[The ultrastructure of ameloblastoma]

The ultrastructural features of five mandibular ameloblastomas were investigated. The morphological comparison between ameloblastoma and enamel organ was made, and the cause of the appearance of granular cells in the tumor was discussed. The peripheral columnar cells were morphologically similar to the inner enamel epithelium of the enamel organ. The central cells were similar to the stellate reticulum cells. There were not stratum intermedium-like cells in the tumors. This implied that the tumors were developed earlier than the enamel organ of bell stage. The squamous cells were sometimes found in the central part of the tumor cell masses. These cells were flat with a few organelles in the plasma, but had a lot of tonofilaments. This suggested that these cells were not active. Upon the ultrastructure, however, it could not be determined whether the appearance of these cells reflected a low differentiation or a degeneracy. Granular cells contained a lot of lysosomes, but no autophage was noticed. We thought that the appearance of these cells was due to accumulation of some unusual substances in the cells, the substances might be related with the glycosaminoglycan.