A 2 × 2 mm firm, sessile, bony-hard nodule is present on the attached gingiva facial to the mandibular lateral incisors. It is the same colour as the surrounding mucosa and has been present for years without change. What would biopsy MOST likely show?

Correct answer: A. Normal surface mucosa overlying mature lamellar bone

• A. CORRECT. A long-standing, firm, BONY-HARD, mucosa-coloured nodule on the attached gingiva is an EXOSTOSIS (a torus when in a characteristic midline palatal or lingual premolar location). Histologically it is simply an outgrowth of NORMAL MATURE LAMELLAR BONE covered by NORMAL surface epithelium and a thin, poorly vascularised lamina propria. There is no neoplasm and no dysplasia — which is why the diagnosis is clinical and biopsy is not required.
• B. SEROUS ACINI would indicate salivary tissue. Minor salivary glands are absent from the attached gingiva and the hard palate midline, so a salivary lesion in this location would be distinctly unusual.
• C. Odontogenic epithelium with dentinoid describes an odontogenic tumour. These arise WITHIN bone and present as radiolucencies or mixed lesions, not as a small mucosa-coloured surface nodule.
• D. Foamy histiocytes suggest Langerhans cell histiocytosis or a xanthomatous process — both of which produce destructive lytic bone lesions, not an asymptomatic hard swelling stable over years.

Note: Clinical relevance: the thin, poorly vascularised mucosa over an exostosis ulcerates readily and heals slowly. It matters most in denture and flap design, where an exostosis may need reduction, and in graft harvesting, where it is a convenient autogenous bone source.