Systematic review of the effect of endodontic irrigants over coronaviruses

Objective: This systematic review aimed to discuss a possible effect of sodium hypochlorite (NaOCl) over the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the new generation of corona virus, which was reported firstly in December 2019 in Wuhan, China. Methods: Electronic search was performed for studies up to March 31, 2021 in the following databases: PubMed, LILACS, BBO, Scopus, web of science and Cochrane considering clinical trials and laboratory studies that evaluated the action of NaOCl over SARS-CoV-2. Results: Numerous founded studies reported effectivity of NaOCl in different concentrations and exposure times over corona viruses including the SARS-CoV-2. However, none of the studies evaluated this action in the root canal system. No metanalysis was conducted due to variability of methods or lack of information of included articles. Conclusion: NaOCl has a possible effectivity over SARS-CoV-2 as it dissolves the organic material of virus membrane, but this should be evaluated in the root canal systems.


Introduction
Severe acute respiratory syndrome coronavirus 2 "SARS-CoV-2", the new generation of coronavirus, was reported firstly in December 2019 in Wuhan, China. The novel virus was detected in patients saliva . As saliva can access the root canal through the periodontal ligament, dentinal tubules, open cavity, faulty restoration, apical foramen and accessory/secondary canals, (Narayanan & Vaishnavi, 2010) then the question is: Can SARS-CoV-2 access the root canal system as many viruses found in the root canal (Glick, Trope, Bagasra, & Pliskin, 1991;Slots, 2005)? Then, are the conventional endodontic irrigants effective over SARS-CoV-2?
Sodium hypochlorite (NaOCl) was introduced into endodontics in the last half of the XIX century. (Sedgley, 2004) It is considered an effective irrigant over various bacteria like Enterococcus faecalis, Escherichia coli and Streptococcus mutans, as well, over fungi like C.albicans. (Abu Hasna, Pereira Da Silva, et al., 2020;Valera et al., 2009) It is also effective over microorganisms' endotoxins like Lipopolysaccharides (LPS) and lipoteichoic acid (LTA) (Maekawa et al., 2011;Valera et al., 2014), and over the matrix metalloproteinases (MMP) . Beside, chlorhexidine (CHX), another wellknown antimicrobial agent used in endodontics, which is effective over variety of microorganisms (Walia, Goswami, Mishra, Walia, & Sahay, 2019). However, its major disadvantage is the reduced pulp tissue dissolution capacity (Arslan, Guneser, Kustarci, Er, & Siso, 2015). Therefore, this review aimed to understand a possible effect of the NaOCl and its behavior over SARS-CoV-2 as the presence of diverse microorganisms including bacteria, viruses and fungi in the root canal system complicates its disinfection.

Methodology
A systematic search using the PICO strategy was performed considering the endodontic infection and the influence of common irrigants over SARS-CoV-2. As the search resulted in no study, the authors reformulated the search to a broader aspect (considering the virus as the only component of the "P" within the PICO question). By changing the search strategy, the authors aim to compile all the information on the virus inactivation. Thus, the research question was as follows: Does NaOCl inactivate coronavirus?
The reformulated search follows: PICO strategy (Populationcoronavirus; Interventionuse of NaOCl solution; Comparison -NaOCl and CHX; Outcomereduction in virus load) considering clinical trials and laboratory studies that evaluated the action of NaOCl and CHX over SARS-CoV-2.
The inclusion and exclusion criteria were defined as the following:

•
In humans, in animals, in vitro and laboratorial studies.
• Quantification of coronaviruses and description of the test • The use of NaOCl solution

Exclusion criteria
• Case report, review article, or opinion article • The publication was based on a population from another study

Search strategy
Then, standard search keys were elaborated to look for studies in six data bases including (Pubmed, LILACS, BBO, Scopus, Web of Science and Cochrane) using the following key words. The initial search consisted in testing the Mesh and Entry terms, on the Medline base, with removal of terms resulting in no or duplicated studies. The initial search strategy was adapted for the other bases tested. The search strategies are presented in Table 1.

Study Selection and Data Collection Process
Eighty studies were obtained by these searches on different databases until 07/05/2021. The selected articles were alphabetically organized by title and duplicates could be identified and removed manually (one duplicated article was removed). Articles were further screened by title and abstract taking into account the eligibility criteria. Then, the full-text of selected articles was obtained and two reviewers (A.AH. and E.B.) classified those that met the inclusion criteria. In total ten articles were included. Relevant information about the study design, type of virus, interventions and exposure time, and outcomes were extracted using customized extraction forms by the authors independently.

Results and Discussion
The relevant extracted information is presented in ( Table 2). The lack of quantitative data in five studies and the lack of standard deviation in the other studies hindered the authors to perform a metanalysis. Also, as the information should be of clinical importance right away, it was decided to not ask the authors of the selected studies for further data.  Development, v. 10, n. 6, e23810615457, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i6.15457 Source: Authors.

Sodium hypochlorite irrigant over SARS-CoV-2
It is not the first time in this century to appear a new coronavirus. According to the study of Gorbalenya et al, (Gorbalenya et al., 2020) two times when a severe or even life-threatening disease was introduced into humans from a zoonotic reservoir: the severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS). Once again, a new coronavirus known at the moment as SARS-CoV-2 belongs to the sequence-based family classification and threatening the human being. (Zhou et al., 2019) In endodontics, there are no studies in the literature evaluated the effect of NaOCl or any other irrigant over SARS-CoV-2. In the literature, all articles evaluated the effect of NaOCl or CHX over coronaviruses, but not the SARS-Cov-2 itself, in wastewater, stool, urine or stainless-steel surfaces, but not in the root canal (in vitro or in vivo studies). Thus, these results found in the literature may not be suitable for root canal treatment as the root canal infection involves diverse factors like micro-organisms, endotoxins, matrix metalloproteinases and growth factors, ( Gomes & Herrera, 2018) in addition to dentin debris and smear layer that reduce irrigants effectivity. Morago et al., 2016) NaOCl is a widely used endodontic irrigant was mentioned in the literature as an effective antimicrobial agent. (Siqueira, Rôças, Favieri, & Lima, 2000) Furthermore, it was mentioned as an effective antiviral agent over many viruses like porcine parvovirus (PPV), pseudorabies and transmissible gastroenteritis viruses after five minutes of incubation. Neither the adequate concentration of NaOCl, nor the exposure time, was mentioned in that study. (Brown, 1981) As well, mouse hepatitis virus (MHV) and canine coronavirus (CCV) are two viruses belonging to the family of Coronaviruses and both can be disinfected by NaOCl in addition to other disinfectant agents, like sodium chloride (Saknimit, Inatsuki, Sugiyama, & Yagami, 1988). On the other hand, a more recent study related that 1:100 NaOCl was not effective in disinfecting two coronaviruses including MHV and transmissible gastroenteritis virus (TGEV) over a stainless steel surface. (Hulkower, Casanova, Rutala, Weber, & Sobsey, 2011) The efficacy of NaOCl over these viruses may be explained by its capacity in dissolving the organic material present in the outer membrane (envelope and membrane proteins). This was mentioned in the literature in many studies that explain this greater capacity in dissolving organic material than other endodontic irrigants like CHX. ( Gomes et al., 2013;Khademi, Usefian, & Feizianfard, 2007;Tartari et al., 2016;Tejada et al., 2019;Wright, Scott, Kahler, & Walsh, 2020) The same explanation was mentioned in the study of Maris et al. (Maris, 1990) that presented 0.8% soda and NaOCl with 1 degree chlorometric as the most active antiviral agent over coronavirus due to its dissolving capacity.
All the coronaviruses are present in air droplets and respiratory liquids including saliva. (Henwood, 2020;Hulkower et al., 2011;Kampf, Todt, Pfaender, & Steinmann, 2020) The severe acute respiratory syndrome coronavirus (SARS-CoV) remains infectious in respiratory specimens for more than 7 days at room temperature. NaOCl (which contains 50,000 ppm of active chlorine) can reduce the virus load by >3 log10 within 5 min. (Lai, Cheng, & Lim, 2005) Similar results were found in another study stating that 0.21% of NaOCl can inactivate SARS-CoV over surfaces after a 30s contact time (Dellanno, Vega, & Boesenberg, 2009) and 0.5% NaOCl with color additive guarantee a complete viral inactivation of human coronavirus 229E. (Tyan, Kang, Jin, & Kyle, 2018) Lastly, SARS-CoV can survive for 3 days in stool, at least 17 days in the urine at 20 °C and for more than 17 days at 4 °C in both stool and urine. However, SARS-CoV could be disinfected by chlorine solution which is derived by dissolving NaOCl. ( Wang et al., 2005) In the literature, it was evaluated the effect of CHX over coronaviruses and related that 0.02% CHX was not effective over MHV, (Dellanno et al., 2009). A more recent study alerting health professionals that chlorhexidine digluconate is ineffective for inactivating some coronavirus subtypes, and thus it is also ineffective over the SARS-CoV-2. (Assis, Araújo, & Lopes, 2020) It was impossible to find studies that evaluate the effect of endodontic irrigants over SARS-CoV-2 in the root canal due to its novel appearance. However, It is believed that SARS-CoV-2 may act like the other viruses in the same category of coronaviruses like SARS-CoV and MERS, (Henwood, 2020) more recently, NaOCl was recommended as effective disinfectant of SARS-CoV-2. (J. Wang et al., 2020) More recent studies stated that sodium hypochlorite concentration (0.1-0.5 %) is effective over the novel SARS-CoV-2. (Akram, 2020;Barbato et al., 2020)

Conclusion
It may be concluded that NaOCl has a possible effectivity over SARS-CoV-2 ( Table.2) but this should be evaluated in the root canal systems.