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

Alginate is an elastic hydrocolloid that undergoes an irreversible chemical crosslinking reaction, so it cannot be remelted or reused unlike reversible hydrocolloid.

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

Addition silicones polymerize without releasing any by-products, so there is no volume loss after setting, resulting in excellent long-term dimensional accuracy.

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

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.

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 solidus temperature is the highest temperature at which the alloy is entirely in the solid state; below this temperature, no liquid phase exists.

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

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.

ADC - Australian Dental Council Practice Test

ADC - Australian Dental Council Practice Test

ADC Dental Materials Science 2