Effect of Age on the Incidence of Experimental Caries in Normal and Castrate Female Rats

Abstract

Attention has recently been focused on the problems of aging of dental structures by Robinson, Boling and Lischer (1). Although these authors have compiled an imposing list of references concerning the changes in the teeth and jaws with age, little is known of the effect of age on experimental caries in the rat. Most of the studies on caries in rats (2-19) have been made over relatively short periods and on young animals. Only a few studies (20-26) have included rats of advanced age or rats which have been observed over a period of 1 year or more. From these long-term studies the general impression is gained that rats on adequate dietary regimes do not develop caries, whereas those fed deficient diets may have carious teeth. No data are available on the incidence of caries in old rats placed on the coarse corn diet. A colony of 17 normal and 12 castrate female rats were put on the Hoppert, Weber, and Caniff diet (3) at the age of 1 year. They were maintained on this diet until death from old age or other causes supervened, with the exception of 4 rats which were sacrificed after 19 months on the diet in order to end the experiment. At death the jaws were removed and the teeth examined under binoculars (15X) according to the technique previously described (25). Missing cusps and microscopic lesions were recorded although it was frequently difficult to distinguish between fractures and carious lesions in the presence of advanced attrition. The data on the normal rats are given in Table I. It is interesting to observe that little evidence of caries was found in some of the rats after periods as long as 13 months on the experimental diet. The number of cavities, the number of cusps involved, and the number of teeth totally destroyed are seen to increase with increasing time on the diet. In Table II are given the corresponding data on the castrate female rats. None of these had any caries up to 9 months on the diet. As in the case of the normal animals the numbers of cavities, of cusps involved, and of teeth totally destroyed increased with the time on the diet. There is little difference between the observations on the normal and on the castrate female rats. The normal rats averaged 2.8 cavities per rat; the castrates 2.2. The normal rats averaged 7.5 cusps involved per rat; the castrates 5.8. The normal rats averaged 0.9 teeth totally destroyed per rat; the castrates 0.7. There is apparently a tendency for the normal rats to have somewhat higher average values per rat. However, these differences can be accounted for by the