A Premolar Missing Its Lingual Cusp

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.

Correct answer: C. Right lateral excursion — the working side

• A. Retrusion is a very small movement of a few tenths of a millimetre from maximum intercuspation to centric relation and does not generate significant wear facets.
• B. Non-working (balancing) interferences occur between the maxillary LINGUAL cusp and the mandibular BUCCAL cusp on the side away from the movement — a different pair of inclines entirely.
• C. CORRECT. This is the BULL relationship — Buccal Upper, Lingual Lower. On the WORKING side (the side toward which the mandible moves), the mandibular buccal cusp slides up the LINGUAL INCLINE of the maxillary buccal cusp. Facets in that location on the right therefore record right lateral, working-side contact.
• D. Protrusive contacts are recorded on the incisal edges and palatal surfaces of the maxillary anterior teeth, and posteriorly on the distal inclines of maxillary cusps against the mesial inclines of mandibular cusps.

Note: The maxillary first premolar's lingual cusp is small and NON-functional, which is exactly why it fractures: it is unsupported, thin, and loaded obliquely by excursive contacts. Reduce interferences before restoring, or the new restoration fails the same way.

Correct answer: A. To retain a core when insufficient coronal tooth structure remains

• A. CORRECT. A post is PURELY RETENTIVE. Its single job is to hold a core build-up in place when there is not enough coronal dentine to retain it on its own. If enough coronal structure remains — a common rule is four sound walls, or enough to give a 1.5–2 mm ferrule — no post is needed.
• B. This is the most persistent misconception in restorative dentistry. Posts do NOT strengthen roots. Preparing the post space REMOVES radicular dentine and measurably WEAKENS the root, which is why post-related vertical root fracture is a leading cause of loss in root-treated teeth.
• C. Load distribution comes from the FERRULE — the 1.5–2 mm circumferential band of sound tooth structure engaged by the crown — not from the post.
• D. The apical seal is provided by the root filling. Post space preparation actually threatens it — always leave at least 4–5 mm of gutta-percha apically.

Note: Ranked determinants of success in a root-treated tooth: (1) ferrule, (2) remaining coronal dentine, (3) coronal seal, (4) cuspal coverage posteriorly. The post ranks nowhere near the top.