The role of enamel matrix proteins in the development of cementum and periodontal tissues.

The role of Hertwig's epithelial root sheath (HERS) and of the enamel-related proteins in the development of acellular cementum are reviewed. The inner layer of HERS is an apical extension of the ameloblastic layer in the crown. A number of studies now indicate that the cells of HERS have a secretory stage similar to the ameloblasts. In rats and mice the secretory product of the HERS cells does not seem to be amelogenin, which is the main protein of the enamel matrix. In humans, however, amelogenin has been demonstrated at the apical ends of the roots of developing teeth. The development and distribution of coronal cementum in various species are discussed. The amelogenins have been remarkably well conserved between species. Experiments in monkeys have shown that it is possible to induce formation of acellular cementum by application of porcine enamel matrix on a denuded root surface, which thereby promotes periodontal regeneration. These results further support the idea that enamel-related proteins are involved in cementum formation.