The localization of epithelial root sheath cells during cementum formation in rat molars

The purpose of this study was to investigate the distribution of epithelial cells and the fate of the basement membrane along the root surface of rat molars during cementogenesis, and to test the hypothesis that the Hertwig's epithelial root sheath (HERS) cells remain on the root surface if mineralization is inhibited. To demonstrate the HERS cells and basement membrane, immunohistochemistry with antibodies against keratin and laminin were used. The dentin matrix mineralization was inhibited by a single injection of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP). A modified Gomori staining method was used to monitor the inhibition of mineral formation in dentin and cementum. Paraffin sections were stained with haematoxylin-eosin, and freeze-dried sections were used for Gomori and immunohistochemical stainings. We found that the formation of acellular cementum was suppressed above the dentin with inhibited mineralization. Instead, a hyperplastic matrix, different from acellular cementum, covered the dentin. This hyperplastic cementum had keratin- and laminin-positive cells incorporated; such cells were never incorporated in normal acellular cementum. The later formation of cellular cementum correlated, in controls, with the disappearance of HERS cells from the root surface. Treatment with HEBP resulted in a persistent presence of epithelial cells, interpreted as an inhibition of their disappearance. In conclusion, there is evidence that the cells of HERS are involved in the development of both acellular and cellular cementum. The developmental processes of these tissues appear in some way to be influenced by or associated with the initial mineralization of the dentin.