A swelling associated with an acute apical abscess should be incised and drained when it is:

Correct answer: D. Localised and fluctuant on palpation

• A. Indurated cellulitis is a spreading infection requiring urgent antibiotics and possible hospital referral, not office incision.
• B. A FIRM swelling contains no drainable pus — it is inflammatory oedema or early cellulitis. Incising it achieves nothing and only creates a fresh portal for infection.
• C. A diffuse, firm swelling is cellulitis in its spreading phase. Management is antibiotics and removal of the source, with drainage deferred until localisation occurs.
• D. CORRECT. FLUCTUANCE means a liquefied collection of pus is present and under pressure. Incision and drainage releases it, giving immediate relief and removing the reservoir of bacteria. A localised, fluctuant swelling is the classic indication.

Note: Firm = no pus yet, so antibiotics and remove the source. Fluctuant = pus present, so incise and drain. Establishing drainage through the canal is equally important.