Fracturing of the Molar Teeth in Caries-susceptible and Caries-resistant Albino Rats (Rattus norvegicus

THE researches of Hunt and Hoppert and their graduate students have sought to discover some of the factors that influence the development of caries in the lower molar teeth of albino rats. A caries-susceptible strain and a caries-resistant strain have been created since 1937 by means of phenotypie selection, progeny testing of breeding pairs, and brother by sister inbreeding.. The caries-producing diet of Hoppert, Webber, and Canniffl 2 (66 per cent coarsely ground hulled rice, 30 per cent whole milk powder, 3 per cent alfalfa leaf meal, and 1 per cent sodium chloride) has provided a constant diet throughout the experiments. About 8,000 rats have been observed to date. The proof is conclusive that hereditary differences are important in the causa-tion of caries in the lower molars of rats.3-8 Use of a tooth facilitates the various process,8 sex is not an important causative factor,9 and age appears to increase resistance more or less.10 The appearance of rat caries is delayed by grinding the rice component of the ration finer than in the standard ration generally used.10 The secretion of the parotid gland does not appear to be o