The Microbial Challenge in Endodontics

Root canal infection is a biofilm problem. Bacteria organize into structured communities attached to the canal wall, dentinal tubules, and anatomical irregularities. Biofilm bacteria are significantly more resistant to antimicrobial agents than their planktonic counterparts.

Sodium Hypochlorite (NaOCl)

NaOCl remains the primary disinfectant in endodontics — the only irrigant with both tissue-dissolving and broad-spectrum antimicrobial properties.

• Concentration range: 0.5–5.25%. Higher concentrations are more effective but more cytotoxic if extruded.
• Tissue dissolution: dissolves organic tissue, including pulp remnants and biofilm matrix.
• Antimicrobial activity: effective against E. faecalis, Candida albicans, and anaerobic species.
• Limitations: does not remove the smear layer; loses activity rapidly in contact with organic matter.

EDTA and Sequential Irrigation

EDTA removes the smear layer and exposes bacteria within dentinal tubules to irrigant action. Sequential use of NaOCl and EDTA — not simultaneous — is the evidence-supported approach. A contact time of 1 minute at working length is generally sufficient for smear layer removal. Available as a solution (e.g., MD-Cleanser EDTA Solution) for final rinse protocols.

Calcium Hydroxide as Interappointment Medicament

Ca(OH)₂ is used in cases with persistent infection, necrotic pulps, or large periapical lesions. It raises canal pH to approximately 12.5, disrupts bacterial biofilm, and supports periapical healing between appointments. It should be removed completely before obturation.

• Water-based paste (e.g., Metapaste Plus): water-soluble, easy to remove, suitable for most interappointment applications.
• Oil-based / iodoform paste (e.g., Metapex Plus): radiopaque, slower release, used where longer-term placement is planned or where iodoform antimicrobial activity is desired.

The Goal of Disinfection

No current protocol eliminates all bacteria. The clinical goal is reduction of microbial load to a level that the periapical immune response can manage, allowing healing to proceed.