MJDF Part 1 - Membership of Joint Dental Faculties Restorative Dentistry Principles 1 — Questions and Answers
Question 1: When performing stepwise excavation of a deep carious lesion approaching the pulp, what is the PRIMARY rationale for leaving softened dentine over the pulp on the first appointment?
- To reduce chair time by staging the procedure across two visits
- To allow remineralisation of affected dentine and secondary dentine deposition, reducing the risk of pulp exposure at re-entry (Correct answer)
- To test the patient's pain tolerance before committing to an indirect restoration
- To ensure all bacteria are eliminated by the temporary dressing before final excavation
Correct answer: To allow remineralisation of affected dentine and secondary dentine deposition, reducing the risk of pulp exposure at re-entry
Stepwise excavation exploits the capacity of affected (not infected) dentine to remineralise when sealed from the oral environment. The temporary seal stimulates tertiary dentine formation, so that at re-entry the remaining carious tissue is firmer and the risk of iatrogenic pulp exposure is substantially reduced.
Question 2: The 'ferrule effect' in the context of a post-retained crown is BEST defined as:
- Extending the post to at least two-thirds of the root length to maximise retention
- Encircling a minimum of 1.5–2 mm of sound coronal tooth structure above the finish line with the crown margin (Correct answer)
- Using a parallel-sided post to distribute occlusal stress along the root
- Bevelling the gingival seat of the preparation to improve marginal seal
Correct answer: Encircling a minimum of 1.5–2 mm of sound coronal tooth structure above the finish line with the crown margin
The ferrule effect refers to the crown encircling at least 1.5–2 mm of sound dentine above the core margin. This band of tooth structure significantly resists lateral forces, prevents root fracture, and improves the resistance form of the restoration — it is considered more important than post design for long-term prognosis.
Question 3: Which statement BEST distinguishes a total-etch (etch-and-rinse) adhesive system from a self-etch adhesive system?
- Total-etch systems use a hydrophobic primer before phosphoric acid, while self-etch systems apply the acid first
- Total-etch systems apply phosphoric acid separately then rinse before priming, while self-etch systems use an acidic monomer primer that simultaneously conditions and primes without a rinse step (Correct answer)
- Self-etch systems achieve higher bond strengths to enamel than total-etch systems
- Total-etch systems are indicated for dentine bonding only; self-etch systems are indicated for enamel only
Correct answer: Total-etch systems apply phosphoric acid separately then rinse before priming, while self-etch systems use an acidic monomer primer that simultaneously conditions and primes without a rinse step
In total-etch systems, 35–37% phosphoric acid is applied, thoroughly rinsed, and then primer and bond are applied to moist dentine. Self-etch systems incorporate acidic functional monomers in the primer that demineralise and infiltrate simultaneously without a rinsing step, reducing technique sensitivity but generally producing less distinct enamel etching.
Question 4: A heavily restored, endodontically treated lower first molar has lost both marginal ridges. The patient is otherwise dentally fit and the tooth is functional. What restorative approach is MOST appropriate?
- Large direct composite restoration replacing both missing marginal ridges
- Extraction and implant placement as the tooth is unrestorable
- Cuspal coverage restoration (e.g. onlay or crown) to protect the remaining tooth structure (Correct answer)
- Observation only, as endodontically treated teeth do not require additional protection
Correct answer: Cuspal coverage restoration (e.g. onlay or crown) to protect the remaining tooth structure
Loss of both marginal ridges combined with endodontic treatment dramatically increases the risk of catastrophic cuspal fracture, as the tooth is both structurally weakened and less sensitive to damaging loads. Cuspal coverage distributes occlusal forces and prevents vertical root fracture, making it the evidence-based choice in this scenario.
Question 5: Which material is now considered the GOLD STANDARD for direct pulp capping, having largely superseded calcium hydroxide in contemporary practice?
- Zinc oxide eugenol (ZOE) cement
- Glass ionomer cement (GIC)
- Mineral trioxide aggregate (MTA) (Correct answer)
- Dycal (hard-setting calcium hydroxide)
Correct answer: Mineral trioxide aggregate (MTA)
MTA has superior biocompatibility, an excellent marginal seal, and induces a more complete and consistent dentine bridge than calcium hydroxide. Studies show calcium hydroxide-induced bridges frequently contain tunnel defects and are associated with internal resorption, whereas MTA produces a denser, more reliable hard-tissue response.
Question 6: What is the recommended total occlusal convergence angle for a full-coverage crown preparation to achieve optimal retention and resistance form?
- 0–2 degrees (near parallel walls)
- 6–12 degrees (Correct answer)
- 20–30 degrees
- 35–45 degrees
Correct answer: 6–12 degrees
A total occlusal convergence of 6–12 degrees provides the best balance between retention (favouring more parallel walls) and the clinical practicality of seating the crown without binding. Angles above 20 degrees significantly reduce retention and resistance form; truly parallel preparations (<3 degrees) are difficult to achieve clinically and risk undercut.
MJDF Part 1 - Membership of Joint Dental Faculties Restorative Dentistry Principles 1
When performing stepwise excavation of a deep carious lesion approaching the pulp, what is the PRIMARY rationale for leaving softened dentine over the pulp on the first appointment?