Dental Materials Science Flashcards
7 cards from real ADC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Dental Materials Science flashcards as text
The flexural strength of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) used in dental frameworks is approximately:
Answer: 900–1200 MPa
Y-TZP exhibits a flexural strength of approximately 900–1200 MPa due to its transformation-toughening mechanism, making it the strongest clinical dental ceramic.
The transformation toughening mechanism of Y-TZP zirconia involves:
Answer: Stress-induced tetragonal-to-monoclinic phase transformation that absorbs fracture energy
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.
The principal monomer in most modern dental composite resin systems is:
Answer: Bisphenol A-glycidyl methacrylate (Bis-GMA)
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.
Volumetric polymerization shrinkage in typical dental composite resins is approximately:
Answer: 1–5%
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.
The bond strength of fourth-generation (total-etch, three-step) dentin bonding agents depends primarily on:
Answer: Micromechanical interlocking via the hybrid layer formed by resin infiltration of demineralized dentin collagen
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.
Etching enamel with 37% phosphoric acid for 15–30 seconds results in:
Answer: Selective dissolution of enamel crystallite cores or peripheries creating microporosities for resin infiltration
Phosphoric acid produces a type I, II, or III etch pattern by preferentially dissolving enamel prism cores or peripheries, creating micropores 5–50 µm deep that allow resin tags to form and provide micromechanical bonding.
For a full-coverage all-ceramic posterior crown requiring maximum fracture resistance in a high-occlusal-load patient, the most appropriate ceramic system is:
Answer: Yttria-stabilized tetragonal zirconia (Y-TZP)
Y-TZP has the highest flexural strength (900–1200 MPa) of all dental ceramics, making it the best choice for posterior crowns under high occlusal loads, though its opacity may limit anterior esthetic use.