CDC Laboratory Techniques & Technology 2 — Questions and Answers
Question 1: Which digital workflow step converts a scanned STL file into a milling or printing path?
- CAD design
- CAM processing (Correct answer)
- Sintering
- Sprue removal
Correct answer: CAM processing
CAM (Computer-Aided Manufacturing) processing translates the CAD design into toolpaths or print instructions for the fabrication device.
Question 2: When using a dental milling unit to produce a zirconia crown, what is the purpose of the pre-sintering stage the blank is in?
- It is fully dense and requires no further firing
- It is partially sintered, making it softer and easier to mill (Correct answer)
- It must be infiltrated with resin before milling
- It contains wax that burns out during milling
Correct answer: It is partially sintered, making it softer and easier to mill
Pre-sintered (green or white) zirconia is in a partially sintered state that is softer, reducing tool wear during milling before final sintering.
Question 3: A ceramist notices micro-cracks forming along the margin of a pressed ceramic restoration after divesting. The MOST likely cause is:
- Over-firing the ingot
- Too-rapid bench cooling of the investment (Correct answer)
- Insufficient wax sprue diameter
- Using the wrong shade of ingot
Correct answer: Too-rapid bench cooling of the investment
Rapid cooling of the investment ring creates thermal shock and uneven contraction, producing marginal micro-cracks in the ceramic.
Question 4: Which bonding agent chemistry is most appropriate for cementing a high-translucency zirconia restoration?
- Zinc phosphate cement
- Polycarboxylate cement
- MDP-containing resin cement (Correct answer)
- Glass ionomer cement
Correct answer: MDP-containing resin cement
MDP (10-methacryloyloxydecyl dihydrogen phosphate) monomers chemically bond to zirconia's oxide surface, providing durable adhesion.
Question 5: In a dental laboratory, the primary purpose of an articulator's condylar guidance setting is to:
- Control incisal pin height
- Replicate posterior disclusion during excursive movements (Correct answer)
- Set the mounting ring angulation
- Determine occlusal vertical dimension
Correct answer: Replicate posterior disclusion during excursive movements
Condylar guidance reproduces the arc of condylar movement so the articulator mimics posterior tooth disclusion during lateral and protrusive excursions.
Question 6: Which furnace atmosphere is recommended when firing cobalt-chromium metal frameworks before porcelain application?
- Carbon-rich reducing atmosphere
- Vacuum or inert gas atmosphere (Correct answer)
- High-humidity steam atmosphere
- Oxygen-enriched atmosphere
Correct answer: Vacuum or inert gas atmosphere
Vacuum or inert-gas firing prevents oxidation of the metal surface beyond the thin oxide layer needed for porcelain bonding.
Question 7: What is the function of a vibrator when pouring dental stone into an impression?
- Accelerate the setting reaction
- Eliminate air bubbles and ensure complete adaptation (Correct answer)
- Increase the water-to-powder ratio
- Raise the temperature of the mix
Correct answer: Eliminate air bubbles and ensure complete adaptation
Vibration encourages air bubbles to rise out of the mix and promotes flow into fine impression detail, reducing voids in the model.
CDC Laboratory Techniques & Technology 2
Which digital workflow step converts a scanned STL file into a milling or printing path?