The adenomatoid odontogenic tumour: ultrastructure of tumour cells and non-calcified amorphous masses.

The ultrastructure of tumour cells and tumour droplets (TD, non-calcified amorphous masses) was studied in three cases of AOT using freshly prepared tissue. The fine structure of the epithelial tumour cells (cell type I-III) corresponded to that of earlier descriptions. The extracellular location of TD was clearly demonstrated. TD were of varying, sometimes bizarre, configuration. Some TD showed a homogeneous matrix; however, in addition most revealed electron-dense plaques. At high magnification, homogeneous types of TD showed only tubular elements; all others revealed granulo-tubular structures. The tubular elements were arranged concentrically. The nature of the TD is discussed and compared to former interpretations. From the present ultrastructural findings, it appears that the TD most probably represent some form of enamel matrix and as such may be considered a type of pre-enamel. Further studies are needed to elucidate the complex structure of the TD-material so characteristic of the AOT.