[Studies on caries of Ishibashi rat--I. Dental caries in Ishibashi rat].

Ishibashi rats (ISR), which have been demonstrated to be excellent experimental animals for congenital vertebral anomaly, are often observed to develop extensive dental caries even when maintained with the conventional diets instead of any caries-producing diets. In this study, dental caries produced in the ISR fed the conventional diets, commercial pellets, was examined and the location and severity of the lesions were compared with those of the albino rats fed the same diet. The results were as follows: 1. Although no caries was detected up to 100 days of age, 70-100% of the ISR of 101 days and over in age had carious teeth. In the albino rats, only 7-30% had carious teeth. 2. The severity of the carious lesions was much greater in the ISR than in the albino rats. 3. Only the mandibular molars were attacked by the dental caries, and the lesions occurred most frequently in the second fissure of the second mandibular molar both in the ISR and the albino rats. Extensive destruction of the crowns of the ISR second mandibular molars were observed in some specimens, but such destruction was not observed in the specimens of the albino rats. These results suggested that the ISR were susceptible to dental caries, and the development of the dental lesions of the ISR seemed to be rapid compared with that of the albino rats.