Silicone differs from polyether polymer with respect to:

 # Silicone differs from polyether polymer with respect to:

A. Affinity for water

B. Place and time of one

C. Area of one

D. Cost effectiveness

The correct answer is A. Affinity for water.

One of the disadvantages of the silicone impression materials (including condensation silicones) is their inherent hydrophobic nature. A nonionic surfactant can be added to the paste in the manufacturing process to render a degree of hydrophilicity to the surface of the material. This surfactant migrates toward the surface of the impression material and has its hydrophilic segment oriented toward the surface—a phenomenon that makes the surface more wettable by water. These impression materials still require a dry field for impression making. Pouring the set impression with a gypsum forming

mixture is facilitated because the wet stone has a greater affinity for the hydrophilic surface. The clinical significance of hydrophilic additives is discussed in subsequent sections.

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One of the best agents used in successful pulp capping is:

 # One of the best agents used in successful pulp capping is:

A. Copper cement

B. Calcium hydroxide

C. Amalgam

D. Zinc oxide

The correct answer is B. Calcium hydroxide.

Calcium hydroxide, because of its high pH value, acts as a pulp irritant and stimulates reparative dentine formation . It is also used as a pulp-capping agent, both in direct and indirect pulp capping.

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The principal ingredient of an irreversible hydrocolloid impression is:

 #  The principal ingredient of an irreversible hydrocolloid impression is:

A. Agar

B. Tri sodium phosphate

C. Sodium alginate

D. Colloidal silica

The correct answer is C. Sodium alginate.

The chief active ingredient in the alginate impression materials is one of the soluble alginates, such as sodium, potassium, or triethanolamine alginate.

The diatomaceous earth acts as a filler to increase the strength and stiffness of the alginate gel. It also produces a smooth texture and ensures the formation of a firm gel surface that is not tacky.

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Metal that expands on solidification from the molten state is:

 # A metal that expands on solidification from the molten state is:

A. Gold

B. Silver

C. Bismuth

D. Copper

The correct answer is C. Bismuth.

Elemental bismuth is denser in the liquid phase than the solid, a characteristic it shares with germanium, silicon, gallium, and water. Bismuth expands 3.32% on solidification; therefore, it was long a component of low-melting typesetting alloys, where it compensated for the contraction of the other alloying components to form almost isostatic bismuth-lead eutectic alloys.

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