AGD Dental Materials and Biomaterials 2 — Questions and Answers
Question 1: Which polymerization shrinkage direction is most clinically significant in composite restorations?
- Shrinkage toward the light source
- Shrinkage away from the cavity walls
- Shrinkage toward the bonded cavity walls (Correct answer)
- Uniform volumetric shrinkage
Correct answer: Shrinkage toward the bonded cavity walls
Composites shrink toward bonded walls, creating stress that can cause cusp deflection, marginal gaps, and post-operative sensitivity.
Question 2: What is the primary purpose of a silane coupling agent in composite systems?
- Increase filler particle size
- Bond the resin matrix to inorganic filler particles (Correct answer)
- Accelerate photoinitiator activation
- Reduce water sorption
Correct answer: Bond the resin matrix to inorganic filler particles
Silane coupling agents create a chemical bridge between the inorganic glass filler and the organic resin matrix, improving mechanical properties.
Question 3: Which cement has the highest compressive strength and is most suitable for high-stress core buildups?
- Zinc oxide eugenol cement
- Glass ionomer cement
- Resin-modified glass ionomer
- Composite resin (Correct answer)
Correct answer: Composite resin
Composite resin offers the highest compressive strength (250–300 MPa) among core buildup materials, making it ideal for high-stress situations.
Question 4: The Vickers hardness test is most appropriate for measuring hardness of which dental material?
- Impression materials
- Dental cements
- Dental ceramics (Correct answer)
- Elastomeric impression materials
Correct answer: Dental ceramics
The Vickers hardness test uses a diamond pyramid indenter suitable for hard, brittle materials like ceramics.
Question 5: Which property of dental amalgam improves over time after placement due to corrosion products?
- Tensile strength
- Marginal seal (Correct answer)
- Surface hardness
- Thermal conductivity
Correct answer: Marginal seal
Corrosion byproducts of amalgam (tin oxides, tin chlorides) accumulate at margins and improve the marginal seal over time.
Question 6: What is the setting reaction of zinc phosphate cement?
- Acid-base reaction forming zinc phosphate salt (Correct answer)
- Free radical polymerization
- Ionic crosslinking of polycarboxylate chains
- Chelation of calcium ions
Correct answer: Acid-base reaction forming zinc phosphate salt
Zinc phosphate sets via an exothermic acid-base reaction between zinc oxide powder and phosphoric acid liquid, forming zinc phosphate salts.
Question 7: Which factor most significantly reduces the working time of polyvinylsiloxane (PVS) impression material?
- High humidity
- Low ambient temperature
- Sulfur contamination from latex gloves (Correct answer)
- High filler content
Correct answer: Sulfur contamination from latex gloves
Sulfur compounds from latex gloves inhibit the platinum catalyst in PVS, drastically reducing or preventing setting.
AGD Dental Materials and Biomaterials 2
Which polymerization shrinkage direction is most clinically significant in composite restorations?