N-Methyl-N-Nitrosourea-Induced Odontogenic Neoplasms in Rats

Abstract

tried to find an optimal pH for N-methyl-N-nitrosourea (NMU) to induce odontogenic neoplasms in rats that were 45 days old at the start of the experiment. Twenty-six Wistar female rats that weighed 75 to 90 gm each were separated into three groups. In group 1, ten rats received a single intragastric dose of 90 mg NMU per kilogram body weight (adjusted to pH 4). in group 2, ten rats received the same treatment, except that the pH was 7. In group 3, six rats were untreated controls. The rats were fed laboratory chow and water ad libitum. After ten months, fibrous neoplasms developed in the anterior part of the mandible of two rats from group 1. The neoplasms were oval and about 4 by 3 mm.Radiographs showed an expansile lesion, which seemed to be in continuity with the mandibular incisor (Fig 1). Regions of calcification were prominent throughout the tumor mass and there was evidence of partial destruction of alveolar bone and regions of tooth resorption. Histological examination showed an apparently keratinized complex odontoma, which was similar to those described in humans. The mass was partially in the periodontal membrane (Fig 2); the greatest extension of the tumor was into the oral vestibule (Fig 3). Neoplasms did not develop in any of the rats in groups 2 and 3. NMU adjusted to a pH of 4 seems to act on the odontogenic epithelium and the gingival epithelium. The gingival epithelium reacquires properties characteristic of the dental lamina, in view of the formation of new "dental laminas" capable of induction of dentinoid tissues and denticles. Gingival epithelium of the rat may be the origin of keratocysts, as well as of regions of ghost cells, masses of dentinoid tissue, and denticles. These results agree with those of Herrold (1968). FIG 2.-Denticles and dentinoid tissue located in periodontal ligament between root of tooth (left) and alveolar bone (right). FIG 1.-Odontogenic neoplasm in rat mandible.Additional information available on request to authors.

Dental Dysplasia in Rats and Mice

“…A few papers have described proliferative lesions (odontomas or ameloblastomas) of the incisors in rodents as rare spontaneous neoplasms (5,8,22,27) or as hamartomas in inbred (32) or genetically altered (14) rodents. Dental tumors can be induced by treatment with carcinogenic (3,7,9,10) or mitogenic (26) agents, by radiation (6), by dietary imbalances (23,28), and by viruses (12,15). The possibility that chronic dental disease in a significant number of animals may result in stress, unthriftiness, and a general shortening of survival times for animals in chronic toxicology/oncogenicity studies has rarely been considered or addressed.…”

Adenomatoid odontogenic tumorlike lesion in a male Wistar rat

“…Odontogenic tumors in rats mostly show a pattern consistent with developing complex odontomas, irrespective of whether spontaneously occurring (4,(6)(7)(8) or experimentally induced (9)(10)(11)(12)(13)(14)(15)(16), Some authors also mention ameloblastoma-like neoplasms (5,12,13,16), odontogenic carcinomas (18) or a kind of lesion bearing some resemblance to the WHO-type odontogenic fibroma as described by GARDNER (17,20), Our case shows some common characteristics with the one reported by LEWIS et al, (5) that also exhibited areas of spindle-shaped epithelium bordered by columnar cells and with hyalinized eosinophilic material juxtaepithelially. These authors classified the tumor as ameloblastoma.…”

“…Spontaneously occurring odontogenic tumors in rats are extremely rare (1), In large series of neoplastic lesions in rats they are not even mentioned (2,3) and, apart from the description of odontoma-like fonnation in a peculiar strain of rats (4), only single cases are reported (5)(6)(7)(8), In contrast, reports on chemically-induced odontogenic tumors in rats are numerous (9)(10)(11)(12)(13)(14)(15)(16)(17)(18),…”

Cemento‐fibrous dysplasia of the periodontal membrane (studies of the European hamster maxillary incisor)

“…As there is evidence that odontogenic tissue in rt)dents may be affected by chemicals, radiation or mechanical trauma (. [5][6][7][8][9][10][11][12]. the incisors of the European hamsters were examined in a comparative study to differentiate between induced and spontaneously occurring lesitins.…”