Substructure for Ceramics Flashcards
7 cards from real CCE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Substructure for Ceramics flashcards as text
For a three-unit PFM bridge, which area of the substructure is most susceptible to porcelain fracture under occlusal load?
Answer: Connector-pontic junction
The connector-pontic junction experiences the highest bending stress during occlusal loading, making it the most fracture-prone ceramic region.
Which firing atmosphere is used during the oxidation/degassing cycle for base metal alloy substructures?
Answer: Air (atmospheric)
Degassing of base metal alloys is performed in air to allow controlled oxide layer formation on the metal surface.
CAD/CAM-milled zirconia substructures must be sintered after milling because the pre-sintered blanks are in a:
Answer: Partially sintered (green or white) state
Zirconia is milled in a partially sintered (pre-sintered) state for easy machining, then sintered to full density and final hardness in a high-temperature furnace.
What effect does repeated firing have on the veneering porcelain overlying a metal substructure?
Answer: It can cause devitrification and loss of translucency
Repeated high-temperature firings cause devitrification (crystallization) of the glass-ceramic matrix, resulting in a white, opaque, and weakened surface.
When fabricating a PFM coping for a maxillary central incisor, which margin design best supports the facial porcelain while allowing an esthetic ceramic margin?
Answer: Shoulder or deep chamfer with ceramic butt joint
A shoulder or deep chamfer preparation supports a ceramic butt joint margin, providing strength for the porcelain edge while eliminating the visible metal collar.
What is the significance of the 'transformation toughening' mechanism in yttria-stabilized tetragonal zirconia polycrystal (Y-TZP)?
Answer: It arrests crack propagation by a stress-induced phase transformation
Under stress, Y-TZP undergoes a tetragonal-to-monoclinic phase transformation that expands the material and clamps advancing cracks, dramatically increasing fracture toughness.
A ceramist notices dark gray discoloration at the ceramic-metal interface after the opaque firing. The most likely cause is:
Answer: Insufficient oxidation of the metal
Insufficient oxidation leaves inadequate oxide layer formation, causing poor bonding and gray metallic bleed-through into the overlying opaque ceramic.