THE INFLUENCE OF AGE IN THE DEVELOPMENT OF DENTAL CARIES IN THE RAT (RATTUS NORVEGICUS)

¹ Departments of Anatomy, Zoology, and Chemistry, Michigan State College, East Lansing, Mich.

The degree of susceptibility to dental caries in genetically susceptible rats is partially dependent on age. The teeth of our rats are significantly more resistant to decay at 100 days and at 150 days of age than at 35 days. When 100 days old, the susceptible rats have a longer caries time than when 150 days old.

The results of Hoppert, Webber, and Canniff^{9, 10} are again confirmed, and several additional facts are discovered. (a) Substitution of the coarse rice for the fine rice in the ration at 35 days of age results in prompt tooth decay in genetically susceptible rats; the difference induced by the diet change is approximately 23 days of caries time. (b) Substitution of rice flour for fine rice in the ration prevented the development of caries in susceptible rats before the ages of 100 or 150 days in 94 per cent of the animals tested. The potency of the environment is clearly indicated by this fact.

Two genetically susceptible animals exhibited unexpected and remarkable resistance to tooth decay when placed on the coarse rice ration at 150 days of age.

Six animals showed extreme susceptibility to dental decay, so that they were unable to attain the age of 150 days on the rice flour ration without developing caries.