Biofilms in Endodontics-Current Status and Future Directions

Abstract

Microbiota are found in highly organized and complex entities, known as biofilms, the characteristics of which are fundamentally different from microbes in planktonic suspensions. Root canal infections are biofilm mediated. The complexity and variability of the root canal system, together with the multi-species nature of biofilms, make disinfection of this system extremely challenging. Microbial persistence appears to be the most important factor for failure of root canal treatment and this could further have an impact on pain and quality of life. Biofilm removal is accomplished by a chemo-mechanical process, using specific instruments and disinfecting chemicals in the form of irrigants and/or intracanal medicaments. Endodontic research has focused on the characterization of root canal biofilms and the clinical methods to disrupt the biofilms in addition to achieving microbial killing. In this narrative review, we discuss the role of microbial biofilms in endodontics and review the literature on the role of root canal disinfectants and disinfectant-activating methods on biofilm removal.

Keywords: bacteria; disinfection; extracellular polysaccharide; irrigation; review; root canal.

Figure 1

Scanning electron microscopic images of the apical of the apical foramen of a tooth showing a mature biofilm of (i) Leuconostoc spp. (10,000×). A multilayered polymeric matrix is evident. Also noticed are communicating channels in the biofilm (A), extracellular fibers secreted by bacterial cells (B), metabolically active cells characterized by cell division (C) and compact extracellular polymers (D); (ii) Biofidobacterium spp. in a maturation state (10,000×). Secretion of polymers in granular form by the bacterial cells (A), microfilaments of extracellular polymers surrounding the rod shape of the microorganism (B) and extracellular polymers in the maturation state (C) can be seen (Courtesy: Dr. Ana Maria González Amaro, Maria Verónica Méndez González, UASLP Mexico).

Figure 2

Scanning electron microscopic images of (i) Clostridium botulinum and Streptococcus anginosus (5000×). Communication channels inside the biofilm (A), fusion of extracellular fibers in laminar shape (B) and the presence of numerous polymeric fibers secreted by rods and cocci forming a crisscross pattern (C) are evident. (Courtesy: Dr. Ana Maria González Amaro, Maria Verónica Méndez González, UASLP Mexico); (ii) 3 weeks biofilm of Enterococcus fecalis on dentin (2000×). The dense EPS matrix is visible and the challenge in eradicating biofilms of this microbe is, in part, attributed to the ability of medicaments to penetrate this matrix. This is the most commonly implicated bacterium in root canal treatment failure.

Figure 3

Confocal laser scanning microscopic (CLSM) image (single slice at 20× magnification) of a 1 week biofilm of Enterococcus fecalis within the root canal. Dense aggregates of bacteria are seen within the dentinal tubules. The advantage of CLSM imaging is to detect the presence of apparently dead (red) and apparently live (green) bacteria. It is also possible to perform 3 dimensional reconstruction of Z-stack images to study biofilm architecture.

Figure 4

Histological section of the isthmus area between two canals in a mandibular molar, stained by Taylor modified Brown and Brenn stain (16× and 100×) showing the presence of numerous bacterial masses with tissue. A higher magnification (100× and 400×) reveals the presence of residual bacteria and debris in the communications between canals after cleaning and instrumentation of root canal systems. This is the existing challenge in root canal treatment (Courtesy: Dr. Domenico Ricucci, Italy).