A radiograph shows a gap between the apical end of a post and the remaining gutta-percha in a well-obturated canal. What does this indicate?

Correct answer: D. The post is too short

• A. A fractured post would show a discontinuity within the post itself, not a gap at its apical terminus.
• B. A periapical lesion is a radiolucency around the apex, which is a separate finding from a gap in the middle of the canal.
• C. The stem states the root canal treatment was well done. The obturation is not the problem.
• D. CORRECT. A void between the post and the gutta-percha means the post did not seat to the depth of the prepared post space. A short post gives inadequate retention for the core, and the unfilled gap is a potential space for bacterial percolation and coronal leakage.

Note: Post length guidelines: the post should be at least equal to the crown height, or two-thirds of the root length, whichever is greater — while leaving a minimum of 4 to 5 mm of apical gutta-percha intact to preserve the apical seal. Post diameter should not exceed one-third of the root width at any level. And once more: the ferrule contributes more to fracture resistance than the post ever does.