GC: Dental Materials practice questions

Answer: A) Zinc oxide-eugenol

• ACorrect. Reinforced for strength.
• BIncorrect. It's zinc oxide-eugenol.
• CIncorrect. It's zinc oxide-eugenol.
• DIncorrect. It's zinc oxide-eugenol.

Answer: C) Agar

Agar is the reversible hydrocolloid: heat turns it into a sol and cooling turns it into a gel. Alginate is the irreversible hydrocolloid, and polyvinyl siloxane and polyether are elastomers.

• AIncorrect. Polyvinyl siloxane (addition silicone) is an elastomer that sets by a chemical reaction. It is not a hydrocolloid.
• BIncorrect. Alginate is a hydrocolloid, but it is irreversible. It gels by a chemical precipitation reaction and cannot be turned back into a sol by heating.
• CCorrect. Agar is a thermally reversible hydrocolloid. It becomes a fluid sol in boiling water and sets to an elastic gel when cooled.
• DIncorrect. Polyether is a rigid elastomeric impression material that sets chemically. It is not a hydrocolloid.

Answer: A) Bite rims and denture setups

• ACorrect. It's firm at room temperature.
• BIncorrect. That's an elastomer.
• CIncorrect. That's gutta-percha.
• DIncorrect. That's paste.

Answer: B) Dispensing base and catalyst from a cartridge through a static mixing tip

Elastomeric impression materials such as PVS are commonly mixed with automix cartridges and static mixing tips, which give consistent mixes with less waste. Hand spatulation and dynamic mechanical mixers are other options.

• AIncorrect. Mixing powder and water in a rubber bowl is how alginate and gypsum products are prepared. Elastomers come as a base and a catalyst (or putty), not as a powder mixed with water.
• BCorrect. Automix cartridges loaded in a dispensing gun push the base and catalyst through a static mixing tip. This gives a consistent, bubble-free mix and wastes less material than hand mixing. Hand spatulation on a pad, kneading putty, and dynamic mechanical mixers are also used.
• CIncorrect. Heating in a water bath is used for reversible (agar) hydrocolloid and impression compound. Elastomers set by a chemical reaction between base and catalyst, not by heating and cooling.
• DIncorrect. Capsule trituration is used for amalgam and some encapsulated glass ionomer cements, not for elastomeric impression materials.

Answer: B) It releases heat as it sets, so a thick mass can become quite warm

Self-curing acrylic resin sets by exothermic addition polymerization, so it gives off heat. Thick masses can get hot enough to irritate tissue.

• AIncorrect. Acrylic polymerization is not endothermic. It releases heat rather than absorbing it.
• BCorrect. Addition polymerization of methyl methacrylate is exothermic. The more material there is, the more heat it gives off, so thick or bulky areas can get hot.
• CIncorrect. Self-curing acrylic sets by chemically activated polymerization, not evaporation, and that reaction gives off heat.
• DIncorrect. Self-curing resin is chemically activated and needs no curing light. The heat comes from the polymerization reaction itself.

Answer: D) Hydrogen peroxide

• AIncorrect. They release hydrogen peroxide.
• BIncorrect. They release hydrogen peroxide.
• CIncorrect. They release hydrogen peroxide.
• DCorrect. The active whitening agent.

Answer: A) Trituration

• ACorrect. Done in an amalgamator.
• BIncorrect. That's packing it into the tooth.
• CIncorrect. That shapes the restoration.
• DIncorrect. That smooths the surface.

Answer: C) Shorten the setting time

• AIncorrect. Temperature affects setting.
• BIncorrect. That's cooler water.
• CCorrect. Cooler water lengthens it.
• DIncorrect. It sets faster.

Answer: C) Bonds filler particles to the resin matrix

• AIncorrect. That's pigment.
• BIncorrect. That's a chemical initiator.
• CCorrect. It strengthens the composite.
• DIncorrect. That's glass ionomer.

Answer: B) Weaker

• AIncorrect. Stone is stronger.
• BCorrect. Used for study models, not dies.
• CIncorrect. Die stone is used for dies.
• DIncorrect. It's softer.