A patient presents with a blue-black pigmented macule on the oral mucosa. Which of the following conditions would NOT be included in the differential diagnosis for an oral blue-black pigmented lesion?

A fibroma (traumatic fibroma) is a benign connective tissue lesion that appears as a pink or white nodule on the oral mucosa. It does not produce pigmentation and would not be included in the differential diagnosis of a blue-black pigmented lesion. The differential diagnosis for blue-black oral pigmented lesions includes: amalgam tattoo (most common, gray-blue focal lesion near restorations), blue nevus (benign melanocytic lesion), melanoma (malignant; requires biopsy), and physiological pigmentation, among others. Fibroma's color is from normal mucosal epithelium, not melanin or metallic deposits.