EFDA Bases, Liners, and Matrices 5 — Questions and Answers
Question 1: Why is zinc oxide eugenol (ZOE) cement considered a 'sedative' base?
- It contains anesthetic agents that numb the pulp permanently
- Eugenol has a palliative effect that reduces pulpal inflammation and sensitivity (Correct answer)
- It hardens to a rigid material that immobilizes the tooth
- It seals the tubules with a crystalline structure
Correct answer: Eugenol has a palliative effect that reduces pulpal inflammation and sensitivity
Eugenol's analgesic and obtundent properties soothe irritated pulp tissue, making ZOE ideal for symptomatic or recently excavated teeth.
Question 2: When using a sectional matrix system, the ring retainer is placed:
- On the occlusal surface to hold the band down
- Into the embrasures to separate teeth and stabilize the band (Correct answer)
- Around the entire circumference of the tooth
- Under the gingival margin to seal the band
Correct answer: Into the embrasures to separate teeth and stabilize the band
The separation ring is inserted into the buccal and lingual embrasures to press the matrix band tight against the proximal box.
Question 3: A liner differs from a base primarily in that a liner:
- Is applied in a thick layer to provide thermal insulation
- Is a thin layer applied mainly for biological protection rather than mechanical support (Correct answer)
- Must always be light-cured before placing the restoration
- Contains higher concentrations of zinc to strengthen dentin
Correct answer: Is a thin layer applied mainly for biological protection rather than mechanical support
Liners are applied in thin layers (under 0.5 mm) to provide biological and chemical protection without the bulk or compressive strength of a base.
Question 4: What happens if the matrix band is not burnished (adapted) to the gingival margin before placing amalgam?
- The amalgam will not condense properly at the occlusal level
- A ledge or flash of amalgam will form at the gingival margin (Correct answer)
- The calcium hydroxide liner will dissolve prematurely
- The matrix retainer will become loose during condensation
Correct answer: A ledge or flash of amalgam will form at the gingival margin
An unadapted band leaves a gap at the gingival margin where amalgam can flow, creating a ledge that predisposes to plaque accumulation.
Question 5: Which liner is appropriate for use directly under composite resin without inhibiting polymerization?
- Zinc oxide eugenol (ZOE)
- Light-cured calcium hydroxide or resin-modified glass ionomer (Correct answer)
- Traditional zinc oxide eugenol base
- Copal varnish
Correct answer: Light-cured calcium hydroxide or resin-modified glass ionomer
Light-cured calcium hydroxide and resin-modified glass ionomer liners are compatible with composite resin and will not inhibit its polymerization.
Question 6: The primary function of a base in a deep cavity preparation is to:
- Bond the restorative material to the enamel surface
- Provide thermal and mechanical protection for the pulp while building up the preparation floor (Correct answer)
- Replace dentin that was removed during cavity preparation only in anterior teeth
- Release fluoride to remineralize residual caries
Correct answer: Provide thermal and mechanical protection for the pulp while building up the preparation floor
Bases replace missing dentin bulk to protect the pulp from thermal shock and resist compressive forces from condensation.
Question 7: When adapting a matrix band to a tooth with an unusual or pronounced cervical contour, which action helps ensure a proper gingival seal?
- Increasing the tightening of the Tofflemire retainer nut only
- Burnishing the band apically against the tooth surface with a ball burnisher (Correct answer)
- Replacing the matrix band with a wider-gauge amalgam
- Removing the wedge to allow the band to flex naturally
Correct answer: Burnishing the band apically against the tooth surface with a ball burnisher
Burnishing the band apically with a ball burnisher adapts it closely to the cervical contour to eliminate gaps at the gingival margin.
EFDA Bases, Liners, and Matrices 5
Why is zinc oxide eugenol (ZOE) cement considered a 'sedative' base?