I think oral ulcer present inside mouth for more than 15 days after eliminating the visible cause should go ideally for biopsy and histopathology!!!!!
Next Steps
As an oral medicine and radiology specialist I will advise you to consult oral medicine and radiology specialist... After proper history and clinical examination.... if any traumatic or other cause will be present ... should be eliminated!!!!
Health Tips
if you want you can consult with me online!!!! with proper clinical photo!!!!!