NBDE Restorative Dentistry 2 — Questions and Answers
Question 1: Which dental material exhibits the highest coefficient of thermal expansion, most closely matching that of dentin?
- Amalgam
- Composite resin (Correct answer)
- Gold alloy
- Porcelain
Correct answer: Composite resin
Composite resin has a coefficient of thermal expansion closest to tooth structure among common restorative materials, though it is still higher than enamel and dentin.
Question 2: A Class II amalgam restoration is being placed. What is the primary purpose of the proximal box form?
- To remove caries at the contact area
- To provide access and extension for the proximal surface (Correct answer)
- To create retention for the restoration
- To establish occlusal clearance
Correct answer: To provide access and extension for the proximal surface
The proximal box of a Class II preparation provides access and extension to include the carious proximal surface and clear the contact area.
Question 3: When placing a composite resin restoration, incremental layering is recommended primarily to:
- Improve color matching
- Reduce polymerization shrinkage stress (Correct answer)
- Increase surface hardness
- Minimize marginal gaps
Correct answer: Reduce polymerization shrinkage stress
Incremental placement reduces the C-factor and allows each layer to partially relieve polymerization shrinkage stress before the next layer is added.
Question 4: Which type of dental cement has the highest compressive strength and is most commonly used for permanent cementation of cast metal restorations?
- Zinc oxide eugenol
- Glass ionomer
- Zinc phosphate (Correct answer)
- Polycarboxylate
Correct answer: Zinc phosphate
Zinc phosphate cement has the highest compressive strength among traditional luting cements and has been used as the gold standard for permanent cast restoration cementation.
Question 5: A patient presents with a large carious lesion approaching the pulp. After caries removal, a thin layer of dentin remains. The BEST liner material to place is:
- Calcium hydroxide (Correct answer)
- Zinc phosphate cement
- Glass ionomer base
- Zinc oxide eugenol
Correct answer: Calcium hydroxide
Calcium hydroxide is used as a direct or indirect pulp capping agent because it induces reparative dentin formation and has a high pH that is bactericidal.
Question 6: In amalgam cavity preparation, resistance form refers to:
- The shape that prevents restoration displacement under functional loads (Correct answer)
- The shape that prevents marginal fracture of the restoration
- Features that anchor the restoration in place
- The removal of unsupported enamel rods
Correct answer: The shape that prevents restoration displacement under functional loads
Resistance form is the preparation feature that prevents fracture of the tooth or restoration under occlusal forces.
Question 7: Which of the following is the MOST critical factor in achieving a good marginal seal with a composite resin restoration?
- Using a high-viscosity composite
- Proper acid etching and bonding technique (Correct answer)
- Placing the restoration in bulk
- Using a self-etching primer only
Correct answer: Proper acid etching and bonding technique
Proper acid etching creates micro-tags in enamel and dentin, and the bonding agent seals the interface, which is essential for marginal integrity and reducing microleakage.
