Have you ever developed a white painful sore with red borders inside your mouth? These are mouth ulcers. Although these lesions are common, the actual cause often remains unclear. A slight injury to the soft tissues in the mouth, ill-fitting dental appliances like dentures or braces, and even irritation from acidic foods are possible contributors. Luckily, mouth ulcers often heal by themselves within a couple of weeks. Still, there are some things that you can do to treat these and reduce pain and discomfort.