Restorative and Impression Materials Flashcards
7 cards from real RDA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Restorative and Impression Materials flashcards as text
Which impression material is most affected by the presence of moisture or blood during the impression-taking procedure?
Answer: Polyvinyl siloxane (PVS)
Polyvinyl siloxane (PVS) is hydrophobic and is significantly affected by moisture, blood, or saliva contamination, leading to voids and inaccurate impressions.
When mixing glass ionomer cement for a base, what is the ideal powder-to-liquid ratio compared to a luting consistency?
Answer: Higher powder ratio than luting
A base consistency of glass ionomer requires a higher powder-to-liquid ratio to achieve a stiffer, more viscous mix that can withstand condensation forces.
What is the purpose of applying a cavity varnish before placing an amalgam restoration?
Answer: To reduce microleakage and protect the pulp from irritants
Cavity varnish seals dentinal tubules to reduce microleakage and protects the pulp from chemical irritants until the amalgam has fully set.
A custom tray for a final impression should be constructed to leave how much space for impression material between the tray and the tissues?
Answer: 2–3 mm
A uniform 2–3 mm space between the custom tray and tissues allows for an adequate thickness of impression material for dimensional accuracy.
Which restorative material undergoes the LEAST thermal expansion and contraction, making it most dimensionally stable in the oral cavity?
Answer: Ceramic (porcelain)
Ceramic/porcelain has a coefficient of thermal expansion very close to that of natural tooth structure, making it the most dimensionally stable under temperature changes.
During the setting of zinc phosphate cement, why is the powder incorporated into the liquid in small increments over a wide, cool glass slab?
Answer: To dissipate heat and extend working time
The setting reaction of zinc phosphate is exothermic; spatulating on a cool slab and adding powder incrementally dissipates heat and prolongs working time.
Which type of gypsum product is used to construct dies for crown and bridge fabrication due to its high compressive strength and minimal setting expansion?
Answer: Die stone (Type IV)
Type IV die stone (high-strength stone) has the greatest compressive strength and lowest setting expansion, making it ideal for accurate die fabrication.