ABE Endodontic Materials 2 — Questions and Answers
Question 1: Which property of mineral trioxide aggregate (MTA) makes it particularly suitable as a perforation repair material?
- High solubility in tissue fluids
- Excellent biocompatibility and sealing ability in the presence of moisture (Correct answer)
- Rapid setting time of under 5 minutes
- Antibacterial activity against E. faecalis
Correct answer: Excellent biocompatibility and sealing ability in the presence of moisture
MTA's biocompatibility, ability to set in moisture, and superior marginal seal make it ideal for perforation repair.
Question 2: The International Organization for Standardization (ISO) specification for gutta-percha points requires the taper of standardized cones to be:
- 0.02 mm/mm (Correct answer)
- 0.04 mm/mm
- 0.06 mm/mm
- 0.08 mm/mm
Correct answer: 0.02 mm/mm
ISO specification 6877 requires standardized gutta-percha cones to have a 0.02 mm/mm taper matching standardized instruments.
Question 3: Calcium hydroxide exerts its antimicrobial effect primarily through:
- Chelation of bacterial cell wall components
- High pH causing protein denaturation and enzyme disruption (Correct answer)
- Release of fluoride ions into dentinal tubules
- Inhibition of bacterial DNA replication
Correct answer: High pH causing protein denaturation and enzyme disruption
Calcium hydroxide's pH of approximately 12.5 causes protein denaturation and disrupts enzyme activity in bacterial cells.
Question 4: Which endodontic sealer has the lowest shrinkage upon setting among the following options?
- Zinc oxide eugenol sealers
- Resin-based sealers (AH Plus) (Correct answer)
- Calcium silicate-based sealers (Biodentine)
- Glass ionomer sealers
Correct answer: Resin-based sealers (AH Plus)
AH Plus epoxy resin sealer exhibits minimal volumetric shrinkage upon polymerization compared to other sealer types.
Question 5: The solvent most commonly used to dissolve gutta-percha during retreatment is:
- Sodium hypochlorite
- Chloroform (Correct answer)
- EDTA
- Hydrogen peroxide
Correct answer: Chloroform
Chloroform is the most effective solvent for dissolving gutta-percha, though its use is restricted in some countries due to carcinogenicity concerns.
Question 6: Bioceramic sealers achieve their adhesion to dentinal walls primarily through:
- Micromechanical interlocking after acid etching
- Formation of hydroxyapatite crystals that bond to dentin (Correct answer)
- Chemical bonding via silane coupling agents
- Van der Waals forces at the sealer-dentin interface
Correct answer: Formation of hydroxyapatite crystals that bond to dentin
Bioceramic sealers react with water in dentinal tubules to form hydroxyapatite, which chemically bonds to the dentin structure.
Question 7: Which component of zinc oxide eugenol (ZOE) sealers is responsible for its cytotoxic effects?
- Zinc oxide particles
- Free eugenol (Correct answer)
- Rosin accelerators
- Canada balsam
Correct answer: Free eugenol
Free unbound eugenol is primarily responsible for the cytotoxicity of ZOE sealers, as it can irritate periapical tissues.
ABE Endodontic Materials 2
Which property of mineral trioxide aggregate (MTA) makes it particularly suitable as a perforation repair material?