The primary purpose of a post (dowel) placed in a root canal–treated tooth BEFORE crown preparation is:

Correct answer: A. To increase retention of the core (build-up material)

• A. Correct. The PRIMARY purpose of a post in a root canal–treated tooth is to retain the core build-up material. The post provides mechanical retention for the core (composite or amalgam) that replaces missing coronal tooth structure, allowing the crown to have an adequate foundation. Posts do NOT strengthen the tooth.
• B. Microleakage prevention is a function of the crown margin and luting cement — not the post.
• C. Posts do NOT strengthen roots — in fact, posts can WEAKEN roots by removing additional dentin during post space preparation. The misconception that posts strengthen teeth is a classic exam trap.
• D. Root canal obturation is completed with gutta-percha/sealer before post placement — the post does not function as obturation material.