CDC Laboratory Techniques & Technology 3 — Questions and Answers
Question 1: During staining and glazing of a monolithic zirconia restoration, what is the critical reason for keeping the glaze layer thin?
- Thick glaze increases opacity
- Thick glaze can chip or delaminate due to CTE mismatch (Correct answer)
- Thick glaze prevents color penetration
- Thick glaze requires a separate condensation step
Correct answer: Thick glaze can chip or delaminate due to CTE mismatch
A glaze layer that is too thick develops residual stress from coefficient of thermal expansion differences, leading to chipping or delamination.
Question 2: Which technique is used to verify the fit of a ceramic restoration on a refractory die before glazing?
- Optical coherence tomography
- Fit-checker silicone or pressure-indicating paste (Correct answer)
- Spectrophotometric analysis
- Radiographic overlay
Correct answer: Fit-checker silicone or pressure-indicating paste
Fit-checker silicone or pressure-indicating paste applied inside the restoration reveals high spots and contact areas when seated on the die.
Question 3: An incisal porcelain layer appears grayish-white after firing rather than translucent. The MOST probable cause is:
- Firing temperature too high
- Insufficient firing time at peak temperature
- Firing in an air atmosphere instead of vacuum (Correct answer)
- Porcelain applied too thin
Correct answer: Firing in an air atmosphere instead of vacuum
Firing translucent porcelain without vacuum traps micro-air bubbles in the glass matrix, scattering light and producing an opaque gray-white appearance.
Question 4: When investing a wax pattern for the lost-wax casting technique, the wax must be:
- Refrigerated immediately after spruing
- Completely surrounded by investment with adequate thickness (Correct answer)
- Coated in plaster before phosphate investment
- Sprued from the occlusal surface only
Correct answer: Completely surrounded by investment with adequate thickness
Adequate investment coverage on all surfaces provides structural strength during burnout and prevents mold cracking under casting pressure.
Question 5: Which property of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) contributes most to its fracture resistance?
- High alumina content
- Transformation toughening mechanism (Correct answer)
- Low coefficient of thermal expansion
- Intrinsic radioopacity
Correct answer: Transformation toughening mechanism
Transformation toughening occurs when tensile stress at a crack tip triggers tetragonal-to-monoclinic phase transformation, absorbing energy and stopping crack propagation.
Question 6: In CAD software for dental restorations, the 'emergence profile' tool is primarily used to:
- Calculate occlusal contact points
- Define the contour of the restoration from the gingival margin to the height of contour (Correct answer)
- Set the axial wall taper
- Generate the connector cross-section for bridges
Correct answer: Define the contour of the restoration from the gingival margin to the height of contour
The emergence profile shapes how the restoration transitions from the subgingival finish line to its widest point, critical for gingival health and esthetics.
Question 7: A ceramist adds a fluorescent modifier to a ceramic build-up. What effect does this achieve in natural lighting?
- Increases ceramic hardness
- Imparts a lifelike warm glow matching natural tooth fluorescence (Correct answer)
- Blocks UV-induced yellowing
- Reduces firing shrinkage
Correct answer: Imparts a lifelike warm glow matching natural tooth fluorescence
Fluorescent modifiers absorb ultraviolet light and re-emit it as visible blue-white light, replicating the natural fluorescence of tooth structure.
CDC Laboratory Techniques & Technology 3
During staining and glazing of a monolithic zirconia restoration, what is the critical reason for keeping the glaze layer thin?