Published on March 11, 2021, Updated on March 11, 2021
The two most common causes of oral ulceration are local trauma (e.g. rubbing from a sharp edge on a broken filling or braces, biting one’s lip, etc.) and aphthous stomatitis (“canker sores”), a condition characterized by recurrent formation of oral ulcers for largely unknown reasons.
Source: https://en.wikipedia.org/wiki/Mouth_ulcer