Present status and future directions - irrigants and irrigation methods

Abstract

Irrigation is considered the primary means of cleaning and disinfection of the root canal system. The purpose of this review was to set the framework for the obstacles that irrigation needs to overcome, to critically appraise currently used irrigants and irrigation methods, to highlight knowledge gaps and methodological limitations in the available studies and to provide directions for future developments. Organization of bacteria in biofilms located in anatomic intricacies of the root canal system and the difficulty to eliminate them is the main challenge for irrigants. Sodium hypochlorite remains the primary irrigant of choice, but it needs to be supplemented by a chelator. Delivery of the irrigants using a syringe and needle and activation by an ultrasonic file are the most popular irrigation methods. There is no evidence that any adjunct irrigation method, including ultrasonic activation, can improve the long-term outcome of root canal treatment beyond what can be achieved by instrumentation and syringe irrigation. It is necessary to redefine the research priorities in this field and investigate in greater depth the penetration of the irrigants, their effect on the biofilm and the long-term treatment outcome. New studies must also focus on clinically relevant comparisons, avoid methodological flaws and have sufficiently large sample sizes to reach reliable conclusions. Future multidisciplinary efforts combining the knowledge from basic sciences such as Chemistry, Microbiology and Fluid Dynamics may lead to more effective antimicrobials and improved activation methods to bring them closer to the residual biofilm in the root canal system.

Keywords: Activation; delivery; irrigant; sodium hypochlorite; syringe; ultrasonic.

FIGURE 1

Approximate number of studies on root canal irrigation published per year between 1960 and 2021 according to the PubMed database (blue columns). The red line indicates what percentage this number is of the total number of studies in endodontology per year. The studies on root canal irrigation were retrieved using the search terms “root canal” AND (irrigation OR irrigant), the latter two being limited to the title or abstract, whilst those retrieved using the search term “root canal” were used as a proxy for the total number of studies in endodontology. None of these searches is exhaustive, but the findings may give an idea of the research interest over the past six decades.

FIGURE 2

Three‐dimensional reconstruction of Confocal Laser Scanning Microscopy scans of natural multi‐species biofilms grown from an infected root canal sample on dentine for 3 weeks: (a) untreated control, (b) after treatment with 2.5% NaOCl for 1 minute, (c) after treatment with 2% CHX for 1 minute. Green‐coloured bacteria are cells with intact membranes and red‐coloured bacteria are cells with damaged membranes following Live/Dead staining (BacLight; Invitrogen, Eugene, OR, USA).

FIGURE 3

Scanning electron microscope photomicrographs of dentine following chemomechanical preparation. A thick contaminated smear layer was evident when distilled water was used as irrigant (a). Irrigation with 2.5% NaOCl during preparation resulted only in partial removal of the smear layer (b) whilst an additional final rinse with 17% disodium EDTA (c) or continuous chelation with a mixture containing 2.5% NaOCl and 9% etidronic acid throughout preparation (d) resulted almost in complete removal.

FIGURE 4

(a) Bubble formation a few seconds after mixing equal amounts of 5% NaOCl and 17% disodium EDTA indicating their chemical reaction. (b) Orange‐brown mass formed due to the interaction between 5% NaOCl and 2% CHX (mixed in equal amounts).

FIGURE 5

Time‐averaged contours of irrigant velocity in the apical part of a size 45/.06 taper root canal during syringe irrigation using different types of needles, according to computer simulations [open‐ended needles: (a) flat, (b) bevelled, and (c) notched; closed‐ended needles: (d) side‐vented, (e) double side‐vented, and (f) multi‐vented]. All needles are positioned at 3 mm short of WL, and they are coloured in red. Reprinted and modified with permission from Elsevier (Boutsioukis et al., 2010a).

FIGURE 6

Time‐averaged contours of irrigant velocity in a mesial root canal of a mandibular molar prepared to apical size 20, 25 and 30/.06 taper during syringe irrigation at 0.05 and 0.15 mL/s using a 30G open‐ended, a 30G closed‐ended and a 31G closed‐ended needle inserted 1 mm short of the binding point, according to computer simulations. The needles are coloured in red. Reprinted and modified with permission from Elsevier (Boutsioukis & Gutierrez Nova, 2021).

FIGURE 7

SEM photomicrographs of eroded dentine following alternate irrigation with 2.5% NaOCl and 17% disodium EDTA.