Origins of cementum.

There are diverging opinions about the role of Hertwig's epithelial root sheath in the formation of cementum. In the present review this role is discussed. There is increasing evidence that Hertwig's epithelial root sheath is actively involved in the formation of both acellular and cellular cementum. The development of acellular cementum seems to be associated with secretion of enamel-related proteins by cells of the epithelial root sheath. Formation of the matrix for cellular cementum appears to be induced by exposure of the inner layer of the epithelial root sheath to the mesenchymal cells in the dental follicle. Experimental studies with 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) indicate that the formation of acellular cementum must be preceded by mineralization of the mantle dentin. If the mineralization is inhibited by means of HEBP, there is precocious separation of the two layers of the epithelial root sheath after which matrix for a cellular type of cementum is formed.