ADC Dental Materials Science 3

Question 1

The flexural strength of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) used in dental frameworks is approximately:

Accepted Answer

900–1200 MPa

Answer

50–100 MPa

Answer

200–350 MPa

Answer

2500–3000 MPa

Question 2

The transformation toughening mechanism of Y-TZP zirconia involves:

Accepted Answer

Stress-induced tetragonal-to-monoclinic phase transformation that absorbs fracture energy

Answer

Addition of alumina to fill grain boundaries

Answer

Yttria permanently preventing any crystallographic phase change

Answer

Sintering at ultra-high temperatures to eliminate porosity

Question 3

The principal monomer in most modern dental composite resin systems is:

Accepted Answer

Bisphenol A-glycidyl methacrylate (Bis-GMA)

Answer

Polymethyl methacrylate (PMMA)

Answer

Methyl methacrylate (MMA)

Answer

Triethylene glycol dimethacrylate (TEGDMA) alone

Question 4

Volumetric polymerization shrinkage in typical dental composite resins is approximately:

Accepted Answer

1–5%

Answer

0.1–0.5%

Answer

8–12%

Answer

15–20%

Question 5

The bond strength of fourth-generation (total-etch, three-step) dentin bonding agents depends primarily on:

Accepted Answer

Micromechanical interlocking via the hybrid layer formed by resin infiltration of demineralized dentin collagen

Answer

Ionic bonding between the primer and calcium ions in dentin mineral

Answer

Covalent crosslinking between the adhesive and dentin collagen fibers

Answer

Chemical adsorption of the adhesive to residual hydroxyapatite only

Question 6

Etching enamel with 37% phosphoric acid for 15–30 seconds results in:

Accepted Answer

Selective dissolution of enamel crystallite cores or peripheries creating microporosities for resin infiltration

Answer

Complete removal of enamel rods and formation of a chemical bond with fluoride ions

Answer

Surface glazing that improves wettability

Answer

Removal of the entire prismatic layer to expose interprism enamel

Question 7

For a full-coverage all-ceramic posterior crown requiring maximum fracture resistance in a high-occlusal-load patient, the most appropriate ceramic system is:

Accepted Answer

Yttria-stabilized tetragonal zirconia (Y-TZP)

Answer

Feldspathic porcelain

Answer

Leucite-reinforced glass ceramic (IPS Empress)

Answer

Lithium disilicate glass ceramic (IPS e.max)