The document discusses various types of single ulcers that can occur in the oral mucosa. The most common type is a traumatic ulcer, which is usually caused by mechanical, chemical, thermal or self-inflicted trauma. Traumatic ulcers present as tender lesions that vary in size and shape and can persist for weeks. Differential diagnoses include carcinomatous and recurrent aphthous ulcers. Other single ulcers discussed include eosinophilic ulcers of the tongue, histoplasmosis, blastomycosis, mucormycosis, and syphilitic ulcers. Diagnosis involves biopsy and cultures. Treatment depends on the specific condition but may include topical steroids, antifungal agents