NBDE Restorative Dentistry 3 — Questions and Answers
Question 1: A dentist is preparing a tooth for a full-coverage metal-ceramic crown. The facial reduction should be approximately:
- 0.5 mm
- 1.0 mm
- 1.5–2.0 mm (Correct answer)
- 2.5–3.0 mm
Correct answer: 1.5–2.0 mm
Facial reduction of 1.5–2.0 mm is required for metal-ceramic crowns to provide adequate space for the metal coping and overlying porcelain without compromising esthetics or strength.
Question 2: Which finish line design provides the best support for an all-ceramic crown margin?
- Knife-edge
- Feather edge
- Deep chamfer or shoulder (Correct answer)
- Reverse bevel
Correct answer: Deep chamfer or shoulder
A deep chamfer or shoulder provides a definitive seat and adequate bulk of ceramic at the margin, reducing the risk of fracture in all-ceramic restorations.
Question 3: The phenomenon where a freshly mixed zinc phosphate cement begins to set rapidly due to excess water is called:
- Hygroscopic expansion
- Chelation
- Early wash-out
- Exothermic acceleration (Correct answer)
Correct answer: Exothermic acceleration
Excess moisture accelerates the exothermic acid-base reaction of zinc phosphate cement, causing premature setting.
Question 4: A patient requires a posterior composite restoration on tooth #19. To prevent cuspal fracture, the dentist should ensure:
- The occlusal contact is on the composite material
- Cuspal coverage is included in the restoration design (Correct answer)
- The composite is placed in a single bulk increment
- The restoration extends to include adjacent proximal surfaces
Correct answer: Cuspal coverage is included in the restoration design
When substantial tooth structure is missing, cuspal coverage with composite or an indirect restoration protects weakened cusps from fracture under occlusal stress.
Question 5: Which property of dental amalgam is primarily responsible for its long-term marginal integrity?
- High tensile strength
- Corrosion byproducts that seal the margin (Correct answer)
- Low coefficient of thermal expansion
- Chemical bonding to tooth structure
Correct answer: Corrosion byproducts that seal the margin
Corrosion products (tin oxides and chlorides) accumulate at the amalgam-tooth interface over time, effectively sealing the margin and reducing microleakage.
Question 6: When restoring a tooth with severe attrition using composite resin, which technique best prevents debonding under heavy occlusal loads?
- Etching only the enamel margins
- Using a high-filled hybrid composite
- Creating mechanical retention features in the preparation (Correct answer)
- Applying multiple thin coats of unfilled resin
Correct answer: Creating mechanical retention features in the preparation
Mechanical retention features such as grooves, boxes, or pins supplement adhesive bonding and are critical when occlusal forces are high.
Question 7: The ideal occlusal thickness for a cast gold onlay on a molar is approximately:
- 0.5 mm
- 1.0 mm
- 1.5–2.0 mm (Correct answer)
- 3.0 mm
Correct answer: 1.5–2.0 mm
Cast gold onlays require 1.5–2.0 mm of occlusal clearance to provide sufficient metal bulk for strength without fracture under functional occlusal loads.
NBDE Restorative Dentistry 3
A dentist is preparing a tooth for a full-coverage metal-ceramic crown.
The facial reduction should be approximately: