The goal of endodontic treatment is the eradication of microorganisms located in the root canal system that lead to apical periodontitis. These microbes colonize the intraradicular space as biofilms. While complete elimination is unrealistic, the practitioner needs to aim for the greatest practical reduction of these biofilms, usually via the use of endodontic irrigants. However, not all biofilms are the same. Biofilm—a matrix of extracellular polymeric substances that houses the microorganisms—varies in viscosity and diffusion resistance to antimicrobials.

Previous studies have focused on biofilms whose bacterial composition was identified, but have done so without reference to their structural organization. Most of these studies have used confocal laser scanning microscopy (CLSM), which effectively evaluates the efficacy of various endodontic irrigants to remove bacteria but has limited application when evaluating the removal of biofilms. Low load compression testing (LLCT) has been used to measure the viscosity of biofilms, information necessary to explain how well disinfectants penetrate and neutralize biofilms. Optical coherence tomography (OCT) can be used to image biofilm samples, measuring their height and illustrating their structure.

Busanello et al from the Federal University of Rio Grande do Sul, Brazil, designed a study that employed CLSM, LLCT and OCT to investigate the impact of biofilm structure on the efficacy of endodontic irrigants. They cultured Streptococcus oralis and Actinomyces naeslundii, 2 bacterial species that have been shown to be resistant to root canal disinfection procedures and that form robust biofilms with viscoelastic properties similar to those found in the mouth. The bacteria were then allowed to form 3 different biofilms with varying densities. Each of these biofilms was treated with 3 different endodontic irrigants:

  • 2% sodium hypochlorite (NaOCl)
  • 17% ethylenediaminetetraacetic acid (EDTA)
  • 2% chlorhexidine (CHX)

Samples were evaluated using OCT to assess biofilm removal, LLCT to assess biofilm viscosity and CLSM to evaluate biofilm composition.

Biofilm structure significantly affected biofilm removal. NaOCl removed significantly less biofilm in the samples that had denser biofilms than it did in the less dense samples, while no relationship existed with density for biofilm removal when EDTA and CHX were applied. However, in samples with less dense biofilms, NaOCl was significantly more effective in removing biofilm than were the other 2 irrigants. Regardless of biofilm density, EDTA was more effective than was CHX in removing biofilm and killing bacteria; indeed, OCT video showed that CHX merely rearranged biofilm structure, rather than removing it.

Conclusion

Given the proven inability of instruments to debride the entire root canal system, this study further illustrated the need for an effective irrigation regime to remove the biofilms that harbor endodontic bacteria. The results of this study suggest that the use of CHX in endodontic treatment should be questioned. On the other hand, the use of NaOCl for biofilm removal, along with adjunctive treatment with EDTA, may prove highly effective.

Busanello FH, Petridis X, So MVR, et al. Chemical biofilm removal capacity of endodontic irrigants as a function of biofilm structure: optical coherence tomography, confocal microscopy and viscoelasticity determination as integrated assessment tools. Int Endod J 2018;doi:10.1111/iej.13027.