Dental Materials Science Flashcards
7 cards from real ADC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Dental Materials Science flashcards as text
Irreversible hydrocolloid (alginate) impression material is classified as:
Answer: An elastic material that sets via irreversible chemical reaction and cannot be reused
Alginate is an elastic hydrocolloid that undergoes an irreversible chemical crosslinking reaction, so it cannot be remelted or reused unlike reversible hydrocolloid.
Addition silicone (polyvinyl siloxane) impression materials have superior dimensional stability compared to condensation silicones because:
Answer: Their addition polymerization produces no volatile by-products
Addition silicones polymerize without releasing any by-products, so there is no volume loss after setting, resulting in excellent long-term dimensional accuracy.
Type III dental stone (improved stone) differs from Type II dental plaster in that it has:
Answer: A lower water-to-powder ratio and higher compressive strength
Type III stone (hemihydrate crystals are more regular in shape) requires less mixing water, producing a denser, stronger set product with compressive strength ~35 MPa compared to ~12 MPa for plaster.
The solidus temperature of a casting alloy is defined as the temperature at which:
Answer: The alloy is completely solidified on cooling
The solidus temperature is the highest temperature at which the alloy is entirely in the solid state; below this temperature, no liquid phase exists.
For a porcelain-fused-to-metal (PFM) restoration to resist porcelain fracture during firing and function, the metal alloy must:
Answer: Have a coefficient of thermal expansion (CTE) close to that of the veneering porcelain
Compatible CTEs (metal slightly higher than porcelain) place the porcelain in slight compression on cooling, which glass ceramics tolerate well; large CTE mismatches cause tensile stresses that crack the porcelain.
Condensation silicone impression materials are less dimensionally stable than addition silicones primarily because:
Answer: They release ethanol as a by-product of the condensation polymerization reaction
Condensation silicones polymerize via a reaction that releases low-molecular-weight ethanol, which evaporates from the set impression over time, causing shrinkage.
The recommended casting temperature for most dental gold alloys is:
Answer: Approximately 100–150°C above the liquidus temperature
Casting at 100–150°C above the liquidus provides enough superheat to ensure the alloy remains fully fluid, fills all mold details, and allows complete compensation for heat loss during casting without premature solidification.