How long should it take for a mouth ulcer to heal?

Patience...: Most mouth ulcers are a virus that will run its course. If you do nothing they usually go away in 14 days. If you try to put something on them, they may feel better and will go away in 2 weeks. If something lasts longer then by all means...Go see a dentist or md.

7-10 days: An ulcer due to minor trauma should heal in 7-10 days if the source of the irritation is removed. If it doesn't heal on its own in this time period you should have it checked by your dentist.

1-2 Weeks: Another common ulcer is the canker sore which doctors call an aphthous ulcer. While the cause is unknown, they are usually small, round, white center with red circle around them and usually painful and sometimes associated with a metallic taste when rubbed with your tongue. They can sometimes be multiple or large and irregular (instead of round). They heal in 7-10 days by themselves.