For decades I'd suffered from canker sores (aka: aphthous ulcers) inside my mouth. A dental study of Japanese communities revealed that their low dental plaque was due to compounds called isothiocyanates in wasabi, the green radish paste. Since that time, 12 years ago, I have not had a SINGLE canker sore, even though I still abrade my mouth, gum and inner lips as much as ever, because every day I brush my teeth using ~1 part wasabi to ~3-4 parts toothpaste, ANY toothpaste.
The wasabi actually inhibits bacteria from attaching to mouth surfaces using their plaque! This is an actual preventive which works.
After years of suffering from painful mouth ulcers (Canker sores) and trying several unsuccessful natural cures, wasabi did the trick. I stumbled on this cure accidentally, but have used it successfully for the last 2 years. At the first sign of sores, I eat wasabi chips or wasabi peas and the development of the ulcers are arrested and they are completely gone in 12-36 hours. Usually just a handful of chips a couple of times a day does the trick. I have also tried wasabi mayonnaise and straight wasabi. They do work well; but the combination of the wasabi and salt in the chips and peas seems to work best. I know it sounds crazy, but try it! Just make sure the wasabi comes in contact with affected area for a minute or two. What used to cause 7-10 days of agony on a regular basis, is now barely a ripple in my life. I don't know if it will work for all types of mouth ulcers, but it worked for mine.