Are called recurrent apthous stomatitis
or trauma ulcers.
There is a relationship to immune system issues. These can be quite painful for a few days, then they hopefully resolve. Avoid acidic foods & toothpaste w sodium lauryl sulfate. Look for zilactin b at your pharmacy. If these lesions are not gone in 10-14 days let ur dentist evaluate the area. There are prescriptions to help as well.