MJDF Restorative Dentistry Principles 2 — Questions and Answers

Question 1: Which of the following BEST describes the 'biologic width' in relation to crown preparation and restoration placement?

The minimum thickness of enamel required beneath a crown preparation
The combined dimension of junctional epithelium and connective tissue attachment above the alveolar crest, approximately 2mm, which must not be violated by restoration margins (Correct answer)
The space required between two crowns to allow proper flossing access
The minimum width of the gingival margin required before crown lengthening

Correct answer: The combined dimension of junctional epithelium and connective tissue attachment above the alveolar crest, approximately 2mm, which must not be violated by restoration margins

Biologic width (approximately 2mm) represents the natural seal of junctional epithelium (~1mm) plus connective tissue attachment (~1mm) above the alveolar crest. Restoration margins placed too close to or into this zone cause chronic inflammation, bone loss, and gingival recession.

The biologic width (also called the biological width) is the dimension of the supracrestal tissue attachment — the combined height of the junctional epithelium and the supracrestal connective tissue fibres that attach to the tooth coronal to the alveolar bone crest. Studies (Gargiulo et al., 1961) established average dimensions: junctional epithelium ~0.97mm; connective tissue attachment ~1.07mm; total biologic width ~2mm; sulcus depth ~0.7mm. The total 'dentogingival complex' height is therefore approximately 3mm (biologic width + sulcus). This varies between individuals and is not a fixed measurement, but the principle is that a certain dimension of healthy tissue is required between the restoration margin and the alveolar bone crest. Clinical relevance: when a crown margin is placed too close to or below the bone crest (violating the biologic width), the body responds by attempting to re-establish its natural tissue dimensions. This causes chronic gingival inflammation (redness, swelling, BOP), alveolar bone resorption (the bone moves apically to re-establish the 2mm dimension), and gingival recession (the gingival margin moves apically). This results in the classic clinical presentation of a crowned tooth with persistently inflamed gingiva, deepened pockets, and sometimes bone loss visible on radiograph. Prevention: restoration margins should be placed supragingivally where possible (best for gingival health and easy finishing); if a subgingival margin is needed for aesthetic reasons, it should be within the sulcus but at least 0.5-1mm from the junctional epithelium; if the tooth structure is subgingival (deep caries, fracture), crown lengthening surgery (or orthodontic forced eruption) is needed before crown placement to expose adequate tooth structure and re-establish biologic width compliance.

Question 2: What is the MAIN advantage of using glass ionomer cement (GIC) as a restorative material in primary (deciduous) teeth?

Glass ionomer cement has the highest compressive strength of all restorative materials
GIC releases fluoride ions, promotes chemical bonding to tooth structure, and is biocompatible, reducing secondary caries risk (Correct answer)
GIC is tooth-coloured and indistinguishable from natural tooth structure on close inspection
GIC bonds to all restorative materials and is ideal as a base under amalgam in primary teeth

Correct answer: GIC releases fluoride ions, promotes chemical bonding to tooth structure, and is biocompatible, reducing secondary caries risk

GIC's key advantages in primary dentition include: fluoride release (cariostatic effect on adjacent margins and dentine), chemical adhesion to enamel and dentine (no etching needed), and biocompatibility — important in the vulnerable primary dentition environment.

Glass ionomer cements (GICs) are water-based cements formed by the acid-base reaction between an alumino-silicate glass powder and polyalkenoic acid. They have several unique properties that make them valuable, particularly in paediatric dentistry: Fluoride release: GICs contain fluoride in the glass phase and release fluoride ions into adjacent tooth structure over time. This reduces the risk of secondary (recurrent) caries at restoration margins and has a remineralisation effect on adjacent enamel and dentine. GICs also recharge fluoride when exposed to fluoride in toothpaste and mouthwash. This property is particularly valuable in children with higher caries risk. Chemical adhesion: GICs bond chemically to tooth structure (enamel and dentine) through ionic exchange with hydroxyapatite — no acid etching or primer is required. This simplifies technique (important for shorter appointments with children) and provides marginal seal. Biocompatibility: GICs have excellent biocompatibility with pulp tissue. They are used as liners/bases under composites (sandwich technique) and as direct restorations in primary teeth. Limitations: lower fracture resistance and wear resistance than composite resin or amalgam — not ideal for high-stress areas in permanent dentition; early moisture sensitivity during setting (requires isolation); aesthetics are acceptable but not as tooth-coloured as modern composites. In primary dentition: GIC (conventional or resin-modified) is widely used for class I and II restorations, especially using Atraumatic Restorative Treatment (ART) technique (hand instrument excavation + GIC) in anxious children or community/outreach settings. Hall Technique (pre-formed metal crowns cemented over carious primary molars with GIC, sealing in caries) is increasingly evidence-supported for managing carious primary molars.

Question 3: A patient presents with a fractured upper central incisor. The fracture line extends through enamel and dentine but does not involve the pulp. What is this classified as and how should it be managed?

Ellis Class IV fracture — requires immediate root canal treatment
Ellis Class II fracture — requires dentine protection and restoration with composite resin bonding, with monitoring of pulp vitality (Correct answer)
Ellis Class I fracture — only enamel is involved and no treatment is necessary
Complicated crown fracture — requires emergency extraction

Correct answer: Ellis Class II fracture — requires dentine protection and restoration with composite resin bonding, with monitoring of pulp vitality

An Ellis Class II fracture (uncomplicated crown fracture) involves enamel AND dentine without pulp exposure. Management prioritises protecting the exposed dentine (to prevent pulp damage) and restoring the tooth with composite resin.

The Ellis classification for traumatic dental injuries to the crown provides a practical clinical framework: Ellis Class I — enamel fracture only: chipping or fracture of enamel with no dentine involvement. Minor smoothing, composite bonding, or monitoring depending on size. Good prognosis. Ellis Class II — enamel and dentine fracture (uncomplicated crown fracture): fracture extends through enamel into dentine but DOES NOT expose the pulp. The dentine tubules communicate with the pulp and the exposed dentine causes sensitivity and, if unprotected, allows bacterial ingress toward the pulp. Management: (1) Immediate dentine protection — glass ionomer liner, calcium hydroxide, or bonded composite applied to the exposed dentine surface; (2) Restoration — composite resin restoration to restore aesthetics and function (ideally reattaching the fractured fragment if available, or building up with composite); (3) Vitality monitoring — periapical radiograph at presentation, 1 month, 6 months, and 1 year to monitor for pulp necrosis (loss of vitality, periapical changes); if tooth loses vitality later, root canal treatment is required. Ellis Class III — enamel, dentine AND pulp fracture (complicated crown fracture): pink dot of pulp visible or pulp can be probed. Requires pulp therapy: in immature teeth, partial pulpotomy (Cvek pulpotomy) with MTA to preserve vitality and allow continued root development; in mature teeth, pulpectomy (RCT) or partial pulpotomy in recent fractures. Ellis Class IV — fracture involving root structure (subgingival): prognosis depends on fracture level; may require crown lengthening, orthodontic extrusion, or extraction. British Society of Paediatric Dentistry (BSPD) and IADT guidelines provide detailed protocols for dental trauma management — important for MJDF candidates.

Question 4: What is the purpose of 'matrix bands and wedges' during the placement of a Class II composite restoration?

To provide anaesthesia to the adjacent teeth during cavity preparation
To create a temporary wall replacing the missing tooth surface, provide contact point formation, and prevent gingival flash of composite material (Correct answer)
To protect the pulp from thermal damage during light curing
To assist in the removal of excess composite after curing

Correct answer: To create a temporary wall replacing the missing tooth surface, provide contact point formation, and prevent gingival flash of composite material

Matrix bands recreate the missing proximal wall and contact point during Class II restorations. Wedges stabilise the band, separate the teeth slightly to compensate for band thickness, and prevent composite from being extruded into the gingival crevice.

A Class II cavity (involving the proximal surface of a posterior tooth) requires special consideration because the proximal wall has been destroyed by caries or during preparation. Without a replacement for this wall, it is impossible to place and condense composite, achieve a proper contact point with the adjacent tooth, or prevent material from flowing into the gingival sulcus. The matrix band system provides: a temporary wall to contain the composite during placement; the shape and contour of the proximal surface; and an approximation of the contact area geometry. Wedges placed gingivally serve multiple purposes: they stabilise the matrix band against the tooth cervically, preventing gingival flash (composite extruding beneath the gingival margin); they create slight separation of the teeth (compensating for the thickness of the matrix band itself, which would otherwise result in a slightly loose contact once removed); they adapt the band tightly to the tooth at the cervical margin to prevent overhangs. Matrix systems for Class II composites: Tofflemire (universal) matrix system — curved band, retainer ring, used with sectional or circumferential placement. Sectional matrix systems (e.g., Palodent, Composi-Tight) — segmental matrices that cover only the proximal area of one tooth, used with separation rings that actively separate adjacent teeth; these provide better contact point formation and contour than full circumferential matrices and are the gold standard for posterior composite Class II restorations. Achieving a proper contact point is critical — too tight causes difficulty in flossing and gingival impingement; too loose causes food packing and secondary caries between teeth. Proper matrix technique is one of the most challenging aspects of posterior composite placement and is frequently assessed in MJDF clinical examinations.

Question 5: Which of the following describes the SMEAR LAYER in the context of dentine bonding?

A protective biofilm on the enamel surface that must be preserved
A thin layer of amorphous debris (cut dentine, bacterial remnants) deposited on dentine surfaces during preparation that must be either removed or modified for optimal bonding (Correct answer)
The outermost layer of intact dentine that provides the main bonding surface
A calcium-rich zone that forms the basis of the bonding mechanism

Correct answer: A thin layer of amorphous debris (cut dentine, bacterial remnants) deposited on dentine surfaces during preparation that must be either removed or modified for optimal bonding

The smear layer is a thin, compacted layer of organic and inorganic debris created during cavity preparation. It blocks dentinal tubules and reduces bond strength — adhesive systems either remove it (etch-and-rinse) or incorporate/modify it (self-etch) to create adhesion.

When dentine is cut with a bur or instrument, the cutting action produces a layer of ground-up dentine debris (ground hydroxyapatite crystals, denatured collagen, bacteria, cutting fluid) approximately 1-5 micrometres thick on the dentine surface and extending as smear 'plugs' into the dentinal tubule openings. This is the smear layer. The smear layer is weakly adherent to the underlying dentine — it is not a reliable bonding surface and its presence reduces the bond strength of adhesive systems because it prevents the adhesive resin from penetrating into the intact underlying dentine and tubules. The three generations of dentine adhesive systems handle the smear layer differently: Etch-and-rinse (total etch) systems (3-step: etch, prime, bond; or 2-step: etch + primer-adhesive): phosphoric acid (30-40%) is applied to enamel and dentine for 15-30 seconds, then rinsed. This completely removes the smear layer, opens tubules, and demineralises the surface of the dentine to expose a collagen fibril network. The primer and adhesive resin then infiltrate this demineralised zone, creating the 'hybrid layer' (resin-reinforced demineralised dentine). These systems generally provide the strongest bonds but require careful technique to avoid over-drying the dentine (which collapses the collagen network, preventing adhesive infiltration — 'wet bonding' technique required). Self-etch systems (2-step: self-etching primer, then adhesive; or 1-step: all-in-one): use acidic monomers that simultaneously etch and prime the dentine, dissolving and incorporating (rather than removing) the smear layer. Simpler technique, no rinsing required, less technique sensitive, lower risk of post-operative sensitivity. Bond strengths to dentine are comparable to total etch in many systems; slightly lower to enamel (so selective enamel etching is often recommended). Understanding adhesive bonding mechanisms is fundamental for MJDF restorative dentistry questions.

Question 6: When providing a complete upper denture for an edentulous patient, which anatomical landmark defines the POSTERIOR limit of the upper denture base?

The retromolar pad
The vibrating line (fovea palatinae), marking the junction between the hard and soft palate (Correct answer)
The pterygomandibular raphe
The posterior limit of the hard palate bony shelf

Correct answer: The vibrating line (fovea palatinae), marking the junction between the hard and soft palate

The posterior border of an upper complete denture is set at the vibrating line — the transition between the immobile hard palate and the movable soft palate — to maximise posterior seal without causing gag reflex or denture dislodgement during function.

The posterior border (post-dam area) of an upper complete denture is one of the most critical aspects of its design for retention. The denture must extend far enough posteriorly to develop a posterior palatal seal (post-dam) but not so far that it impinges on the mobile soft palate and causes gagging, discomfort, or dislodgement during function. The vibrating line (also called the 'ah line') is identified clinically by asking the patient to say 'ah' — the visible movement between the immobile hard palate and the movable soft palate defines this line. It corresponds to the junction of the palatine aponeurosis (which anchors the hard palate's mucosal covering) and the beginnings of the movable soft palate musculature. The fovea palatinae are two small pits or depressions in the midline of the posterior hard palate, typically located at or just anterior to the vibrating line. They are useful clinical landmarks for identifying the approximate posterior limit of the upper denture. The post-dam (posterior palatal seal): a slight compression or additional depth built into the denture base in this area creates continuous intimate contact between the denture and the soft tissue, excluding air from beneath the posterior border. This is critical for retention of an upper complete denture by peripheral seal. The resilience of the soft tissue allows the denture to be slightly compressed into the mucosa without displacing it, creating a functional seal. Extending beyond the vibrating line into the mobile soft palate causes the denture to be lifted during function (e.g., swallowing, speaking), breaking the peripheral seal and dislodging the denture. Landmarks such as the pterygomandibular raphe (lower denture relevant) and retromolar pad (lower denture posterior limit) are important for mandibular complete dentures.

MJDF Restorative Dentistry Principles 2

Which of the following BEST describes the 'biologic width' in relation to crown preparation and restoration placement?