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.

Present status and future directions – irrigants and irrigation methods

The oral cavity is the habitat of several hundreds of microbial taxa that have evolved to coexist in multispecies communities in this unique ecosystem. By contrast, the internal tissue of the tooth, i.e., the dental pulp, is a physiologically sterile connective tissue in which any microbial invasion is a pathological sign. It results in inflammation of the pulp tissue and eventually to pulp death and spread of inflammation/infection to the periradicular tissues. Over the past few decades, substantial emphasis has been placed on understanding the pathobiology of root canal infections, including the microbial composition, biofilm biology and host responses to infections. To develop clinically effective treatment regimens as well as preventive therapies, such extensive understanding is necessary. Rather surprisingly, despite the definitive realisation that root canal infections are biofilm mediated, clinical strategies have been focused more on preparing canals to radiographically impeccable levels, while much is left desired on the debridement of these complex root canal systems. Hence, solely focusing on ‘canal shaping’ largely misses the point of endodontic treatment as the current understanding of the microbial aetiopathogenesis of apical periodontitis calls for the emphasis to be placed on ‘canal cleaning’ and chemo-mechanical disinfection. In this review, we dissect in great detail, the current knowledge on the root canal microbiome, both in terms of its composition and functional characteristics. We also describe the challenges in root canal disinfection and the novel strategies that attempt to address this challenge. Finally, we provide some critical pointers for areas of future research, which will serve as an important area for consideration in Frontiers in Oral Health.

/pdf/microbiological-aspects-of-root-canal-infections-and-2p5ivqw957.pdf

Microbiological Aspects of Root Canal Infections and Disinfection Strategies: An Update Review on the Current Knowledge and Challenges

Chlorhexidine compounds and their different formulations have been investigated several times, especially in the dentistry field. Chlorhexidine application for mouth rinsing immediately underwent oral contraindications, linked to the possibility of causing pigmentation to the teeth or relating to possible cytotoxic events after oral surgery. The positive effects, however, are considerable and its topical antiseptic action has been widely demonstrated by in vitro and clinical research. That’s the reason for its large application in different fields of dentistry. The aim of this study is to collect all the literature regarding the use of chlorhexidine gel in dentistry and all the numerous applications. The initial search on search engines obtained 232 results; then, following the application of the inclusion criteria there were 24 selected articles. The chlorhexidine gel appliance in the dental daily practice is direct to oral surgery, conservative endodontics, prevention and prophylaxis. The use of chlorhexidine has shown some positive effects, also in the case of systemic diseases prevention. Surely, this topical medicine used both professionally and prescribed for home use, can be considered a great help for the prevention of several oral pathologies with systemic implications too.

Chlorhexidine Gel Use in the Oral District: A Systematic Review.

https://tspace.library.utoronto.ca/bitstream/1807/97851/1/Chan_Rebecca_201906_MSc_expandedabstract.pdf

Efficacy of 3 Supplementary Irrigation Protocols in the Removal of Hard Tissue Debris from the Mesial Root Canal System of Mandibular Molars.

Effect of Root Canal Irrigants on the Mechanical Properties of Endodontically Treated Teeth: A Scoping Review.

Endodontic irrigating solutions may interact chemically with one another. This is important, because even when solutions are not admixed, they will come into contact with one another during an alternating irrigation technique, forming unwanted by-products, which may be toxic or irritant. Mixing or alternating irrigants can also reduce their ability to clean and disinfect the root canal system of teeth by changing their chemical structure with subsequent loss of the active agent, or by inducing precipitate formation in the root canal system. Precipitates occlude dental tubules, resulting in less penetration of antimicrobials and a loss of disinfection efficacy. Sodium hypochlorite is not only a very reactive oxidizing agent, but is also the most commonly used endodontic irrigant. As such, many interactions occurring between it and other irrigants, chelators and other antimicrobials, may occur. Of particular interest is the interaction between sodium hypochlorite and the chelators EDTA, citric acid and etidronate and between sodium hypochlorite and the antimicrobials chlorhexidine, alexidine, MTAD and octenisept.

Alkaline sodium hypochlorite irrigant and its chemical interactions

Numerous in vitro studies highlight the role of quorum sensing in the pathogenicity and virulence of biofilms. This narrative review discusses general principles in quorum sensing, including Gram-positive and Gram-negative models and the influence of flow, before focusing on quorum sensing and quorum quenching in cariogenic and periodontopathic biofilms. In cariology, quorum sensing centres on the role of Streptococcus mutans, and to a lesser extent Candida albicans, while Fusobacterium nucleatum and the red complex pathogens form the basis of the majority of the quorum sensing research on periodontopathic biofilms. Recent research highlights developments in quorum quenching, also known as quorum sensing inhibition, as a potential antimicrobial tool to attenuate the pathogenicity of oral biofilms by the inhibition of bacterial signalling networks. Quorum quenchers may be synthetic or derived from plant or bacterial products, or human saliva. Furthermore, biofilm inhibition by coating quorum sensing inhibitors on dental implant surfaces provides another potential application of quorum quenching technologies in dentistry. While the body of predominantly in vitro research presented here is steadily growing, the clinical value of quorum sensing inhibitors against in vivo oral polymicrobial biofilms needs to be ascertained.

/pdf/quorum-sensing-and-quorum-quenching-with-a-focus-on-1u1crr19.pdf

Quorum Sensing and Quorum Quenching with a Focus on Cariogenic and Periodontopathic Oral Biofilms

Aim: To identify chelators which when mixed with sodium hypochlorite (NaOCl) are stable, exhibiting minimal loss of free available chlorine (FAC) over 80 min and to further investigate potential mixtures by assessing FAC over 18 h and the capacity to remove smear layer. 
Methodology: 0.25 mol L−1 EDTA (10%), 0.25 mol L−1 EGTA (egtazic acid), 0.25 mol L−1 CDTA (cyclohexanediaminetetraacetic acid), 0.25 mol L−1 DTPA (pentetic acid), 0.5 mol L−1 ATMP (aminotri(methylene phosphonic acid)) and 1 mol L−1 HPAA, (hydroxyphosphonoacetic acid), all at alkaline pH, were mixed equally with 5% NaOCl. 0.5 mol L−1 alkaline clodronate and 0.5 mol L−1 Na4etidronate (15%) were mixed equally with 10% NaOCl. For all mixtures, the pH and temperature were measured over 80 min and additionally for the clodronate mixture over 18 h. Iodometric titration was used to measure the FAC of all mixtures except for HPAA. The following were compared with respect to their ability to remove smear layer: 1 mol L−1 clodronate + 10% NaOCl, 0.5 mol L−1 clodronate + 10% NaOCl, 1 mol L−1 etidronate + 10% NaOCl, 0.5 mol L−1 clodronate + 10% NaOCl and the sequences 5% NaOCl/17% EDTA/5% NaOCl and 5% NaOCl/17% EDTA. The area fraction occupied by open dentinal tubules as a percentage of the total area (% AF) from scanning electron microscopy micrographs was calculated using Image J. The results were statistically analysed with alpha set at 0.05. 
Results: Compared to its control, the mixture 0.5 mol L−1 clodronate + 10% NaOCl lost no FAC over 18 h (P > 0.05). The FAC of 0.25 mol L−1 CDTA mixed with 5% NaOCl fell to 96%, 92%, 75% and 4.9% at 20, 40, 60 and 80 min, respectively. Temperature rises were observed in all cases except in the etidronate and clodronate mixtures. Only in the clodronate mixture did the pH remain above pH 12 for the whole experiment. Although smear layer was removed, the % AF in 1 mol L−1 clodronate + 10% NaOCl, 0.5 mol L−1 clodronate + 10% NaOCl, 1 mol L−1 etidronate + 10% NaOCl was less than for 0.5 mol L−1 etidronate + 10% NaOCl and 5% NaOCl/17% EDTA/5% NaOCl and 5% NaOCl/17% EDTA. 
Conclusion: Alkaline 0.5 mol L−1 clodronate mixed equally with 10% NaOCl has potential for use in continuous chelation, based on this assessment of stability and smear layer removal. Further research is needed to establish its efficacy and safety.

From an assessment of multiple chelators, clodronate has potential for use in continuous chelation.

In endodontic (root canal) treatment, a multispecies bacterial and fungal infection is present in a place that is inaccessible to the host immune system and which offers physical protection from applied topical agents. All current protocols for irrigation suffer various deficits in performance, which is why further research on alternative approaches to using antimicrobial substances is warranted. This chapter examines the technical and clinical factors which influence the performance of antimicrobial biocide-based therapies used in endodontics within dental practice, addressing issues around instability of biocides, the influence of pH, the role of physical agitation and the challenge of penetration into biofilms and into confined spaces. A range of methods to overcome the challenges in performance are described, including novel solvents and vehicles for biocides, stabilizing agents, physical agitation and the use of activation protocols including the use of intense light, ultrasound and laser-generated shockwaves to improve the effect of biocides. While specific examples are given from the dental setting of endodontics, the principles have broader application to medicine and to general industry.

/pdf/optimizing-antimicrobial-agents-in-endodontics-522t28abe2.pdf

Optimizing Antimicrobial Agents in Endodontics

Organic Tissue Dissolution in Clodronate and Etidronate Mixtures with Sodium Hypochlorite.

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