Pulpal and periapical infections are biofilm-mediated. Planktonic bacterial models underestimate the antimicrobial challenge: organisms within biofilms are 100–1000× more resistant than their planktonic counterparts due to matrix diffusion barriers, metabolic heterogeneity, and persister cells.
Endodontic biofilms are polymicrobial, with a shift over time:
- Primary infections: broad polymicrobial flora dominated by anaerobes — Fusobacterium, Porphyromonas, Prevotella, Dialister, and streptococci.
- Post-treatment infections: more restricted community, often dominated by facultative gram-positives such as Enterococcus faecalis and Candida albicans, organisms that tolerate high pH and nutrient limitation.
Biofilms colonize the main canal walls, dentinal tubules (to ~1 mm depth), isthmuses, apical deltas, and lateral canals. The apical portion is anatomically complex and the hardest to disinfect mechanically.
- Mechanical shaping alone removes ~30–50% of canal surface area — the rest depends on irrigation.
- Sodium hypochlorite at 3–6% is the only common irrigant that dissolves biofilm matrix and kills organisms; contact time and volume matter more than higher concentration alone.
- Activation (sonic, ultrasonic, multisonic) dramatically improves penetration into isthmuses and tubules.
- Intracanal calcium hydroxide between visits helps reduce residual bioburden, especially for E. faecalis-prone retreatments.