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Dentistry · Dental materials and radiology: dental porcelain
Sample itemWhy is porcelain fused to a metal substructure for posterior crowns?
Original practice item, not a recalled exam question. Nothing here is recorded.
The answer and the reasoning
C. Porcelain is strong in compression but brittle in tension, so metal gives support
Porcelain gives excellent colour and wear resistance but fractures readily under tensile forces. A metal coping supplies strength, as in metal-ceramic crowns.
Option by option
A. Metal is added to make the crown lighter
Adding metal increases weight, not reduces it.
B. Porcelain bonds poorly to any substrate
Porcelain bonds well to oxide on the metal coping.
C. Porcelain is strong in compression but brittle in tension, so metal gives support (correct)
Correct. The metal copes with tensile stress that porcelain cannot.
D. Porcelain is a poor aesthetic material
Porcelain is an excellent aesthetic material.
Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.
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