ABE Endodontic Materials 3 — Questions and Answers
Question 1: EDTA is used as an endodontic irrigant primarily for its ability to:
- Kill anaerobic bacteria in the root canal
- Remove the smear layer by chelating calcium from dentin (Correct answer)
- Dissolve pulp tissue remnants
- Bleach intrinsically stained dentin
Correct answer: Remove the smear layer by chelating calcium from dentin
EDTA chelates calcium ions from dentinal hydroxyapatite, effectively removing the inorganic component of the smear layer.
Question 2: The working length of a nickel-titanium rotary file is typically confirmed using:
- Periapical radiographs alone
- Electronic apex locators and radiographic confirmation (Correct answer)
- Tactile sensation only
- Cone beam CT scan
Correct answer: Electronic apex locators and radiographic confirmation
A combination of electronic apex locators and periapical radiographs provides the most accurate and reliable working length determination.
Question 3: Which irrigant is most effective at dissolving necrotic pulp tissue in the root canal?
- Chlorhexidine 2%
- Sodium hypochlorite 5.25% (Correct answer)
- EDTA 17%
- Citric acid 10%
Correct answer: Sodium hypochlorite 5.25%
Sodium hypochlorite is the only endodontic irrigant with tissue-dissolving capability, making it superior for removing pulp remnants.
Question 4: Biodentine differs from ProRoot MTA primarily in its:
- Calcium silicate chemistry
- Much faster setting time due to calcium chloride accelerator (Correct answer)
- Biocompatibility with periapical tissues
- Ability to set in a moist environment
Correct answer: Much faster setting time due to calcium chloride accelerator
Biodentine contains calcium chloride as an accelerator in its liquid component, reducing setting time to approximately 12 minutes versus several hours for MTA.
Question 5: The alpha phase of gutta-percha differs from the beta phase in that it:
- Is used for thermoplastic obturation techniques
- Has a lower melting point and greater brittleness
- Contains a higher percentage of zinc oxide filler
- Is found in the naturally occurring form in the Palaquium tree (Correct answer)
Correct answer: Is found in the naturally occurring form in the Palaquium tree
Alpha-phase gutta-percha occurs naturally in the Palaquium tree and has a higher melting point, while beta-phase is used in clinical endodontic cones.
Question 6: When mixing zinc oxide eugenol cement for an interim restoration, increasing the powder-to-liquid ratio will result in:
- Longer working time and decreased strength
- Shorter setting time and increased compressive strength (Correct answer)
- Increased eugenol release and cytotoxicity
- No change in setting time but reduced viscosity
Correct answer: Shorter setting time and increased compressive strength
A higher powder-to-liquid ratio accelerates the zinc oxide eugenol reaction and increases the final compressive strength of the set material.
Question 7: The primary function of the smear layer removal protocol (NaOCl followed by EDTA) in endodontics is to:
- Increase the pH of the root canal system
- Improve sealer penetration into dentinal tubules (Correct answer)
- Eliminate all biofilm from the root canal
- Prevent post-operative pain after obturation
Correct answer: Improve sealer penetration into dentinal tubules
Removing the smear layer exposes dentinal tubules and allows sealer to penetrate more deeply, improving the quality of the obturation seal.
ABE Endodontic Materials 3
EDTA is used as an endodontic irrigant primarily for its ability to: