THE LOCALIZATION OF EPITHELIAL ROOT SHEATH-CELLS DURING CEMENTUM FORMATION IN RAT MOLARS

The purpose of this study was to investigate the distribution of epith elial cells and the fate of the basement membrane along the root surfa ce of rat molars during cementogenesis, and to test the hypothesis tha t 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 k eratin and laminin were used. The dentin matrix mineralization was inh ibited by a single injection of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP). A modified Gomori staining method was used to monitor the inh ibition 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 f ormation of acellular cementum was suppressed above the dentin with in hibited mineralization. Instead, a hyperplastic matrix, different from acellular cementum, covered the dentin. This hyperplastic cementum ha d keratin- and laminin-positive cells incorporated; such cells were ne ver incorporated in normal acellular cementum. The later formation of cellular cementum correlated, in controls, with the disappearance of H ERS cells from the root surface. Treatment with HEBP resulted in a per sistent presence of epithelial cells, interpreted as an inhibition of their disappearance. In conclusion, there is evidence that the cells o f 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.