Dental Materials Science Flashcards

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

Answer: Gamma-2 phase (Sn8Hg)

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.

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

Answer: 3–5 minutes

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.

Which impression material is classified as an irreversible hydrocolloid?

Answer: Alginate

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.

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

Answer: Reduced sensitivity to moisture during initial setting

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.

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

Answer: Microfilled composite (0.04–0.4 μm)

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.

What is the role of the silane coupling agent in composite resin?

Answer: Forms a chemical bond between the organic resin matrix and inorganic filler particles

Silane coupling agents create a chemical (covalent) bond between the organic resin matrix and the inorganic filler particle surface, which is critical for load transfer and durability.

The Vickers Hardness (VHN) test measures which material property?

Answer: Resistance to permanent surface indentation

The Vickers Hardness test measures a material's resistance to permanent surface deformation by pressing a diamond pyramid indenter into the surface under a defined load and measuring the indentation size.