EFDA Impression Materials and Techniques 3

Question 1

Which impression material is classified as a reversible hydrocolloid?

Accepted Answer

Agar

Answer

Agar (colloid) is reversible because it can be repeatedly liquefied by heating and re-gelled by cooling, unlike alginate which sets irreversibly.

Question 2

When taking a preliminary alginate impression, the dentist notices voids in the palate area. What is the most likely cause?

Accepted Answer

Air entrapment during spatulation or tray seating

Answer

Voids in the impression are commonly caused by air bubbles trapped during mixing or when the material fails to flow into all areas during tray placement.

Question 3

The water-to-powder ratio for alginate primarily affects which property?

Accepted Answer

Tear strength and flow

Answer

Altering the water-to-powder ratio changes both the consistency (flow) and the tear strength of the set alginate.

Question 4

A polysulfide impression has a distinctive smell. What causes this?

Accepted Answer

Sulfur-containing compounds in the base paste reacting with lead dioxide

Answer

Polysulfide rubber contains mercaptan (thiol) sulfur groups that react with lead dioxide accelerator, producing a strong sulfur odor.

Question 5

What is the recommended action if an alginate impression cannot be poured immediately?

Accepted Answer

Store in an airtight bag with a moist paper towel for up to 1 hour

Answer

Alginate should be wrapped in a damp towel and sealed in a bag to prevent syneresis and imbibition; ideally poured within 1 hour.

(EFDA) Expanded Function Dental Auxiliary Practice Test

(EFDA) Expanded Function Dental Auxiliary Practice Test

EFDA Impression Materials and Techniques 3