When placing a post in an endodontically treated tooth, the minimum length of gutta-percha that should be retained apically to preserve the apical seal is about:

Correct answer: C. 4–5 mm

• A. 2 mm is generally considered insufficient for a reliable apical seal.
• B. 3 mm is borderline; the accepted minimum is greater.
• C. Correct. Retain at least 4–5 mm of apical gutta-percha for an adequate seal when preparing the post space.
• D. Leaving 6–7 mm unnecessarily shortens the post and reduces retention.