Histological study of an acid red caries-disclosing dye.

When 20 extracted teeth were examined histologically after using a 1.0% acid red caries-disclosing dye before excavation of carious dentin, 25% showed the presence of bacteria in the dentin. The use of a solution of 1.0% acid red in propylene glycol to identify infected dentin will greatly decrease but not completely eliminate the changes of viable bacteria remaining in a cavity preparation.