What are oral plaque-disclosing tablets?

Plaque-disclosing tablets, sold over the counter, are used after brushing and flossing. They produce a red stain that clings to plaque, a thin film of bacteria that forms constantly on the teeth and gums. (Plaque that is not removed regularly can harden into rough porous deposits called calculus, or tartar. Once the hardened tartar forms, it can be removed only when the teeth are cleaned in the dental office.) The disclosing tablet's red stain, which is brushed away easily, is produced by harmless food coloring and indicates where plaque was not removed entirely.