CDT CDT Ceramics & Porcelain Techniques 1 — Questions and Answers
Question 1: What is the primary purpose of applying an opaque layer in a porcelain-fused-to-metal (PFM) restoration?
- To mask the metal substrate and establish base shade (Correct answer)
- To add translucency to the final restoration
- To strengthen the porcelain build-up
- To improve marginal fit of the crown
Correct answer: To mask the metal substrate and establish base shade
The opaque layer masks the dark metal coping and creates the foundation shade for the overlying porcelain layers.
Question 2: Which firing stage in porcelain condensation produces the greatest shrinkage?
- Glaze firing
- Opaque firing
- Body/dentin firing (Correct answer)
- Wash bake
Correct answer: Body/dentin firing
Body/dentin firing involves the largest volume of porcelain and therefore produces the most significant shrinkage during sintering.
Question 3: What does a 'wash bake' accomplish in ceramic fabrication?
- Applies a thin porcelain wash to correct minor shade discrepancies (Correct answer)
- Removes excess wax from a ceramic coping
- Initiates the sintering of zirconia
- Bonds the ceramic to metal with a bonding agent
Correct answer: Applies a thin porcelain wash to correct minor shade discrepancies
A wash bake adds a very thin layer of porcelain to blend or correct localized shade or surface irregularities before glazing.
Question 4: What causes a 'chipping' or delamination failure in a PFM restoration?
- Excessive metal thickness
- Inadequate bond between opaque and body porcelain
- Over-glazing the surface
- Using high-fusing porcelain on a low-fusing alloy (Correct answer)
Correct answer: Using high-fusing porcelain on a low-fusing alloy
Using high-fusing porcelain on a low-fusing alloy creates thermal expansion mismatches that result in cohesive or adhesive failures.
Question 5: Which technique is used to characterize the internal structure of a ceramic crown for a more lifelike appearance?
- Layering technique with dentin, enamel, and effect powders (Correct answer)
- Single-layer pressing and staining only
- Glazing with a tinted glaze paste
- Sandblasting with alumina oxide
Correct answer: Layering technique with dentin, enamel, and effect powders
The layering technique uses multiple porcelain powders (dentin, enamel, incisal, effects) to replicate natural tooth structure.
Question 6: What is the coefficient of thermal expansion (CTE), and why is it critical in PFM restorations?
- The rate at which porcelain sets; it determines firing time
- A measure of how a material expands/contracts with temperature; metal and ceramic CTEs must be compatible (Correct answer)
- The strength rating of dental porcelain; higher is better
- A measure of porcelain translucency used to select shade
Correct answer: A measure of how a material expands/contracts with temperature; metal and ceramic CTEs must be compatible
CTE compatibility between metal and porcelain prevents internal stresses that would cause cracking or delamination during cooling.
CDT CDT Ceramics & Porcelain Techniques 1
What is the primary purpose of applying an opaque layer in a porcelain-fused-to-metal (PFM) restoration?