MJDF Clinical Dentistry 2 — Questions and Answers
Question 1: A patient requires an anterior crown on an upper central incisor. What minimum ferrule height is recommended for adequate resistance form, and why is it important?
- No ferrule is needed if a post is placed
- A minimum ferrule of 1.5-2 mm of sound supragingival dentine circumferentially is recommended; it provides resistance to lateral forces, prevents root fracture, and significantly improves the retention and longevity of the crown-post-core assembly (Correct answer)
- A 0.5 mm ferrule is sufficient for all situations
- Ferrule is only relevant for posterior teeth
Correct answer: A minimum ferrule of 1.5-2 mm of sound supragingival dentine circumferentially is recommended; it provides resistance to lateral forces, prevents root fracture, and significantly improves the retention and longevity of the crown-post-core assembly
The ferrule effect describes the encirclement of sound tooth structure by the crown margin, providing a 'hoop' of metal or ceramic that resists lateral forces, functional loads, and the wedging effect of tapered posts. A minimum of 1.5-2 mm of sound dentine above the preparation finish line is recommended circumferentially. Without adequate ferrule, post-retained crowns have significantly higher failure rates from root fracture, post decementation, or core failure. If insufficient ferrule exists, crown lengthening surgery or orthodontic extrusion may be considered.
Question 2: What are the indications for prescribing high-concentration fluoride toothpaste (2800 ppm or 5000 ppm) in the UK?
- For all patients as routine toothpaste
- For patients aged 10 years and over with active or high caries risk, including those with xerostomia, patients undergoing orthodontic treatment, root caries in older adults, and radiation-induced caries (Correct answer)
- Only for patients with fluorosis
- High-concentration fluoride toothpaste is not available in the UK
Correct answer: For patients aged 10 years and over with active or high caries risk, including those with xerostomia, patients undergoing orthodontic treatment, root caries in older adults, and radiation-induced caries
High-concentration fluoride toothpastes (2800 ppm for patients aged 10+, 5000 ppm for patients aged 16+) are prescription-only in the UK and indicated for patients at elevated caries risk: active caries, xerostomia (including medication-related and Sjögren's syndrome), head and neck radiotherapy patients, orthodontic patients, root caries in older adults, and patients with reduced manual dexterity. They promote remineralisation and inhibit demineralisation more effectively than standard 1450 ppm toothpaste. Patients should spit but not rinse after brushing.
Question 3: A 7-year-old child presents with a fractured upper central incisor involving enamel and dentine with a visible pulp exposure. The tooth root is immature (open apex). What is the most appropriate pulp therapy?
- Immediate root canal treatment with gutta percha obturation
- Partial pulpotomy (Cvek pulpotomy) using mineral trioxide aggregate (MTA) or Biodentine to maintain pulp vitality and allow continued root development (Correct answer)
- Extraction and space maintenance
- No treatment — the tooth will be replaced by the permanent successor
Correct answer: Partial pulpotomy (Cvek pulpotomy) using mineral trioxide aggregate (MTA) or Biodentine to maintain pulp vitality and allow continued root development
For a traumatic pulp exposure in an immature permanent incisor, a partial pulpotomy (Cvek pulpotomy) is the treatment of choice. The inflamed superficial pulp tissue (1-2 mm) is removed, and a biocompatible material (MTA or Biodentine) is placed over the vital pulp. This preserves pulp vitality, allowing continued root development (apexogenesis) with root lengthening, dentinal wall thickening, and eventual apical closure. Success rates exceed 90% when performed within 24-48 hours of exposure.
Question 4: What is the biological width (now termed 'supracrestal tissue attachment') and why must it be respected during restorative procedures?
- It is the width of the dental pulp chamber
- It is the dimension of soft tissue attachment above the alveolar bone crest, comprising approximately 1 mm of junctional epithelium and 1 mm of connective tissue attachment (approximately 2 mm total); violation leads to chronic inflammation, bone loss, and gingival recession (Correct answer)
- It is the distance between adjacent teeth at the contact point
- It refers to the width of attached gingiva only
Correct answer: It is the dimension of soft tissue attachment above the alveolar bone crest, comprising approximately 1 mm of junctional epithelium and 1 mm of connective tissue attachment (approximately 2 mm total); violation leads to chronic inflammation, bone loss, and gingival recession
The supracrestal tissue attachment (formerly 'biological width') comprises the junctional epithelium (approximately 0.97 mm) and connective tissue attachment (approximately 1.07 mm) between the base of the gingival sulcus and the alveolar bone crest (total approximately 2 mm, Gargiulo et al. 1961). Placing restoration margins within this zone causes chronic inflammation as the body attempts to re-establish its biological seal, resulting in persistent gingival inflammation, pocket formation, bone resorption, and/or gingival recession. Subgingival margins must remain at least 2 mm above the bone crest.
Question 5: What are the advantages and disadvantages of a resin-bonded bridge (adhesive bridge/Maryland bridge) compared to a conventional fixed bridge?
- Resin-bonded bridges are stronger and last longer than conventional bridges in all situations
- Advantages include minimal or no tooth preparation (conservative), reversibility, and preservation of tooth structure; disadvantages include lower retention than conventional bridges, technique sensitivity of bonding, and limited to specific clinical situations (short spans, favourable occlusion, adequate enamel for bonding) (Correct answer)
- Resin-bonded bridges require more tooth preparation than conventional bridges
- There are no clinical differences between the two types
Correct answer: Advantages include minimal or no tooth preparation (conservative), reversibility, and preservation of tooth structure; disadvantages include lower retention than conventional bridges, technique sensitivity of bonding, and limited to specific clinical situations (short spans, favourable occlusion, adequate enamel for bonding)
Resin-bonded bridges (RBBs) use adhesive cementation to a minimally prepared or unprepared abutment tooth, requiring little or no enamel removal (compared to 1-2 mm circumferential reduction for conventional crowns). Advantages: maximum conservation of tooth structure, reversibility if they debond, lower cost, often no anaesthesia needed. Disadvantages: technique-sensitive bonding (moisture control critical), lower retention than conventional bridges (debonding rates 10-20% over 5 years), limited to 1-2 unit spans, require adequate enamel surface area, and cantilever designs preferred over fixed-fixed to prevent differential tooth movement causing debonding.
Question 6: A patient presents with dentine hypersensitivity affecting multiple cervical lesions. What is the underlying mechanism and what is the most effective professional treatment?
- Sensitivity is caused by bacterial infection requiring antibiotic treatment
- The hydrodynamic theory explains that fluid movement within exposed dentinal tubules stimulates mechanoreceptors on intradental nerve fibres; professional treatments include fluoride varnish application, desensitising agents (potassium oxalate, glutaraldehyde-HEMA), or resin/GIC restoration of the defect to seal the tubules (Correct answer)
- Sensitivity is caused by pulp necrosis and requires root canal treatment
- There is no effective treatment for dentine hypersensitivity
Correct answer: The hydrodynamic theory explains that fluid movement within exposed dentinal tubules stimulates mechanoreceptors on intradental nerve fibres; professional treatments include fluoride varnish application, desensitising agents (potassium oxalate, glutaraldehyde-HEMA), or resin/GIC restoration of the defect to seal the tubules
Dentine hypersensitivity is explained by the hydrodynamic theory (Brännström): stimuli (thermal, tactile, osmotic, evaporative) cause rapid fluid movement within exposed patent dentinal tubules, which activates mechanoreceptors on A-delta nerve fibres at the pulp-dentine border. Treatment aims to occlude tubules or desensitise nerves. Professional options include: fluoride varnish (e.g., Duraphat 22,600 ppm), potassium oxalate (precipitates calcium oxalate crystals in tubules), glutaraldehyde/HEMA desensitising agents, resin sealant application, or GIC/composite restoration for significant cervical defects. Home care includes desensitising toothpaste (potassium nitrate or stannous fluoride).
MJDF Clinical Dentistry 2
A patient requires an anterior crown on an upper central incisor.
What minimum ferrule height is recommended for adequate resistance form, and why is it important?