Canker sores are so annoying. They are those little ulcers in your mouth that sting like crazy. They are often confused for cold sores, which they are not. Unfortunately we still haven’t found out exactly what causes them. There are ways to treat them though. See one dentists explanations and treatments for them here: Dr. Jeff Hersh: What causes a canker sore?
Non-Surgical Mouth Reconstruction and Facelift Dentistry, Santa Monica, CA