Study on the caries incidence of tetracycline administered rats.

Abstract

This study was designed to examine the caries incidence of tetracycline administered rats. The experiment was divided into three series. In the first series, the rats were daily injected subcutaneously with tetracycline hydrochloride (50mg/kg body weight) from 10 days of age to weaning at 21 days of age. Rats injected with saline solution served as controls, and caries incidence was compared. In the second series, the caries inhibitory effects of fluorides (NaF in drinking water or topical application of APF) on tetracycline administered rats were assessed. In the third series, the acid resistance and the Vickers microhardness of enamel were measured in lower first molars. The results obtained were as follows: 1) Compared with the control group, dental caries was significantly increased in tetracycline administered rats. 2) Dental caries in tetracycline administered rats was drastically reduced when fluorides were applied. 3) The acid resistance in tetracycline-affected enamel was decreased, but it was increased when fluorides were applied. Microhardness of tetracycline-affected enamel was decreased, but a rehardening was shown when APF was topically applied. On the basis of these results, I conclude that the caries resistance is decreased in tetracycline administered rats by reduction in acid resistance and hardness of tetracycline-induced hypoplastic enamel, but it is increased when fluorides are applied.