NBDHE Dental Materials and Procedures Flashcards

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

Answer: Leucite-reinforced ceramic (IPS Empress)

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

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

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

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

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

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

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.

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

Answer: Insufficient metal support (coping) beneath the porcelain

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

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

Answer: Self-sealing behavior due to corrosion products

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

When fabricating a custom acrylic tray, why is a spacer wax placed over the diagnostic cast?

Answer: To create space for an adequate thickness of impression material

The spacer wax creates a uniform space between the tray and the tissue, ensuring there is enough room for the impression material to flow and record fine detail.

What is the role of eugenol in zinc oxide eugenol (ZOE) cement?

Answer: It acts as a chelating agent that reacts with zinc oxide to form zinc eugenolate

Eugenol chelates with zinc oxide to form an amorphous zinc eugenolate matrix that is the primary reaction product giving ZOE its sedative and setting properties.