ADC Dental Materials Science 2

Question 1

Irreversible hydrocolloid (alginate) impression material is classified as:

Accepted Answer

An elastic material that sets via irreversible chemical reaction and cannot be reused

Answer

A thermoplastic, non-elastic material

Answer

An elastomeric addition-polymerization material

Answer

A rigid non-elastic impression material

Question 2

Addition silicone (polyvinyl siloxane) impression materials have superior dimensional stability compared to condensation silicones because:

Accepted Answer

Their addition polymerization produces no volatile by-products

Answer

They contain more filler particles

Answer

They absorb water from the oral environment

Answer

They have a much lower viscosity

Question 3

Type III dental stone (improved stone) differs from Type II dental plaster in that it has:

Accepted Answer

A lower water-to-powder ratio and higher compressive strength

Answer

A higher water-to-powder ratio and lower compressive strength

Answer

Greater setting expansion and more porosity

Answer

A faster setting time due to added accelerators

Question 4

The solidus temperature of a casting alloy is defined as the temperature at which:

Accepted Answer

The alloy is completely solidified on cooling

Answer

The alloy first begins to melt on heating

Answer

The alloy should be poured into the mold

Answer

The alloy undergoes annealing

Question 5

For a porcelain-fused-to-metal (PFM) restoration to resist porcelain fracture during firing and function, the metal alloy must:

Accepted Answer

Have a coefficient of thermal expansion (CTE) close to that of the veneering porcelain

Answer

Have a much higher melting point than the porcelain

Answer

Contain at least 75% gold by weight

Answer

Have low hardness so porcelain can indent it slightly

Question 6

Condensation silicone impression materials are less dimensionally stable than addition silicones primarily because:

Accepted Answer

They release ethanol as a by-product of the condensation polymerization reaction

Answer

They have higher viscosity and trap more air

Answer

They absorb oral fluids during setting

Answer

They require longer intraoral setting time

Question 7

The recommended casting temperature for most dental gold alloys is:

Accepted Answer

Approximately 100–150°C above the liquidus temperature

Answer

Equal to the solidus temperature of the alloy

Answer

Equal to the liquidus temperature of the alloy

Answer

Approximately 50°C below the liquidus temperature