ORE Part 1 Dental Materials Science

Question 1

Which phase in conventional dental amalgam is most susceptible to corrosion?

Accepted Answer

Gamma-2 phase (Sn8Hg)

Answer

The gamma-2 phase (Sn8Hg) is the weakest and most corrosion-susceptible phase in conventional amalgam, which is why high-copper amalgams were developed to eliminate it.

Question 2

What is the approximate working time of zinc phosphate cement when mixed at room temperature (23°C)?

Accepted Answer

3–5 minutes

Answer

Zinc phosphate cement has a working time of approximately 3–5 minutes at 23°C, which can be extended by cooling the mixing slab to slow the exothermic reaction.

Question 3

Which impression material is classified as an irreversible hydrocolloid?

Accepted Answer

Alginate

Answer

Alginate is an irreversible hydrocolloid because its gel formation proceeds via a chemical reaction that cannot be reversed by temperature change, unlike agar which is reversible.

Question 4

What is the primary clinical advantage of resin-modified glass ionomer cement (RMGIC) over conventional GIC?

Accepted Answer

Reduced sensitivity to moisture during initial setting

Answer

RMGIC incorporates a resin component that provides an immediate light-cure set, greatly reducing the moisture sensitivity that is the chief clinical weakness of conventional GIC during early setting.

Question 5

Which type of composite resin contains the smallest filler particle size?

Accepted Answer

Microfilled composite (0.04–0.4 μm)

Answer

Microfilled composites contain colloidal silica particles of 0.04–0.4 μm, giving them outstanding polish retention and smooth surface finish, though at the cost of lower mechanical strength.

ORE Part 1 Practice Test

ORE Part 1 Practice Test

ORE Part 1 Dental Materials Science