CCA Impression Techniques & Molding 3 — Questions and Answers
Question 1: Which impression technique is preferred when the anaplastologist needs to capture an auricular defect with deep concavities and significant undercuts?
- Single-step monophase alginate
- Two-stage putty-wash technique using VPS (Correct answer)
- Zinc oxide eugenol impression paste
- Impression plaster with gauze reinforcement
Correct answer: Two-stage putty-wash technique using VPS
The two-stage putty-wash VPS technique records undercuts accurately while the light-body wash captures fine detail without trapping.
Question 2: What is the primary function of adding a gauze mesh or burlap reinforcement within a plaster mold?
- To provide intrinsic color to the prosthesis
- To increase mold strength and prevent cracking during processing (Correct answer)
- To accelerate stone setting time
- To create a smooth mold surface
Correct answer: To increase mold strength and prevent cracking during processing
Fiber reinforcement embedded in the mold body resists fracture forces during clamping and demold, extending mold lifespan.
Question 3: Polysulfide rubber base impression material is less commonly used in anaplastology primarily because:
- It does not capture adequate surface detail
- It has an unpleasant odor and longer set time compared to VPS (Correct answer)
- It is incompatible with stone materials
- It cannot be used near mucosal tissue
Correct answer: It has an unpleasant odor and longer set time compared to VPS
Polysulfide materials produce sulfurous odors and require extended setting times, making patient management more difficult compared to VPS alternatives.
Question 4: During impression making for a mid-facial prosthesis, a 'vent hole' in the tray is used to:
- Allow the patient to breathe through the tray
- Provide an escape path for excess material and reduce hydraulic pressure (Correct answer)
- Enable introduction of additional impression material after seating
- Mark the midline of the prosthesis
Correct answer: Provide an escape path for excess material and reduce hydraulic pressure
Vent holes prevent hydraulic pressure buildup that could displace soft tissue and distort the recorded anatomy.
Question 5: When is a custom impression tray preferred over a stock tray for facial prosthetic impressions?
- When the defect is small and regular in shape
- When the defect anatomy is irregular, large, or requires controlled material thickness (Correct answer)
- When alginate is the chosen impression material
- When the patient has no remaining facial landmarks
Correct answer: When the defect anatomy is irregular, large, or requires controlled material thickness
Custom trays ensure uniform material thickness, reduce material waste, and provide better control over border extension in complex defects.
Question 6: The 'snap set' characteristic of alginate is clinically significant because it:
- Allows extended working time for complex impressions
- Reduces patient discomfort by minimizing the set wait period (Correct answer)
- Produces finer surface detail than VPS
- Eliminates the need for a separating medium
Correct answer: Reduces patient discomfort by minimizing the set wait period
Alginate's rapid, abrupt gelation minimizes the time patients must remain motionless, which is especially important for patients with limited cooperation.
Question 7: A mold seam line appearing on the finished silicone prosthesis most directly results from:
- Inadequate intrinsic pigmentation
- Misalignment or incomplete closure of the two mold halves (Correct answer)
- Using a high water-to-powder ratio in the stone mix
- Over-packing the mold with silicone
Correct answer: Misalignment or incomplete closure of the two mold halves
Poor mold registration or incomplete seating creates a gap where excess silicone flashes, leaving a visible seam on the prosthesis surface.
CCA Impression Techniques & Molding 3
Which impression technique is preferred when the anaplastologist needs to capture an auricular defect with deep concavities and significant undercuts?