I got cankers a lot when I wore braces. The chemical balance inside my mouth was way off...that's when I ended up w/tons of cankers. Also, when I used the Rembrandt teeth whitening system after I got them off, same thing happened. I learned that my body was too acidic, so taking this drink called GreensFirst began to make my body more alkaline. That seemed to do the trick. Otherwise, I got some weird paste stuff from my doctor (prescription) that I would put directly on the cankers that cleared them up in a matter of days. It's some brown, gritty, pasty stuff w/a really long name.