RAX, SIX3, and PAX6. These findings suggest that SCAPs may stimulate retinal induction in hPSCs [99].

SCAPs exhibit chondrogenic differentiation potential, as indicated by positive Alcian Blue staining for proteoglycans after three weeks in induction media [100]. Transcription factors distal-less homeobox 5(DLX5) and homeobox protein C8(HOXC8) may enhance this capacity by downregulating the long non-coding RNA LINC01013, suggesting a potential target for cartilage regeneration [25]. The physical microenvironment, particularly substrate stiffness, also significantly influences chondrogenic differentiation. Cai et al. [101] found that SCAPs on soft substrates display chondrocyte-like features, including limited spreading, cortical actin organization, elevated proteoglycan production, and upregulation of chondrogenic markers such as Sox9, Col2, and aggrecan. These effects are mediated through mechanosensing and mechanotransduction pathways involving integrin β1, focal adhesion kinase, and the Rho-associated coiled-coil kinase(ROCK)/Smad family member 3(Smad3)/Sox9 signaling axis. The differentiation potential and regenerative applications of SCAPs are summarized in Fig. 5. Tables 3 and 4 synthesized and summarized studies from the past 10 years on the applications of SCAPs in regenerative medicine, providing readers with a concise overview of the current research landscape in this field. The detailed search strategy employed for compiling these tables is available in the Appendix.

Fig. 5.

Schematic summary of SCAPs’ differentiation potential and regenerative applications

Table 3.

Studies on applications of SCAPs in regenerative dentistry

Refs	Applications	Treatment	Conclusion
Dental regeneration
[21]	Pulpal vasculogenesis/ neurogenesis	SCAP monolayers and spheres underwent neuronal induction via a small molecule neural induction medium.	Induced SCAP spheres interacted with SCAPs and HUVECs, facilitating vasculogenesis and neurogenesis.
[44]	osteo/odontogenic differentiation	SCAPs were cocultured with mineral trioxide aggregate.	Mineral trioxide aggregate at appropriate concentration enhanced osteo/odontogenic differentiation of SCAPs by activating p38 and extracellular signal-regulated kinases signaling pathways.
[45]	Odontogenesis	Used VitroGel 3D system as an injectable scaffold with SDF-1α and BMP-2 and embedded SCAPs for pulp-dentin regeneration.	VitroGel 3D system enhanced SCAP proliferation and differentiation, with SDF-1α synergistically boosting BMP-2-induced odontogenic differentiation both in vitro and in vivo.
[46]	Odontogenesis	SCAPs were cocultured with Biodentine, ProRootMTA, and RetroMTA groups.	Biodentine, ProRootMTA, and RetroMTA promoted SCAP proliferation, with Biodentine showing the strongest enhancement of odontogenic differentiation.
[47]	Osteo/odontogenic differentiation	SCAPs were cocultured with human platelet lysate of different concentrations.	Application of 5% platelet lysate significantly enhanced SCAP proliferation and osteo/odontogenic differentiation.
[48]	Osteo/odontogenic differentiation	Short hairpin RNAs and full-length RNA were used to deplete or overexpress lysine demethylase 4D gene expression in SCAPs.	Lysine demethylase 4D gene promoted osteo/dentinogenic differentiation and migration potential of SCAPs in combination with Ribosomal Protein S55.
[49]	Odontogenesis	Examined contribution of SDF-1α signaling to odontogenic differentiation of stem cells from SCAP induced by BMP-2.	SDF-1α markedly enhanced SCAP migration, while the SDF-1α/CXCR4 axis was essential for BMP-2-mediated odontogenic differentiation signaling pathways.
[50]	Odontogenic differentiation	Investigated the role of protein arginine methyltransferase 6(PRMT6) gene in odontogenic differentiation and migration capacity by using SCAPs.	Knockdown of gene PRMT6 promoted odontogenic differentiation.
[51]	Odontogenesis/ pulpal neurogenesis	Cocultured SCAPs with VEGF or nerve growth factor and tested expression of osteogenic and dentinogenic markers.	SCAPs exhibited promising dentinogenic and neurogenic potential after coculturing with VEGF and nerve growth factor.
[102]	Odontogenic differentiation	SCAPs were subjected to direct current electric fields (DC EFs) at intensities ranging from 100 to 300 mV/mm.	A direct current electric field of 100 mV/mm promoted the proliferation of SCAPs, whereas 200 mV/mm enhanced their polarization and odontogenic differentiation capacity. In contrast, 300 mV/mm inhibited cellular activity.
[103]	Odontogenic differentiation	SCAPs were exposed to heat stress at 41 °C for 1 h every three days.	Exposure to 41 °C heat stress markedly promoted the osteogenic and odontogenic differentiation of SCAPs.
[52]	Pulpal neurogenesis	SCAPs were encapsulated in gelatin methacryloyl covalently grafted multi-walled carbon nanotubes (GelMA–MWCNTs) and cobalt-incorporated GelMA–MWCNTs (GelMA–MWCNTs/Co) hydrogels and subjected to electrical stimulation.	Electrical stimulation significantly enhanced SCAP neuronal differentiation, inducing cell morphological changes and increased neuronal marker expression in the electroconductive GelMA–MWCNTs/Co hydrogel scaffolds.
[59]	Osteogenesis	Developed RA-VEGF/BMP-2 peptide delivery systems to evaluate RA-VEGF scaffolds’ effects on HUVEC angiogenesis and SCAP osteoblastic differentiation.	rhVEGF165/BMP-2 promoted angiogenesis of HUVECs as well as osteogenesis of SCAPs abilities.
[27]	Pulpal vasculogenesis	Co-culture of HUVECs and SCAPs was performed to evaluate the role of protein ephrinB2 on stabilization of vascular-like structures.	HUVECs and SCAPs generated vascular-like structures.
[65]	Pulp revascularization	Extracted PRF from the patient’s blood via low-speed centrifugation to form a gel-like substance enriched with growth factors, serving as a biological scaffold for filling the pulp chamber.	The tooth implanted with PRF met both radiographic and clinical success criteria, with pulp sensitivity successfully restored.
[73]	Periodontal regeneration	SCAPs were applied in periodontal tissue regeneration in swine through local injection.	Clinical assessments, CT scans, and histopathological analyses demonstrated significant improvements in periodontal regeneration attributed to SCAPs.
[74]	Periodontal regeneration	SFRP2 protein-overexpressing SCAPs were injected into damaged sites in a minipig periodontitis model.	The injection of SFRP2-overexpressing SCAPs significantly reduced gingival inflammation, and regenerated bone, periodontal ligament, and cementum.
[96]	Pulpal vasculogenesis	Coculture of HUVECs and SCAPs under hypoxia atmosphere.	SCAPs cocultured with HUVECs at a 1:5 ratio increased the number of endothelial tubules, tubule lengths, and branching points.
[104]	Odontogenesis	Exposed SCAPs to bacterial lipopolysaccharide and investigated cell viability and odontogenic differentiation.	Inflammatory conditions may suppress SCAP osteo/odontogenic differentiation through autophagy-mediated mechanisms.

Table 4.

Studies on applications of SCAPs in non-dental regenerative medicine

Refs	Applications	Treatment	Conclusion
Bone regeneration
[17]	Extraskeletal vertical bone augmentation	Embedded SCAPs into a structural pergola-like scaffold with BMP9 and VEGF.	BMP9 effectively promoted osteogenic differentiation of SCAPs.
[78]	Craniofacial repair	SCAPs were cultured in an osteogenic medium cell with PRF and low-level laser (660 nm, 6 J/m2-irradiation).	Combination of PRF and low-level laser induced osteogenic differentiation of SCAPs.
[79]	Bone defects	Cocultured SCAPs with platelet-derived growth factor and thermo-sensitive hydrogel.	SCAPs improved bone formation in calvarial defects.
[80]	Calvaria defect	Printed with SCAPs as bioink.	In vivo application of this new ink formulation regenerated critical size bone defect and promoted formation of bone volume fraction without affecting vascularization of neo-formed tissue.
[105]	Osteogenesis	SCAPs were cultured for 24 h and exposed to low-level lasers with different doses, energy, and wavelengths.	Low-level laser promoted proliferation, osteogenic differentiation, vascular endothelial growth factor and tumor necrosis factor-β2 expression on SCAPs.
Neural regeneration
[21]	Vasculogenesis/ neurogenesis	SCAP monolayers and spheres were neuronally induced using a small molecule neural induction medium. Direct coculture or pulp-on-chip models examined iSCAP sphere interactions with SCAPs and HUVECs.	iSCAP-formed spheres interacted with SCAPs and HUVECs, promoting vasculogenesis and neurogenesis.
[81]	Neurogenesis	Coculture system with human SCAPs and rat trigeminal sensory neurons to determine effect of SCAP coculture on neuronal responses using whole-cell patch-clamp electrophysiology.	SCAPs released trophic factors that acted on afferent neurons to enhance cold-sensitive ion channel activity.
[83]	Neurogenesis	Cultured SCAPs with neurogenic commercial differentiation medium.	Differentiated cells exhibited neuron-like morphologies with axons, dendrites, and perikaryons, accompanied by upregulated mRNA and protein levels of neuronal markers MAP2 and β-tubulin III, though GFAP remained undetected.
[84]	Spinal cord repairing	SCAPs were isolated and identified in vitro, then green fluorescent protein-labeled stem cells with pellets were transplanted into completely transected spinal cord.	SCAPs demonstrated the potential in repairing the completely transected spinal cord and promoted functional recovery after injury.
[85]	Peripheral nerve injury	SCAPs were used to treat a 10 mm nerve gap defect in a rat sciatic nerve injury model.	SCAPs significantly enhanced axon regeneration after two weeks and showed neuroprotective effects on dorsal root ganglia neurons.
[88]	Spinal cord injury	SCAP were co-cultured with lipopolysaccharide-activated microglia, lipopolysaccharide-activated rat spinal cord organotypic sections, and lipopolysaccharide-activated co-cultures of spinal cord organotypic sections and spinal cord adult oligodendrocyte progenitor cell.	SCAPs induced a reduction of TNF-α expression and secretion in inflamed spinal cord tissues and stimulated oligodendrocyte progenitor cell differentiation via activin-A secretion.
[90]	Neurogenesis	SCAPs were cultured for three days in a neural induction medium supplemented with seven small molecules.	Small molecules induce SCAPs into neural progenitor cells within three days, followed by neuron-like differentiation.Tubular sheets constructed from these cells, when transplanted into rat sciatic nerve injury models, significantly improved sciatic functional index and preserved gastrocnemius mass.
[91]	Neurogenesis	SCAPs were cultured in agarose molds for 3 days, forming 150–200 μm spheres in α-MEM with 10% FBS, without neural induction factors.	SCAPs in 3D spheres exhibit longer, more abundant neurites and elevated neural marker expression compared to 2D cultures, indicating enhanced neural differentiation.
[92]	Neurogenesis	SCAPs were treated with small molecule-containing neural induction medium for 7 days to generate neural-like cells. These induced cells were formed into neural spheres and embedded in collagen hydrogel to mimic the dental pulp microenvironment. Subsequently, the neural spheres were co-cultured with different states of SCAP.	When co-cultured with different SCAP states, uninduced SCAPs showed the highest neurotrophic factor secretion and most effectively promoted neural sphere differentiation.
[93]	Neurogenesis	Researchers knocked down MLL1 in SCAPs with lentiviral transfection, cultured them under neural induction conditions to assess neural differentiation potential, and transplanted them into rat spinal cord injury models to evaluate motor function recovery.	MLL1 knockout boosted SCAP neural marker expression and enhanced motor recovery in spinal cord injury model rats.
Vascular regeneration
[19]	Angiogenesis	Extract the exosomes derived from the SCAPs of hypoxia preconditioning and co-culture them with HUVECs.	Hypoxia preconditioning can enhance the angiogenic ability of SCAPs exosomes.
[21]	Neurovasculogenesis	SCAP monolayer cultures and spheres were neuronally induced with small molecule medium, while direct coculture and pulp-on-chip systems were employed to study their interactions with SCAPs and HUVECs.	Induced SCAP spheres interacted with SCAPs and HUVECs, promoting vasculogenesis and neurogenesis.
[94]	Angiogenesis	SCAPs were collected and analyzed from immature permanent teeth with pulp necrosis and periapical periodontitis to evaluate their viability and stemness characteristics under inflammatory conditions.	Even in the chronic inflammatory environment of pulp necrosis and periapical periodontitis, SCAPs maintained viability, stemness, and enhanced angiogenic potential.
[95]	Angiogenesis	Small molecule compounds were combined with growth factors to induce SCAPs for eight days.	SCAPs differentiate into endothelial-like cells and form functional vasculature in vitro and in vivo.
[96]	Angiogenesis	Co-culture SCAPs and HUVECs in an oxygen-deficient environment at a ratio of 1:5.	SCAPs can enhance angiogenesis in an oxygen-deficient environment and promote the formation of three-dimensional vascular-like structures when co-cultured with HUVECs.
[97]	Pericyte-supported vascular capillaries	Encapsulated SCAPs into gelatin methacrylate hydrogel.	Formation of microvascular networks after culturing.
[106]	Angiogenesis	Exosomes were collected from SCAPs cultured under hypoxic conditions.	SCAP-derived exosomes could be internalized by HUVECs and elevated their miR-126 levels. miR-126 enhanced the angiogenic capacity of HUVECs by suppressing SPRED1 and activating the ERK signaling pathway. Both in vitro and in vivo experiments demonstrated that SCAP-derived exosomes significantly promote angiogenesis.
Potential applications in other tissue types
[25]	Cartilage tissue regeneration	Chondrogenic differentiation of SCAPs was assessed using Alcian Blue staining, pellet culture, and rabbit knee cartilage defect transplantation.	DLX5 and HOXC8 enhanced SCAP chondrogenic differentiation by suppressing LINC01013, offering a potential target for cartilage tissue regeneration.
[107]	Cartilage tissue regeneration	In a rabbit knee cartilage defect model, KDM6B-overexpressing SCAPs were transplanted into the defect sites.	After 12 weeks, samples were harvested and evaluated using histological staining and immunohistochemistry, revealing superior cartilage defect repair compared to the control group.
[99]	Retinal regeneration	Co-cultured hPSC and SCAPs on matrigel.	SCAPs significantly enhanced neural differentiation of hPSCs.
[38]	Retinal regeneration	Extracellular vesicles derived from SCAPs were enriched using a lab-on-chip MEMS approach and conventional ultrafiltration techniques.	SCAP-derived extracellular vesicles exhibited anti-inflammatory and neuroprotective effects in vitro. In the retinal degeneration model of RCS rats, MEMS-enriched extracellular vesicles significantly preserved visual function, reduced retinal cell apoptosis, and maintained the thickness of the outer nuclear layer.

Challenges and potential strategies in the application of SCAPs for regenerative medicine

Challenges in clinical applications of SCAPs and epigenetic solutions

Despite SCAPs’ therapeutic promise, clinical translation faces key challenges. Firstly, stem cells obtained from autogenous molars need to be expanded in vitro to a sufficient quantity to meet the demand for clinical regenerative applications. However, the number of primary stem cells that can be extracted from autogenous molars is limited. Prolonged expansion and excessive passaging may alter SCAP phenotype, compromising differentiation potential and hindering clinical translation [16, 108]. For example, by the 10th passage, SCAPs lose CD24 expression, which is a key identity marker, regardless of their differentiation status, indicating diminished stemness with continued culture [13]. Concurrently, prolonged culture induces typical senescence phenotypes, including upregulated P21/P16/P53, elevated SA-β-gal activity, and increased reactive oxygen species levels [109]. Redaelli et al. [110]observed that while long-term cultured MSCs maintain genetic stability, they acquire highly reproducible epigenetic alterations, such as specific DNA methylation and histone modifications. Wagner et al. [111] posits that these acquired epigenetic changes likely constitute the core mechanism driving MSCs senescence and functional decline. Thus, understanding epigenetic mediators regulating self-renewal and lineage commitment is crucial for advancing regenerative medicine.

Epigenetic regulation modulates gene expression and function without altering DNA sequence, playing a vital role in embryonic development, bone homeostasis, and stem cell fate. Its advantage lies in preserving genomic integrity, avoiding irreversible damage, unintended effects, or harmful mutations [112]. Common epigenetic mechanisms, including DNA methylation, histone modification, and non-coding RNA regulation, enhance stem cell differentiation potential, highlighting their promise in regenerative medicine [113]. Epigenetic regulation plays a key role in cell fate determination and differentiation control. SCAPs undergo lineage-specific differentiation via epigenetic modulation [112]. For instance, Li et al. demonstrated that long non-coding RNA(lncRNA) H19 overexpression enhances SCAP osteo/odontogenic differentiation, while its knockdown inhibits this process. Mechanistically, lncRNA H19 competitively binds mircroRNA(miR)-141, preventing sperm associated antigen 9 degradation, thereby increasing p38 and c-Jun N-terminal kinase phosphorylation and promoting SCAP differentiation [114]. Additionally, circular RNA signal-induced proliferation-associated 1L1(CircSIPA1L1) upregulates alkaline phosphatase gene by targeting miR-204-5p, facilitating SCAP osteogenic differentiation [115], while lysine-specific demethylase 3B(KDM3B) further enhances this process [116]. In a rabbit knee cartilage model, Zhang et al. [107]demonstrated that lysine-specific demethylase 6B (KDM6B) enhances chondrogenic differentiation of SCAPs by suppressing the transcription factor Hairy and Enhancer of Split-1(HES1).

Secondly, modulating the inflammatory response in injured tissues is essential for successful regeneration. During the initial repair phase, inflammatory cells release cytokines and growth factors that activate resident stem cells and initiate repair mechanisms, facilitating tissue regeneration. This response also clears pathogens and prevents infection. A balanced inflammatory reaction regulates immune activity, preventing both excessive tissue damage and fibrosis, thereby promoting functional tissue restoration [117, 118]. Although the related studies with SCAPs are limited, epigenetic regulation has been proven to modulate this inflammatory response, with stem cells treated with specific epigenetic drugs exhibiting anti-inflammatory properties, thereby reducing tissue damage and promoting healing [104]. For example, histone modifications can regulate the expression of inflammatory genes. Histone deacetylase inhibitors can suppress pro-inflammatory cytokine production and enhance anti-inflammatory responses. These modifications alter chromatin structure, making it accessible for transcription factors and controlling the transcription of inflammatory genes [112]. DNA methylation patterns are dynamically regulated during inflammation. Hypomethylation promotes the over-expression of pro-inflammatory genes, while hypermethylation can silence these genes. Epigenetic drugs targeting DNA methyltransferases can modulate these methylation patterns, reducing inflammation and promoting tissue healing [119]. Non-coding RNAs play a pivotal role in post-transcriptional regulation of inflammatory responses. Specific mRNAs can either promote or inhibit inflammation by targeting mRNAs of inflammatory mediators [112].

Finally, effective homing directs stem cells to injury sites, ensuring targeted tissue repair and regeneration. Successful engraftment enables integration into host tissue, supporting differentiation and enhancing therapeutic efficacy [120]. Epigenetic modifications upregulate homing receptors on SCAPs, improving migration and retention in target tissues [112].

Although epigenetic regulation technologies theoretically enable precise control of stem cell differentiation, their clinical translation faces significant hurdles. For instance, commonly used epigenetic editing tools such as the CRISPR-dCas9 system carry the risk of inducing unintended epigenetic modifications at off-target sites [121]. These so-called “off-target effects” may disrupt the methylation or demethylation balance of critical genes, leading to unpredictable changes in cell fate. Moreover, histone modifications induced in vitro is difficult to sustain within the complex in vivo microenvironment, potentially compromising therapeutic efficacy. For example, reactive oxygen species and inflammatory signaling can modulate cell fate through histone modifications and interact with therapeutic interventions [122]. In summary, while epigenetic regulation has shown great promise in both in vitro and in vivo studies, its path toward clinical application remains long and challenging.

Challenges and solutions in stem cell delivery and scaffold integration

Recent advances in stem cell research highlight promising therapeutic potential, yet developing effective delivery methods remains essential to ensure successful integration following transplantation. Conventionally, stem cells have been administered through direct injection into the target area or systemic circulation. However, the effectiveness of such approaches remains debatable, given that empirical evidence indicates suboptimal cell viability, integration, and inconsistent differentiation post-transplantation [123].

Tissue engineering, which involves stem cells, scaffold and growth factors, can be seen as a promising strategy to solve the problem. The prospective effectiveness of stem cell delivery and subsequent differentiation could be substantially enhanced through the integration of tissue-engineered scaffolds. These scaffolds provide structural support as well as mechanical and biochemical signals, including growth factors and integrin receptor interactions, which are crucial for stem cells [124].

Scaffold properties are instrumental in promoting cellular proliferation and differentiation, facilitating cell adhesion and migration, and replicating the microenvironment found in native tissues and organs. As Fig. 6 shows, scaffold is analogous to assemble architectural design, featuring a hierarchical structure in which each tier fulfills specific roles to create a cohesive system. Contrary to injection-based methodologies, scaffolds provide enhanced precision in stem cell delivery and permit the incorporation of time-release growth factors, as well as the modulation of physical parameters such as stiffness, pore size, and cell-substrate interactions.

Fig. 6.

The application of scaffold in regenerative medicine. A Schematic illustration of the scaffold’s hierarchically structured architecture, where each level performs distinct functions to form an integrated system. Reproduced with permission [125]. Copyright © 2023 Zhou et al. B Scaffold design should ensure functional compatibility between material properties and cellular behavioral requirements(Created by BioRender.com). C-E The illustration depicts cell survival at various time points following direct transplantation without a scaffold, showing that most cells disappear within seven days. Reproduced with permission [126]. Copyright © 2015 Qazi et al. F Differentiation of human skeletal myoblasts within scaffolds, as observed under varying magnifications. Reproduced with permission [126]. Copyright © 2015 Qazi et al

Apart from stem cells and scaffold, growth factors are also required by tissue engineering to induce specific differentiation pathways and maintain cellular phenotypes. Integration of growth factors and cytokines has been demonstrated to augment the effectiveness of cell-based regenerative therapies [127, 128]. This enhancement is evident in both the administration of exogenous and endogenous cells. These growth factors bolster the functions of dental stem cells by facilitating the migration of native cells, followed by their proliferation, differentiation, angiogenesis, and neurogenesis. Functioning in an autocrine or paracrine manner, growth factors and cytokines orchestrate cellular activities through the regulation of intracellular signaling pathways [129].

Scaffolds, as critical frameworks supporting cell growth and tissue formation, it must satisfy rigorous criteria to be viable for clinical translation. These requirements encompass structural, biological, and functional parameters essential for successful tissue regeneration.

Firstly, scaffold should facilitate cell attachment and migration, allowing localized and sustained delivery of growth factors and enabling oxygen influx to meet the high metabolic demands of cells and tissues during formation [130, 131]. Secondly, mechanical properties of the scaffold must be highly compatible with the surrounding tissue and meet the specific requirements of native tissue [126, 132, 133]. For example, enhancement of scaffold stiffness can promote the differentiation of stem cells into neurons, myoblasts, and osteoblasts, in the specific sequence [134]. Size and pore numbers in a scaffold can impact the surface area, permeability, and mechanical properties of scaffold, which are critical factors influencing cell differentiation and tissue formation [130, 135, 136]. Increased number and larger extent of pores enhance the cellularity, but compromise scaffold’s mechanical properties. Additionally, pore interconnectivity also plays an important role in sustaining tissue growth [136–138]. Achieving balance between porosity and mechanical properties is important for designing bioactive scaffolds. While higher pore density promotes cell infiltration and nutrient exchange, it is essential to consider overall structural integrity of scaffold. Pore interconnectivity ensures efficient transport of oxygen, nutrients, and waste products, supporting tissue regeneration.

Thirdly, scaffold should gradually reabsorb once it has fulfilled its role as a template for tissue regeneration, so degradation process should occur at a rate compatible with the formation of new tissue [126, 130, 138, 139]. More importantly, by-products generated during degradation process must biocompatible and easily removal or resorbed to minimize the risk of inflammatory response [140]. So balancing degradation kinetics is essential for bioactive scaffold. The scaffold should maintain structural integrity during tissue regeneration but gradually degrade to adapt to regeneration process. Researchers need to explore various biomaterials and fabrication methods to achieve this delicate balance.

Due to variations in the mechanical properties, porosity, and degradation rates required for different tissues, personalized scaffold design is essential. However, the subtle differences among scaffolds lead to diverse regenerative outcomes whose underlying mechanisms remain poorly understood. In vivo, cell signaling is a highly complex system influenced by cellular interactions and external stimuli. The intricate molecular interplay that triggers varied cellular responses poses a significant challenge in developing cell-based therapies.

Clinical translational challenges

The isolation of SCAPs is typically limited to the early stages of root development, which inevitably results in a very low yield. A major challenge is the high cost of therapies once they become widely available. Regenerative medicine requires extra procedures and specialized personnel for cell handling, which increases costs and affects patient accessibility. Researchers must work to streamline these processes and reduce costs to facilitate broader adoption.

While a definitive solution remains elusive, existing research offers promising insights. Approximately 70% of patients require prophylactic extraction of impacted teeth threatening adjacent structures [10]; additionally, some undergo extraction of healthy supernumerary teeth for orthodontic reasons. These extracted teeth represent an ideal SCAP source. Cryopreserving one’s own tooth immediately post-extraction to establish a permanent ‘stem cell bank’ is therefore a viable strategy. Studies confirm SCAPs retain characteristics, proliferative and differentiation potential after 6 months of cryopreservation [10], though long-term viability requires further study. Given their low immunogenicity and immunosuppressive properties, SCAPs are also suitable for allogeneic use [12]. Even without personal banking, collecting and cryopreserving healthy teeth from routine extractions can establish a large-scale ‘SCAP cryo-store’ to ensure timely cell availability. These findings support the future clinical use of SCAPs, although translational feasibility warrants further validation.

What’s more significant regulatory and ethical hurdles remain. Regulatorily, SCAPs’ nature as dynamic living cells complicates standardization compared to conventional drugs, as their efficacy and safety depend on processing, transport, and storage conditions; product heterogeneity can also lead to batch variability and inconsistent outcomes. Furthermore, residual proliferative capacity in incompletely differentiated cells raises concerns about abnormal differentiation or tumorigenesis, necessitating both rigorous quality standards with defined acceptable variability ranges and long-term trials to assess post-implantation viability and functional longevity. Ethically, sourcing SCAPs often involves teeth extracted from adolescents, demanding explicit informed consent from patients and guardians regarding therapeutic use of ‘discarded tissue’, particularly concerning future commercialization and benefit-sharing, alongside robust measures to protect donor genetic privacy and database security. Clinicians must also clearly communicate with patients about the inherent uncertainties and risks, including treatment failure or abnormal differentiation, alongside alternative options.

In summary, while SCAPs hold immense regenerative potential, their clinical translation faces multifaceted barriers; realizing their full therapeutic impact will require extensive collaboration among scientists, clinicians, public health experts, bioethicists, and broader society, including government entities.

Opportunities for future research and development

Understanding the molecular mechanisms of SCAPs is crucial for developing novel dental therapies and expanding regenerative applications [6]. However, lack of knowledge persist regarding SCAPs’ spatiotemporal distribution in different microenvironments, dynamic functional changes, and underlying regulatory mechanisms. These limitations stem from significant cell heterogeneity [5]. The origins of this heterogeneity remain unclear. This frequently causes discrepancies between in vitro and in vivo results, hindering consensus. Collectively, these issues have severely constrained deeper SCAPs research and application. Single-cell sequencing technology has brought new opportunities for future developments in this field by enabling genomic, transcriptomic, and epigenomic analysis at the single-cell level. This approach can clarify heterogeneity and reveal cellular physiology and mechanisms.

Emerging technologies are revolutionizing SCAPs research. Organoids model the dentin-pulp complex’s 3D physiology through stem cell self-organization, integrating vascular and neural components to dissect SCAPs’ paracrine signaling and contact-dependent regulation in pathological contexts [141, 142]. These platforms enable high-throughput screening of epigenetic modulators while evaluating off-target effects in near-native microenvironments [143, 144]. Patient-derived organoids further predict individualized therapeutic responses [145]. Concurrently, artificial intelligence transforms stem cell research [146]: deep learning analyzes multi-modal datasets (imaging/multi-omics) to pinpoint regulatory factors and cellular subpopulations governing SCAPs behavior [146]. Predictive models forecast differentiation trajectories [147] and accelerate drug discovery [148]. Synergistic convergence of these technologies are propelling SCAPs research into an innovative era.

Conclusion

In conclusion, this review comprehensively examined the biological characteristics and therapeutic potential of SCAPs in regenerative medicine, synthesizing the latest advances in their applications from the past ten years. SCAPs, of neural crest origin, exhibit high plasticity, multilineage differentiation potential, and potent paracrine activity, making them promising for tissue engineering. Clinically sourced from discarded immature teeth, they can be expanded and differentiated into osteogenic, chondrogenic, and neuronal lineages while secreting angiogenic, neurotrophic, and immunomodulatory factors. SCAP-derived exosomes offer cell-free therapeutic potential due to their bioactive cargo and low immunogenicity. However, clinical translation faces challenges such as phenotypic instability during expansion, suboptimal engraftment microenvironments, immune modulation, and manufacturing standardization. Recent advances in epigenetic modulation, functionalized scaffolds, growth factor delivery, and exosome engineering show promise in enhancing SCAP function and vascularization. Fully realizing SCAPs’ potential requires further mechanistic insight, quality control standards, and preclinical and clinical validation.

Supplementary Information

Below is the link to the electronic supplementary material.

Abbreviations

ALP

Alkaline phosphatase

BMP

Bone morphogenetic protein

CD

Cluster of differentiation

CircSIPA1L

Circular RNA signal-induced proliferation-associated 1L1

Co

Cobalt

Col2

Collagen type II

CXCR4

C-X-C chemokine receptor type 4

DFPCs

Dental follicle progenitor cells

DLX5

Distal-less homeobox 5

DPSCs

Dental pulp stem cells

GelMA

Gelatin methacryloyl

HES1

Hairy and enhancer of split 1

HOXC8

Homeobox protein C8

hPSCs

Human pluripotent stem cells

HUVECs

Human umbilical vein endothelial cells

KDM3B

Lysine-specific demethylase 3B

KDM6B

Lysine-specific demethylase 6B

lncRNA

Long non-coding RNA

miR

MicroRNA

MLL1

Mixed lineage leukemia 1

MSCs

Mesenchymal stem cells MSCs

MWCNTs

Multi-walled carbon nanotubes

Nanog

Homeobox protein NANOG

Notch1

Neurogenic locus notch homolog protein 1

Notch3

Neurogenic locus notch homolog protein 3

Oct3/4

Octamer-binding transcription factor 3/4

PAX6

Paired box protein 6

PDGFBB

Platelet-derived growth factor subunit B

PDLSCs

Periodontal ligament stem cells

PRF

Platelet-rich fibrin

PRMT6

Protein arginine methyltransferase 6

RAX

Retinal homeobox

ROCK

Rho-associated coiled-coil kinase

SCAPs

Stem cells from apical papilla

SCAPs-Exos

Exosomes derived from SCAPs

SDF-1α

Stromal-derived factor-1α

SHEDs

Stem cells from human exfoliated deciduous teeth

SIX3

SIX homeobox 3

Smad3

Smad family member 3

Sox2

SRY-Box transcription factor 2

Sox9

Sex-determining region Y-box 9

SSEA-4

Stage-specific embryonic antigen 4

TNF-α

Tumor necrosis factor-α

VEGF

Vascular endothelial growth factor

WDR5

WD repeat domain 5

Author contributions

Mengyu Huang conducted literature review and wrote the main manuscript text, Waruna Lakmal Dissanayaka reviewed the manuscript and Cynthia KY YIU supervised the manuscript development.

Funding

This research was supported by the Seed Fund for Basic Research, the University of Hong Kong (Project code: 2202100856).

Data availability

Not applicable.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.