FIGURE 1.

Scheme of murine molar and incisor development. Placode stage: At E12.5, interactions between the oral epithelium and the underlying mesenchyme cause the formation of the dental placode. Bud stage: At E13.5 the dental epithelium proliferates into the mesenchyme and buds. Cap stage: At E14.5 the primary enamel knot forms at the tip of the bud and orchestrates the proliferation of the surrounding epithelium. In the molar, the dental epithelium grows downward, while in the incisor it grows in the longitudinal axis, the expansion is led by cervical loops at the base of the tooth. The enamel organ and is composed of: stellate reticulum, stratum intermedium and enamel epithelium (inner and outer). Molar bell and late bell stages: In molars, at bell stage, secondary EKs mark the sites where the cusps will form. Mineralization starts from the crown and, when it reaches the cervical loops, the tooth starts to erupt and root formation starts. By this time, all enamel-producing cells are lost. Incisor bell and late bell stages: During bell stage, the incisor becomes asymmetrically patterned in the labial-lingual axis, the larger labial cervical loop contains stem cells that continuously generate enamel-producing ameloblasts. Enamel is deposited only on the labial side of the incisor while the lingual side is covered by dentin and cementum. EK, Enamel knot; OEE, Outer enamel epithelium; IEE, Inner enamel epithelium; SR, Stellate reticulum; liCL, lingual cervical loop; laCL, labial cervical loop.