CDC Prosthetics Design & Fabrication 2 — Questions and Answers
Question 1: Which wax technique involves building up contours incrementally using small additions of molten wax to establish axial walls of a dental prosthesis?
- Carve-back technique
- Additive wax-up technique (Correct answer)
- Sprue placement method
- Investing technique
Correct answer: Additive wax-up technique
The additive wax-up technique builds form by progressively adding molten wax rather than removing bulk material.
Question 2: When designing a three-unit fixed partial denture, the connector dimensions should typically be at least:
- 2 mm × 2 mm cross-section
- 4 mm × 4 mm cross-section (Correct answer)
- 1 mm × 1 mm cross-section
- 6 mm × 6 mm cross-section
Correct answer: 4 mm × 4 mm cross-section
A minimum 4 mm × 4 mm connector cross-section provides adequate strength to resist fracture under occlusal forces in a three-unit FPD.
Question 3: A dental ceramist notices that a PFM crown has metal showing through the incisal ceramic after firing. The MOST likely cause is:
- Excessive opalescent modifier application
- Insufficient porcelain build-up thickness over the metal (Correct answer)
- Over-firing the porcelain
- Using the wrong shade of body porcelain
Correct answer: Insufficient porcelain build-up thickness over the metal
Inadequate porcelain thickness allows the underlying metal substrate to remain visible through translucent incisal porcelain.
Question 4: Which occlusal scheme is MOST often recommended for a full-arch implant-supported fixed prosthesis to protect implants from lateral forces?
- Balanced occlusion
- Group function occlusion
- Mutually protected occlusion
- Canine-guided occlusion with posterior disclusion (Correct answer)
Correct answer: Canine-guided occlusion with posterior disclusion
Canine-guided occlusion with posterior disclusion distributes lateral forces to the canines and protects posterior implants from damaging off-axis loading.
Question 5: During the lost-wax casting process, the elimination of the wax pattern from the investment mold is accomplished by:
- Sandblasting the investment block
- Burnout in a furnace at high temperature (Correct answer)
- Immersing the mold in warm water
- Applying ultrasonic vibration to the mold
Correct answer: Burnout in a furnace at high temperature
High-temperature burnout in a furnace vaporizes the wax pattern and preheats the mold for molten metal casting.
Question 6: The primary purpose of a palatal index or silicone stent during porcelain layering is to:
- Control firing temperature
- Maintain correct lingual contour and thickness reference (Correct answer)
- Prevent dehydration of the ceramic
- Guide sprue placement
Correct answer: Maintain correct lingual contour and thickness reference
A silicone stent fabricated from the diagnostic wax-up provides a reference to ensure consistent lingual contour and porcelain thickness during build-up.
Question 7: When fabricating a zirconia-based restoration, the most critical factor affecting final fit accuracy after sintering is:
- Firing temperature of the veneering ceramic
- Correct application of the manufacturer's sintering shrinkage compensation factor (Correct answer)
- The shade of the zirconia blank
- Surface texture of the milling bur
Correct answer: Correct application of the manufacturer's sintering shrinkage compensation factor
Zirconia undergoes approximately 20–25% linear shrinkage during sintering, so the CAD/CAM system must enlarge the pre-sintered framework using the manufacturer's compensation factor for accurate final fit.
CDC Prosthetics Design & Fabrication 2
Which wax technique involves building up contours incrementally using small additions of molten wax to establish axial walls of a dental prosthesis?