Disclosing tablets 20 pack are chewable tablets used to make dental plaque visible. They contain a dye (typically a vegetable dye, such as Phloxine B) that stains plaque a bright colour (typically red or blue). After brushing, one chews a tablet and rinses. The plaque you have missed while brushing is now visible. (You must now brush the dye away)
Using disclosing tablets can actually help you improve your tooth brushing technique, as they can show you parts of your teeth that you might not be cleaning as thoroughly as you should.