Just to clarify for anyone who is still confused.... canker sore = mouth ulcer.
And I used to get them all. the. time. I had one so big once, that I could stick the entire tip of my tongue into the center of it without touching the edges. That one was painful. The doc gave me some topical anesthetic and a silver nitrate stick. I numbed it, and held the silver nitrate stick in the middle of the ulcer for a few seconds. That cauterized it. And yes...it hurt. Even with through the numbness.
Fortunately, it went away two days after that.
Lately, I've found that since I started using Listerine twice a day to rinse out my mouth, I only get ulcers 2-3 times a year instead of once a month.
Still, when I do get them, I dry them out and dab some Anbesol on there.
Kank-a works too. It forms a protective coating over the ulcer.
So - to sum up...
Listerine and Anbesol are your friends.