NBDHE Dental Materials and Procedures 2

Question 1

Which property of amalgam restorations is responsible for the initial poor marginal seal shortly after placement?

Accepted Answer

Dimensional change — initial contraction before expansion

Answer

Fresh amalgam undergoes slight contraction immediately after setting, before its later characteristic expansion, creating initial marginal gaps that may allow microleakage.

Question 2

Which bonding mechanism primarily explains the adhesion of glass ionomer cement to tooth structure?

Accepted Answer

Chemical adhesion through ionic bonding with hydroxyapatite

Answer

Glass ionomer cements adhere to tooth structure primarily through ionic bonding between the carboxylate groups of the polyacrylic acid and the calcium in hydroxyapatite.

Question 3

What is the purpose of the smear layer in restorative dentistry, and how does acid etching affect it?

Accepted Answer

It plugs dentinal tubules; acid etching removes it and opens tubules

Answer

The smear layer is a thin film of debris on prepared dentin that plugs tubule openings; acid etching dissolves it and opens dentinal tubules, enabling resin tag formation.

Question 4

Which type of impression material is classified as an irreversible hydrocolloid?

Accepted Answer

Alginate

Answer

Alginate is an irreversible hydrocolloid because its gelation is a chemical reaction that cannot be reversed; it cannot be re-liquefied and reused.

Question 5

Composite resin restorations undergo polymerization shrinkage. Which technique BEST reduces the clinical consequences of this shrinkage?

Accepted Answer

Incremental placement technique with each increment ≤2 mm

Answer

Placing composite in increments of 2 mm or less and curing each layer independently reduces the volume contracting at any one time, minimizing stress at the tooth-restoration interface.

NBDHE Test Practice Test

NBDHE Test Practice Test

NBDHE Dental Materials and Procedures 2