Crown Preparation — ORE Part 1 MCQ
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Correct answer: C — 6-12 degrees total occlusal convergence
The answer is C: 6–12 degrees total occlusal convergence. Retention of a cemented crown peaks in the 6–12° range; this is the established optimum supported by Jorgensen's classical retention studies and modern systematic reviews of dental student preparations. Option E (0°/parallel walls) is theoretically unachievable clinically and unnecessary—absolute parallelism does not exist and would prevent restoration insertion. Option D (20–30°) and D (45°) exceed the clinically acceptable range and progressively sacrifice retention. Option B (2°) is below the optimal range, difficult to achieve without excessive tooth tissue loss, and provides no retention advantage. For posterior teeth, 6–12° is the standard taught in UK dental schools and represents best international practice.
Reference: Jorgensen KD. The relationship between retention and convergence angle in cemented veneer crowns. Journal of the American Dental Association. 1997 (classic study); confirmed by Strain KJ et al., Crown Taper Angles Achieved by Dental Students: A Systematic Review, Journal of Dental Education 2018; and Assessment of Convergence Angle of Tooth Preparations for Complete Crowns Among Dental Students: Typodont vs Simulator. PMC, 2022. https://pubmed.ncbi.nlm.nih.gov/9227101/ and https://pubmed.ncbi.nlm.nih.gov/30385687/