MJDF Clinical Dentistry 2

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?

Accepted 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

Answer

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?

Accepted 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

Answer

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?

Accepted Answer

Partial pulpotomy (Cvek pulpotomy) using mineral trioxide aggregate (MTA) or Biodentine to maintain pulp vitality and allow continued root development

Answer

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?

Accepted 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

Answer

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?

Accepted 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)

Answer

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.

MJDF Part 1 Practice Test

MJDF Part 1 Practice Test

MJDF Clinical Dentistry 2