Granular cell ameloblastic fibroma, ultrastructure and histogenesis.

A case of peripheral granular cell ameloblastic fibroma arising in the right upper premolar gingiva in a 34-year-old Japanese woman is reported. Ultrastructural examination revealed a clear separation of granular cells and epithelial component, and indicated granular cells were derived from mesenchymal cells, probably fibroblasts. Direct communication between the overlying gingival epithelium and the epithelial component of the tumor was found. It is postulated that residual ectomesenchymal influence may be responsible for proliferation of both epithelial and mesenchymal components which subsequently are transformed into granular cells.