Avoid! Leaves black flecks on teeth and in gum line! [SEP] This stuff is HORRIBLE! I followed the directions, and didn't make a mess or have a mess in my sink, as others stated; however, I can't get it out of my gums!! The directions say to rinse several times after use, which I did. It still looks like I just ate ambunch of Oreos. I brushed my teeth with Crest FOUR times and there are still black flecks along my gum line. I rinsed my mouth with Crest Whitening mouth wash... STILL have black flakes. As if that isn't bad enough, my teeth started hurting immediately after I used is stuff. I don't know how this is even on the market. It's a complete waste of money, and now I'm afraid I'll never get the black flecks out of my gum line.