NBDHE NBDHE Dental Materials and Procedures 5

Question 1

Which type of elastomeric impression material requires the use of a custom or stock tray with adhesive AND has the longest setting time among elastomers?

Accepted Answer

Polysulfide (mercaptan)

Answer

Polysulfide (mercaptan) impression materials have the longest setting time of all elastomers, require an adhesive for tray retention, and must be poured promptly due to poor dimensional stability.

Question 2

What is the primary function of a cavity varnish when used under amalgam restorations?

Accepted Answer

To reduce microleakage and protect the pulp from chemical irritants

Answer

Cavity varnish seals the dentinal tubules to reduce penetration of corrosion products and chemical irritants from amalgam into the pulp until self-sealing occurs.

Question 3

In an ideal casting procedure, what is the purpose of the sprue former attached to the wax pattern?

Accepted Answer

To provide a channel for molten metal to enter the mold cavity

Answer

The sprue former, when removed, creates a channel (sprue) through which molten alloy is forced under centrifugal or pressure casting into the mold space.

Question 4

Which characteristic of zirconia (Y-TZP) makes it the strongest all-ceramic material available for posterior crowns?

Accepted Answer

Transformation toughening mechanism that arrests crack propagation

Answer

Yttria-stabilized zirconia undergoes stress-induced phase transformation from tetragonal to monoclinic at crack tips, which increases volume and closes the crack — a toughening mechanism called transformation toughening.

Question 5

A patient reports sensitivity after placement of a resin composite in a Class II preparation. Which procedural step most likely prevented adequate hybrid layer formation?

Accepted Answer

Over-drying the etched dentin, causing dentin collapse

Answer

Over-drying etched dentin collapses the collagen fibril network, preventing resin monomer penetration and resulting in an incomplete hybrid layer with residual sensitivity.

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NBDHE Test Practice Test

NBDHE NBDHE Dental Materials and Procedures 5