Mouth sores usually go away on their own within a week, but one that lasts longer should be examined by a dentist or doctor.
The American Dental Association mentions these possible causes:
- Having a fungal, bacterial or viral infection.
- Having irritation from sources such as a loose orthodontic wire, poorly fitted dentures or the sharp edge of a broken filling or tooth.
- Having a disease or disorder that produces mouth sores as a side effect.