查看文章

Mammalian teeth develop from oral ectoderm and neural crest derived mesenchyme. The first morphological sign is the primary dental lamina forming as a thickening of oral epithelium at the site of the future tooth row. Dental placodes form along the dental lamina and they share common morphological and molecular features with placodes of other ectodermal organs, such as hairs and many glands. The size and shape of the tooth crown result from epithelial morphogenesis during the bud, cap and bell stages. The tooth-specific hard tissues, enamel and dentin, are secreted by ameloblasts and odontoblasts respectively, which differentiate at the junction between the epithelium and mesenchyme. After the crown is complete root formation is initiated in most teeth and cementum, the third hard tissue of the tooth is formed by cementoblasts differentiating from dental follicle mesenchyme. The majority of the epithelial tissue is lost when the teeth erupt into the oral cavity and the roots have reached their final length. In continuously growing teeth such as the rodent incisor epithelial stem cells are maintained in the cervical loop, the epithelial stem cell niche. Typical for tooth morphogenesis and cell differentiation as well for the maintenance of the stem cell niche are reciprocal interactions between epithelial and mesenchymal compartments which are mediated by conserved signaling molecules. The instructive capacity for tooth formation shifts from oral epithelium to the underlying mesenchyme prior to the bud stage. However, the genetic basis of odontogenic competence is not known either for the dental epithelium or the mesenchyme although the …