Endodontics · patient case with 2 questions
Radiographic gap between a post and the root filling
Patient: Adult with a post-retained restoration
Chief complaint: Routine review of a previously treated tooth.
Background: The root canal treatment itself was well executed.
Current findings: The radiograph shows a space between the apical end of the post and the remaining gutta-percha.
Question 1
Why has this space appeared?
Show answer and explanation
Correct answer: A. The post is too short for the space that was prepared
- A. CORRECT. The obturation is stated to be sound, so the void is not an obturation failure. Gutta-percha was removed to create the post space, and the post subsequently placed does not extend to the full depth prepared, leaving a dead space between post tip and remaining root filling. This void is a potential reservoir for bacterial contamination and reflects a mismatch between preparation depth and post length.
- B. A perforation would appear as a lateral defect with associated bone loss, not an axial gap within the canal.
- C. Gutta-percha does not resorb in this manner.
- D. The case explicitly states the root canal treatment was well done, which rules this out.
Note: Guidelines for post length: roughly two-thirds of the root length, at least equal to the crown height, while preserving 4–5 mm of apical gutta-percha to maintain the seal.
Question 2
How much apical gutta-percha should be retained when preparing a post space?
Show answer and explanation
Correct answer: B. 4–5 mm
- A. 1 mm is far too little and does not provide a reliable apical seal.
- B. CORRECT. At least 4–5 mm of apical gutta-percha must remain to preserve the apical seal. Removing more risks compromising the seal and predisposes to periapical breakdown.
- C. 8–10 mm would leave insufficient length for adequate post retention in most roots.
- D. Removing all obturation destroys the apical seal entirely.