A pigmented lesion is present in the retromolar pad region. Each of the following belongs in the differential diagnosis EXCEPT one. Which is the EXCEPTION?

Correct answer: B. Fibroma

• A. AMALGAM TATTOO is the single most common cause of oral pigmentation — amalgam particles implanted into the mucosa during restorative or surgical procedures. It is typically blue-grey, flat and asymptomatic, and may show radiopaque flecks if the particles are large enough.
• B. CORRECT — this is the exception. A FIBROMA is a firm, dome-shaped reactive hyperplasia of fibrous connective tissue that is the SAME COLOUR as the surrounding mucosa or slightly paler. It is NOT pigmented, so it does not belong in the differential for a pigmented lesion.
• C. BLUE NEVUS is a benign proliferation of dendritic melanocytes deep in the connective tissue. The depth is what produces the blue colour, through the Tyndall effect. The palate is the commonest oral site.
• D. MELANOMA is the critical lesion never to miss. Oral melanoma is rare but aggressive, most often arising on the PALATE or MAXILLARY GINGIVA, and carries a poor prognosis because it is typically detected late.

Note: Any pigmented oral lesion that is NEW, ENLARGING, has an IRREGULAR border, VARIEGATED colour, or is ULCERATED requires BIOPSY. If a radiograph shows no radiopaque particles and no dental history explains an amalgam tattoo, biopsy rather than observe.