What is the recommended TOTAL OCCLUSAL CONVERGENCE (taper) for a full-coverage crown preparation?

Correct answer: A. Approximately 5–10 degrees

• A. CORRECT. The generally taught ideal TOTAL occlusal convergence is around 6 degrees — roughly 2–3 degrees of taper per axial wall — with a practically achievable and clinically acceptable range of about 5–10 degrees. This balances two competing requirements: enough convergence to allow the restoration to seat without binding and to permit the escape of cement, but little enough to preserve maximum retention and resistance form.
• B. 30–35 degrees would leave a preparation approaching a cone, with minimal retention and resistance — a common cause of repeated decementation.
• C. 20–25 degrees is excessive. Retention falls steeply as taper increases, and this degree of convergence markedly compromises resistance to lateral dislodging forces.
• D. 0–2 degrees produces near-parallel walls. In principle this maximises retention, but in practice it creates undercuts, prevents complete seating and traps cement — it is not clinically achievable or desirable.

Note: Retention and resistance depend on more than taper: preparation HEIGHT (the taller the axial walls the better), SURFACE AREA, and the SURFACE-AREA-TO-TAPER relationship all matter. For short clinical crowns, add grooves or boxes to improve resistance form rather than accepting a stubby, over-tapered preparation.