NBDHE NBDHE Dental Materials and Procedures 4

Question 1

Which dental ceramic material is most commonly used for all-ceramic crowns requiring the highest esthetics in the anterior region?

Accepted Answer

Leucite-reinforced ceramic (IPS Empress)

Answer

Leucite-reinforced glass ceramics provide excellent optical properties and translucency that mimic natural tooth enamel, making them preferred for anterior esthetic restorations.

Question 2

What is the working time of a dental material defined as?

Accepted Answer

Time from start of mix until the material can no longer be manipulated

Answer

Working time is the period from the beginning of mixing during which the material can be manipulated and placed without compromising its final properties.

Question 3

What is the significance of the 'critical surface tension' concept when bonding to enamel?

Accepted Answer

The adhesive must have lower surface tension than the substrate to wet and spread properly

Answer

For proper wetting and adhesion, the surface tension of the adhesive must be lower than the critical surface tension of the substrate so the adhesive can spread and flow into surface irregularities.

Question 4

A patient's porcelain-fused-to-metal crown shows repeated porcelain fracture at the incisal edge. What is the most likely cause?

Accepted Answer

Insufficient metal support (coping) beneath the porcelain

Answer

Porcelain requires adequate metal support; without it, flexure of the metal coping during function creates tensile stresses in the brittle porcelain, causing fracture.

Question 5

Which property of dental amalgam is most responsible for its long clinical service life despite inferior marginal integrity compared to composites?

Accepted Answer

Self-sealing behavior due to corrosion products

Answer

Corrosion products (oxides and chlorides) at amalgam margins expand to seal the marginal gap over time, reducing microleakage despite the initially poor marginal fit.

NBDHE Test Practice Test

NBDHE Test Practice Test

NBDHE NBDHE Dental Materials and Procedures 4