A margin that has to go subgingival

Correct answer: C. A cast metal margin

• A. Pressed lithium disilicate, at roughly 350–400 MPa, is far stronger than feldspathic porcelain and excellent esthetically, but it is still well below cast metal. Monolithic zirconia at roughly 900–1200 MPa is the strongest ceramic option, though it is opaque and abrasive to the opposing dentition.
• B. The porcelain butt joint gives the esthetics of an all-ceramic margin on a metal-supported crown — but it deliberately places the WEAKEST material at the most vulnerable point of the restoration.
• C. CORRECT. CAST METAL has far greater flexural strength and fracture toughness than any dental ceramic, and that matters most exactly where this margin sits. A metal margin can be finished to a thin, burnishable chamfer or knife-edge that adapts closely to the preparation without chipping — which is precisely what a subgingival margin needs, since it must be thin, accurately fitting and finishable, and a bulky ceramic shoulder in that position encroaches on the biologic width and provokes chronic inflammation.
• D. Feldspathic porcelain has the LOWEST flexural strength of the dental ceramics, roughly 60–120 MPa. At a thin margin under heavy load it will chip, and in a bruxist it is indefensible.

Note: The metal-versus-ceramic comparison at a subgingival margin is what this item adds. The overriding principle remains that a SUPRAGINGIVAL margin is preferable whenever esthetics permit — it is easier to prepare, impress, finish and clean, and it does not threaten the attachment.