Prosthodontics & Occlusion · single question
What is the ideal taper (convergence angle) for a complete crown preparation?
Show answer and explanation
Correct answer: B. 6–10 degrees total convergence (standard)
B) 6–10 degrees total convergence — CORRECT.
The ideal total occlusal convergence (TOC) for crown preparation is 6–10 degrees (3–5 degrees per wall). This provides optimal balance between: retention/resistance (closer to 0° = more parallel = more retentive) and clinical accessibility (wider = easier to prepare but less retentive). Studies show clinicians typically achieve 12–20° — the ideal is 6–10°.
A) 2–5°: Too parallel — difficult to seat a casting and traps impression material; not clinically achievable consistently.
C) 10–20°: This is the range most clinicians actually achieve but exceeds the ideal for optimal retention.
D) 20+°: Excessive taper — greatly compromises retention and resistance form.
The ideal total occlusal convergence (TOC) for crown preparation is 6–10 degrees (3–5 degrees per wall). This provides optimal balance between: retention/resistance (closer to 0° = more parallel = more retentive) and clinical accessibility (wider = easier to prepare but less retentive). Studies show clinicians typically achieve 12–20° — the ideal is 6–10°.
A) 2–5°: Too parallel — difficult to seat a casting and traps impression material; not clinically achievable consistently.
C) 10–20°: This is the range most clinicians actually achieve but exceeds the ideal for optimal retention.
D) 20+°: Excessive taper — greatly compromises retention and resistance form.
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