Short assay periods and restricted feeding procedures in caries assays with cotton rats

Abstract

Three varieties of rice hulls were assayed under equivalent conditions by either long, 98-day assays or by short, 28-day assays. In the long assays, 18-day-old weanlings were used, and caries scores were evaluated in all three molar teeth. In the short assays, 12-day-old weanlings were used, and caries was observed in first and second molars. A mixture of three rice hull varieties was tested in two 18-day assays under the same conditions as the 28-day assays. All assays readily detected anticariogenicity in the hull samples. It was concluded that for detecting rice hull activity, assays longer than 18 days and inclusion of third molar scores were unnecessary. The usefulness of assays employing only short preliminary feeding of rice hulls was also studied. An initial, 3-day feeding of hulls did not influence caries scores measured 15 days later at 30 days of age, but 18 days of hulls significantly decreased scores at 30 days and for as long as 30 days after feeding hulls was discontinued. These studies confirmed the advantages of such assays. They allow a substance to be evaluated for its ability to exert prolonged protection. If extended to 50 days of age or longer, they permit an evaluation of anticariogenic effects on unerupted teeth. The assay periods may be short if the agent being tested is sufficiently potent to protect after a few days of feeding. Sensitivity to short feedings can be increased by controlling dietary sucrose. Evidence reviewed indicated that the short assays and the restricted feeding procedures described would be useful for evaluating agents other than rice hulls and that the results of the assays would be of significance in caries studies other than those using cotton rats.