MJDF Part 1 - Membership of Joint Dental Faculties Prosthodontics and Tooth Replacement Questions and Answers — Questions and Answers
Question 1: An elderly patient returns one week after the insertion of new complete dentures, complaining that the lower denture lifts when they open their mouth wide or protrude their tongue. Which of the following is the most likely cause of this instability?
- A. The occlusal vertical dimension is too high.
- B. The posterior palatal seal of the upper denture is inadequate.
- C. The lingual flange of the lower denture is overextended. (Correct answer)
- D. The posterior teeth are set outside of the neutral zone.
Correct answer: C. The lingual flange of the lower denture is overextended.
The floor of the mouth is formed by the mylohyoid muscle. When the patient opens wide or protrudes their tongue, this muscle contracts and elevates. If the lingual flange of the lower denture is too long (overextended), it impinges on this muscle and its attachments, causing the denture to be lifted and dislodged.
Question 2: A 22-year-old patient with a congenitally missing, unrestored upper lateral incisor (UR2) is considering a fixed replacement. The adjacent canine and central incisor are sound. According to UK best practice guidelines, which of the following is the most suitable design for a long-term successful resin-retained bridge?
- A. A cantilever design with a single retainer on the canine. (Correct answer)
- B. A fixed-fixed design with retainers on both the canine and central incisor.
- C. A design with significant tooth preparation to create parallel guide planes.
- D. A design luted with a conventional glass ionomer cement.
Correct answer: A. A cantilever design with a single retainer on the canine.
Current UK evidence and guidelines favour a cantilever design for resin-retained bridges, particularly for replacing a single anterior tooth. A single retainer on the canine avoids stresses from the differential mobility between the canine and central incisor, a common cause of debonding in fixed-fixed designs. This minimally invasive approach preserves tooth tissue on the central incisor.
Question 3: A patient is missing the following teeth: UL4, UL5, UL6, UR4, and UR5. All other teeth are present and sound. According to the Kennedy classification system, how should this dental arch be classified?
- A. Kennedy Class II Modification 1.
- B. Kennedy Class I.
- C. Kennedy Class IV.
- D. Kennedy Class III Modification 1. (Correct answer)
Correct answer: D. Kennedy Class III Modification 1.
According to Applegate's rules for Kennedy classification, the most posterior edentulous area determines the classification. In this case, there are two bounded saddles. The UL4-UL6 area is a Class III space (unilateral bounded saddle). The UR4-UR5 area is an additional edentulous space, which is designated as a modification. Therefore, the arch is classified as Kennedy Class III, Modification 1.
Question 4: A dentist is taking a definitive impression for a crown on the LR6 using a polyvinyl siloxane (addition-cured silicone) material. The dentist is wearing standard latex examination gloves while mixing the putty. Which of the following issues is most likely to occur?
- A. Sulphur compounds in the latex gloves may inhibit the polymerisation of the impression material. (Correct answer)
- B. The material will experience significant dimensional shrinkage due to the latex.
- C. The latex will accelerate the setting reaction, reducing the working time.
- D. The impression material will become excessively rigid and difficult to remove from the mouth.
Correct answer: A. Sulphur compounds in the latex gloves may inhibit the polymerisation of the impression material.
The setting reaction of polyvinyl siloxane (PVS) materials is based on a platinum salt catalyst. This catalyst can be inhibited or 'poisoned' by sulphur compounds, which are often used in the vulcanisation process of latex gloves. This inhibition prevents the material from setting properly where it has been in contact with the gloves, resulting in a weak or unset surface.
Question 5: When designing a cobalt-chromium removable partial denture, what is the primary function of an occlusal rest?
- A. To provide resistance to lateral displacement.
- B. To engage an undercut and resist vertical dislodgement.
- C. To link components on one side of the arch to the other.
- D. To transmit occlusal forces along the long axes of the abutment teeth. (Correct answer)
Correct answer: D. To transmit occlusal forces along the long axes of the abutment teeth.
The primary function of a rest is to provide vertical support for the partial denture. By sitting in a prepared rest seat, it transmits occlusal forces down the long axis of the abutment tooth, preventing the denture from moving towards the soft tissues and providing stability during function.
Question 6: During the jaw registration stage for new complete dentures, the clinician guides the patient's mandible into centric relation. What is the main clinical significance of recording this position?
- A. It establishes the patient's desired smile line and tooth display.
- B. It is a repeatable reference position from which to build the occlusion. (Correct answer)
- C. It represents the position of maximum tooth intercuspation.
- D. It is primarily used to select the correct size and shade of the denture teeth.
Correct answer: B. It is a repeatable reference position from which to build the occlusion.
Centric relation is a maxillomandibular relationship that is independent of tooth contact. It is defined by the position of the condyles in the glenoid fossae. Crucially for prosthodontics, especially in edentulous patients, it is the only reliable and clinically reproducible position that can be used as a starting point to construct a stable and functional occlusion.
MJDF Part 1 - Membership of Joint Dental Faculties Prosthodontics and Tooth Replacement Questions and Answers
An elderly patient returns one week after the insertion of new complete dentures, complaining that the lower denture lifts when they open their mouth wide or protrude their tongue.
Which of the following is the most likely cause of this instability?