ELATIVE DENTIN ABRASION VALUE
Once you have determined the aesthetic material and the purpose of polishing, the polishing agent itself should be evaluated for its main abrasive ingredient. The relative dentin abrasion orradioactive dentin abrasivity (RDA) should be reviewed and assessed (Table 1). This value indicates the abrasivity of a material in relation to dentin. The relative enamel abrasion (REA) value can be taken into consideration as well, but the RDA value relates better to the sensitivity of dentin. Abrasives are based on the hardness, particle size, and quantity of the abrasive. The ADA has adopted a standardized test to determine the RDA and REA value of a product. Basically, to determine RDA value, extracted human teeth are irradiated with mild neutrons, stripped of enamel, and subjected to simulated tooth cleaning procedures. The rinse water is then measured for its radioactivity and recorded. Thus, after a few calculations (taking into consideration speed of rotation of the prophy cup, time, and the pressure applied, etc), a score or index is given to the product being tested (Table 1). Any value over 100 is considered to be abrasive.6 The ADA recommended limit is 250, whereas the FDA limit is 200. (Note: Toothpastes are also given a RDA value for FDA approval, but often are not published for marketing purposes). As for the hardness, abrasives are ranked on the Mohs scale of mineral hardness. The hardness is based upon 10 readily available minerals, on a scale of 1 to 10. Diamonds are assigned a 10 since it is the hardest mineral, and talc, the softest, is assigned a 1.0.7
