Free NBDE Prosthodontics and Operative Dentistry Questions and Answers — Questions and Answers
Question 1: A patient with a Kennedy Class I removable partial denture complains that the denture lifts away from the tissue when they eat sticky foods. Which component is specifically designed to counteract this rotational movement away from the tissues on the opposite side of the fulcrum line?
- Major connector
- Indirect retainer (Correct answer)
- Direct retainer
- Denture base
Correct answer: Indirect retainer
An indirect retainer is a component of an RPD that assists the direct retainer in preventing the displacement of a distal extension base. It functions through lever action on the opposite side of the fulcrum line to counteract forces that would lift the denture base away from the tissues.
Question 2: When preparing a posterior tooth for a full cast gold crown, what is the generally accepted ideal total occlusal convergence (taper) between opposing axial walls to provide adequate retention and resistance form?
- 0-2 degrees
- 25-30 degrees
- 6-10 degrees (Correct answer)
- 15-20 degrees
Correct answer: 6-10 degrees
A total occlusal convergence of 6-10 degrees is considered ideal for crown preparations. This taper allows for the restoration to seat properly while providing sufficient parallelism of the axial walls to retain the crown through friction and resist dislodging forces. While a range of 10-22 degrees is sometimes cited as clinically achievable, the ideal goal is closer to 6 degrees.
Question 3: A patient complains of poor retention of their new maxillary complete denture, noting it frequently drops when they talk or yawn. Which of the following is the most critical factor for maintaining the peripheral seal and retention of a maxillary complete denture?
- Anterior flange extension into the vestibule
- Accurate replication of the rugae
- Proper placement of the posterior palatal seal (Correct answer)
- Occlusal plane height
Correct answer: Proper placement of the posterior palatal seal
The posterior palatal seal (PPS) is the most critical element for the retention of a maxillary complete denture. It creates an intimate contact with the displaceable soft tissue at the junction of the hard and soft palates, completing the peripheral seal and utilizing atmospheric pressure to hold the denture in place.
Question 4: Which of the following describes a G.V. Black Class II carious lesion?
- Caries in the pits and fissures of an occlusal surface
- Caries on the proximal surface of a posterior tooth (Correct answer)
- Caries on the gingival third of the facial or lingual surface
- Caries on the proximal surface of an anterior tooth not involving the incisal angle
Correct answer: Caries on the proximal surface of a posterior tooth
According to G.V. Black's classification system, a Class II lesion is defined as caries affecting the proximal (mesial or distal) surfaces of posterior teeth (premolars and molars).
Question 5: The primary purpose of applying 37% phosphoric acid to enamel during an adhesive restorative procedure is to:
- Disinfect the tooth surface to eliminate bacteria
- Chemically bond directly to the hydroxyapatite crystals
- Remove the smear layer and create microporosities for mechanical retention (Correct answer)
- Condition the dentin to promote collagen cross-linking
Correct answer: Remove the smear layer and create microporosities for mechanical retention
Acid etching with phosphoric acid demineralizes the enamel surface, selectively dissolving hydroxyapatite crystals to create microscopic irregularities or 'tags'. This process increases the surface area and creates microporosities, allowing the adhesive resin to flow in and establish a strong micromechanical bond upon polymerization. It also removes the smear layer.
Question 6: Conventional glass ionomer cements (GICs) are composed of a powder and a liquid that undergo an acid-base reaction. The liquid component is primarily an aqueous solution of which acid?
- Hydrochloric acid
- Phosphoric acid
- Maleic acid
- Polyacrylic acid (Correct answer)
Correct answer: Polyacrylic acid
The liquid component of a conventional glass ionomer cement is an aqueous solution of a polyalkenoic acid, most commonly polyacrylic acid. This acid reacts with the fluoroaluminosilicate glass powder to initiate the setting reaction.
Free NBDE Prosthodontics and Operative Dentistry Questions and Answers
A patient with a Kennedy Class I removable partial denture complains that the denture lifts away from the tissue when they eat sticky foods.
Which component is specifically designed to counteract this rotational movement away from the tissues on the opposite side of the fulcrum line?