REVIEW ARTICLE |
https://doi.org/10.5005/jp-journals-10015-2227 |
Comparison of Antimicrobial Efficacy of Octenidine Dihydrochloride and Chlorhexidine as Endodontic Irrigant: A Systematic Review
1,2,4-6Department of Conservative Dentistry and Endodontics, Amrita School of Dentistry, Amrita Vishwa Vidyapeetham, Kochi, Kerala, India
3Department of Public Health Dentistry, Amrita School of Dentistry, Amrita Vishwa Vidyapeetham, Kochi, Kerala, India
Corresponding Author: Manasi Mohan, Department of Conservative Dentistry and Endodontics, Amrita School of Dentistry, Amrita Vishwa Vidyapeetham, Kochi, Kerala, India, Phone: +91 7560938446, e-mail: manasimohanmanasi@gmail.com">Manasi Mohan, Department of Conservative Dentistry and Endodontics, Amrita School of Dentistry, Amrita Vishwa Vidyapeetham, Kochi, Kerala, India, Phone: +91 7560938446, e-mail: manasimohanmanasi@gmail.com
Received on: 09 March 2023; Accepted on: 11 April 2023; Published on: 02 June 2023
ABSTRACT
Aim: This systematic review aims to evaluate the antimicrobial efficacy of octenidine dihydrochloride (OCT) and chlorhexidine (CHX) as endodontic irrigants when used against Enterococcus faecalis (E. faecalis) and to compare the efficacy of both when used as a chemomechanical agent.
Background: This systematic review literature search was undertaken in the databases Medical Literature Analysis and Retrieval System Online (MEDLINE) Ovid (from 1946), Scopus, and Google Scholar, as well as a hand search of the references of included publications. Ex vivo and in vitro, studies were included. The risk of bias was assessed using a customized tool. In vitro and ex vivo studies were done on a natural tooth and agar cultures to measure the colony forming unit (CFU), zone of inhibition (ZOI), minimum inhibitory concentration (MIC), and proportion of dead cells to evaluate the antimicrobial efficacy of octenidine and CHX were considered outcomes in this review.
Review results: From 152 articles, 25 were reviewed for full text. A total of 12 in vitro studies were included for qualitative analysis. Out of 12 studies, eight studies reported better antimicrobial efficacy for OCT than CHX; two studies showed comparable results, and two studies favored CHX.
Conclusion: Octenidine was a more potent disinfectant in the root canal for better antimicrobial efficacy than CHX as an irrigant against E. faecalis.
Clinical significance: Octenidine dihydrochloride (OCT) has been described as a potential substitute for CHX during chemomechanical debridement in endodontic treatment. OCT is less cytotoxic to the periapical tissues than CHX; however, as an antimicrobial, it is highly effective against a range of gram-positive and gram-negative oral bacterial species. The substance of CHX in dentin seems to be an advantage over OCT. Thus, different studies have been conducted to compare the effectiveness of OCT and CHX for disinfection of the root canal, and the evidence seems to support the clinical use of OCT more.
How to cite this article: Mohan M, Muddappa SC, Venkitachalam R, et al. Comparison of Antimicrobial Efficacy of Octenidine Dihydrochloride and Chlorhexidine as Endodontic Irrigant: A Systematic Review. World J Dent 2023;14(4):373-381.
Source of support: Nil
Conflict of interest: None
Keywords: Antimicrobial efficacy, Chlorhexidine, Enterococcus faecalis, Endodontic irrigants, Octenidine dihydrochloride
INTRODUCTION
Bacteria are the primary causative factor in pulpal and periapical diseases, which can contribute to the development of periapical infection, pulpal pathosis, and posttreatment afflictions even after endodontic treatment.1 Pulpal spaces and dentinal tubules act as primary sources of residual microorganisms and can cause persistent inter radicular infections.2 The free-floating bacteria in the root canal can form mature biofilms by adhering to one another. Bacteria in the mature biofilms have an inherent resistance to antimicrobial agents, which probably makes it harder to eradicate the microbial biofilms from the root canal system.3
Enterococcus faecalis (E. faecalis), an anaerobic gram-positive bacterium that is facultative, nonfastidious, rapidly colonizing, and resistant microbial species in the oral environment, is the main possible cause of endodontic treatment failures and persistent asymptomatic infections.4,5E. faecalis mainly exists as biofilms in the root canal system and can penetrate deep into dentinal tubules, accumulate, and form communities that usually have multifold times more resistance to antimicroorganisms, phagocytes, and antibodies. Once E. faecalis invades the root canal system, it will become harder to disinfect the root canal space.5 Thorough cleaning and shaping of the root canal space removes any vital or necrotic pulpal tissues, microorganisms, and their by-products, along with the elimination of the smear layer and debris. Due to the high complexity of the canal system, mechanical instrumentation alone is inadequate to eliminate all microorganisms within the micro canals, and it is more likely that about half of the root canal walls will be left unprepared.6
As a result, several irrigating solutions have been suggested for usage in conjunction with root canal preparation. To effectively clean and disinfect the canal system, an irrigant should penetrate the dentinal tubules, provide a long-term antimicrobial action, smear layer removal, and be nonantigenic, nontoxic, and also non-carcinogenic.7
Chlorhexidine (CHX) has been considered a promising irrigating agent in root canal disinfection. Chemically, CHX is a positively charged synthetic cationic bisguanide with a pH of 5.5–7.8 It shows a broad spectrum of antibacterial and antifungal action, where higher concentrations (2%) exert bactericidal effect and lower concentration (0.2%) provides bacteriostatic action.8 CHX marks a unique property of substantivity that seems to be an advantage over the gold standard sodium hypochlorite (NaOCl) and also proves to be less cytotoxic than NaOCl.9-11 In addition, it improves resin dentin bond stability because of its matrix metalloproteinases inhibitory effect.12
By the time 1990s, OCT, a potent antimicrobial agent, was developed by Sterling-Winthrop Research Institute, which is chemically a bipyridine group having two cationic active centers per molecule with a pH 5–9.13 It exhibits broad-spectrum antimicrobial action by covering both gram-positive and gram-negative bacteria and fungi. OCT showed good potency against biofilm-forming organisms13 and also proved to be more effective than CHX by means of prolonged bacterial anti-adhesive activity.14 Thus, OCT has been suggested as an alternative endodontic irrigant based on its antimicrobial effects and lower cytotoxicity. It was also reported that various concentrations of OCT were as effective as 5.25% NaOCl solution.15
It is still in debate about the differences in the antibacterial efficacy of CHX and OCT. Results from previous studies have shown variations in the antimicrobial effectiveness of OCT and CHX. Few studies favored OCT,16,17 but few reported CHX as a better irrigant.18 Antimicrobial efficacy is undeniably the foremost important chemical property of irrigant solutions used in root canal treatment. Thus, there is a need for a systematic review to find out which one of the following irrigants has a better outcome.
MATERIALS AND METHODS
This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) reporting guidelines. The focused question is whether the antimicrobial efficacy [Outcome (O)] of octenidine [Intervention (I)] is superior to CHX [Comparator (C)] as an endodontic irrigant during root canal treatment [Population (P)].
In vitro and ex vivo studies that were done on a natural tooth and agar cultures to measure the CFU, ZOI, MIC, and proportion of dead cells to evaluate the antimicrobial efficacy of octenidine and CHX were considered in this review. Only studies that have used 0.1–0.2% of octenidine and 2% of CHX as root canal irrigants against E. faecalis were included. The research objective was to identify to assess the antimicrobial efficacy, which is typically done using in vitro study models.
Literature Search
Medical Literature Analysis and Retrieval System Online (MEDLINE) Ovid (from 1946 onwards), Scopus, Google Scholar, and EBSCO database searches were undertaken to identify articles on the topic. No restrictions were imposed on the date and country of publication. Only articles in the English language were included. The search strategies for the databases were modeled on that designed for MEDLINE Ovid. Further reference lists of the studies that were included were also searched for further references, and hand searching of studies was also tried. The search was performed in the month of February 2021.
Search Strategy
(Octenidine hydrochloride) or (OCT) OR (octenidine) or (octenisept) OR (OCT)) and [(CHX gluconate) or (CHX digluconate) or (CHX)] and [(antimicrobial) or (antibacterial)] and (root canal).
Study Selection
The obtained articles were imported to Covidence, and the process of screening was completed. Two authors (MM) and (SCM) individually excluded further duplicates from the collected results, and the relevant articles were examined by title and abstract. After the title and abstract were screened, the complete text of those articles was examined. Inclusion/exclusion criteria were obtained and analyzed from the full text.
Inclusion criteria were (1) all the in vitro studies comparing the antimicrobial efficacy of OCT and CHX as endodontic irrigants were taken, (2) 0.1–0.2% of octenidine and 2% of CHX concentrations against E. faecalis were only included, (3) restrictions on the different microbial methodologies were placed, (4) only one standard microbial strain of E. faecalis were obtained for culturing, (5) dentin disks and agar media were only used to assess the microbiological analysis of the irrigants, (6) only natural teeth were selected as samples, and (7) studies that were in English language with full-text articles were abstracted.
Exclusion criteria included (1) animal studies and review articles, (2) studies that do not describe the standardization of sample size and preparation, (3) E. faecalis preparation, (4) studies that do not describe the concentration, contact time, and volume of the irrigants.
Any disagreements were resolved by discussion or, if necessary, by consulting with a third review author (RV) in order to reach a consensus.
Data Extraction
The data was extracted onto an Excel sheet, which was then pilot-tested using a sample of the included studies. From every included study, the following details were extracted—details about publications, such as year of publication and journal, country of origin, sample size, intervention group (octenidine) characteristics, control group (CHX) characteristics, outcome measurements [CFU and ZOI), intervention, results, and funding details. Mean differences and standard deviations (SD) were used to summarize the treatment effect for each research.
Quality Assessment
Two reviewers (MM and SCM) independently assessed the risk of bias. There was no standardized tool available for assessing the risk of bias for in vitro studies. Previous studies have used customized tools. The present study also used a customized tool adapted from the study.19 For calculating the risk of bias, the following parameters were evaluated and graded:
-
Presence of a control group.
-
Description of the sample size calculation.
-
Standardization of sample preparation.
-
Standardization of E. faecalis preparation.
-
Blinding of the observer.
If the parameters were reported by the authors, the article received a Y (yes); if the information could not be found, the article received an N (no). The articles that reported one to two items were classified as high risk of bias, three as medium risk, and four to five as low risk. Only two of the studies included had a high risk of bias, and the rest of the studies showed medium bias. This shows the high heterogeneity of the studies.
RESULTS
In the first stage of study selection, a total of 152 potentially relevant records were identified from all the databases. Duplicates were removed, resulting in 18 records that underwent title and abstract screening. The studies were reduced to 25 for full-text reading as 109 studies did not meet the eligibility criteria. A total of 13 studies were excluded from the 25 studies retained for detailed review. Of the 13 articles excluded, two articles showed the wrong intervention,20,21 three studies used different comparators,22-24 and eight articles used the wrong study design.25-32 A total of 12 studies15,16-18,33-40 were able to fulfill all of the selection criteria and were taken up in this systematic review. The article selection process has been summarized in Flowchart 1 in the form of a flowchart according to the PRISMA statement.
Flowchart 1: Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) flowchart
The efficacy of CHX and OCT was closely related to the frequency and volume of the irrigation; however, this information varied among the studies, and these parameters were not precisely described in the studies. Also, taking into account different methodological procedures, different forms of culture, and different presentations of microorganisms were the modulating factors that could affect the accurate comparison of inherent antibacterial activity. Due to high heterogeneity in the study designs of the included studies, a high heterogeneity meta-analysis was not able to perform.
Descriptive Analysis
Characteristics of Included Studies
A total of 12 studies were included; all were comparative in vitro studies. All studies were screened under four main categories such as CFU (Table 1), ZOI15,35,36 (Table 2), MIC (Table 3), and proportion of dead cells (Table 4).
Study ID | Intervention | Control | Microorganism | Outcome | EF initial incubation time | Time of contact | Volume of irrigant | Final suspension amount and incubation time | Sample size | Test group mean ± SD |
Control group mean ± SD |
---|---|---|---|---|---|---|---|---|---|---|---|
Jain et al.33 | 0.1% OCT | 2% CHX | E. faecalis (MTCC 439) 1.5x 108 CFU 0.5 McFarland standards |
CFU Natural tooth |
37°C for 7 days | 3 minutes | - | 1 µL 37°C for 24 hours |
Test group: 18 Control group: 18 |
200 µm: 51.33 ± 1.72 400 µm: 52.16 ± 1.16 |
200 µm: 60.83 ± 1.72 400 µm: 62.50 ± 1.22 |
Cherian et al.16 | 0.1% OCT | 2% CHX | E. faecalis (ATCC 29212) 1.5 × 108 CFU/mL 0.5 McFarland standards |
CFU Natural tooth |
37°C for 7 days | 2 minutes | 4 mL | 1 µL 37°C for 24 hours |
Test group: 12 Control group: 12 |
200 µm: 425.42 ± 51.85 400 µm: 339.08 ± 52.18 |
200 µm: 613.33 ± 33.41 400 µm: 516.92 ± 41.44 |
Tirali et al.15 | 0.1% OCT | 2% CHX | E. faecalis (ATCC 29212) 1.5 x 108CFU/mL |
CFU Natural tooth |
37°C for 21 days | 30 seconds 1 minute 5 minutes |
1 mL | 10 µL 37°C for 24 hours |
Test group: 8 Control group: 8 |
30 seconds: 33.25 ± 17.44 1 minute: 22.12 ± 13.66 5 minutes: 6.12± 4.54 |
30 seconds: 60.25 ± 9.00 1 minute: 42.50 ± 10.58 5 minutes: 10.12 ± 5.74 |
Palazzi et al.34 | 0.1% OCT | 2% CHX | E. faecalis (ATCC 29212) CFU 0.5 1 McFarland standard |
CFU Natural tooth |
37°C for 28 days | 10 minutes | - | 100 µL 37°C for 28 days |
Test group: 10 Control group: 25 |
0 day: 1.64 ± 0.33 7 days: 9.23 ± 2.33 14 days: 16.36 ± 2.37 21 days: 34.65 ± 2.67 28 days: 51.66 ± 3.39 |
0 day: 3.68 ± 2.60 7 days: 10.77 ± 2.40 14 days: 16.58 ± 1.89 21 days: 35.10 ± 2.71 28 days: 51.33 ± 3.62 |
Guneser et al.35 | 0.1% OCT | 2% CHX | E. faecalis (A197A) CFU |
CFU Natural tooth |
37°C for 21 days | 3 minutes | 5 mL | 100 µL 37°C for 48 hours |
Test group: 10 Control group: 10 |
0 | 0 |
Anuradha36 | 0.1% OCT | 2% CHX | E. faecalis (ATCC 29212) 2.4 x 105 CFU/mL 0.5 McFarland standard |
CFU Natural Tooth |
37°C for 7 days | 1 minute | 3 mL | 10 µL 37°C for 48 hours |
Test group: 10 Control group: 10 |
0 | 0 |
Ghivari et al.37 | 0.1% OCT | 2% CHX | E. faecalis (ATCC 29212) 0.5 McFarland standards |
CFU Nitrocellulose biofilm model |
37°C for 21 days | 1 second, 5 seconds, 10 seconds, 30 seconds, and 60 seconds | 200 µL | 10 µL 37°C for 24 hours |
- | 1 second: 2.40 ± 1.34 5 seconds: 1.60 ± 0.89 10 seconds: 1.40 ± 0.89 30 seconds: 0.20 ± 0.45 60 seconds: 0.20 ± 0.45 |
1 second: 0.00 ± 0.00 5 seconds: 0.20 ± 0.45 10 seconds: 0.20 ± 0.45 30 seconds: 0.80 ± 1.79 60 seconds:1.00 ± 1.00 |
EF, Enterococcus faecalis
Study ID | Intervention | Control | Microorganism | Outcome | Broth used | E. Faecalis initial incubation | Time of contact of irrigant | Amount of irrigant used | Final inoculation and suspension time | Test group mean ± SD | Control group mean ± SD |
---|---|---|---|---|---|---|---|---|---|---|---|
Tirali et al.35 | 0.1% OCT | 2% CHX | E. faecalis (ATCC 29212) 0.5 McFarland standard |
ZOI Agar diffusion procedure |
BHI agar | 37°C at 24 hours | - | 20 µL | 37°C for 24 hours | 17* | 11* |
Alper et al.18 | 0.1% OCT | 2% CHX | E. faecalis (ATCC 29212) 0.5 McFarland standard |
ZOI Agar diffusion procedure |
Muller Hinton agar | 37°C at 24 hours | - | 20 µL | 37°C for 24 hours | 7.25* | 17.75* |
Thusha et al.38 | 0.1% OCT | 2% CHX | E. faecalis (ATCC 29212) 0.5 McFarland standard |
ZOI Agar well diffusion method |
Blood agar | 37°C at 24 hours | - | 20 µL | 37°C for 48 hours | 13.95 ± 0.56 | 16.26 ± 0.56 |
*No SD reported
Study ID | Intervention | Control | Microorganism | Outcome | E. faecalis initial incubation | Time of contact of the irrigant | Irrigant (dilution) | Final incubation | Test group | Control group |
---|---|---|---|---|---|---|---|---|---|---|
Akriti et al.37 | 0.2% OCT | 2% CHX | E. faecalis (ATCC 29212) 0.5 McFarland |
MIC | 24 hours | - | 10-fold dilution | 37°C for 48 hours | Number of colonies visible-17 | Number of colonies visible-73 |
Anuradha36 | 0.1% OCT | 2% CHX | E. faecalis (ATCC 29212) 2.4 x 105 CFU/ml 0.5-McFarland standard |
MIC | 37˚C for 48 hours | - | OCT-1/10 CHX-1/75 |
37°C for 18 hours | 0.62 µg/mL (potency) |
3.33 µg/mL (potency) |
Study ID | Control | Intervention | Microorganism | Outcome | E. faecalis initial incubation | E. faecalis initial inoculation | Volume of irrigant | Time of contact of the irrigant | Test group | Control group |
---|---|---|---|---|---|---|---|---|---|---|
Bukhary and Balto40 | 0.1% OCT | 2% CHX | E. faecalis (ATCC 29212) 0.5-McFarland standard 1 x 108 CFU/mL | The proportion of dead cells by confocal laser scanning microscopy | 37˚C for 24 hours | 37°C for 21 days | 2 mL | 10 minutes | Median and range values of dead cells (%): 74.14 (70.03–78.96) |
Median and range values of dead cells (%): 42.79 (25.45–55.06) |
Around 10 of the 12 included (83.3%) studies had a medium (score 3) risk of bias. Description of sample size and blinding of the observer were the factors missing in all studies, while two studies had a high risk of bias (score 2) with no clear mention of standardization of E. faecalis preparation (Table 5).
Study ID | Presence of a control group | Description of sample size calculation | Standardization of sample preparation | Standardization of E. faecalis preparation | Blinding of the observer | Overall risk of bias |
---|---|---|---|---|---|---|
Jain et al.33 | Yes | No | Yes | Yes | No | 3 |
Cherian et al.16 | Yes | No | Yes | Yes | No | 3 |
Tirali et al.15 | Yes | No | Yes | Yes | No | 3 |
Palazzi et al.34 | Yes | No | Yes | Yes | No | 3 |
Guneser et al.35 | Yes | No | Yes | Yes | No | 3 |
Anuradha36 | Yes | No | Yes | Yes | No | 3 |
Ghivari et al.37 | Yes | No | Yes | Yes | No | 3 |
Tirali et al.29 | Yes | No | Yes | Yes | No | 3 |
Alper et al.18 | Yes | No | Yes | Yes | No | 3 |
Tusha et al.36 | Yes | No | No | Yes | No | 2 |
Akriti et al.37 | Yes | No | No | Yes | No | 2 |
Bukhary and Balto40 | Yes | No | Yes | Yes | No | 3 |
The outcome measurements described in the included studies were grouped under the following—CFU, ZOI, MIC, and proportion of dead cells.
Studies Reporting CFU Unit as an Outcome
Seven studies had CFU16,17,33,37 as the primary outcome, of which six studies16,17,33,36 were done on natural tooth, and one was37 on nitrocellulose biofilm model. Four studies16,17,33,34 undertook the qualitative analysis, whereas two studies35,36 were quantitative studies. From the six studies conducted on natural teeth, three16,17,33 studies concluded OCT had better antimicrobial properties than CHX, whereas Guneser et al.35 and Anuradha36 reported that CFU for both irrigants were zero (CFU = 0) and Palazzi et al.34 showed comparable results between two irrigants. The qualitative studies16,17,33 favored OCT. The quantitative studies35,36 done to count the CFU reported that both OCT and CHX could eliminate all E. faecalis from the culture, that is, CFU = 0. But the study33 also included MIC and minimum bacterial concentration (MBC) along with CFU; with all these parameters, it had been concluded that OCT was considered the most potent antimicrobial agent against E. faecalis.
Studies which were categorized under CFU/mL,17,33,36 In which studies17,33 showed more antimicrobial efficacy for OCT, whereas OCT and CHX eliminated all E. faecalis, CFU = 0.36 Four studies were reported under CFU16,34,35,37 in which two studies16,37 favored OCT, while Palazzi et al.34 reported a comparable result between two irrigants, while Gunesar et al.35 concluded that both OCT and CHX could eliminate all E. faecalis. CFU, when counted in nitrocellulose biofilm model at 30s and 60s,37 showed OCT had a better antimicrobial efficacy.
In two studies,16,33 methodologies for tooth preparation, cultivation of E. faecalis, specimen contamination, and microbial analysis were the same except for irrigation time. According to Cherian et al.,16 0.1% OCT was more potent than 2% CHX against E. faecalis both at 200 and 400 μm depth, but according to Jain et al.,33 it showed statistically nonsignificant differences when comparing OCT with CHX at 200 µm and 400 µm depth suggestive of comparable results in limiting the CFU counts, but values in the table of the article reported CHX 200 µm versus OCT 200 µm and CHX 400 µm versus OCT 400 µm, there was statistical significance in p-value with a positive mean difference showing that OCT had more antimicrobial efficacy when compared to CHX.
Studies Reporting ZOI as an Outcome
Zone of inhibition (ZOI) was calculated to check the antimicrobial efficacy in three studies.15,18,38 Two studies15,18 followed the same methodology except for the broth that was used for cultivation, in which Tirali et al.15 concluded that OCT showed more ZOI and was more effective, whereas the study18 showed CHX had greater ZOI. According to Thusha et al.,38 ZOI was more for CHX when compared to OCT and also reported that though the values are highly statistically significant, OCT could be recommended as an intracanal irrigant with higher concentration and can be used as a substitute in the place of 2% CHX.
Studies Reporting MIC as an Outcome
Minimum inhibitory concentration (MIC) test36,39 inhibits the visible growth of a microorganism by the use of antimicrobial agents and concluded from the studies that 0.2% OCT showed more efficacy in inhibiting E. faecalis39 and MIC of OCT was less compared to CHX; thus, 0.1% OCT proved a better antimicrobial efficacy.36
A Study Reporting the Proportion of Dead Cells as an Outcome
A significant increase in the number of dead cells was identified using confocal laser microscopy in the OCT group than in CHX, suggestive of more antimicrobial efficacy of OCT.40
To summarize, out of seven studies of CFU, four studies16,17,33,37 favored OCT, two studies35,36 reported CFU = 0 for both irrigants and one study34 showed a comparable result. Out of three studies of ZOI, one study favored OCT,15 and two studies reported ZOI was more for CHX.18,38 Two studies focusing on MIC suggested OCT had better efficacy than CHX,36,39 and in one study, OCT showed good antimicrobial efficacy.
DISCUSSION
Persistent endodontic infections are attributed due to the retention of microorganisms in the root canal system. When the host defense loses its access to the necrotic pulpal tissues, opportunistic bacteria might congregate in the canal system under severe environmental conditions and at low oxygen levels.7 A bacteria-free root canal system cannot be achieved solely through mechanical instrumentation.11 Thus, during endodontic treatment, a chemomechanical preparation would promote appropriate disinfection. E. faecalis was considered the microorganism of interest due to its frequent presence even in root canal treated teeth causing tenacious lesions and also considered to be a possible cause of endodontic treatment failure.4 Its presence had been extensively seen in 63% of teeth having posttreatment diseases.41
Enterococcus faecalis (E. faecalis) has the ability to multiply within the deep layers of dentinal tubules, as well as inside the ramifications and isthmuses, which enhances its adherence to the collagen fibers of the dentin matrix33E. faecalis contain certain virulence factors like aggregation substances, lytic enzymes, pheromones, cytolysin, and lipoteichoic acid. It can express certain proteins by adhering to host cells which permits it to compete with other bacterial cell walls, suppressing the lymphocytes of the host cells and thus altering the host responses. It can also share its virulence factors among the species, which further contribute to its ability to survive and cause endodontic diseases.5 Adherence, which would be mediated by bacterial cell-specific surface proteins (adhesins), could be appraised as the beginning of microbial colonization, including the tubular invasion. Gelatinases, serine proteases, and collagen-binding proteins of Enterococci such as angiotensin-converting enzyme promote E. faecalis to get adhered to certain extracellular matrix proteins, including the type I collagen fibers.42 The bacterial adherence at different locations can also vary according to the extent of peritubular dentine deposition; this contributes to the evidence that organic matrix components play a significant role in bacterial binding. E. faecalis has the ability to grow as long chains, which has also been considered as the grounds for tubular invasion.43 On long-term infections, the root canal microbes can invade the adjacent dentin via open dentinal tubules. E. faecalis overcomes the constraints of root canal survival in a variety of ways. It has been observed to exhibit a widespread genetic polymorphism. It is small enough to penetrate and thrive within dentinal tubules with ease and also has the ability to endure starvation for long periods until a sufficient nutritional source becomes available.
The depth of penetration of the microorganisms and the number of bacterial colonies that were residing in the tubule before and after irrigation is a requisite for understanding the antimicrobial efficacy. Bacterial invasion occurs more frequently as the smear layer has been removed from the dentinal tubules. An increase in the exposure time of bacteria can also increase the number of infected tubules and depth of penetration.1,44 Tubular geometry, stresses like low nutrient concentration during the incubation period, and the culture time taken for the bacteria were all directly related to the depth penetration of dentinal tubules.43,45 During prolonged infection, more tubules will get infected, but the average penetration depth of infected tubules will only slowly increase with time. The invasion of E. faecalis into dentinal tubules was markedly reduced under glucose-starvation stress and alkaline conditions, likely due to an increase in the hydrophobicity and downregulation of some adhesion genes.46
The bacteria remaining in the root canal at the time of root Ⴁlling cause persistent infection and treatment failure. To achieve adequate disinfection, mechanical instrumentation should be supplemented with chemical irrigation. Therefore, comparing the properties of two commonly used irrigating solution, especially the foremost important property, antimicrobial efficacy, is essential to know which have a better outcome.
The antibacterial property of CHX and OCT was mainly due to its chemical structure. CHX, a positively charged bis-guanide, interacts with phospholipids and lipopolysaccharides on the bacterial cell wall/membrane.8,47 Thus, the bacterial cell wall permeability increases, which permits the CHX molecule to penetrate deeper into the bacteria cell wall and alter the cell’s osmotic equilibrium,47 whereas OCT belongs to a positively charged bipyridines and exhibits a particular affinity to the lipid components of microbial cell membranes, such as cardiolipin. This property unveils a broad-spectrum antimicrobial action by interfering with the positively charged molecule with the negatively charged microbial lipid component of the cell wall and thus causes disruption of intercellular contents with a minimal cytotoxic effect on the living tissues.22
The surface tension of the irrigating solution determines its capacity to penetrate into the tubular dentin.7,44 High surface tension could limit the irrigant’s capacity to penetrate dentin, and, as a result, their antibacterial efficacy within dentinal tubules will be reduced. Shear viscosity is a significant fluid flow property that describes the resistance produced by the fluid once it is deformed by a shear force; the lower the viscosity, the easier will be the fluid movement. The surface tension and the shear viscosity for OCT are less compared to CHX and thus show better intratubular disinfection.16 The time of contact of the irrigants can increase the antimicrobial efficacy. The antibacterial action of the irrigant should be immediately exerted against resistant microorganisms which are prevalent in the root canal and dentinal tubules.17 On longer irrigating time (the 30s and 60s), OCT exerted more antimicrobial activity. The limited antibiofilm activity of CHX is mainly due to the inactivation of cationic biguanide by an organic matrix of the biofilm. The results of this study indicated that OCT showed better efficacy in increasing the application time. The substantive property of OCT and CHX can directly influence the antibacterial property and can be due to their positively charged cationic, as they get absorbed by the anionic structures like hydroxyapatite crystals on the radicular dentin, and thus gradual release in the form of active cation would take place.40,45 For CHX, substantivity depends on the number of molecules of CHX present to interact with the dentin.48 In addition to dentin, other molecules present in the root canal could alter the potency of irrigants, such as collagen, serum albumin, and as well as killed microbes. Bacteria which are going through rapid growth could be sensitive to irrigants, whereas stressed microbes are usually not; these factors might shorten the efficacy of CHX.45 But, OCT could remain unchanged even in the presence of blood, mucin, and albumin.40 Also, OCT could resist the organic challenges when compared to CHX, even in the presence of organic material.22 According to Haapasalo, in a root canal system, the presence of both organic and inorganic inhibitory factors could be the reason for weakening the antimicrobial efficacy of the irrigants.49 Bacterial cells in biofilm could adhere to dentinal walls with the help of their exopolymeric matrix, which would be difficult to remove by root canal irrigants.50 Differences in the concentrations of irrigating solution showed a significant effect on antimicrobial actions. OCT showed a broad-spectrum antimicrobial effect as it would act as an active biocide even at low concentrations and bactericidal as well as candidacidal at higher concentrations. Increasing concentrations of OCT caused a proportional reduction in microflora.51 Similarly, for CHX at low concentrations (0.1%), low-molecular-weight substances such as phosphorous and potassium would seep out from the cell, resulting in a bacteriostatic action. Whereas at higher concentrations (2%), CHX had a bactericidal action due to cytoplasmic precipitation or coagulation, which resulted in cell death.46 Antimicrobial efficacy for OCT showed an equal potency at even lower concentrations when compared to CHX.15 Makker also reported that OCT was as effective as CHX on the tested microorganism, a 3-week-old homogenous and dense biofilm. OCT showed a more antibiofilm effect, which could be attributed due to its potency to penetrate through the biofilm matrix.40 OCT’s antibiofilm effect could also be related to the study by Thaha et al.13
Thus the review showed that OCT had been described as a potential substitute for CHX during chemomechanical debridement in endodontic treatment with good antimicrobial action. OCT also proved to be effective against biofilm-forming organisms and has remarkable and substantive antimicrobial effects because it readily binds to negatively charged surfaces. Its efficacy remains unchanged in the presence of blood, mucin, and albumin. Moreover, it has been proven to be nontoxic after topical application, and it is not absorbed via the skin, mucous membranes, or wounds. Besides the antimicrobial action, two important properties of OCT, which appeared to be more potent than CHX, is by means of prolonged bacterial anti-adhesive activity14 and less cytotoxicity,52 making OCT a promising irrigating solution.
None of the studies mentioned the sample size estimation method, and no information was available about the blinding of the observer. Two studies did not report the standardization of sample preparation in sufficient detail to allow replication. We recommend that studies should report the above to ensure methodological rigor.
Due to the limited data sources, we tried to abstract all the possible studies having the same parameters irrespective of natural tooth or agar. Most of the antibacterial studies were commonly conducted in agar plates,15 but the studies using dentin disks were also retrieved because the dentin powder model, developed by Haapasalo and Ørstavik, was preferred because the grinding and culturing of dentin disks provided more quantitative information about the extent of the infection even though the accuracy in the replication of clinical conditions were not feasible to achieve in both the scenarios.1 The various laboratory procedures used in the included studies played an important factor in understanding the variability of the findings. In this systematic review, all the included studies used microbiological analysis to assess the efficiency of irrigants in dentin disks and agar media. Teeth samples utilized for making dentin disks varied from maxillary anterior teeth,34 mandibular permanent molars,33 mandibular premolars.16,36 In the majority of the studies, single-rooted teeth were used. The use of single-rooted teeth for the majority of the studies imposes a significant limitation on the findings because these results cannot be applied to multi-rooted teeth samples. The microorganisms which are found in canal niches, due to the anatomic intricacies of root canals present in molars, make root disinfection difficult. The isthmus, curvatures, and lateral canals that makeup root canal systems present as a substantial anatomic and morphologic obstacle for efficient root canal disinfection.53 In most of the studies in this review, E. faecalis ATCC 29212 strain was taken except for a few studies,30,32 strains MTCC 439 and A197A were used, respectively. Concentration equivalency was adjusted to 0.5–1 McFarland Units in the majority of studies except in a few. In microbial analysis, the broth used for culturing and the incubation period too varied according to the studies. The agar well diffusion method was employed to assess the ZOI rather than the usually employed disk diffusion method. This can be due to the lack of customized disks available for analyzing the antibacterial assay of test material and the uncertainty of the irrigant solubility. For MIC, the direct exposure method was used where other variables became independent and feasible in the laboratory when compared with agar diffusion and dilution methods.36 The antibacterial studies on agar plates depend on the test substance’s dissolvability through the agar media; thus, it may not express its full effective potential and can be the reason for the result variation. The diameter/gauge of the irrigating needle in relation to the preparation size determines how well an irrigant penetrates the instrumented root canal system, and this standardization was lacking in many studies. Irrigating needles with a safety tip to a working length or 1 mm short of it is a promising strategy for increasing irrigant efficacy.7 Even faster-acting biocides require enough time to achieve their potential. Using larger volumes of solution yielded better outcomes than using smaller volumes of the same solution.17,54
The differences in the methodological designs of each investigation, such as standardization of the limit of preparation, choice of the preparation technique, tooth type standardization, sample size, heterogeneity in the concentration, contact time, activation techniques, and volume of the irrigants, make difficult to compare the studies retrieved in this review. The antimicrobial efficacy of CHX and OCT were closely related to the frequency and volume of the irrigation used, and this information was not precisely described in most of the studies. Due to these variations, meta-analysis was not performed.
CONCLUSION
Even though the methodologies used for each study differed but the final outcome was to find the antimicrobial efficacy. With CFU, it was found that out of seven studies, four studies showed more antimicrobial efficacy for OCT, two studies reported that CFU = 0 for both irrigants and one study showed a comparable result. For ZOI, out of three studies, one study substantiates the effect of OCT more. For MIC, both two studies revealed OCT to be better, and the final study regarding the proportion of dead cells showed OCT had better efficacy. Thus, out of 12 studies, eight studies showed OCT exhibited good antimicrobial efficacy and also concluded from this review that the antimicrobial properties were also dependent on many factors like depth of penetration of microbes and irrigant, substantivity, concentration, and time of contact of the irrigant as well as microbes.
Limitations
The studies, which used dentin disks as samples, evaluated only the efficacy of root canal disinfection with the irrigating solution immediately after mechanical instrumentation and did not relate the microbiological and laboratory results to the clinical outcomes, which limited the findings’ use in clinical practice. None of the studies included in this review reported patient-relevant outcomes, which were highly related to the success of root canal disinfection and might be used as a direct recommendation to clinicians. Future clinical trials should compare the microbiological characteristics of the root canal system before and after the usage of the irrigating solution and the clinical outcomes. The absence of clinical signs and symptoms, as well as the healing efficacy of periapical tissues, could be validated by radiography or cone-beam computed tomography. In vitro—due to the high heterogeneity in the methodology used for antimicrobial testing and its difficulty in implementing the clinical situation, the literature showed a lack of in vivo studies; thus, only in vitro studies were only used for this study.
Clinical Significance
Octenidine dihydrochloride (OCT) has been described as a potential substitute for CHX during chemomechanical debridement in endodontic treatment. OCT is less cytotoxic to the periapical tissues than CHX; however, as an antimicrobial, it is highly effective against a range of gram-positive and gram-negative oral bacterial species. The substantivity of CHX in dentin seems to be an advantage over OCT. Thus, different studies have been conducted to compare the effectiveness between OCT and CHX for disinfection of the root canal, and the evidence seems to support the clinical use of OCT more.
ACKNOWLEDGMENTS
Nanitha Sashindran, Department of Microbiology, Amrita Institute of Medical Sciences.
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