ABE Regenerative Endodontics 1 — Questions and Answers
Question 1: Which of the following is the PRIMARY goal of regenerative endodontic procedures (REPs) in immature permanent teeth with necrotic pulps?
- Elimination of infection followed by apexification with MTA
- Continued root development and thickening of dentinal walls (Correct answer)
- Obturation of the canal with gutta-percha after disinfection
- Placement of a collagen barrier to allow bone fill
Correct answer: Continued root development and thickening of dentinal walls
The primary goal of REPs is to allow continued root development (increased root length and wall thickness) in immature teeth, ideally restoring a functional pulp-dentin complex.
Question 2: According to the AAE clinical considerations for REPs, which irrigant should be used CAUTIOUSLY or avoided at full concentration in immature teeth because it can damage Hertwig's epithelial root sheath and stem cells?
- Chlorhexidine 2%
- Sodium hypochlorite at concentrations above 1.5% (Correct answer)
- EDTA 17%
- Saline
Correct answer: Sodium hypochlorite at concentrations above 1.5%
Sodium hypochlorite at concentrations greater than 1.5% can be cytotoxic to stem cells of the apical papilla (SCAP) and Hertwig's epithelial root sheath, so concentrations ≤1.5% are recommended.
Question 3: What is the significance of EDTA in the final irrigation step of a regenerative endodontic procedure?
- It eliminates residual bacteria not killed by NaOCl
- It releases growth factors from dentin and promotes stem cell differentiation (Correct answer)
- It bleaches blood clot components to improve visibility
- It dissolves the triple antibiotic paste remnants
Correct answer: It releases growth factors from dentin and promotes stem cell differentiation
EDTA demineralizes the dentin surface and releases bioactive molecules such as TGF-β, FGF, and BMP, which promote stem cell attachment, proliferation, and differentiation.
Question 4: Triple antibiotic paste (TAP) used in regenerative endodontics is classically composed of which three antibiotics?
- Metronidazole, ciprofloxacin, and minocycline (Correct answer)
- Amoxicillin, metronidazole, and tetracycline
- Clindamycin, ciprofloxacin, and doxycycline
- Penicillin, metronidazole, and erythromycin
Correct answer: Metronidazole, ciprofloxacin, and minocycline
The classic TAP formulation consists of metronidazole, ciprofloxacin, and minocycline, first described by Hoshino et al. to disinfect infected root canals.
Question 5: Which intracanal medicament for REPs is preferred over triple antibiotic paste when tooth discoloration is a primary concern?
- Calcium hydroxide alone
- Double antibiotic paste (metronidazole + ciprofloxacin) (Correct answer)
- Chlorhexidine gel
- Ledermix paste
Correct answer: Double antibiotic paste (metronidazole + ciprofloxacin)
Double antibiotic paste (metronidazole + ciprofloxacin, without minocycline) eliminates the tetracycline-class drug responsible for intrinsic crown discoloration while retaining broad-spectrum antibacterial activity.
Question 6: During a regenerative procedure, a blood clot is induced by over-instrumenting the periapical tissue. What is the role of the blood clot scaffold?
- It provides a physical barrier preventing bacterial reentry
- It serves as a fibrin scaffold for stem cell migration and tissue ingrowth (Correct answer)
- It releases calcium ions that mineralize the canal walls
- It acts as an antimicrobial reservoir releasing cytokines
Correct answer: It serves as a fibrin scaffold for stem cell migration and tissue ingrowth
The blood clot provides a fibrin scaffold rich in growth factors (PDGF, TGF-β, VEGF) that supports migration, proliferation, and differentiation of stem cells from the apical papilla.
Question 7: Following a successful regenerative endodontic procedure, which radiographic finding would indicate a FAVORABLE outcome in an immature tooth?
- Periapical radiolucency reducing in size with no change in root dimensions
- Increased root length and widening of dentinal walls with periapical healing (Correct answer)
- Complete canal calcification preventing further treatment
- Apex closure only without change in root length
Correct answer: Increased root length and widening of dentinal walls with periapical healing
A truly favorable REP outcome demonstrates continued root development — increased root length and thickening of canal walls — along with resolution of periapical pathology.
ABE Regenerative Endodontics 1
Which of the following is the PRIMARY goal of regenerative endodontic procedures (REPs) in immature permanent teeth with necrotic pulps?