(a) Shown is the diagram of a developing molar during root morphogenesis. Enamel is produced by ameloblasts derived from inner enamel epithelium (IEE). Dentin is produced by odontoblasts derived from dental papilla mesenchyme. Cementum is produced by cementoblasts derived from dental follicle mesenchyme. HERS is formed by fusion of outer and inner enamel epithelia, and becomes a physical demarcation between dental papilla and follicle. HERS eventually breaks down and becomes epithelial rests of Malassez (ERM). (b) Shown is the diagram of a tamoxifen-inducible creERT2 system for lineage tracing. CreERT2 recombinase is expressed by a named promoter. It excises the stop codons in the Rosa26 locus only in the presence of tamoxifen. Once the stop codons are removed, the targeted cells permanently express tdTomato in a ubiquitously active CAG promoter-dependent manner. A low-dose tamoxifen (0.1 mg) is administered intraperitoneally, when murine molar root morphogenesis starts around postnatal day 3 (P3). Tamoxifen stays active upto 48 h after injection.