RDA Restorative and Impression Materials 2

Question 1

What is the setting reaction of amalgam?

Accepted Answer

Reaction between silver-tin alloy and mercury (trituration) forming gamma-1 and gamma-2 phases

Answer

Amalgam sets through a reaction between the silver-tin alloy particles and mercury (during trituration/mixing) to form gamma-1 (Ag2Hg3) and gamma-2 (Sn7-8Hg) crystalline phases. Modern non-gamma-2 alloys are stronger and more corrosion-resistant.

Question 2

Which type of impression material is used for final impressions of crown and bridge preparations due to its high dimensional accuracy?

Accepted Answer

Polyvinyl siloxane (PVS/addition silicone)

Answer

Polyvinyl siloxane (PVS, addition-cured silicone) provides excellent dimensional stability, high detail reproduction, and can be poured multiple times, making it the material of choice for crown and bridge final impressions.

Question 3

What is the purpose of bonding agent in composite resin restorations?

Accepted Answer

To chemically bond the composite resin to acid-etched enamel and/or dentin

Answer

Bonding agents (adhesives) form a chemical and micromechanical bond between composite resin and the acid-etched tooth structure (enamel and/or dentin), creating a durable interface that resists microleakage.

Question 4

What is the purpose of the zinc oxide eugenol (ZOE) temporary restoration?

Accepted Answer

Temporary coverage and sedative effect on the pulp between appointments

Answer

ZOE temporary restorations provide a sedative (soothing) effect on the pulp due to eugenol's analgesic and anti-inflammatory properties, temporary cavity coverage, and a seal between appointments.

Question 5

When mixing type III gypsum dental stone for a diagnostic model, what does an increased water-to-powder (W:P) ratio result in?

Accepted Answer

Weaker model with decreased strength and increased porosity

Answer

Too much water (high W:P ratio) produces excess porosity as water evaporates, resulting in a weaker, softer model with poor surface detail and lower compressive strength.

(RDA) Registered Dental Assistant Practice Test

(RDA) Registered Dental Assistant Practice Test

RDA Restorative and Impression Materials 2