Root formation.

This paper provides an overview of recent studies that have enhanced our understanding of the biological mechanisms that operate during root development. For the most part, these studies have been performed on rodents. As significant species differences have been shown to exist, this data cannot necessarily be extrapolated to the human model. The events associated with root odontoblast differentiation are reviewed in comparison to similar events in coronal odontoblast differentiation. Morphological as well as phenotypic differences are outlined and the inductive role of the epithelial root sheath is discussed. Both acellular and cellular cementum formation are reviewed highlighting morphological and phenotypic differences. The potential influence of the epithelial root sheath in the formation of both tissues is compared and contrasted. Finally, a discussion of the fate of the epithelial root sheath is presented with emphasis placed upon the possible roles of apoptosis and epithelium-mesenchymal transition.