They are annoying and painful and there are plenty of things that can cause them such as bacterial, viral or fungal infections. A loose orthodontic wire, a denture that doesn’t fit, or a sharp edge from a broken tooth or filling may also be the culprit.

Mouth sores may be symptoms of a disease or disorder. A dentist should examine any mouth sore that lasts a week or longer.

What's the difference between a canker sore and a cold sore?

Canker sores are often confused with cold sores. An easy way to distinguish between the two is to remember that canker sores occur inside the mouth, and cold sores usually occur outside the mouth.

A canker sore (also called aphthous ulcers) is a small ulcer with a white or gray base and red border. There can be one or a number of sores in the mouth. Canker sores are very common and often recur.