What is the diagnosis of a white lesion with a red border that has healed with scarring?

The diagnosis of a white lesion with a red border that has healed with scarring aligns with major aphthous ulcers. Major aphthous ulcers are typically larger and deeper than minor aphthous ulcers and are known to cause significant discomfort and have a prolonged healing time. They can leave behind scars due to the extent of epithelial loss and tissue damage. The presence of a white lesion surrounded by a red halo is characteristic, as the white may represent necrotic tissue, while the red border indicates inflammation and healing response.

In contrast, minor aphthous ulcers are usually smaller and do not typically leave scars. Herpes simplex lesions present with vesicles that can also cause ulceration but usually do not lead to a white lesion with a red border in the same manner as described. Lichen planus presents with a different clinical appearance such as a reticular pattern or white striations known as Wickham's striae and does not typically heal in a way that results in prominent scarring associated with a distinct white lesion and red border. Therefore, major aphthous ulcers best fit the clinical presentation given in the question.