Sources of putative oral and craniofacial stem cells. DFPCs, dental follicle precursor cells; DPSCs, dental pulp stem cells; hABMSCs, human alveolar bone-derived mesenchymal stem cells; HOMSCs, human oral mucosa stem cell; PDLSCs, periodontal ligament stem cells; SCAP, stem cells of the apical papilla; SHED, stem cells of human exfoliated deciduous teeth.