Prosthodontics & Occlusion · single question
What is the correct finish line for a porcelain-fused-to-metal (PFM) crown?
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Correct answer: D. Circumferential shoulder
- A. A chamfer is used for all-ceramic crowns (zirconia, lithium disilicate) and for the lingual/metal-only margin of PFM. It is NOT the primary PFM finish line at porcelain-bearing areas.
- B. Shoulder with bevel is used for cast metal (all-metal) crown preparations to improve marginal fit of gold — not typically for PFM.
- C. Feather edge is used only for cast metal crowns with gold, NOT for PFM — insufficient bulk for porcelain.
- D. A circumferential shoulder (360° shoulder) finish line is the classic preparation for PFM crowns. The shoulder provides adequate bulk (1–1.5 mm) for both the metal coping and porcelain layer, ensuring structural integrity and proper marginal adaptation. At the metal-only areas (lingual/posterior), a chamfer may be used.
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