The secretion of amelogenins is associated with the induction of enamel and dentinoid in an ameloblastic fibro-odontoma

Ameloblastic fibro-odontoma is the unique entity of epithelial-ectomesenchymal odontogenic tumors, which is characterized by enamel formation in addition to dentine. We examined immunohistochemically a case of this tumor in which enamel having prism structures was developed in the absence of odontoblast differentiation but was in contact with mesenchymal matrices. Histological examination showed diverse morphological features of epithelial tumor cells, e.g., cuboidal cells comprising tooth bud-like projections, ameloblast- and stellate reticulum-like cells, and residual cells in forms of extended cords or islands of odontogenic epithelium. Immunostaining with anti-amelogenin sera proved that the intracellular production of amelogenins was initiated at the tooth bud-like stage. The secreted amelogenins were detected almost exclusively in the induced enamel and dentinoid areas, as well as in the core region of cementicle-like spheres deposited in the encapsulating stroma. The results obtained indicate that the odontogenic tumor epithelia and its products, i.e., amelogenins, participate in multifaceted aspects of dental hard tissue formation that takes place during oncogenesis.