Figure 2.

Developmental plasticity of dental epithelium. Dental epithelium can be divided into 4 classes based on its potency and role during development and in the adult organism. The epithelium belonging to “class I” (primordial epithelium) is capable of giving rise to all dental epithelial subtypes. In adult organisms, it is maintained only in diphyodont or polyphyodont species. The differentiation capability of “class II” and “class III” is more restricted to the crown or root phenotype, respectively, and is preserved in species having hypselodont teeth, where it contributes to the continuous formation of crown and root analogues. The last, “class IV,” can be retained until adulthood also in noncontinuously growing teeth. Its role exhibits remarkable evolutionary plasticity since it contributes to the formation and maintenance of tooth-neighboring tissues like junctional epithelium or periodontal ligaments.