All of the following would help retain a cusp-replacing restoration on this tooth EXCEPT:

Correct answer: B. Adhesion to the remaining enamel

• A. A dentine PIN is the classic auxiliary retention feature for a cusp-replacing amalgam. It has real disadvantages (crazing, perforation, pulpal irritation) but it is undeniably retentive.
• B. CORRECT — this is the EXCEPTION as the item was written, and the reason is the material. Enamel ADHESION is a bonded (micromechanical) retention mechanism. It is genuine retention for a composite or a bonded ceramic, but it provides NO retention for the amalgam or cast restoration the classical cusp-replacement question refers to, and the remaining enamel here is thin, unsupported and at the margin — the least reliable bonding substrate available.
• C. A SLOT — a horizontal channel cut into sound dentine — is a recognised auxiliary retention feature and is generally preferred over pins because it does not stress the dentine.
• D. Because the tooth is ROOT TREATED, a POST becomes available as a retention option for the core. It reinforces nothing, but it does retain.

Note: ⚑ FLAG FOR THE GROUP. The recall recorded three options (enamel adhesion, slot, pin) with a post added as a fourth, and noted that this scenario follows the root canal treatment. If the intended restoration were a bonded composite, enamel adhesion would be legitimate and the answer would change. Discuss — but the principle to carry into the exam is that pins, slots, grooves and posts are MECHANICAL retention while adhesion is not, and for a root-treated posterior tooth that has lost a cusp the definitive answer is cuspal coverage, not patchwork retention.