A radiograph of a central incisor shows a well-defined radiolucency ballooning out from within the canal; the tooth is tender. Diagnosis and treatment?

Correct answer: A. Internal resorption — treat with root canal therapy

• A. Correct. Internal resorption is driven by odontoclasts within the pulp, producing a symmetric balloon-like radiolucency centered on the canal. Removing the resorbing tissue with root canal therapy is the treatment when the tooth is restorable.
• B. Incorrect. Condensing osteitis is a radiopaque (not radiolucent) bony reaction at the apex.
• C. Incorrect. A dentigerous cyst surrounds the crown of an unerupted tooth, not the canal of an erupted incisor.
• D. Incorrect. A symptomatic expanding intracanal radiolucency is pathologic, not normal anatomy.

Note: Internal resorption is caused by odontoclasts (clastic cells), not odontoblasts. RCT halts it by removing the resorbing tissue.