Dental Materials Flashcards

Which property of wax allows it to be shaped by hand pressure and retain that shape at room temperature?

Answer: Plasticity

Plasticity is the property that allows wax to be permanently deformed under stress and maintain the new shape once pressure is removed.

A provisional crown material that sets via an exothermic reaction and requires removal from the mouth during polymerization is most likely:

Answer: PMMA (polymethyl methacrylate) acrylic

PMMA acrylic generates significant exothermic heat during polymerization and must be removed and replaced in water repeatedly to protect the pulp.

The working time of an impression material is defined as:

Answer: Time available from the start of mixing until insertion must be complete

Working time is the period from the start of mixing during which the material can be manipulated and loaded into the tray before insertion.

Which dental cement is contraindicated as a base under composite resin restorations?

Answer: Zinc oxide eugenol (ZOE)

Eugenol in ZOE cement inhibits the polymerization of composite resin, preventing proper curing when the two materials contact each other.

What does the term 'snap set' describe in alginate impression material?

Answer: A rapid, abrupt change from sol to gel state

Snap set refers to alginate's characteristic rapid transition from a flowable sol to a firm gel with little intermediate stage.

Amalgam's dimensional change after setting is significant because excessive expansion can cause:

Answer: Postoperative pain from pressure on the pulp and cusps

Excessive post-setting expansion creates pressure within the rigid tooth cavity, causing sensitivity, fracture lines, or restoration failure.

Which mixing technique is recommended for zinc oxide eugenol impression paste?

Answer: Figure-eight folding and stropping on a glass slab

ZOE impression paste is mixed by folding and stropping the two equal-length ribbons on a paper pad until a uniform color is achieved.