ADAP Dental Materials 3 — Questions and Answers
Question 1: Which property of wax allows it to be shaped by hand pressure and retain that shape at room temperature?
- Thermal conductivity
- Plasticity (Correct answer)
- Elasticity
- Viscosity
Correct answer: Plasticity
Plasticity is the property that allows wax to be permanently deformed under stress and maintain the new shape once pressure is removed.
Question 2: A provisional crown material that sets via an exothermic reaction and requires removal from the mouth during polymerization is most likely:
- Bis-acryl composite
- Polycarbonate shell
- PMMA (polymethyl methacrylate) acrylic (Correct answer)
- Zinc oxide eugenol temporary cement
Correct 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.
Question 3: The working time of an impression material is defined as:
- Time from mixing until the material is fully set
- Time available from the start of mixing until insertion must be complete (Correct answer)
- Time the impression must remain in the mouth
- Time required to disinfect the impression
Correct 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.
Question 4: Which dental cement is contraindicated as a base under composite resin restorations?
- Glass ionomer cement
- Resin-modified glass ionomer
- Calcium hydroxide (Dycal)
- Zinc oxide eugenol (ZOE) (Correct answer)
Correct 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.
Question 5: What does the term 'snap set' describe in alginate impression material?
- A rapid, abrupt change from sol to gel state (Correct answer)
- The audible click when the tray seats fully
- A gradual, progressive stiffening
- The material cracking during removal
Correct 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.
Question 6: Amalgam's dimensional change after setting is significant because excessive expansion can cause:
- Mercury toxicity
- Postoperative pain from pressure on the pulp and cusps (Correct answer)
- Staining of adjacent teeth
- Corrosion of the amalgam surface
Correct 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.
Question 7: Which mixing technique is recommended for zinc oxide eugenol impression paste?
- Circular stirring motion
- Figure-eight folding and stropping on a glass slab (Correct answer)
- Mechanical spatulation in an auto-mix syringe
- Shaking in a capsule triturator
Correct 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.
ADAP Dental Materials 3
Which property of wax allows it to be shaped by hand pressure and retain that shape at room temperature?