EFDA Impression Materials and Techniques 5 — Questions and Answers
Question 1: A heavy-body PVS material placed in the impression tray is also called:
- Wash material
- Light body
- Putty or tray material (Correct answer)
- Monophase material
Correct answer: Putty or tray material
Heavy-body or putty PVS fills the tray and provides bulk support while light-body (wash) material captures fine detail.
Question 2: Which factor most significantly shortens the working time of alginate?
- Using cold water during mixing
- Using warm water during mixing (Correct answer)
- Increasing the powder-to-water ratio slightly
- Spatulating for a shorter time
Correct answer: Using warm water during mixing
Warm water accelerates the chemical setting reaction of alginate, reducing working time; cold water retards it.
Question 3: What is the purpose of the 'two-step putty-wash' PVS technique?
- To use two different brands of PVS for cost savings
- To allow putty to set first, creating a rigid tray, then a thin wash captures fine detail (Correct answer)
- To capture both arches simultaneously in one appointment
- To reduce the need for tray adhesive
Correct answer: To allow putty to set first, creating a rigid tray, then a thin wash captures fine detail
The set putty acts as a rigid custom tray, and the subsequent thin wash flows to capture precise marginal detail without distortion from tray flex.
Question 4: Which impression material contains eugenol and is contraindicated in patients with eugenol sensitivity?
- Condensation silicone
- Polyvinyl siloxane
- Zinc oxide eugenol (ZOE) paste (Correct answer)
- Polyether
Correct answer: Zinc oxide eugenol (ZOE) paste
ZOE impression paste contains eugenol (oil of cloves) and can cause allergic reactions or tissue irritation in sensitive patients.
Question 5: An impression that records only the occlusal surfaces and interproximal contacts without capturing soft tissue is called a:
- Quadrant impression
- Bite registration (Correct answer)
- Sectional impression
- Functional impression
Correct answer: Bite registration
A bite registration records the spatial relationship of opposing teeth in occlusion and is not intended to capture tissue or tooth detail for a restoration.
Question 6: Why is a custom tray with uniform spacer thickness preferred over a stock tray for final impressions?
- It is faster to fabricate than selecting a stock tray
- It ensures a uniform layer of impression material, reducing distortion and improving accuracy (Correct answer)
- It eliminates the need for retraction cord
- It allows the use of alginate for final impressions
Correct answer: It ensures a uniform layer of impression material, reducing distortion and improving accuracy
Uniform material thickness distributes seating pressure evenly and reduces the risk of areas where tray contact displaces material and distorts the impression.
Question 7: What characteristic of polyether impression material makes it well-suited for use in a moist or slightly wet field?
- It is hydrophobic and repels moisture
- It is hydrophilic and can set accurately in the presence of moisture (Correct answer)
- It chemically bonds to enamel in wet conditions
- It expands slightly in moisture to compensate for die stone shrinkage
Correct answer: It is hydrophilic and can set accurately in the presence of moisture
Polyether's hydrophilic nature allows it to wet tooth surfaces effectively even when saliva or moisture is present, capturing detail accurately.
EFDA Impression Materials and Techniques 5
A heavy-body PVS material placed in the impression tray is also called: