CCA Impression Techniques & Molding 2 — Questions and Answers
Question 1: Which impression material is most appropriate for capturing fine surface detail on a hairless scalp area for a cranial prosthesis?
- Irreversible hydrocolloid (alginate)
- Vinyl polysiloxane (VPS) (Correct answer)
- Zinc oxide eugenol paste
- Impression plaster
Correct answer: Vinyl polysiloxane (VPS)
Vinyl polysiloxane provides superior dimensional stability and captures fine detail with minimal distortion, making it ideal for cranial prosthetic impressions.
Question 2: What is the primary reason a two-part (matrix and core) mold is used for complex auricular prostheses?
- To reduce material cost
- To allow removal of undercut areas without tearing the prosthesis (Correct answer)
- To speed up the curing process
- To improve color matching
Correct answer: To allow removal of undercut areas without tearing the prosthesis
A two-part mold allows the anaplastologist to demold prostheses with undercuts without distortion or tearing of the silicone material.
Question 3: When taking a facial impression for an orbital prosthesis, the patient's eye should be:
- Open and looking upward
- Closed with a protective conformer or gauze in place (Correct answer)
- Covered with petroleum jelly only
- Left untreated as tissue movement aids impression accuracy
Correct answer: Closed with a protective conformer or gauze in place
A protective conformer or gauze shields the orbital cavity and remaining ocular structures from impression material during the procedure.
Question 4: What does the term 'working time' refer to in the context of impression materials?
- Total time from mixing to final set
- Time available to manipulate the material after mixing before it begins to set (Correct answer)
- Duration required to clean and disinfect the mold
- Time needed to pour the stone model
Correct answer: Time available to manipulate the material after mixing before it begins to set
Working time is the window during which the clinician can seat, adapt, and position the impression material before gelation or polymerization begins.
Question 5: Which type of separator (release agent) is most commonly applied to stone or plaster molds before packing intrinsic silicone?
- Petroleum jelly
- Tin foil substitute (alginate separator)
- Silicone mold release spray (Correct answer)
- Isopropyl alcohol
Correct answer: Silicone mold release spray
Silicone-specific mold release agents prevent adhesion between cured silicone and the mold surface without interfering with color or cure.
Question 6: An impression of the nasal defect yields a distorted model. The most likely cause is:
- Using too little impression material
- Premature removal of the impression before adequate set (Correct answer)
- Mixing the stone at a low water-to-powder ratio
- Using a rigid tray
Correct answer: Premature removal of the impression before adequate set
Removing an impression before it has fully set causes elastic rebound and permanent distortion of the recorded anatomy.
Question 7: When fabricating a mold for a nasal prosthesis using Type III dental stone, what is the purpose of vibrating the stone during pour?
- To accelerate setting time
- To eliminate air bubbles and ensure complete adaptation to surface detail (Correct answer)
- To increase the water-to-powder ratio
- To improve the final color of the mold
Correct answer: To eliminate air bubbles and ensure complete adaptation to surface detail
Vibration encourages entrapped air bubbles to rise and escape, producing a void-free stone model that accurately reproduces surface detail.
CCA Impression Techniques & Molding 2
Which impression material is most appropriate for capturing fine surface detail on a hairless scalp area for a cranial prosthesis?