EFDA - Expanded Function Dental Auxiliary Bases, Liners, and Matrices Questions and Answers — Questions and Answers
Question 1: A dentist completes a deep cavity preparation on a molar with a suspected microscopic pulp exposure. Which material is specifically placed in a thin layer over the site to promote the formation of reparative dentin?
- Zinc Oxide-Eugenol (ZOE)
- Calcium Hydroxide (Correct answer)
- Zinc Phosphate Cement
- Glass Ionomer
Correct answer: Calcium Hydroxide
Calcium hydroxide is well-known for its high alkalinity (high pH) which provides an antibacterial effect and stimulates odontoblasts to form a dentin bridge, also known as reparative or tertiary dentin, over a pulp exposure.
Question 2: An EFDA is preparing materials for a large Class II composite restoration. The dentist requests a base for thermal insulation. Which of the following materials must be AVOIDED for use as a base directly under a composite resin restoration?
- Resin-Modified Glass Ionomer (RMGI)
- Flowable Composite
- Zinc Oxide-Eugenol (ZOE) (Correct answer)
- Calcium Hydroxide
Correct answer: Zinc Oxide-Eugenol (ZOE)
The eugenol component in ZOE is known to inhibit the polymerization (setting reaction) of resin-based materials like composite. This interference compromises the bond and the overall integrity of the final restoration.
Question 3: For a Class II MO composite restoration on tooth #29, which matrix system is generally preferred to achieve the most anatomically correct contact and contour?
- Universal (Tofflemire) matrix
- Mylar strip and wedge
- Pre-formed metal shell crown
- Sectional matrix with a separating ring (Correct answer)
Correct answer: Sectional matrix with a separating ring
Sectional matrix systems are designed to recreate the tight, convex contacts and natural contours of posterior teeth more effectively than a universal Tofflemire band, which tends to flatten the proximal surface. The separating ring provides the necessary tooth separation to ensure a firm contact after the matrix is removed.
Question 4: When placing a posterior matrix band for a Class II restoration, what is the primary function of a wooden or plastic wedge?
- To adapt the band tightly against the gingival margin of the preparation. (Correct answer)
- To etch the interproximal tooth surface.
- To hold the matrix band retainer in place.
- To prevent moisture contamination from the pulp.
Correct answer: To adapt the band tightly against the gingival margin of the preparation.
The wedge is placed firmly in the gingival embrasure to seal the gingival margin of the matrix band against the tooth. This critical step prevents an overhang of restorative material and helps create a proper gingival contour. It also provides slight separation of the teeth to compensate for the band's thickness.
Question 5: Which of the following statements best describes the primary difference between a dental liner and a dental base?
- Liners are used for thermal insulation, while bases are used to stimulate reparative dentin.
- Liners are placed in a thin layer for pulpal protection, while bases are placed in a thicker layer for mechanical support. (Correct answer)
- Liners are only used under amalgam restorations, while bases are only used under composite restorations.
- Liners release high levels of fluoride, while bases are primarily sedative in nature.
Correct answer: Liners are placed in a thin layer for pulpal protection, while bases are placed in a thicker layer for mechanical support.
The main distinction lies in their thickness and primary function. Liners are thin coatings (typically <0.5mm) designed to seal dentinal tubules and protect the pulp chemically or therapeutically. Bases are thicker layers that provide thermal insulation and, importantly, distribute occlusal forces, acting as a supportive foundation for the final restoration.
Question 6: When an EFDA assembles a universal (Tofflemire) retainer and band for a Class II restoration on tooth #19 (lower left quadrant), the U-shaped head of the retainer should be oriented:
- towards the patient's cheek (buccal).
- towards the occlusal surface.
- towards the anterior of the mouth.
- towards the gingiva. (Correct answer)
Correct answer: towards the gingiva.
The head of the Tofflemire retainer, which holds the band, should always be oriented towards the gingiva. This keeps the bulk of the retainer out of the occlusal field, preventing interference with opposing teeth and instruments during restoration placement. The smaller circumference of the band loop also faces the gingiva.
EFDA - Expanded Function Dental Auxiliary Bases, Liners, and Matrices Questions and Answers
A dentist completes a deep cavity preparation on a molar with a suspected microscopic pulp exposure.
Which material is specifically placed in a thin layer over the site to promote the formation of reparative dentin?