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

Y-TZP exhibits a flexural strength of approximately 900–1200 MPa due to its transformation-toughening mechanism, making it the strongest clinical dental ceramic.

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

When a crack propagates in Y-TZP, the tensile stress at the crack tip triggers a tetragonal-to-monoclinic transformation accompanied by ~4% volume expansion that closes the crack and absorbs energy.

Question 3

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

Accepted Answer

Bisphenol A-glycidyl methacrylate (Bis-GMA)

Answer

Bis-GMA is the backbone monomer in the majority of composite resins; its high molecular weight and two reactive methacrylate groups produce a rigid, highly cross-linked polymer network.

Question 4

Volumetric polymerization shrinkage in typical dental composite resins is approximately:

Accepted Answer

1–5%

Answer

Most composites shrink 1–5% by volume during free-radical polymerization as van der Waals gaps between monomer molecules are replaced by shorter covalent bonds, generating internal stresses at the cavity margin.

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

Total-etch systems remove the smear layer and demineralize dentin, allowing primer/adhesive monomers to infiltrate and polymerize within exposed collagen fibers, creating a hybrid layer that provides micromechanical retention.

ADC - Australian Dental Council Practice Test

ADC - Australian Dental Council Practice Test

ADC Dental Materials Science 3