MFDS Part 1 - Membership of Faculty of Dental Surgery Restorative and Adhesive Dentistry Questions and Answers — Questions and Answers
Question 1: In line with the UK's implementation of the Minamata Convention on Mercury, the use of dental amalgam is restricted. In which of the following patient groups is the use of dental amalgam prohibited, except where deemed strictly necessary by the practitioner for the specific medical needs of the patient?
- Patients with a known allergy to base metals.
- Children under 15 years of age, and pregnant or breastfeeding women. (Correct answer)
- Adult patients over the age of 65 requiring multi-surface posterior restorations.
- Patients undergoing fixed orthodontic appliance therapy.
Correct answer: Children under 15 years of age, and pregnant or breastfeeding women.
The Minamata Convention on Mercury is a global treaty to protect human health and the environment from mercury. In the UK, as in the EU, this has led to specific restrictions on the use of dental amalgam. From 1 July 2018, dental amalgam must not be used for the dental treatment of deciduous teeth, of children under 15 years, and of pregnant or breastfeeding women, unless there is a specific medical necessity.
Question 2: A dentist is preparing to permanently cement a lithium disilicate onlay. To achieve a strong and durable adhesive bond, what is the mandatory surface pre-treatment for the intaglio (fitting) surface of this specific type of ceramic restoration before applying a silane coupling agent?
- Sandblasting with 50-micron aluminium oxide particles.
- Etching with 37% phosphoric acid for 60 seconds.
- Cleaning with a sodium hypochlorite solution.
- Etching with approximately 5% hydrofluoric acid for 20 seconds. (Correct answer)
Correct answer: Etching with approximately 5% hydrofluoric acid for 20 seconds.
Lithium disilicate is a silica-based ceramic. To create the micromechanical retention necessary for a strong adhesive bond, its fitting surface must be etched with hydrofluoric acid (HF). This process selectively dissolves the glassy matrix, creating a porous surface for the resin cement to penetrate. The typical manufacturer's recommendation for lithium disilicate (e.g., IPS e.max) is to use approximately 5% HF for 20 seconds. Phosphoric acid is ineffective, and sandblasting is the primary pre-treatment for zirconia, not lithium disilicate.
Question 3: A 24-year-old patient presents with a deep carious lesion in the mandibular first molar (LR6). The tooth is asymptomatic and responds normally to sensibility testing. A radiograph shows the lesion extending into the pulpal third of the dentine. According to contemporary minimally invasive dentistry principles widely accepted in the UK, what is the most appropriate management for the deepest part of the cavity?
- Complete removal of all caries until 'hard' or 'scratchy' dentine is felt over the pulp.
- Selective removal of caries, leaving soft, wet, necrotic dentine directly over the pulp to avoid exposure.
- Selective removal of caries to leave firm, leathery dentine in the pulpal aspect, having secured a peripheral seal on sound dentine. (Correct answer)
- Immediate placement of a calcium hydroxide liner without any caries excavation to promote pulpal healing.
Correct answer: Selective removal of caries to leave firm, leathery dentine in the pulpal aspect, having secured a peripheral seal on sound dentine.
Contemporary evidence supports selective caries removal to preserve pulp vitality in deep, asymptomatic lesions. The goal is to remove the outer, heavily infected and non-remineralisable dentine while preserving the deeper, affected but repairable dentine. This involves clearing the cavity walls and enamel-dentine junction to sound tissue to ensure an effective peripheral seal, but leaving firm or leathery dentine directly over the pulp to avoid iatrogenic exposure. Complete removal to hard dentine risks unnecessary pulp exposure, while leaving soft, wet dentine is not recommended.
Question 4: A conventional glass ionomer cement (GIC) is selected for a Class V restoration. Which of the following statements most accurately describes the primary bonding mechanism of this material to tooth structure?
- It forms a micromechanical bond via a resin-infiltrated hybrid layer.
- It sets via an acid-base reaction and forms a true chemical bond through ionic exchange. (Correct answer)
- It requires a separate phosphoric acid etchant and a bonding agent to adhere.
- It relies solely on mechanical undercuts in the cavity preparation for retention.
Correct answer: It sets via an acid-base reaction and forms a true chemical bond through ionic exchange.
Conventional glass ionomer cements are self-adhesive materials. Their setting is an acid-base reaction between the polyalkenoic acid liquid and the basic fluoroaluminosilicate glass powder. Adhesion to the tooth occurs via a chemical bond, specifically an ionic exchange between the carboxyl groups of the polyacid and calcium ions in the hydroxyapatite of enamel and dentine.
Question 5: When planning a full coverage crown for a root-filled molar, which of the following factors is considered most critical for the long-term prognosis and fracture resistance of the tooth?
- The type of luting cement used for the crown.
- The presence of a circumferential ferrule of 1.5-2.0 mm of sound tooth structure. (Correct answer)
- The length and diameter of the post placed within the root canal.
- The use of a resin-modified glass ionomer core material.
Correct answer: The presence of a circumferential ferrule of 1.5-2.0 mm of sound tooth structure.
The ferrule effect, which is a 360-degree collar of sound tooth structure coronal to the crown margin, is widely regarded as the most important determinant for the fracture resistance of a restored, root-filled tooth. A ferrule of at least 1.5-2.0 mm in height braces the tooth against functional forces, reducing stress on the post and within the root, thereby significantly improving the long-term prognosis. While other factors are important, the presence of an adequate ferrule is the most critical.
Question 6: A dentist is restoring a shallow Class V abrasion lesion with composite resin in a patient who reports significant dentine hypersensitivity. To minimise the risk of post-operative sensitivity, which adhesive strategy is generally considered most appropriate?
- A three-step total-etch (etch-and-rinse) adhesive system.
- A one-step self-etch adhesive system applied in a single layer.
- A two-step self-etch adhesive system (self-etching primer and bond). (Correct answer)
- A selective-enamel etch technique followed by application of a one-step self-etch adhesive.
Correct answer: A two-step self-etch adhesive system (self-etching primer and bond).
Self-etch adhesive systems are generally associated with a lower risk of post-operative sensitivity compared to total-etch systems, particularly in sensitive areas like Class V lesions. This is because they do not completely remove the smear layer and involve fewer steps, reducing the risk of over-drying or over-etching the dentine, which can leave open dentinal tubules. A two-step self-etch system, with a separate primer and bond, is often considered more reliable and effective at sealing the dentine than a one-step ('all-in-one') system, providing a good balance of reduced sensitivity and effective bonding.
MFDS Part 1 - Membership of Faculty of Dental Surgery Restorative and Adhesive Dentistry Questions and Answers
In line with the UK's implementation of the Minamata Convention on Mercury, the use of dental amalgam is restricted.
In which of the following patient groups is the use of dental amalgam prohibited, except where deemed strictly necessary by the practitioner for the specific medical needs of the patient?