CCE Substructure for Ceramics 3 — Questions and Answers
Question 1: In a PFM crown, which layer is applied directly over the oxidized metal coping to mask the metal color?
- Dentin porcelain
- Opaque porcelain (Correct answer)
- Enamel porcelain
- Glaze porcelain
Correct answer: Opaque porcelain
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?
- The casting shrinks unevenly, causing porosity near the occlusal (Correct answer)
- The metal becomes too soft
- The ceramic bonds more strongly
- The marginal fit improves
Correct answer: The casting shrinks unevenly, causing porosity near the occlusal
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?
- Hydrofluoric acid etching
- Airborne particle abrasion with 50-µm alumina (Correct answer)
- Silane application only
- Electrochemical etching
Correct answer: Airborne particle abrasion with 50-µm alumina
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:
- Cleaning the coping in an ultrasonic bath
- Applying a very thin opaque layer and firing to verify bond (Correct answer)
- Firing the glaze layer
- The final characterization firing
Correct answer: Applying a very thin opaque layer and firing to verify bond
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:
- Excess alumina abrasion pressure
- CTE mismatch between zirconia and veneering ceramic (Correct answer)
- Insufficient occlusal clearance for metal
- Overglaze applied too thick
Correct answer: CTE mismatch between zirconia and veneering ceramic
A CTE mismatch creates tensile stress in the veneering ceramic during cooling, causing spontaneous chipping or delamination.
Question 6: Which substructure design concept reduces occlusal porcelain thickness to prevent fracture in posterior PFM crowns?
- Ceramic occlusal onlay design
- Full metal occlusal coverage (Correct answer)
- Lingual ceramic extension
- Hybrid layer technique
Correct answer: Full metal occlusal coverage
Full metal occlusal coverage eliminates unsupported ceramic on the functional surface, significantly reducing the risk of fracture under heavy posterior loads.
Question 7: What is the recommended minimum ceramic thickness for veneering porcelain over a metal coping to achieve adequate esthetics?
- 0.3 mm
- 0.7 mm
- 1.5 mm (Correct answer)
- 3.0 mm
Correct answer: 1.5 mm
A minimum of 1.5 mm of veneering ceramic is required to mask the opaque layer and achieve natural-looking color depth and translucency.
CCE Substructure for Ceramics 3
In a PFM crown, which layer is applied directly over the oxidized metal coping to mask the metal color?