Odontogenic tumors in Fischer rats.

The formation of odontogenic tumors in rats is rare unless they are treated with known carcinogens. In this study, male Fischer rats were continuously fed aflatoxins M1, B1, or control diets, then killed at 1, 6, 10, 16, 17, 19 and 21 months. Of the 186 rats fed aflatoxin M1 at 3 concentrations, 12 developed odontogenic tumors; 7 of 63 rats fed an agar-based diet also developed odontogenic tumors in 17-21 months. The purpose of this study is to describe these tumors. All the tumors were located in the upper jaw associated with the incisor teeth. The tumors developed in the periodontal ligament area and were composed mainly of highly cellular fibrous connective tissue. The fibroblastic nuclei were clustered in poorly defined swirls in areas and were evenly scattered in a myxomatous stroma in other areas. Within this tissue were ovoid sometimes coalescing, calcified bodies resembling cementum. Occasional inclusions of solid epithelial cell nests were present. Scattered nests were composed of ovoid epithelial ghost cells. Acellular cementum-like material surrounded many of these nests. An inductive phenomenon was present around occasional epithelial nests. Rare structures composed of globular dentin with irregular tubules were also observed. These tumors caused distortion of the facial areas and disruption of incisor tooth development. No metastatic lesions were noted but other neoplastic lesions occurred in these animals.