 Orthopantomogram X-ray, with representative sources of various dental mesenchymal stem cells. (1) Dental pulp stem cells; (2) Stem cells from human exfoliated teeth; (3) Periodontal ligament stem cells; (4) Stem cells from apical papilla; (5) Dental follicle stem cells; and (6) Gingiva-derived mesenchymal stem cells.