EFDA Impression Materials and Techniques 2 — Questions and Answers
Question 1: Which impression material is most appropriate for capturing a final impression for a complete denture?
- Polyvinyl siloxane (PVS)
- Zinc oxide eugenol (ZOE) paste (Correct answer)
- Alginate
- Plaster of Paris
Correct answer: Zinc oxide eugenol (ZOE) paste
Zinc oxide eugenol paste is a mucostatic material commonly used for final complete denture impressions because it records tissues in a resting state.
Question 2: What is the primary reason polyether impression materials require careful storage conditions?
- They are sensitive to light exposure
- They absorb water and dimensional changes occur in humid environments (Correct answer)
- They release toxic fumes at room temperature
- They harden prematurely if stored above 50°F
Correct answer: They absorb water and dimensional changes occur in humid environments
Polyether materials are hydrophilic and can absorb moisture from the air or storage environment, causing dimensional inaccuracies.
Question 3: When mixing addition silicone (PVS) impression material, what should the clinician avoid?
- Mixing on a glass slab
- Using latex gloves during mixing (Correct answer)
- Using an automix cartridge
- Loading the tray within 30 seconds
Correct answer: Using latex gloves during mixing
Sulfur compounds in latex gloves can inhibit the polymerization of addition silicone, resulting in a tacky, unset surface.
Question 4: A 'monophase' impression technique using PVS means:
- Only light-body material is used throughout
- The same viscosity material is used in both the syringe and tray simultaneously (Correct answer)
- Two separate appointments are required
- A custom tray is not needed
Correct answer: The same viscosity material is used in both the syringe and tray simultaneously
In the monophase technique, a medium-viscosity PVS is loaded in both the syringe and the tray and placed simultaneously.
Question 5: Which property of addition silicone makes it preferred for implant-level impressions?
- Rapid set time under 1 minute
- Excellent dimensional stability allowing delayed pours (Correct answer)
- High compressibility that captures thread detail
- Biocompatibility with titanium
Correct answer: Excellent dimensional stability allowing delayed pours
PVS impressions can be stored for days to weeks without significant dimensional change, making them ideal when models must be poured remotely or later.
Question 6: What does the term 'snap set' refer to in alginate impressions?
- A rapid transition from a fluid to a gel state in a short time window (Correct answer)
- The sound alginate makes when removed from the mouth
- A technique where the tray is snapped onto the arch quickly
- Slow progressive setting over 10–15 minutes
Correct answer: A rapid transition from a fluid to a gel state in a short time window
Alginate undergoes snap set — a relatively abrupt gel transition rather than a gradual stiffening, which helps the clinician identify when setting is complete.
Question 7: Which of the following tray types is required when using polyvinyl siloxane for a full-arch impression?
- Rimlock tray with adhesive (Correct answer)
- Stock perforated tray without adhesive
- Thermoplastic disposable tray
- Water-cooled metal tray
Correct answer: Rimlock tray with adhesive
PVS requires mechanical or chemical retention to the tray; rimlock trays and/or tray adhesive prevent the set material from separating when the impression is removed.
EFDA Impression Materials and Techniques 2
Which impression material is most appropriate for capturing a final impression for a complete denture?