Irrigants: solutions and techniques

The aim of root canal therapy is either the treatment or the prevention of periapical periodontitis (or better, periradicular, taking into account lateral lesions). Kakehashi and coworkers, in 1965, were the first to demonstrate the relationship between periradicular lesions of endodontic origin and microbiota in the endodontic space. This result was confirmed later by most cited papers by Bergenholz in 1974 and Sundqvist in 1976. Since periradicular inflammation is usually caused by microbes within the root canal, the goal of endodontic treatment should be the complete disinfection of endodontic space. The disinfection can be achieved only by chemomechanical means, because the complex internal anatomy of the teeth prevents the possibility to reach all the internal walls with instrumentation, either manual, rotary or reciprocating.
Proper cleaning, shaping and filling of the root canal system, as well as the presence of a good coronal seal are key requirements for ensuring the periapical health. Longitudinal studies show that endodontic treatment can achieve high percentage of success, but epidemiological studies conducted in several countries have assessed an high prevalence of periradicular periodontitis in endodontically treated teeth, ranging from 21.5% to 64.5%. One of the key factors is the persistance of bacteria in the endodontic space, or the contamination during the endodontic treatment or later, because of an incomplete seal of the coronal restoration. First of all, such contamination should be prevented, by the use of an aseptic technique, including obviously the rubber dam; this improves the outcome of endodontic treatment. More, failure to use rubber dam can negatively influence the choice of endodontic irrigants.
The topic of endodontic irrigants has been treated extensively in dental literature; more than 1000 papers are listed in PubMed, and a lot of chemicals have been proposed for endodontic disinfection, including extracts of neem leaf, grape seed, aloe vera, garlic, propolis, passion fruit, morinda citrifolia, azadirachta indica and other herbs. However, the gold standard is still Sodum Hypochlorite; other widely used or studied products include chlorexidine, hydrogen peroxide and mixtures of antibiotics, disinfectants and acidic substances.
Unfortunately, most if not all of these products have been studied only in vitro; only 17 papers are available about in vivo studies of irrigants, four of them are randomized clinical trials and one nonrandomized, and there is a lack of agreement between the results. In vitro and ex vivo models should be used only for screening for the best candidates for in vivo screening, and their results should not influence clinical decisions; so, the available evidence on this topic is scarce, and the findings of studies were not consistent. In the hierarchy of evidence, however, in vitro researches are usually ranked well below expert opinions. Surveys have been conducted among general practitioners in different countries, finding out that about 93% used Sodium Hypochlorite as primary irrigant, and the results were similar among Endodontists, showing that the favourite concentration was 5% or higher.
So, it can be stated that there is a widespread agreement that sodium hypochlorite 5% is the most commonly used irrigant, and this makes sense, because of its characteristics: it has a broad spectrum of antimicrobial activity, high organic tissue-dissolving ability, does not leave toxic residues, is inexpensive and fast acting, removes dried or fixed organisms and biofilms from surfaces, and has a low incidence of serious toxicity. Its disadvantages are mostly the danger of accidental extrusion into periapical tissues, accidental ingestion with oropharyngeal burns, accidental ocular irritation, corrosiveness to metals, release of toxic substances when mixed with other chemicals. Sodium hypochlorite presents high surface tension, and this can limit its penetration in the anatomic irregularities of the root canal system and deeper penetration into dentinal tubules, and reduce the contact of the irrigant with the dentin walls and debris. L. Giardino and coworkers have recently proposed to add surfactants to NaOCl, thus enhancing the ability of NaOCl to dissolve organic material. One of the key factors in irrigation is not the efficacy of the solution itself, but the penetration in the apical portions, lateral canals, isthmuses and so on, where it can kill the bacteria and dissolve the tissues. The solution is soon inactivated by various factors, and so it needs to be exchanged frequently. Endodontic instruments must create space, in order to allow efficient penetration of the irrigants; also the time of contact of irritant with dentinal wall and debris is important. Sodium Hypochlorite so must be agitated and exchanged by mechanical, hydrodynamic, sonic/ultrasonic or other methods.