Five
Your user name says it all. Get the Zapper named The Terminator.
Also you could use Magnets. I have some that are quite strong yet small,(1/3").
I occasionaly) got those little canker sores inside the mouth. I would tape one of these magnets over the area for a few hours. And it would go away.
Regular use of the Terminator should put them into remission or cure them.