NBDE Prosthodontics and Operative Dentistry 4 — Questions and Answers
Question 1: The 'ferrule effect' in crown preparation refers to:
- The extension of the crown margin 1.5-2 mm onto sound tooth structure above the finish line (Correct answer)
- The use of a metal collar to reinforce the cervical area of a ceramic crown
- The parallel walls of the axial box that provide resistance form
- The crown margin placed 0.5 mm subgingivally for esthetic reasons
Correct answer: The extension of the crown margin 1.5-2 mm onto sound tooth structure above the finish line
The ferrule effect is a 360° band of tooth structure at least 1.5-2 mm above the CEJ or finish line, which dramatically increases resistance to fracture.
Question 2: Which type of impression technique is most appropriate for a distal extension removable partial denture?
- Mucostatic (passive pressure) impression
- Mucocompressive impression of the entire arch
- Functional (selective pressure) impression (Correct answer)
- Dual-arch impression technique
Correct answer: Functional (selective pressure) impression
A functional impression records the distal extension tissue under simulated functional load, ensuring the denture base is supported under pressure.
Question 3: Glass ionomer cement is uniquely beneficial as a base or liner because it:
- Provides the highest compressive strength of all bases
- Bonds chemically to tooth structure and releases fluoride (Correct answer)
- Can be used directly against the pulp without any protection
- Sets without any dimensional change
Correct answer: Bonds chemically to tooth structure and releases fluoride
Glass ionomer forms a chemical bond with both enamel and dentin and releases fluoride ions, providing both adhesion and cariostatic benefits.
Question 4: When surveying a cast for a removable partial denture, tilting the cast anteriorly will:
- Increase undercuts on the posterior teeth and decrease them on anterior teeth
- Eliminate all undercuts on the buccal surfaces
- Increase undercuts on the anterior teeth and decrease them on posterior teeth (Correct answer)
- Have no effect on the amount of undercut available
Correct answer: Increase undercuts on the anterior teeth and decrease them on posterior teeth
Tilting the cast anteriorly changes the path of insertion, increasing mesial undercuts and decreasing distal undercuts on posterior abutments.
Question 5: The term 'centric relation' in prosthodontics refers to:
- The maximum intercuspation of the teeth regardless of condyle position
- The most retruded, superior position of the condyles in the glenoid fossae (Correct answer)
- The position of the mandible when the muscles are most relaxed
- The position of maximum tooth contact during lateral excursion
Correct answer: The most retruded, superior position of the condyles in the glenoid fossae
Centric relation is a jaw position (not tooth position) defined as the most superior, anterior position of the condyles in the glenoid fossae, reproducible and joint-based.
Question 6: The primary purpose of a rubber dam during operative procedures is to:
- Improve visibility by retracting cheeks and tongue
- Maintain a dry, contamination-free field for bonding procedures (Correct answer)
- Prevent the patient from swallowing small instruments
- Reduce aerosol generation during high-speed cutting
Correct answer: Maintain a dry, contamination-free field for bonding procedures
The rubber dam isolates the operating field from saliva and crevicular fluid, which is essential for achieving optimal bonding of adhesive restorations.
Question 7: A patient presents with a fractured cusp on a maxillary molar. The fracture extends 2 mm below the gingival margin but remains supracrestal. The best restorative option is:
- Extraction and implant placement
- Intracoronal amalgam restoration with a cusp coverage extension
- Crown lengthening followed by full coverage crown (Correct answer)
- Core buildup with fiber post and full coverage crown
Correct answer: Crown lengthening followed by full coverage crown
Crown lengthening establishes biologic width clearance below the new finish line, after which a full coverage crown provides necessary cuspal protection.
NBDE Prosthodontics and Operative Dentistry 4
The 'ferrule effect' in crown preparation refers to: