Their margins may merge and leave a single lesion, even if they enlarge only slightly after their initial appearance. With multiple lesions that vary in size, the morphology of peripheral lesions becomes important in deciding whether the lesions should be classified as separate or coalescing. Whenever both separate and coalescing lesions are present , the predominant type of lesion determines the correct morphologic classification. If neither separate nor coalescing lesions is predominant, it may be described as either. A depressed lesion is one in which the surface is below the normal plane of the mucosa.
Most depressed lesions are ulcers.
An ulcer is a loss in continuity of the oral epithelium . Clinically, the center of the ulcer is often yellow to grey with a red periphery . Occasionally, a red center may be observed. Ulcers often result from the rupture of elevated lesions such as vesicle, bullae, pustules, and papules. Some depressed lesions are the result of atrophy or scarring and have an intact epithelial surface.