avoid leaves black flecks on teeth and in gum line [SEP] this stuff is horrible i followed the directions and did not make a mess or have a mess in my sink as others stated however i cannot 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 is not bad enough my teeth started hurting immediately after i used is stuff i do not know how this is even on the market it is a complete waste of money and now i am afraid i will never get the black flecks out of my gum line