Age-dependent odontogenic lesions in rats after a single i.p. injection of N-nitroso-N-methylurea

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Abstract
The development of a variety of odontogenic lesions was elicited by a single i.p. injection of N-nitroso-N-methylurea [NMU, a carcinogen] at a dose of 150 mg/kg body weight. A total of 190 male Wistar/Furth rats were used in this study. The odontogenic lesions appeared macroscopically, mainly as supernumerary lower incisors, 88 .+-. 3.48 (SE) days after administration of the carcinogen. Tumors were classified as compound and complex odontomas, odontoameloblastomas and ameloblastomas. Of rats 6 wk old at the time of inoculation, 72% (31 of 43) developed microscopic alterations in the odontogenic organs of the incisors; only 4% (2 of 49) of rats injected at 8 wk of age developed similar alterations. The presence of an ontogenic mechanism susceptible to damage by chemical carcinogens is suggested.