For a post placed in a root canal–treated tooth, how many millimeters of gutta-percha should be left APICALLY to maintain the apical seal?

Correct answer: A. 4-5 mm (standard recommendation to maintain apical seal)

• A. Correct. When creating post space, a MINIMUM of 4-5 mm of gutta-percha must be preserved apically to maintain the APICAL SEAL. This prevents microleakage of bacteria and fluids from the periapical region into the root canal system. Removing too much GP (less than 4mm apically) risks apical seal compromise and treatment failure.
• B. 1-2 mm is insufficient — too little apical seal, risk of failure.
• C. 0 mm would completely eliminate the apical seal — never acceptable.
• D. 8-10 mm of remaining GP would leave inadequate post length for retention.