A Centrifugal Technique of Measuring Food Retention

¹ Eastman Dental Dispensary, Rochester, New York

In a search for a suitable in vitro technique for measuring the retention of foods to tooth surfaces, it was decided that centrifugal force offered the most convenient method of breaking food-tooth bonds and thereby gauging the retention properties of test foodstuffs. The technique consisted of placing a test food/saliva mixture around teeth mounted in the caps of centrifuge tubes. After controlled centrifugation, the teeth were removed from the caps, washed in standard volume of water, and the total carbohydrate in the washings determined, using a modified anthrone colorimetric technique. These values were used to determine the total amount of food adhering to the teeth after centrifugation, and this amount, in milligrams, was taken as the centrifugal retention index.

Increasing the temperature of the test sample was shown to decrease the values obtained for the centrifugal retention index. Variations in speed and period of centrifugation were demonstrated to influence the retention values obtained. At a low rotational speed, poor reproducibility of results was seen, but at a high rotational speed, good reproducibility with duplicate trials was apparent, and the centrifugal retention index decreased with increasing periods of centrifugation. Most of the food was thrown off the teeth during the first 5 minutes of centrifugation. Varying the proportions of saliva in the test mixture produced variations in the retention values, but this effect varied from food to food.

To afford a basis for comparison, twelve representative foods were tested using both the intra-oral recovery technique and the centrifugal retention technique. With the latter technique, three mixtures of each food, employing different proportions of saliva, were tested. Considerable variation in the retention properties of the different foods and of the different mixtures of each food was recorded. Correlation of results of the two techniques was only moderate. The various factors which may affect the retention of foodstuffs in the mouth and the centrifugal retention indexes and those factors which may have contributed to the complexity and difficulty of interpretation of results of the centrifugal retention technique and the relatively poor degree of correlation between results of the two retention techniques were discussed.