EFDA Impression Materials and Techniques 4

Question 1

What is the function of a tray adhesive when used with elastomeric impressions?

Accepted Answer

To bond the impression material to the tray and prevent separation

Answer

Tray adhesive creates a chemical and mechanical bond between the impression material and the tray walls, preventing distortion on removal.

Question 2

Which dimension error occurs when an alginate impression is left in the mouth too long after setting?

Accepted Answer

Syneresis causing shrinkage

Answer

Prolonged oral contact allows syneresis — expulsion of liquid from the gel — causing the alginate to shrink slightly.

Question 3

A bite registration material's primary requirement is:

Accepted Answer

Dimensional rigidity after setting to maintain occlusal relationship

Answer

Bite registrations must be rigid after setting so that casts can be reproducibly articulated without movement.

Question 4

Polyvinyl siloxane impression materials release which byproduct during setting?

Accepted Answer

Hydrogen gas

Answer

Early-generation addition silicones released hydrogen gas, which could cause porosity in poured stone if models were made too soon after the impression.

Question 5

What is the purpose of applying a retraction cord before taking a crown impression?

Accepted Answer

To displace gingival tissue and expose the margin subgingivally

Answer

Retraction cord mechanically (and sometimes chemically) retracts and displaces gingival tissue to expose the prepared margin for complete capture.

(EFDA) Expanded Function Dental Auxiliary Practice Test

(EFDA) Expanded Function Dental Auxiliary Practice Test

EFDA Impression Materials and Techniques 4