Introduction

Endodontic therapy aims to eliminate germs from the root canal(s) and prevent microbial infection of the pulp and periapical tissues [1]. The primary method for removing canal germs is chemomechanical debridement of the root canal, which uses mechanical instruments and chemical cleaning solutions. Nevertheless, even after thorough mechanical and chemical cleaning, resistant bacterial strains might persist in the root canal, resulting in a root canal infection [2]. Planktonic bacteria in the root canal are readily responsive to antibacterial agents. Still, bacteria in biofilms attached to the canal wall or in more complex root canal areas, such as the end portions of dentinal tubules and lateral channels, are less accessible to certain treatments. There is a need for specific therapeutic techniques to get over these restrictions [3].

The most efficient root canal irrigation solution is NaOCl, a potent disinfectant with advantageous properties, including tissue solubility, proteolytic impacts on microorganisms, and bactericidal effects on bacterial endodontic biofilms. NaOCl is most frequently utilized as a root canal detergent in endodontic procedures at concentrations between 0.5 and 5.25% [4]. The structure of the E. faecalis biofilm calcifies with increased biofilm growth, making it more challenging to remove this mature and mineralized biofilm using traditional procedures and eventually increasing the risk of resistant root canal infections. The E. faecalis biofilm is known to show symptoms of mineralization and complete maturity after six weeks. As a result, the biofilm maturity index is determined by the development of the biofilm during six weeks. While most earlier research used young biofilms, most biofilms in root canals at the time of treatment are several weeks or months old. As a result, there are no exact correlations between laboratory study findings and clinical reality. Examine the various phases of biofilm to comprehend the connection between the organization and development of biofilm and its susceptibility to antimicrobial therapy [5].

The current study sought to determine the bactericidal effects of various NaOCl concentrations on biofilms on the results of root canal therapy.

This study used PubMed, Medline, and ScienceDirect to conduct a comprehensive literature search spanning 2000–2023. Search terms included "systematic review," ""sodium hypochlorite" "root canal treatment." To illustrate how we chose which papers to search, we used the PRISMA flowchart (Figure 1).

Inclusion criteria

Case-control and randomized-control trials

published in English between 2000 and 2023 were included.

Exclusion criteria

tabExpert opinion, narrative reviews, systematic reviews

research conducted outside the given time frame

studies conducted in languages other than English

studies conducted in vitro

Risk of bias assessment

Cochrane risk of bias assessment method was used to assess the quality of the studies included (Table 1).

Table 1. Summary of Cochrane Risk of Bias Assessment

Results and Discussion

Table 2 shows that Ulin et al., 2020 [6] conducted a trial, where 298 individuals were enrolled and divided into two random groups: 0.5% NaOCl and 3% NaOCl. Included were all endodontic diagnoses..The percentage of NaOCl. variation had no appreciable effect on the number of positive cultures, and it had no bearing on the frequency or intensity of postoperative pain. Patients who received a higher concentration (3% NaOCl) experienced a considerably higher incidence of postoperative edema.

The research done by Radcliffe et al., 2004  [7]  reported that for A. naeslundii and Candida albicans, all NaOCl doses reduced cfu below the detection limit within 10 seconds. NaOCl showed to be more effective against E. faecalis, though. Both studied strains had their cfu reduced to zero by 0.5% NaOCl after 30 minutes. This contrasts with 1.0% for 10 minutes, 2.5% for 5 minutes, and 5.25% for 2 minutes (P 0.001).

The study represented by Siqueira et al., 2000  [8] assessed the in vitro intracanal bacterial decrease from irrigation with saline or sodium hypochlorite (NaOCl) solutions at 1%, 2.5%, and 5.25%. Before and after preparation, samples of canals were taken. Test solutions drastically decreased the amount of bacterial cells in the root canal (p 0.05). The three NaOCl solutions under test did not differ significantly from one another (p > 0.05). However, all NaOCl solutions considerably reduced the number of bacterial cells in the root canal more than the saline solution (p=0.05).

The study accomplished by  Verma et al., 2019  [9] aimed to compare the effects of 2 different sodium hypochlorite concentrations on post-primary endodontic treatment recovery and discomfort.. Each patient was required to rate their pain level on a visual analog scale every 24 hours for a week. The teeth were permanently repaired during the second appointment after the canals had been obturated. For 12 months, clinical and radiographic examinations were conducted every three months. At the one-year follow-up, 86 teeth were available for review. The observed healing rate was 76.7% overall. The HC group (72.1%) showed more healing than the LC group (81.4%). Still, the difference was not statistically significant (P >.05).

The investigation presented by  Reyhani et al., 2017 [10] assessed how different sodium hypochlorite (NaOCl) solution concentrations inhibited the establishment of Enterococcus faecalis biofilms in root canals. One hundred four patients' maxillary central incisor root canals underwent chemomechanical debridement. The root canals were filled with 5.25% sodium hypochlorite solution for 3 minutes to eliminate the smear layer. Due to the complete elimination of E. faecalis biofilms in groups 2 and 3, there was no bacterial growth (P 0.0001). In contrast, group 1 had lower bacterial counts at intervals of 4, 6, and 10 weeks compared to the control group. Compared to young biofilms, the bacteria in mature and elderly biofilms are more resistant to 1% NaOCl solution. However, the growth of the E. faecalis biofilm was completely inhibited by the 2.5% and 5.25% NaOCl solutions at every stage of development.

The objective of the experimental work done by Shakouie et al., 2014  [11] was to evaluate the antibacterial activity of sodium hypochlorite (NaOCl) at concentrations of 0.5, 1, 2.5, and 5% with that of Triphala, a plant-derived solution, against Enterococcus faecalis (E. faecalis) [12]. The mean diameter of the inhibition zones in the Triphala group was considerably larger than those in the 0.5 and 1% NaOCl groups, according to the Mann-Whitney U test (P 0.05). Triphala showed superior antibacterial efficacy in this investigation compared to 0.5 and 1% NaOCl against E. faecalis (P=0.05).

A randomized clinical experiment was done by [13] Rôças et al., 2016, who examined fifty single-rooted teeth with apical periodontitis had their root canals cleaned with BioRaCe rotary equipment and 2.5% NaOCl (n = 25) irrigation. There were microbes in every S1 sample, which is a favorable result. In 44% and 40% of the root canals after chemomechanical preparation with 2.5% NaOCl, bacterial traces were still visible. Regarding total bacterial counts, the NaOCl group's S1 samples had an average of 3.7 105 bacterial cell equivalents, while S2 samples had a significantly lower average of 5.49 102 cell equivalents (P<.001).

The in vitro study conducted by Zand (2016) [14] used sixty removed single-rooted teeth from patients had their root canals contaminated with E. faecalis and cultured for six weeks. Compared to 2.5% NaOCl gel, the results of 2.5% and 5.25% NaOCl solutions were significantly better (P 0.05).

This study performed by [15] Torabinejad et al. 2003 revealed that when modest concentrations of NaOCl are utilized as an intracanal irrigant before using MTAD as a final rinse, the ability of MTAD to entirely remove the smear layer is improved. The dentinal tubules' structural makeup appears unaffected remarkably by this regimen.

Câmara et al., 2009 [12] conducted a vitro study; the objective was to assess the antibacterial activity of sodium hypochlorite at concentrations of 0.5%, 1%, and 2.5% when used in root canals utilizing the ProTaper Universal system as the instrumentation. According to the irrigant used, the specimens were randomly divided into five groups with ten root canals each: group 1 received 0.5% NaOCl, group 2 received 1% NaOCl, group 3 received 2.5% NaOCl, group 4 received 0.85% sterile saline solution as a positive control, and group 5 received 0.85% clean saline solution as a negative control, free of microorganisms. Except for one sample in S1 at 0.5% NaOCl, which demonstrated positive development, all the tested irrigants were clean after experimenting with the S1 file. The studied irrigants showed no discernible statistical difference (P = 1.000).

Table 2. Summary of the findings from included studies