Rinse well to see the different blue and red plaque.  Always stains tongue though.
I tried these with my kids. First off, I think the flavor is pretty good, unlike most reviewers here.  My kids thought it was really gross but to me it tasted like Smarties candies.  This is pretty ironic because I don't like candies, whereas my kids love them.<br /><br />Secondly, the way I used them was to chew them then swish them around and in between my teeth, spit out, and rinse really well about 10x.  After that I could see different blue older plaque between my teeth in the areas of recessed gums more towards the back, and some red plaque on my front teeth near the biting surface as well as on the top edge of my bottom incisors.  These are definitely spots that I would miss easily.  I had to floss to get rid of the plaque that was in between the gum pockets.<br /><br />One of my kids had blue plaque only -- but she is pretty bad at brushing and definitely misses those areas all the time (near the gumline esp the top incisors).  The other kid had a different staining pattern with blue and red areas.  So if you are getting only one color on all your teeth, just keep rinsing out the excess dye until you can see a difference.<br /><br />We all had to brush our tongue a lot but could not get the last 10% of the stain out.  In the morning it seemed to have vanished, which means that we probably swallowed a bunch of red dye, not the best scenario.<br /><br />Anyway, it does work and is a useful learning tool to shock the kids into brushing better, so I am happy with it.
Rating: 4 stars