DENTAL DYSPLASIA IN RATS AND MICE

Malformations of the maxillary incisors, diagnosed as dental dysplasia , were observed as a spontaneous background lesion in 3% (females) to 9% (males) of CD-1(R) mice and 14.5% (females) to 10.5% (males) of CD( R) (Sprague-Dawley) rats in a chronic inhalation study. Lesions were r eported grossly as overgrown, maloccluded, or malformed incisors. Micr oscopic findings included tooth pulp and periodontal abscesses, fractu red and necrotic teeth, periodontal cysts, malformations of the inciso r roots, and expansile masses, including odontomas, of the incisor roo ts. Development of lesions followed a pattern of tooth pulp necrosis a nd/or traumatic disruption of the epithelial root sheath at the base o f the tooth. Feeding a powdered ration, which reduced the normal weari ng of the incisors, and repeated clipping of overgrown incisors were b elieved to contribute to the incidence of disease.