Elsevier

Journal of Endodontics

Volume 20, Issue 2, February 1994, Pages 78-82
Journal of Endodontics

Bacterial retention in canal walls in vitro: Effect of smear layer

https://doi.org/10.1016/S0099-2399(06)81186-6Get rights and content

When dentin is planed by endodontic instruments, a smear layer forms. Whether this layer should be removed is unknown and controversial. This study was conducted to assess the effect of the smear layer on retention of bacteria using an in vitro root canal bacterial colonization model. Canals of 26 extracted human canines were step-back prepared using 2.5% NaOCl. Teeth were then randomly divided into two groups based on the type of high volume final flush: 1–20 ml of sterile saline (0.85% wt/vol) or (2–10 ml of 17% EDTA followed by 10 ml of 2.5% NaOCl which removes smear layer. Streptococcus anginosus (milleri) was cultured in trypticase soy broth supplemented with 0.5% yeast extract at 37°C in 5% CO2. Cells were harvested by centrifugation and resuspended in fresh media. Serial dilutions were performed to achieve inocula of 106 colony-forming units in a 30-μl volume. Teeth were inoculated and incubated for 2 h in 5% CO2 at 37°C. Following incubation, teeth were split and processed for microbiological analysis. Numbers of colonizing bacteria were determined by a spiral-plating system. Enumeration of the numbers of bacteria revealed a reproducible, order of magnitude difference (p = 0.0002) between teeth with smear layer (104 colony-forming units) versus teeth without smear layer (105 colony-forming units). This suggests that smear layer produced during root canal therapy may inhibit bacterial colonization of root canals. One suggested mechanism is that smear layer may block bacterial entry into dentinal tubules.

References (16)

There are more references available in the full text version of this article.

Cited by (85)

  • 13 - Lasers in Endodontics

    2015, Principles and Practice of Laser Dentistry
  • The effect of smear layer on the push-out bond strength of root canal calcium silicate cements

    2013, Dental Materials
    Citation Excerpt :

    On one hand, it is a loosely adherent layer that can provide a pathway for microbial micro-leakage [19], it potentially harbors bacteria and can serve as a reservoir of irritants [20], it can provide a substrate for any remaining bacteria following chemo-mechanical disinfection of the pulp space [21], and can prevent the penetration of irrigation solutions and inter-appointment medication into the dentinal tubules, thus jeopardizing the effective disinfection during root canal treatment [22]. On the other hand, the smear layer can block the dentinal tubules and alter their permeability which can limit bacterial and toxin penetration [23]. Furthermore, bacteria surviving the disinfection protocol can be entombed within the dentinal tubules by the smear layer and the obturation material [24].

View all citing articles on Scopus
1

Dr. Drake is associated professor, Department of Endodontics and Dows Institute for Dental Research, University of Iowa, College of Dentistry, Iowa City, IA.

2

Dr. Wiemann is a former graduate student, Department of Endodontics, University of Iowa, College of Dentistry.

6

Dr. Wiemann was awarded first prize in the graduate student competition for this work at the annual meeting of the AAE, Washington, DC, 1991.

3

Dr. Rivera is assistant professor, Department of Endodontics, University of Iowa, College of Dentistry.

4

Dr. Walton is professor and head, Department of Endodontics, University of Iowa, College of Dentistry.

View full text