EFDA Bases, Liners, and Sealants 4 — Questions and Answers
Question 1: Which of the following bases has the highest compressive strength and is most suitable beneath a large amalgam restoration?
- Calcium hydroxide
- Zinc oxide eugenol (ZOE)
- Zinc phosphate cement (Correct answer)
- Glass ionomer liner
Correct answer: Zinc phosphate cement
Zinc phosphate cement has the highest compressive strength among traditional bases, providing adequate mechanical support under amalgam.
Question 2: An EFDA notices the sealant appears chalky white and opaque after rinsing the acid etchant. This appearance indicates:
- The etchant was left on too long and demineralized the enamel excessively
- Proper acid etching has created the correct micro-porous enamel surface (Correct answer)
- The tooth needs re-etching because the surface is too dry
- Contamination with saliva has occurred during etching
Correct answer: Proper acid etching has created the correct micro-porous enamel surface
A chalky, frosted white appearance after rinsing is the expected sign that phosphoric acid has correctly etched the enamel surface for bonding.
Question 3: Resin-modified glass ionomer (RMGI) liners differ from conventional glass ionomer liners primarily in that they:
- Do not release fluoride
- Set exclusively by acid-base reaction with no light curing
- Contain resin components allowing light-cured, faster initial set (Correct answer)
- Are contraindicated under composite restorations
Correct answer: Contain resin components allowing light-cured, faster initial set
RMGI contains resin monomers that allow light-cured polymerization for immediate command set, while also undergoing the glass ionomer acid-base reaction.
Question 4: When mixing zinc phosphate cement for a base, the powder is incorporated into the liquid in:
- All at once to reduce working time
- Large increments to build viscosity rapidly
- Small increments over a large, cool glass slab to dissipate heat (Correct answer)
- A warm environment to accelerate setting
Correct answer: Small increments over a large, cool glass slab to dissipate heat
Small powder increments are added gradually to the liquid on a cool glass slab to control the exothermic setting reaction and extend working time.
Question 5: Which of the following is the correct etch time for permanent enamel when applying a pit and fissure sealant?
- 10 seconds
- 15–20 seconds (Correct answer)
- 30–60 seconds
- 90 seconds
Correct answer: 15–20 seconds
Current clinical guidelines recommend etching permanent enamel for 15–20 seconds to achieve adequate micro-mechanical retention without over-etching.
Question 6: A liner is different from a base primarily in terms of:
- Chemical composition — liners always contain fluoride while bases do not
- Thickness — liners are thin coatings while bases are built up for bulk and support (Correct answer)
- Setting time — liners take longer to set than bases
- Application method — liners require mixing while bases are single-component
Correct answer: Thickness — liners are thin coatings while bases are built up for bulk and support
A liner is applied in a thin layer to protect the pulp, whereas a base is applied in greater thickness to provide mechanical support and thermal insulation.
Question 7: After sealant placement, the patient complains of a high bite on the sealed tooth. The EFDA should:
- Tell the patient it will wear down on its own
- Adjust the occlusion with a finishing bur (Correct answer)
- Remove the sealant and replace it
- Apply additional sealant to even out the surface
Correct answer: Adjust the occlusion with a finishing bur
Excess sealant material that creates a high bite should be reduced using a finishing bur to restore proper occlusal contacts.
EFDA Bases, Liners, and Sealants 4
Which of the following bases has the highest compressive strength and is most suitable beneath a large amalgam restoration?