Structure of hamster palatal gingiva and intermolar mucosa after intraperitoneal dosing with N-methyl-N-nitrosourea:...

The palatal gingiva and intermolar mucosa from normal hamsters and from hamsters that had received N-methyl-N-nitrosourea (NMU) intraperitoneally were examined by scanning electron microscopy over a 22-week period. The normal gingiva and rostral two-thirds of the intermolar mucosa were covered by flat polygonal cells that had a regular honeycomb surface pattern of interconnecting micro-ridges, distinct cell boundaries and imprints of cells that had been desquamated. The caudal third of the intermolar mucosa in normal and NMU-treated hamsters was covered by soft-palate type mucosa whose smooth surfaced cells surrounded scattered fungiform-like papillae. In NMU-treated hamsters changes were more common in the rostral two-thirds of the intermolar mucosa than in the gingiva. At 10 weeks there were sessile and conical surface projections and saucer-shaped and conical epithelial-lined depressions. At 16 weeks these projections and depressions were larger and more numerous, and groups of conical projections formed papillomatous-like lesions. At 22 weeks the projections and depressions were further increased in number and size and there were distinct papillomas. At 10 and 16 weeks the entire epithelium showed cells, cell boundaries and cell imprints resembling those in the controls, except that there were defects or dilated intercellular spaces at the base of the conical depressions and some of the cells were thicker. Much of the 22-week epithelial had a similar structure, but in some areas that did not show the projections or depressions the cells varied in size and shape and were covered by elongated micro-ridges. Here the surface was irregular as were the cell boundaries. Examination of sections by light microscopy, both from these irregular areas and from areas that appeared normal by scanning electron microscopy, revealed that the deeper epithelial strata could be either normal, dysplastic or at times malignant. However, scanning electron microscopy failed to reveal dysplastic or malignant epithelium.