RDA Restorative and Impression Materials 5 — Questions and Answers
Question 1: A patient bites through an alginate impression before it has fully set. What is the MOST likely result?
- The impression will be unaffected
- Permanent deformation and inaccurate reproduction of the arch (Correct answer)
- The alginate will re-flow and self-correct
- The material will set faster due to pressure
Correct answer: Permanent deformation and inaccurate reproduction of the arch
Applying pressure to alginate during gelation causes permanent deformation (tearing or distortion) because the material cannot recover elastically until fully set.
Question 2: What property of polyether impression material makes it advantageous in humid clinical conditions?
- It is highly hydrophobic
- It is hydrophilic and wets oral tissues well (Correct answer)
- It releases fluoride during setting
- It requires no mixing
Correct answer: It is hydrophilic and wets oral tissues well
Polyether is hydrophilic, which allows it to flow into moist sulcular areas and wet oral tissues effectively, producing detailed impressions even in humid conditions.
Question 3: When preparing an amalgam restoration, the dental assistant mixes the amalgam and notices it is crumbly and dry. What is the MOST likely cause?
- Overtrituration
- Undertrituration (Correct answer)
- Using too much mercury
- Contamination with water
Correct answer: Undertrituration
Undertrituration results in insufficient mercury-alloy contact, producing a crumbly, grainy mix with reduced strength and poor adaptation.
Question 4: Which composite resin curing light wavelength range is needed to activate camphorquinone, the most common photoinitiator?
- 350–380 nm (ultraviolet)
- 400–500 nm (blue light) (Correct answer)
- 550–600 nm (green light)
- 650–700 nm (red light)
Correct answer: 400–500 nm (blue light)
Camphorquinone is activated by blue light in the 400–500 nm range, with peak absorption at approximately 468 nm.
Question 5: A bis-acryl composite provisional material was used to fabricate a temporary crown. What is an important property that distinguishes it from PMMA provisional materials?
- Bis-acryl generates more heat during polymerization
- Bis-acryl can be easily relined chairside with more material
- Bis-acryl generates less exothermic heat during setting (Correct answer)
- Bis-acryl is more opaque and less aesthetic than PMMA
Correct answer: Bis-acryl generates less exothermic heat during setting
Bis-acryl provisional materials produce significantly less exothermic heat during polymerization compared to PMMA, reducing risk of pulpal irritation.
Question 6: An impression is removed from the mouth and a void is found at the margin of the preparation. Which of the following is the MOST likely cause?
- Impression material was too viscous
- Air was trapped during syringing of light-body material (Correct answer)
- The tray was removed too quickly
- The patient opened their mouth too wide
Correct answer: Air was trapped during syringing of light-body material
Voids at critical margin areas are most commonly caused by air entrapment during injection of the light-body material around the preparation.
Question 7: Which of the following describes the correct storage condition for elastomeric impression materials to maintain their shelf life?
- Room temperature (68–77°F) away from heat and sunlight (Correct answer)
- Refrigerator at 35–40°F
- Freezer at 0°F
- Warm cabinet at 100°F to prevent moisture absorption
Correct answer: Room temperature (68–77°F) away from heat and sunlight
Elastomeric materials should be stored at room temperature (68–77°F), away from heat and direct sunlight, which can accelerate premature polymerization.
RDA Restorative and Impression Materials 5
A patient bites through an alginate impression before it has fully set.
What is the MOST likely result?