Abstract

Introduction

Stem cells are a promising tool for the treatment of many different human diseases. An enormous variety of stem cells have been isolated and studied from different tissues, such as bone marrow,¹1. Ding L, Morrison SJ. Haematopoietic stem cells and early lymphoid progenitors occupy distinct bone marrow niches. Nature. 2013 14;495(7440):231-5. adipose tissue,²2. Chen L, Song J, Cui J, Hou J, Zheng X, Li C, et al. MicroRNAs regulate adipocyte differentiation. Cell Biol Int. 2013 Jun;37(6):533-46. skin,³3. Blanpain C, Fuchs E. Epidermal homeostasis: a balancing act of stem cells in the skin. Nat Rev Mol Cell Biol. 2009 Mar;10(3):207-17. and umbilical cord.⁴4. Yan M, Sun M, Zhou Y, Wang W, He Z, Tang D, et al. Conversion of human umbilical cord mesenchymal stem cells in Wharton’s jelly to dopamine neurons mediated by the Lmx1a and neurturin in vitro: potential therapeutic application for Parkinson’s disease in a rhesus monkey model. PLoS One. 2013;8(5):e64000. Among them, mesenchymal stem cells (MSCs) are the most promising for clinical purposes.⁵5. Ménard C, Tarte K. Immunoregulatory properties of clinical grade mesenchymal stromal cells: evidence, uncertainties, and clinical application. Stem Cell Res Ther. 2013 Jun;4(3):64.

Recently, MSCs were identified in the dental pulp. These cells represent a novel and promising stem cell population with self-renewal and multilineage differentiation capacities that are similar to other MSC populations.⁶6. Gronthos S, Mankani M, Brahim J, Robey PG, Shi S. Postnatal human dental pulp stem cells (DPSCs) in vitro and in vivo. Proc Natl Acad Sci U S A. 2000 Dec;97(25):13625-30.^,77. Seo BM, Miura M, Gronthos S, Bartold PM, Batouli S, Brahim J, et al. Investigation of multipotent postnatal stem cells from human periodontal ligament. Lancet. 2004 Jul;364(9429):149-55. Since the discovery of stem cells in the dental pulp of permanent⁶6. Gronthos S, Mankani M, Brahim J, Robey PG, Shi S. Postnatal human dental pulp stem cells (DPSCs) in vitro and in vivo. Proc Natl Acad Sci U S A. 2000 Dec;97(25):13625-30. and deciduous teeth,⁸8. Miura M, Gronthos S, Zhao M, Lu B, Fisher LW, Robey PG, et al. SHED: stem cells from human exfoliated deciduous teeth. Proc Natl Acad Sci U S A. 2003 May;100(10):5807-12. a large number of animal studies have evaluated the suitability of these cells for dental⁹9. Hu B, Nadiri A, Kuchler-Bopp S, Perrin-Schmitt F, Peters H, Lesot H. Tissue engineering of tooth crown, root, and periodontium. Tissue Eng. 2006 Aug;12(8):2069-75. as well as non-dental¹⁰10. Liu HC, E LL, Wang DS, Su F, Wu X, Shi ZP, et al. Reconstruction of alveolar bone defects using bone morphogenetic protein 2 mediated rabbit dental pulp stem cells seeded on nano-hydroxyapatite/collagen/ poly(l-lactide). Tissue Eng Part A. 2011 Oct;17(19-20):2417-33.^,1111. Sasaki R, Aoki S, Yamato M, Uchiyama H, Wada K, Okano T, et al. Tubulation with dental pulp cells promotes facial nerve regeneration in rats. Tissue Eng Part A. 2008 Jul;14(7):1141-7. tissue engineering applications. Here, we present a systematic review of in vivo studies investigating the use of dental pulp stem cells for the repair or regeneration of non-dental tissues.

Methodology

Two independent researchers, following the PRISMA guidelines,¹²12. Moher D, Liberati A, Tetzlaff J, Altman DG; PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Ann Intern Med. 2009 Aug;151(4):264-9. carried out an electronic customised search of scientific papers published between 2000 and 2012 using the Entrez PubMed, CAB Abstracts, Scopus and Web of Science databases. The following combination of keywords and abbreviations was used: [Stem Cells from Human Exfoliated Deciduous teeth (SHED)], [Dental Pulp Stem Cells (DPSC)] AND [tissue regeneration] AND [tissue repair]. Only full-text research manuscripts that were written in English and described in vivo analysis of tissue repair and/or regeneration of non-dental tissues using SHED or DPSCs were included in this review. Duplicate papers were excluded.

Results

Our search yielded a total of 2309 papers. Based on the abstracts, 1072 papers were excluded according to the previously mentioned inclusion/exclusion criteria. An additional 1221 papers were determined to be duplicates and were also excluded. Finally, of the 16 selected manuscripts, 2 were excluded because the full-text was not available in English. Thus, 14 manuscripts formed the basis of this review (Figure 1). The included manuscripts are summarised in Table 1.

In 7 of the studies included in this review (50%), the cells were isolated from human tissue. In all 14 studies, the cells were transplanted into animals of other species, including pigs, rats and mice.

Eight manuscripts investigated bone tissue repair and/or regeneration. Liu et al.,¹⁰10. Liu HC, E LL, Wang DS, Su F, Wu X, Shi ZP, et al. Reconstruction of alveolar bone defects using bone morphogenetic protein 2 mediated rabbit dental pulp stem cells seeded on nano-hydroxyapatite/collagen/ poly(l-lactide). Tissue Eng Part A. 2011 Oct;17(19-20):2417-33. Seo et al.,¹³13. Seo BM, Sonoyama W, Yamaza T, Coppe C, Kikuiri T, Akiyama K, et al. SHED repair critical-size calvarial defects in mice. Oral Dis. 2008 Jul;14(5):428-34. de Mendonça Costa et al. ¹⁴14. de Mendonça Costa A, Bueno DF, Martins MT, Kerkis I, Kerkis A, Fanganiello RD, et al. Reconstruction of large cranial defects in nonimmunosuppressed experimental design with human dental pulp stem cells. J Craniofac Surg. 2008 Jan;19(1):204-10. and Riccio et al.,¹⁵15. Riccio M, Maraldi T, Pisciotta A, La Sala GB, Ferrari A, Bruzzesi G, et al. Fibroin scaffold repairs critical-size bone defects in vivo supported by human amniotic fluid and dental pulp stem cells. Tissue Eng Part A. 2012 May;18(9-10):1006-13. investigated new bone formation in critical-size calvarial bone defects, while Yamada et al.,¹⁶16. Yamada Y, Ito K, Nakamura S, Ueda M, Nagasaka T. Promising cell-based therapy for bone regeneration using stem cells from deciduous teeth, dental pulp and bone marrow. Cell Transplant. 2011 Jan;20(7)1003-13. and Zheng et al.,¹⁷17. Zheng Y, Liu Y, Zhang CM, Zhang HY, Li WH, Shi S, et al. Stem cells from deciduous tooth repair mandibular defect in swine. J Dent Res. 2009 Mar;88(3):249-54. studied critical-size mandibular bone defect repair. Ito et al.,¹⁸18. Ito K, Yamada Y, Nakamura S, Ueda M. Osteogenic potential of effective bone engineering using dental pulp stem cells, bone marrow stem cells, and periosteal cells for osseointegration of dental implants. Int J Oral Maxillofac Implants. 2011 Sep-Oct; 26(5):947-54. studied the osseointegration of dental implants and Zhang et al.,¹⁹19. Zhang W, Walboomers F, Van Osch GJVM, Dolder JVD, Jansen AJA. Hard tissue formation in a porous HA/TCP ceramic scaffold loaded with stromal cells derived from dental pulp and bone marrow. Tissue Eng Part A. 2008 Feb;14(2):285-94. investigated bone formation by subcutaneously implanted DPSCs. In these studies, the association of the stem cells with scaffolds, growth factors or recombinant proteins was common. Hydroxyapatite/tricalcium phosphate (HA/TCP),¹³13. Seo BM, Sonoyama W, Yamaza T, Coppe C, Kikuiri T, Akiyama K, et al. SHED repair critical-size calvarial defects in mice. Oral Dis. 2008 Jul;14(5):428-34.^,1818. Ito K, Yamada Y, Nakamura S, Ueda M. Osteogenic potential of effective bone engineering using dental pulp stem cells, bone marrow stem cells, and periosteal cells for osseointegration of dental implants. Int J Oral Maxillofac Implants. 2011 Sep-Oct; 26(5):947-54. recombinant human nanohydroxyapatite/collagen/poly (L-lactide) (nHAC/PLA),¹⁰10. Liu HC, E LL, Wang DS, Su F, Wu X, Shi ZP, et al. Reconstruction of alveolar bone defects using bone morphogenetic protein 2 mediated rabbit dental pulp stem cells seeded on nano-hydroxyapatite/collagen/ poly(l-lactide). Tissue Eng Part A. 2011 Oct;17(19-20):2417-33. platelet-rich plasma (PRP), fibrin,¹⁷17. Zheng Y, Liu Y, Zhang CM, Zhang HY, Li WH, Shi S, et al. Stem cells from deciduous tooth repair mandibular defect in swine. J Dent Res. 2009 Mar;88(3):249-54. bone morphogenetic protein 2 (rhBMP-2)¹⁰10. Liu HC, E LL, Wang DS, Su F, Wu X, Shi ZP, et al. Reconstruction of alveolar bone defects using bone morphogenetic protein 2 mediated rabbit dental pulp stem cells seeded on nano-hydroxyapatite/collagen/ poly(l-lactide). Tissue Eng Part A. 2011 Oct;17(19-20):2417-33. and collagen membranes¹⁶16. Yamada Y, Ito K, Nakamura S, Ueda M, Nagasaka T. Promising cell-based therapy for bone regeneration using stem cells from deciduous teeth, dental pulp and bone marrow. Cell Transplant. 2011 Jan;20(7)1003-13. were used. Three groups of researchers used cells from deciduous teeth in their experiments, 3 groups used cells from permanent teeth and the remaining 2 groups compared both types of cells. Notably, both sources of cells (i.e., the pulp of deciduous and permanent teeth) presented bone-formation capacity¹³13. Seo BM, Sonoyama W, Yamaza T, Coppe C, Kikuiri T, Akiyama K, et al. SHED repair critical-size calvarial defects in mice. Oral Dis. 2008 Jul;14(5):428-34.^,1414. de Mendonça Costa A, Bueno DF, Martins MT, Kerkis I, Kerkis A, Fanganiello RD, et al. Reconstruction of large cranial defects in nonimmunosuppressed experimental design with human dental pulp stem cells. J Craniofac Surg. 2008 Jan;19(1):204-10.^,1515. Riccio M, Maraldi T, Pisciotta A, La Sala GB, Ferrari A, Bruzzesi G, et al. Fibroin scaffold repairs critical-size bone defects in vivo supported by human amniotic fluid and dental pulp stem cells. Tissue Eng Part A. 2012 May;18(9-10):1006-13.^,1616. Yamada Y, Ito K, Nakamura S, Ueda M, Nagasaka T. Promising cell-based therapy for bone regeneration using stem cells from deciduous teeth, dental pulp and bone marrow. Cell Transplant. 2011 Jan;20(7)1003-13.^,1818. Ito K, Yamada Y, Nakamura S, Ueda M. Osteogenic potential of effective bone engineering using dental pulp stem cells, bone marrow stem cells, and periosteal cells for osseointegration of dental implants. Int J Oral Maxillofac Implants. 2011 Sep-Oct; 26(5):947-54. and, in some cases, their osteogenic ability was superior to that of bone marrow-derived SCs.¹⁴14. de Mendonça Costa A, Bueno DF, Martins MT, Kerkis I, Kerkis A, Fanganiello RD, et al. Reconstruction of large cranial defects in nonimmunosuppressed experimental design with human dental pulp stem cells. J Craniofac Surg. 2008 Jan;19(1):204-10.^,1515. Riccio M, Maraldi T, Pisciotta A, La Sala GB, Ferrari A, Bruzzesi G, et al. Fibroin scaffold repairs critical-size bone defects in vivo supported by human amniotic fluid and dental pulp stem cells. Tissue Eng Part A. 2012 May;18(9-10):1006-13.

In addition, DPSCs were shown to promote the repair of facial nerve gaps in rats¹¹11. Sasaki R, Aoki S, Yamato M, Uchiyama H, Wada K, Okano T, et al. Tubulation with dental pulp cells promotes facial nerve regeneration in rats. Tissue Eng Part A. 2008 Jul;14(7):1141-7. and induce neuroplasticity within the recipient nervous system in chicks.²⁰20. Arthur A, Shi S, Zannettino ACW, Fujii N, Gronthos S, Koblar SA. Implanted adult human dental pulp stem cells induce endogenous axon guidance. Stem Cells. 2009 Sep;27(9):2229-37. In another nerve repair study, both SHED and DPSCs promoted the recovery of hind limb locomotor function in rats.²¹21. Sakai K, Yamamoto A, Matsubara K, Nakamura S, Naruse M, Yamagata M, et al. Human dental pulp-derived stem cells promote locomotor recovery after complete transection of the rat spinal cord by multiple neuro-regenerative mechanisms. J Clin Invest. 2012 Jan;122(1):80-90. DPSCs also exhibited therapeutic potential for the repair of a myocardial infarction (MI) in a MI mouse model. Although the cells were able to engraft into the infarcted heart, they did not differentiate into cardiac, endothelial or smooth muscle cells. Nevertheless, angiogenesis was increased compared to that observed in animals that received a control treatment.²²22. Gandia C, Armiñan A, García-Verdugo JM, Lledó E, Ruiz A, Miñana D, et al. Human dental pulp stem cells improve left ventricular function, induce angiogenesis, and reduce infarct size in rats with acute myocardial infarction. Stem Cells. 2008 Mar;26(3):638-45. Angiogenesis was found to be improved when endothelial progenitor cells from swine deciduous and permanent teeth were used to treat ischemia in a hind limb ischemia mouse model, as the cells helped to increase the blood supply and contributed to the formation of a new capillary network.²³23. Iohara K, Zheng L, Wake H, Ito M, Nabekura J, Wakita H, et al. A novel stem cell source for vasculogenesis in ischemia: subfraction of side population cells from dental pulp. Stem Cells. 2008 Sep;26(9):2408-18. Lastly, SHED were reported²⁴24. Nishino Y, Ebisawa K, Yamada Y, Okabe K, Kamei Y, Ueda M. Human deciduous teeth dental pulp cells with basic fibroblast growth factor enhance wound healing of skin defect. J Craniofac Surg. 2011. Mar;22(2):438-42. to help accelerate wound healing when associated with fibroblast growth factor (b-FGF).

Discussion

Regenerative medicine is defined as the use of a combination of cells, engineering materials and suitable biochemical factors to improve or replace biological function.²⁵25. Murray PE, Garcia-Godoy F, Hargreaves KM. Regenerative endodontics: a review of current status and a call for action. J Endod. 2007 Apr;33(4):377-90. Thus, regenerative medicine treatments have the potential to restore damaged tissues and organs. Importantly, the regenerative potential of DPSCs and SHED has been studied in a variety of non-dental tissues. In vivo studies have shown that these cells can form bone, blood vessels, nerves, myocardium and skin. However, the majority of the studies described in the literature have investigated bone formation.¹⁰10. Liu HC, E LL, Wang DS, Su F, Wu X, Shi ZP, et al. Reconstruction of alveolar bone defects using bone morphogenetic protein 2 mediated rabbit dental pulp stem cells seeded on nano-hydroxyapatite/collagen/ poly(l-lactide). Tissue Eng Part A. 2011 Oct;17(19-20):2417-33.^,1313. Seo BM, Sonoyama W, Yamaza T, Coppe C, Kikuiri T, Akiyama K, et al. SHED repair critical-size calvarial defects in mice. Oral Dis. 2008 Jul;14(5):428-34.^,1414. de Mendonça Costa A, Bueno DF, Martins MT, Kerkis I, Kerkis A, Fanganiello RD, et al. Reconstruction of large cranial defects in nonimmunosuppressed experimental design with human dental pulp stem cells. J Craniofac Surg. 2008 Jan;19(1):204-10.^,1515. Riccio M, Maraldi T, Pisciotta A, La Sala GB, Ferrari A, Bruzzesi G, et al. Fibroin scaffold repairs critical-size bone defects in vivo supported by human amniotic fluid and dental pulp stem cells. Tissue Eng Part A. 2012 May;18(9-10):1006-13.^,1616. Yamada Y, Ito K, Nakamura S, Ueda M, Nagasaka T. Promising cell-based therapy for bone regeneration using stem cells from deciduous teeth, dental pulp and bone marrow. Cell Transplant. 2011 Jan;20(7)1003-13.^,1717. Zheng Y, Liu Y, Zhang CM, Zhang HY, Li WH, Shi S, et al. Stem cells from deciduous tooth repair mandibular defect in swine. J Dent Res. 2009 Mar;88(3):249-54.^,1818. Ito K, Yamada Y, Nakamura S, Ueda M. Osteogenic potential of effective bone engineering using dental pulp stem cells, bone marrow stem cells, and periosteal cells for osseointegration of dental implants. Int J Oral Maxillofac Implants. 2011 Sep-Oct; 26(5):947-54.^,1919. Zhang W, Walboomers F, Van Osch GJVM, Dolder JVD, Jansen AJA. Hard tissue formation in a porous HA/TCP ceramic scaffold loaded with stromal cells derived from dental pulp and bone marrow. Tissue Eng Part A. 2008 Feb;14(2):285-94.

Our systematic review aimed to analyse in vivo studies that were performed in humans and animals. The keyword [animals] was not an inclusion criteria, nor was [human] an exclusion one. Nevertheless, we did not find any in vivo studies in humans. Dental stem cells were first isolated from the dental pulp⁶6. Gronthos S, Mankani M, Brahim J, Robey PG, Shi S. Postnatal human dental pulp stem cells (DPSCs) in vitro and in vivo. Proc Natl Acad Sci U S A. 2000 Dec;97(25):13625-30. of permanent teeth and subsequently from the dental pulp of deciduous teeth.⁸8. Miura M, Gronthos S, Zhao M, Lu B, Fisher LW, Robey PG, et al. SHED: stem cells from human exfoliated deciduous teeth. Proc Natl Acad Sci U S A. 2003 May;100(10):5807-12. Because of the relative novelty of this research area, there is most likely insufficient research to enable the approval of human testing or clinical protocols.

Apparently, SHED, which can differentiate into neural cells, adipocytes, osteoblasts and odontoblasts⁸8. Miura M, Gronthos S, Zhao M, Lu B, Fisher LW, Robey PG, et al. SHED: stem cells from human exfoliated deciduous teeth. Proc Natl Acad Sci U S A. 2003 May;100(10):5807-12. have higher plasticity than DPSCs. In vivo, SHED are capable of spontaneously generating robust amounts of bone,⁸8. Miura M, Gronthos S, Zhao M, Lu B, Fisher LW, Robey PG, et al. SHED: stem cells from human exfoliated deciduous teeth. Proc Natl Acad Sci U S A. 2003 May;100(10):5807-12.^,2020. Arthur A, Shi S, Zannettino ACW, Fujii N, Gronthos S, Koblar SA. Implanted adult human dental pulp stem cells induce endogenous axon guidance. Stem Cells. 2009 Sep;27(9):2229-37. while DPSCs can only form bone and dentine.⁶6. Gronthos S, Mankani M, Brahim J, Robey PG, Shi S. Postnatal human dental pulp stem cells (DPSCs) in vitro and in vivo. Proc Natl Acad Sci U S A. 2000 Dec;97(25):13625-30. This difference suggests that DPSCs are distinct from SHED with respect to odontogenic differentiation and osteogenic induction. Furthermore, both DPSCs and SHED have a higher proliferative capacity than other well-known MSCs, such as bone marrow stem cells.⁶6. Gronthos S, Mankani M, Brahim J, Robey PG, Shi S. Postnatal human dental pulp stem cells (DPSCs) in vitro and in vivo. Proc Natl Acad Sci U S A. 2000 Dec;97(25):13625-30.^,77. Seo BM, Miura M, Gronthos S, Bartold PM, Batouli S, Brahim J, et al. Investigation of multipotent postnatal stem cells from human periodontal ligament. Lancet. 2004 Jul;364(9429):149-55. SHED, in particular, are considered an outstanding source of stem cells. Considering that humans typically exfoliate 20 deciduous teeth throughout life and quite often have impacted and unerupted third molars extracted for clinical or orthodontic purposes,²⁶26. Kaminishi RM, Lam PS, Kaminishi KS, Marshall MW, Hochwald DA A 10-year comparative study of the incidence of third molar removal in the aging population. J Oral Maxillofac Surg. 2006 Feb;64(2):173-4.^,2727. Dodson TB, Susarla SM. Impacted wisdom teeth. Clin Evid [Internet]. 2010 Apr 8 [cited 2014 07 22];2010:1302. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2907590/.
http://www.ncbi.nlm.nih.gov/pmc/articles... teeth could represent an important, easily accessible and non-invasive (particularly for the deciduous teeth) source of stem cells.

As previously mentioned, most of the selected manuscripts in this review studied the use of DPSCs and SHED for bone tissue repair or regeneration.¹⁰10. Liu HC, E LL, Wang DS, Su F, Wu X, Shi ZP, et al. Reconstruction of alveolar bone defects using bone morphogenetic protein 2 mediated rabbit dental pulp stem cells seeded on nano-hydroxyapatite/collagen/ poly(l-lactide). Tissue Eng Part A. 2011 Oct;17(19-20):2417-33.^,1313. Seo BM, Sonoyama W, Yamaza T, Coppe C, Kikuiri T, Akiyama K, et al. SHED repair critical-size calvarial defects in mice. Oral Dis. 2008 Jul;14(5):428-34.^,1414. de Mendonça Costa A, Bueno DF, Martins MT, Kerkis I, Kerkis A, Fanganiello RD, et al. Reconstruction of large cranial defects in nonimmunosuppressed experimental design with human dental pulp stem cells. J Craniofac Surg. 2008 Jan;19(1):204-10.^,1515. Riccio M, Maraldi T, Pisciotta A, La Sala GB, Ferrari A, Bruzzesi G, et al. Fibroin scaffold repairs critical-size bone defects in vivo supported by human amniotic fluid and dental pulp stem cells. Tissue Eng Part A. 2012 May;18(9-10):1006-13.^,1616. Yamada Y, Ito K, Nakamura S, Ueda M, Nagasaka T. Promising cell-based therapy for bone regeneration using stem cells from deciduous teeth, dental pulp and bone marrow. Cell Transplant. 2011 Jan;20(7)1003-13.^,1717. Zheng Y, Liu Y, Zhang CM, Zhang HY, Li WH, Shi S, et al. Stem cells from deciduous tooth repair mandibular defect in swine. J Dent Res. 2009 Mar;88(3):249-54.^,1818. Ito K, Yamada Y, Nakamura S, Ueda M. Osteogenic potential of effective bone engineering using dental pulp stem cells, bone marrow stem cells, and periosteal cells for osseointegration of dental implants. Int J Oral Maxillofac Implants. 2011 Sep-Oct; 26(5):947-54.^,1919. Zhang W, Walboomers F, Van Osch GJVM, Dolder JVD, Jansen AJA. Hard tissue formation in a porous HA/TCP ceramic scaffold loaded with stromal cells derived from dental pulp and bone marrow. Tissue Eng Part A. 2008 Feb;14(2):285-94. The use of SHED or DPSCs may avoid the inconvenience and morbidity associated with the removal of autogenous grafts from other sites.²⁸28. Dinopoulos H, Dimitriou R, Giannoudis PV. Bone graft substitutes: what are the options? Surgeon. 2012 Aug;10(4):230-9. Moreover, in contrast to the use of autologous bone grafts, DPSCs or SHED can be expanded in vitro prior to their use in vivo to generate an adequate number of cells for the tissue being repaired. This approach could prevent or decrease problems associated with autogenous grafting techniques, such as the limited amount of tissue that can be removed from the donor site and the risk of infection.

In general, SHED and DPSC-based bone repair/regeneration strategies were found, at least in animals, to significantly increase bone formation compared to the control groups studied.¹³13. Seo BM, Sonoyama W, Yamaza T, Coppe C, Kikuiri T, Akiyama K, et al. SHED repair critical-size calvarial defects in mice. Oral Dis. 2008 Jul;14(5):428-34.^,1414. de Mendonça Costa A, Bueno DF, Martins MT, Kerkis I, Kerkis A, Fanganiello RD, et al. Reconstruction of large cranial defects in nonimmunosuppressed experimental design with human dental pulp stem cells. J Craniofac Surg. 2008 Jan;19(1):204-10.^,1515. Riccio M, Maraldi T, Pisciotta A, La Sala GB, Ferrari A, Bruzzesi G, et al. Fibroin scaffold repairs critical-size bone defects in vivo supported by human amniotic fluid and dental pulp stem cells. Tissue Eng Part A. 2012 May;18(9-10):1006-13.^,1616. Yamada Y, Ito K, Nakamura S, Ueda M, Nagasaka T. Promising cell-based therapy for bone regeneration using stem cells from deciduous teeth, dental pulp and bone marrow. Cell Transplant. 2011 Jan;20(7)1003-13.^,1717. Zheng Y, Liu Y, Zhang CM, Zhang HY, Li WH, Shi S, et al. Stem cells from deciduous tooth repair mandibular defect in swine. J Dent Res. 2009 Mar;88(3):249-54.^,1919. Zhang W, Walboomers F, Van Osch GJVM, Dolder JVD, Jansen AJA. Hard tissue formation in a porous HA/TCP ceramic scaffold loaded with stromal cells derived from dental pulp and bone marrow. Tissue Eng Part A. 2008 Feb;14(2):285-94. However, Liu et al.,¹⁰10. Liu HC, E LL, Wang DS, Su F, Wu X, Shi ZP, et al. Reconstruction of alveolar bone defects using bone morphogenetic protein 2 mediated rabbit dental pulp stem cells seeded on nano-hydroxyapatite/collagen/ poly(l-lactide). Tissue Eng Part A. 2011 Oct;17(19-20):2417-33. found no significant differences in bone formation when DPSCs associated with nHAC/PLA and rhBMP-2 were used compared to autologous bone. In this study, the nHAC/PLA + DPSCs + rhBMP-2 composite did prove to be suitable for maxillary bone tissue repair, but DPSCs were apparently not required for successful regeneration. Similarly, Zhang et al.,¹⁹19. Zhang W, Walboomers F, Van Osch GJVM, Dolder JVD, Jansen AJA. Hard tissue formation in a porous HA/TCP ceramic scaffold loaded with stromal cells derived from dental pulp and bone marrow. Tissue Eng Part A. 2008 Feb;14(2):285-94. did not observe bone formation when rat or human DPSCs associated with HA/TCP were transplanted subcutaneously in nude mice. However, it should be noted that, according to these authors, a high number of cell passages was needed to obtain enough viable cells for the experiments. Furthermore, in contrast to their in vivo experiments, all four types of cells used by Zhang et al., ¹⁹19. Zhang W, Walboomers F, Van Osch GJVM, Dolder JVD, Jansen AJA. Hard tissue formation in a porous HA/TCP ceramic scaffold loaded with stromal cells derived from dental pulp and bone marrow. Tissue Eng Part A. 2008 Feb;14(2):285-94. (i.e., rat bone marrow, rat DPSCs, human bone marrow and human DPSCs) were able to form mineralised tissues in vitro. DPSCs have also attracted interest as an alternative to improve the outcome of dental implants,¹⁸18. Ito K, Yamada Y, Nakamura S, Ueda M. Osteogenic potential of effective bone engineering using dental pulp stem cells, bone marrow stem cells, and periosteal cells for osseointegration of dental implants. Int J Oral Maxillofac Implants. 2011 Sep-Oct; 26(5):947-54. and this cell population has been shown to possess higher osteogenic potential than bone marrow stem cells, which are still considered the gold standard for bone tissue formation.

The analysis of the neural repair capacity of DPSCs and SHED was ambiguous, in our opinion, due to the differences in the methodology used by the different authors.¹¹11. Sasaki R, Aoki S, Yamato M, Uchiyama H, Wada K, Okano T, et al. Tubulation with dental pulp cells promotes facial nerve regeneration in rats. Tissue Eng Part A. 2008 Jul;14(7):1141-7.^,2020. Arthur A, Shi S, Zannettino ACW, Fujii N, Gronthos S, Koblar SA. Implanted adult human dental pulp stem cells induce endogenous axon guidance. Stem Cells. 2009 Sep;27(9):2229-37.^,2121. Sakai K, Yamamoto A, Matsubara K, Nakamura S, Naruse M, Yamagata M, et al. Human dental pulp-derived stem cells promote locomotor recovery after complete transection of the rat spinal cord by multiple neuro-regenerative mechanisms. J Clin Invest. 2012 Jan;122(1):80-90. DPSCs are apparently able to stimulate the formation of blood vessels and myelinating tissue in the peripheral nerves of adult rats. However, the authors did not perform any functional assays to prove a gain of function.¹¹11. Sasaki R, Aoki S, Yamato M, Uchiyama H, Wada K, Okano T, et al. Tubulation with dental pulp cells promotes facial nerve regeneration in rats. Tissue Eng Part A. 2008 Jul;14(7):1141-7. To investigate this limitation, a more recent study showed that engrafted SHED and DPSCs were able to differentiate toward mature oligodendrocytes and promote functional recovery of the peripheral nervous system in hind limb defects in a rat model. The rats that received SHED were able to walk without weight support, while those that received bone marrow stem cells or fibroblasts exhibited only subtle joint movements.²¹21. Sakai K, Yamamoto A, Matsubara K, Nakamura S, Naruse M, Yamagata M, et al. Human dental pulp-derived stem cells promote locomotor recovery after complete transection of the rat spinal cord by multiple neuro-regenerative mechanisms. J Clin Invest. 2012 Jan;122(1):80-90.

DPSCs have also been reported to have potential for use in cell-based therapies for systemic diseases, such as cardiac disease.²²22. Gandia C, Armiñan A, García-Verdugo JM, Lledó E, Ruiz A, Miñana D, et al. Human dental pulp stem cells improve left ventricular function, induce angiogenesis, and reduce infarct size in rats with acute myocardial infarction. Stem Cells. 2008 Mar;26(3):638-45.^,2323. Iohara K, Zheng L, Wake H, Ito M, Nabekura J, Wakita H, et al. A novel stem cell source for vasculogenesis in ischemia: subfraction of side population cells from dental pulp. Stem Cells. 2008 Sep;26(9):2408-18. When DPSCs were injected into mice with myocardial infarctions, they had a significant effect on recovery compared to the control group. Notably, none of the injected cells differentiated into cardiac, endothelial or smooth muscle cells. Rather, according to the authors, the fact that the treated mice had a significantly improved recovery suggests that DPSCs can contribute to cardiac repair by some other mechanism.²²22. Gandia C, Armiñan A, García-Verdugo JM, Lledó E, Ruiz A, Miñana D, et al. Human dental pulp stem cells improve left ventricular function, induce angiogenesis, and reduce infarct size in rats with acute myocardial infarction. Stem Cells. 2008 Mar;26(3):638-45. This result agrees with previous reports that support the ability of MSCs to induce cardiac repair, despite extremely rare fusion/differentiation events.²⁹29. Miyahara Y, Nagaya N, Kataoka M, Yanagawa B, Tanaka K, Hao H, et al. Monolayered mesenchymal stem cells repair scarred myocardium after myocardial infarction. Nat Med. 2006 Apr;12(4):459-65. The benefits resulting from DPSC transplantation were possibly due to the secretion of paracrine factors.²²22. Gandia C, Armiñan A, García-Verdugo JM, Lledó E, Ruiz A, Miñana D, et al. Human dental pulp stem cells improve left ventricular function, induce angiogenesis, and reduce infarct size in rats with acute myocardial infarction. Stem Cells. 2008 Mar;26(3):638-45.

More recently, it has been shown that it is possible to isolate a sub-fraction of endothelial cells from dental pulp tissue based on the expression of cell surface markers.²³23. Iohara K, Zheng L, Wake H, Ito M, Nabekura J, Wakita H, et al. A novel stem cell source for vasculogenesis in ischemia: subfraction of side population cells from dental pulp. Stem Cells. 2008 Sep;26(9):2408-18. These cells have been shown to have a high proliferative and migratory capacity as well as multilineage differentiation potential, including angiogenic, chondrogenic, adipogenic, neurogenic and odontogenic-potential. When these cells were applied in a mouse model to reverse hind limb ischemia, the results demonstrated successful engraftment and an increase in blood supply due to the formation of new capillaries. Hence, the use of endothelial progenitor cells derived from dental pulp might represent an alternative approach for the transplantation of autologous endothelial progenitor cells in which cells are obtained by an invasive and potentially painful biopsy procedure.³⁰30. Crosby JR, Kaminski WE, Schatteman G, Martin PJ, Raines EW, Seifert RA, et al. Endothelial cells of hematopoietic origin make a significant contribution to adult blood vessel formation. Circ Res. 2000 Oct;87(9):728-30.

Lastly, Nishino Y et al., ²⁴24. Nishino Y, Ebisawa K, Yamada Y, Okabe K, Kamei Y, Ueda M. Human deciduous teeth dental pulp cells with basic fibroblast growth factor enhance wound healing of skin defect. J Craniofac Surg. 2011. Mar;22(2):438-42. showed that the use of SHED, in association with basic fibroblasowth factor (b-FGF), in a nude mouse full-thickness skin defect model significantly accelerated wound healing compared with other groups. This work highlights SHED as a promising stem cell population for future wound healing therapies as well.

The lack of a standardised type and pattern of cell types and scaffolds may influence cellular responses and alter their properties for clinical bioengineering. Indeed, the different types of cells and the different structures and porosities of scaffolds and/or delivery systems are some of the issues that complicated comparisons between the studies included in our review. In addition, without standardised protocols that include cell culture conditions, sources, numbers, passages and their adhesion properties on tissue surfaces, it is not possible to guarantee the appropriate clinical management of these techniques.

Conclusion

In summary, most of the retrieved in vivo studies using SHED or DPSCs focused on bone tissue repair/regeneration, and the results of these studies indicated that the use of DPSCs and SHED seems to be effective for these applications. However, very few studies were found regarding the potential of these cells to promote functional recovery of neuronal tissue, blood vessels, muscle, cartilage or other tissues. As a result, the potential of DPSCs and SHED for the repair of other non-dental tissues remains unclear.

References

Publication Dates

History