CCE Substructure for Ceramics 3

Question 1

In a PFM crown, which layer is applied directly over the oxidized metal coping to mask the metal color?

Accepted Answer

Opaque porcelain

Answer

Opaque porcelain is the first ceramic layer applied to the coping; it masks the metal color and forms the initial bond to the oxide layer.

Question 2

What happens to a metal substructure if the sprue is attached too close to the occlusal surface during casting?

Accepted Answer

The casting shrinks unevenly, causing porosity near the occlusal

Answer

Sprue placement too close to a thin area causes solidification shrinkage porosity at the occlusal, compromising structural integrity.

Question 3

Which type of zirconia surface treatment is most effective for promoting adhesion of veneering ceramic?

Accepted Answer

Airborne particle abrasion with 50-µm alumina

Answer

Airborne particle abrasion with 50-µm alumina creates micro-mechanical retention on zirconia, since HF acid does not effectively etch this material.

Question 4

The term 'wash firing' in the context of PFM fabrication refers to:

Accepted Answer

Applying a very thin opaque layer and firing to verify bond

Answer

A wash firing applies an extremely thin opaque coat to test the metal–ceramic bond quality before full opaque buildup.

Question 5

When a ceramist notices that veneering porcelain is chipping off a zirconia substructure, the most likely cause is:

Accepted Answer

CTE mismatch between zirconia and veneering ceramic

Answer

A CTE mismatch creates tensile stress in the veneering ceramic during cooling, causing spontaneous chipping or delamination.

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