FREE NBDE Prosthodontics and Operative Dentistry 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?

Accepted Answer

Indirect retainer

Answer

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?

Accepted Answer

6-10 degrees

Answer

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?

Accepted Answer

Proper placement of the posterior palatal seal

Answer

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?

Accepted Answer

Caries on the proximal surface of a posterior tooth

Answer

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:

Accepted Answer

Remove the smear layer and create microporosities for mechanical retention

Answer

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.

NBDE - National Board Dental Examination Practice Test

NBDE - National Board Dental Examination Practice Test

FREE NBDE Prosthodontics and Operative Dentistry Questions and Answers