MFDS Part 1 - Membership of Faculty of Dental Surgery Endodontics and Prosthodontics Questions and Answers — Questions and Answers
Question 1: A 35-year-old patient presents with a sharp, lingering pain to cold stimuli in the lower left first molar (LL6). A deep distal carious lesion is visible on the bitewing radiograph, approaching the pulp. To confirm a diagnosis of irreversible pulpitis, which of the following sensibility tests is generally considered most reliable according to UK endodontic practice guidelines?
- Percussion test
- Electric Pulp Test (EPT)
- Cold test using a refrigerant spray (e.g., Endo-Frost) (Correct answer)
- Heat test using warm gutta-percha
Correct answer: Cold test using a refrigerant spray (e.g., Endo-Frost)
The British Endodontic Society and European Society of Endodontology guidelines recommend pulp sensibility testing to assess pulp status. Cold testing with a refrigerant spray is considered highly reliable and more accurate than EPT for routine diagnosis. It effectively elicits a response in cases of irreversible pulpitis, which is often sharp and lingering, helping to differentiate it from reversible pulpitis. The percussion test assesses periapical inflammation, not pulpal vitality, and heat tests are less commonly used as a primary diagnostic tool due to potential for causing pain and less predictable results.
Question 2: A 68-year-old edentulous patient requires new complete dentures. On examination, the mandibular ridge is severely resorbed, with inadequate height and width, presenting a flat or even concave form. According to the Cawood and Howell classification, which class best describes this clinical presentation?
- Class II
- Class VI (Correct answer)
- Class III
- Class IV
Correct answer: Class VI
The Cawood and Howell classification is a widely used system in UK prosthodontics to describe the morphology of the edentulous alveolar ridge. Class VI represents the most severe stage of resorption, described as a depressed ridge form with some basalar process loss, which corresponds to the clinical finding of a flat or concave ridge with inadequate height and width. Class III is a well-rounded ridge, and Class IV is a 'knife-edge' ridge.
Question 3: Which component of traditional Mineral Trioxide Aggregate (MTA) formulations is primarily responsible for the potential greyish discolouration of tooth structure, particularly when it interacts with common endodontic irrigants like sodium hypochlorite?
- Tricalcium silicate
- Calcium sulphate
- Bismuth oxide (Correct answer)
- Dicalcium phosphate
Correct answer: Bismuth oxide
Bismuth oxide is added to MTA as a radiopacifier. However, it has been widely shown to be the primary cause of tooth discolouration. This staining can be exacerbated when bismuth oxide interacts with sodium hypochlorite, a common root canal irrigant, or with blood, leading to the formation of a dark precipitate that can leach into the dentinal tubules.
Question 4: A dentist is planning a post-retained crown for a root-canal-treated upper central incisor. To maximise the fracture resistance of the final restoration, what is the minimum recommended height of circumferential coronal tooth structure (ferrule) that should be preserved above the crown margin?
- 0.5 mm
- 1.0 mm
- 3.0 mm
- 1.5 - 2.0 mm (Correct answer)
Correct answer: 1.5 - 2.0 mm
The ferrule effect is a crucial principle in prosthodontics for improving the longevity of post-retained crowns. A circumferential band of healthy tooth structure is required to resist functional lever forces and reduce stress concentration. UK and international guidelines consistently recommend a minimum ferrule height of 1.5 to 2.0 mm to significantly enhance the fracture resistance of the restored tooth.
Question 5: A 50-year-old patient complains of a sharp, intermittent pain on biting on their lower right first molar (LR6), which has a large MOD amalgam restoration. The pain disappears immediately on release. There is no lingering pain to thermal stimuli and no periapical pathology is evident on the radiograph. Transillumination reveals a crack line extending from the mesial marginal ridge. What is the most appropriate immediate management to prevent crack propagation?
- Place the tooth on a watch-and-wait protocol
- Immediate root canal treatment
- Placement of a full-coverage cuspal protection restoration (e.g., a crown) (Correct answer)
- Extraction of the tooth
Correct answer: Placement of a full-coverage cuspal protection restoration (e.g., a crown)
The symptoms are classic for 'cracked tooth syndrome'. The immediate priority is to stabilise the tooth and prevent the crack from propagating, which could lead to pulpal involvement or a vertical root fracture. The most effective way to achieve this is by placing a restoration that provides cuspal coverage, such as a crown or a protective orthodontic band. This braces the tooth structure together, distributing occlusal forces and alleviating the symptoms. Root canal treatment is only indicated if the pulp becomes irreversibly inflamed or necrotic.
Question 6: When selecting an all-ceramic material for a full-coverage crown on a maxillary second molar in a patient with evidence of bruxism, which of the following materials offers the highest flexural strength and fracture toughness, making it the most suitable choice?
- Feldspathic porcelain
- Leucite-reinforced glass-ceramic
- Lithium disilicate glass-ceramic
- Monolithic zirconia (Correct answer)
Correct answer: Monolithic zirconia
Monolithic zirconia has superior mechanical properties compared to other dental ceramics, with a flexural strength often exceeding 900-1200 MPa. This makes it the material of choice for posterior crowns in high-stress situations, such as in patients who are bruxists. Lithium disilicate, while having excellent aesthetics, has a lower flexural strength (around 400 MPa) and is more susceptible to fracture under heavy occlusal loads. Feldspathic and leucite-reinforced ceramics are weaker still and are not indicated for high-load posterior restorations.
MFDS Part 1 - Membership of Faculty of Dental Surgery Endodontics and Prosthodontics Questions and Answers
A 35-year-old patient presents with a sharp, lingering pain to cold stimuli in the lower left first molar (LL6).
A deep distal carious lesion is visible on the bitewing radiograph, approaching the pulp.
To confirm a diagnosis of irreversible pulpitis, which of the following sensibility tests is generally considered most reliable according to UK endodontic practice guidelines?