EFDA Bases, Liners, and Matrices 3 — Questions and Answers
Question 1: The Automatrix system differs from the Tofflemire system primarily in that it:
- Requires a separate retainer device to hold the band
- Is a self-tightening matrix that needs no external retainer (Correct answer)
- Can only be used for anterior restorations
- Must be placed on the lingual surface
Correct answer: Is a self-tightening matrix that needs no external retainer
The Automatrix system is a retainerless matrix that is self-contained and tightened by its own internal mechanism.
Question 2: What thickness of remaining dentin requires placement of a protective base before an amalgam or composite restoration?
- Greater than 3 mm
- Less than 0.5 mm (Correct answer)
- Exactly 1 mm
- Greater than 2 mm
Correct answer: Less than 0.5 mm
When remaining dentin thickness is less than 0.5 mm, a protective base is required to shield the pulp from thermal and chemical insults.
Question 3: Which type of matrix system is most appropriate for Class III and Class IV composite restorations?
- Tofflemire matrix
- Automatrix band
- Celluloid strip matrix (Correct answer)
- Sectional matrix
Correct answer: Celluloid strip matrix
Celluloid (Mylar) strip matrices are transparent and used for anterior composite restorations to allow light curing through the band.
Question 4: Zinc phosphate base is indicated primarily in situations requiring:
- Pulp capping in deep carious lesions
- Thermal insulation under metallic restorations (Correct answer)
- Fluoride release to the dentin
- Direct bonding to enamel
Correct answer: Thermal insulation under metallic restorations
Zinc phosphate provides excellent thermal insulation and compressive strength, making it ideal as a base under metallic restorations.
Question 5: When removing the Tofflemire matrix after condensing amalgam, what is the correct sequence?
- Remove wedge first, then loosen retainer, then slide band occlusally
- Loosen retainer first, then remove wedge, then remove band facially (Correct answer)
- Slide the band gingivally without removing the wedge
- Remove the band before the amalgam begins to set
Correct answer: Loosen retainer first, then remove wedge, then remove band facially
The retainer is loosened first to free the band, the wedge is removed, and then the band is carefully pulled facially to avoid fracturing the marginal ridge.
Question 6: Which liner is considered the gold standard for indirect pulp capping procedures?
- Zinc oxide eugenol
- Copal varnish
- Calcium hydroxide (Correct answer)
- Glass ionomer cement
Correct answer: Calcium hydroxide
Calcium hydroxide's high pH creates an alkaline environment that stimulates odontoblasts to form a reparative dentin bridge.
Question 7: What is the main disadvantage of calcium hydroxide as a liner?
- It inhibits composite polymerization
- It dissolves over time and has poor compressive strength (Correct answer)
- It releases toxic fluoride ions
- It is opaque and blocks light curing
Correct answer: It dissolves over time and has poor compressive strength
Calcium hydroxide liners have low compressive strength and tend to dissolve if microleakage occurs, which can undermine the restoration.
EFDA Bases, Liners, and Matrices 3
The Automatrix system differs from the Tofflemire system primarily in that it: