Use of Twelve-Day-Old Cotton Rats for Dental Caries Studies

¹ University of Texas Dental Branch, Houston, Texas

Cotton rats, usually weaned at 16-21 days of age, were weaned satisfactorily at 12 days of age. These weanlings adapted well to either of two natural diets. No difficulties were experienced in survival, growth, or breeding performance. The growth in females was lower in the animals weaned at the earlier age, but caries scores in both sexes were found equal at 40 days of age.

Cotton rats weaned at 12 days of age had higher caries scores at 40 and 60 days of age than did 18-day weanlings at these ages. The higher scores were caused primarily by an increased caries sensitivity of the first molars, which were newly erupted at 12 days of age. The caries sensitivity of the second molars, which erupted during the 12-18-day period, was slightly increased by the earlier weaning age. It appeared that only 6 days' exposure to the breeding-cage environment protected these teeth for a prolonged time. The results emphasized the importance of weaning age in caries production and confirmed earlier studies that demonstrated that young teeth are very sensitive to protective effects.

Caries production was very rapid in all three molars of the 12-day weanling. Caries scores nearly equivalent to those usually obtained at 116 days of age with all three molars using the 18-day weanling were obtained at 40 days of age by using only the first two molars of the 12-day weanling. Evaluation of caries at 60 days of age enabled the study of caries in the third molars and the advantage of higher caries scores. The longer cariogenic period was necessary to study the third molar, since only 49 per cent had erupted at 40 days of age.

It appeared that weaning cotton rats at 12 days of age and studying each of the three molars separately would simplify the investigation of factors that influence teeth during their development and maturation.