NBDE Ultimate 4 — Questions and Answers
Question 1: The recommended pulpal depth for a Class I cavity preparation using amalgam is approximately:
- 0.2 mm into dentin
- 0.5 mm into dentin (Correct answer)
- 2.0 mm into dentin
- 1.5 mm into enamel only
Correct answer: 0.5 mm into dentin
A Class I amalgam preparation should extend approximately 0.5 mm into dentin to ensure adequate pulpal depth (~1.5-2 mm total) for bulk and retention.
Question 2: Which impression material is considered the gold standard for fixed prosthodontic impressions?
- Alginate (irreversible hydrocolloid)
- Zinc oxide eugenol paste
- Polyvinyl siloxane (addition silicone) (Correct answer)
- Reversible hydrocolloid (agar)
Correct answer: Polyvinyl siloxane (addition silicone)
Polyvinyl siloxane (addition silicone) offers superior dimensional stability, excellent detail reproduction, and extended pour time, making it ideal for fixed prosthodontic impressions.
Question 3: Compared to a permanent molar, a primary molar pulp is characterized by:
- Thicker dentinal walls
- More prominent pulp horns and thinner dentinal walls (Correct answer)
- Smaller pulp chamber relative to crown size
- Fewer accessory canals
Correct answer: More prominent pulp horns and thinner dentinal walls
Primary molars have proportionally larger pulp chambers, more prominent (coronally positioned) pulp horns, and thinner dentinal walls, increasing pulp exposure risk during cavity preparation.
Question 4: Formocresol pulpotomy in a primary molar is indicated when:
- The radicular pulp is necrotic with furcal bone loss
- The radicular pulp is vital and hemorrhage is controlled (Correct answer)
- Internal root resorption is evident on radiograph
- Root resorption exceeds one-third of root length
Correct answer: The radicular pulp is vital and hemorrhage is controlled
Formocresol pulpotomy is indicated when the coronal pulp is inflamed but radicular pulp remains vital, asymptomatic, and hemostasis is achievable after amputation.
Question 5: The primary mechanism by which acid etching improves composite resin bonding to enamel is:
- Chemical bonding to hydroxyapatite crystals
- Micromechanical retention through resin tag formation (Correct answer)
- Van der Waals forces between resin and enamel rods
- Covalent bonding to enamel matrix proteins
Correct answer: Micromechanical retention through resin tag formation
Acid etching creates microporosities in enamel by selectively dissolving prism cores or peripheries, allowing resin monomers to penetrate and form resin tags for micromechanical retention.
Question 6: Which Class of cavity preparation, according to Black's classification, involves pit and fissure lesions on the occlusal surfaces of posterior teeth?
- Class I (Correct answer)
- Class II
- Class V
- Class VI
Correct answer: Class I
Class I cavity preparations involve pits and fissures on occlusal surfaces of molars and premolars, lingual surfaces of maxillary incisors, and buccal surfaces of molars.
Question 7: A full cast gold crown preparation requires a minimum axial wall reduction of approximately:
- 0.5 mm
- 1.0 mm
- 1.5 mm (Correct answer)
- 2.5 mm
Correct answer: 1.5 mm
Full cast gold crown preparations require at least 1.5 mm of axial reduction to provide adequate metal thickness for strength while maintaining tooth structure.
NBDE Ultimate 4
The recommended pulpal depth for a Class I cavity preparation using amalgam is approximately: