Ultrastructural study of adenomatoid odontogenic tumor.

Two cases of adenomatoid odontogenic tumor were examined by light and electron microscopy. Morphologically the tumors could be divided into four layers. The ultrastructure of the tumor cells of each layer was revealed to be similar respectively to that of four layers seen in the enamel organ of a normal tooth germ. Duct-like structures and eosinophilic small areas were frequently present in compactly proliferating cell layers. Short columnar cells forming duct-like structures and eosinophilic small areas appeared similar ultrastructurally to ameloblasts during predentin formation. Therefore it seems reasonable to assume that this tumor originates from the enamel organ. The contents in the lumen of each eosinophilic small area varied, and seemed to be secreted into the stroma by circumscribing epithelial tumor cells. A fine filamentous layer was present in both of the duct-like structures and some of the eosinophilic small areas, and the former was different from the latter with respect to the alcian blue (pH 2.5) and toluidine blue (pH 4.4) staining reactions.