AGD Dental Materials and Application 4 — Questions and Answers
Question 1: The modulus of elasticity of a restorative material is clinically important because it describes:
- How much a material deforms before fracturing
- The stiffness of the material under load (Correct answer)
- The material's resistance to surface wear
- The force required to permanently deform the material
Correct answer: The stiffness of the material under load
The modulus of elasticity (Young's modulus) quantifies stiffness — a high modulus means the material resists elastic deformation, which is critical for load-bearing restorations.
Question 2: When using a total-etch adhesive technique, what is the critical risk of over-drying the dentin after acid etching?
- The enamel rods will be insufficiently etched
- Collagen fiber collapse prevents adhesive infiltration and reduces bond strength (Correct answer)
- The primer becomes hydrophobic and cannot penetrate
- Residual moisture causes secondary caries
Correct answer: Collagen fiber collapse prevents adhesive infiltration and reduces bond strength
Over-drying demineralized dentin causes collagen network collapse, blocking adhesive monomer infiltration and dramatically reducing dentin bond strength.
Question 3: Which type of zirconia is used in monolithic posterior crowns and valued for its high strength?
- Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) (Correct answer)
- Leucite-reinforced ceramic
- Lithium disilicate
- Alumina-based ceramic
Correct answer: Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP)
Y-TZP zirconia has flexural strength of 900–1200 MPa due to transformation toughening, making it the strongest ceramic for monolithic posterior crowns.
Question 4: What is the purpose of the oxygen inhibition layer that forms on the surface of light-cured composites?
- It provides a protective seal against moisture contamination
- It allows chemical bonding to the next increment of composite (Correct answer)
- It reduces the risk of postoperative sensitivity
- It increases the surface hardness of the restoration
Correct answer: It allows chemical bonding to the next increment of composite
The oxygen-inhibited layer contains unreacted monomers that allow subsequent increments or surface sealers to chemically bond, ensuring interlaminar adhesion.
Question 5: A gold alloy classified as Type IV (extra hard) would most appropriately be used for:
- Full-cast crowns on anterior teeth
- Inlays replacing small Class I cavities
- Thin-gauge clasps for removable partial dentures and long-span bridges (Correct answer)
- Cast post and core foundations
Correct answer: Thin-gauge clasps for removable partial dentures and long-span bridges
Type IV gold alloys have the highest hardness and yield strength, making them suitable for thin sections under high stress such as clasps and long-span bridge frameworks.
Question 6: Which factor most significantly affects the depth of cure of a composite resin?
- The shade and translucency of the composite (Correct answer)
- The viscosity of the composite material
- The ambient room temperature during curing
- The brand of curing light used
Correct answer: The shade and translucency of the composite
Darker and more opaque composite shades scatter and absorb light more readily, limiting depth of cure compared to lighter, more translucent shades.
Question 7: Which surface treatment is recommended before bonding a feldspathic porcelain veneer to improve resin bond strength?
- Sandblasting with alumina particles followed by silane application
- Acid etching with phosphoric acid followed by primer
- Hydrofluoric acid etching followed by silane application (Correct answer)
- Tribochemical silica coating only
Correct answer: Hydrofluoric acid etching followed by silane application
Hydrofluoric acid (9.5% for 20 seconds) creates microretentive surface irregularities in feldspathic porcelain, and silane coupling agent then promotes chemical bonding to resin.
AGD Dental Materials and Application 4
The modulus of elasticity of a restorative material is clinically important because it describes: