Continuous Soft Chelation in Endodontics

Introduction

The goal of root canal therapy is to prevent or treat apical periodontitis. This pathosis is a host reaction to microbial challenges from an infected root canal systems. Basically, endodontic therapy is the chemo-mechanical debridement of the latter. An ideal endodontic irrigant should have broad antimicrobial efficacy, dissolve necrotic tissue, remove smear layer and cause minimal systemic toxicity. There is currently no single solution that meets all four requirements.¹ Sodium hypochlorite (NaOCl) has unique necrotic tissue dissolution potency, is an effective antiseptic, and is minimally caustic at low concentrations. NaOCl is important in root canal therapy because of these characteristics. In contrast, it has little effect on the inorganic components of the smear layer, which prevents access to dentinal tubules and hence protects bacteria in root dentin. To dissolve the smear layer, biocompatible calcium complexing agents such as ethylenediaminetetraacetic acid (EDTA) and citric acid should be used alternately with NaOCl solution. As they decrease the amount of free available chlorine in NaOCl solutions, potentially rendering them useless.^2,3

As a result, Zehnder introduced the concept of continuous chelation in 2005⁴ , with Neelakantan using the actual terminology for the first time in 2012.³² Continuous chelation involves combining a chelator with NaOCl and employing it as a single irrigant in the chemomechanical preparation of the root canal to perform all of the key functions of an endodontic irrigant all at once.⁵

Why continuous soft chelation???

 The sequential application of EDTA and NaOCl removed the smear layer entirely, but induced progressive dentin dissolution and erosive effects at the expense of the peritubular and intertubular regions. This compromised the mechanical integrity of dentin.

 When strong chelators like EDTA and citric acid are used with shaping instruments, it can result in preparation errors.

 They interfere with the organic tissue dissolution properties and antimicrobial efficacy of sodium hypochlorite.

To address these issues, continuous chelation was introduced as a simplified single multi-functional irrigant solution that combined ideal irrigant properties.

Available continuous chelators

 Bisphosphonates which are non-nitrogenous compounds like etidronate and clodronate.

 Alkaline edta in the form of Na₄ edta (tartari 2017)⁶ Commercial products in market:

 Dual rinse hedp® (medcem weinfelden, switzerland) zollinger et al. 2018.⁷

 Twin kleen (Innovations endo, India) Mandar Pimprikar 2019.

Effect of continuous chelation on root dentin

Maintenance of Free Available Chlorine (FAC): Because of NaOCl’s oxidizing ability, mixing many chemical substances with it causes chemical interactions. Thus, in continuous chelation, the maintenance of NaOCl levels, as measured by FAC, is of prime importance. When FAC levels drop, NaOCl’s ability to dissolve tissue and kill microorganisms drops as well. The useful lifespan of mixtures is determined by the reduction of FAC over time. The “therapeutic window”, or “use-life,” is yet another term for this.

 Alkaline Edta: Chemical stability is significantly lower than that of etidronate mixtures at concentrations as low as 5% Na₄ EDTA and 2.5% NaOCl, with a usage life of just 30 minutes after mixing.

 Etidronate: A 1:1 mixture of 1% NaOCl: 9% etidronate maintains all of its free available chlorine at 1 min, and this declines to 80% at 60 min and to 20% after 24 hours

 Clodronate: The combination of 0.26 mol/L (7.6%) clodronate-2.5% NaOCl dissolves organic materials as well as 2.5% NaOCl. However, mixtures of double these concentrations dissolve less organic material than the 5% NaOCl control. Clodronate mixtures dissolve organic material with higher residual FAC more effectively than etidronate mixes of similar concentration.

The type of chelator, the concentrations of NaOCl and chelators, and the time after mixing have all been shown to affect FAC in continuous chelation mixtures. The value of the pH of the chelator solution is shown in the studies above. Only those with a high pH in NaOCl mixtures held their FAC over time. Acidic mixtures lacked stability.

Nonetheless, because of the purity of the chemicals used, there may be some confusion in the literature about etidronate and clodronate, and the FAC data for continuous chelation may be too optimistic.

1) Dentine debris and smear layer removal:

Dentine debris appears to accumulate less during continuous chelation. According to a micro-computed tomography study, debris accumulated less in the isthmuses of the mesial roots of mandibular molars when teeth were irrigated with 9%HEDP-2.5%NaOCl compared to 2.5%NaOCl.¹² However, comparing NaOCl alone is inappropriate as a result of EDTA treatment after NaOCl application has been demonstrated to minimise the accumulation of dentine debris.¹³ Comparing etidronate mixtures to standard sequences would have been more conclusive.

Continuous chelation research on the smear layer can be classified into two categories:

Only etidronate is used in the studies that only use a chelator as a final rinse, and they serve to demonstrate the difference in chelation in teeth between 17 percent EDTA at neutral pH and etidronate at roughly pH 11. Because of the lower stability constant and higher pH of etidronate solutions, it is projected that it will remove less smear layer than EDTA at neutral pH.^{15, 19}

Yadav et al. and Emre Erik et al. did not indicate the pH or the brand of etidronate utilized in their research. As a result, the conclusions of these studies cannot be compared to those of other researchers, casting doubt on their credibility. Some authors also did not recognize that continuous chelation uses a Chelator-NaOCl mixture throughout the irrigation process. They only included groups in which the mixture is only used as a final rinse for short periods of time. Because etidronate is a weak chelator and is used at a high pH, removing the smear layer takes longer than chelators with a higher stability constant and used at a lower pH.

Dissolution of organic tissue:

As the amount of FAC in continuous chelation declines with time, the capacity to dissolve organic tissue will degrade.

The percentage reduction in bovine muscle was not significantly different when Tartari et al. compared combinations of 5-10% Na₄ EDTA-2.5% NaOCl to a 2.5% NaOCl control over 15 minutes.⁶ This contradicts the findings of Tartari et al. for etidronate combinations.²⁴ The tissue mass of the etidronate mixture and the control were lowered by 27% and 41%, respectively, in a study using 9% HEDP-2.5% NaOCl and bovine muscle. Na₄ EDTA mixture performed better than the etidronate mixture due to experimental conditions. The Na₄ EDTA analysis was performed at room temperature with 5-minute irrigant refreshment.

Ulusoy et al. used 2.5%NaOCl, 2.5%NaOCl/17%EDTA, 9% etidronate-2.5% NaOCl, and water as irrigants in another etidronate trial.¹⁷ The sequence resulted in the same amount of tissue removal as the control when neither activation nor passive ultrasonic irrigation was applied. Despite this the results of the etidronate mixture were identical to plain NaOCl. Agitation had no effect on the etidronate-hypochlorite mixture’s effectiveness.

Previous research highlights the importance of differences in experimental details between investigations, as well as the interpretation of their impact on the conclusions. The etidronate mixture yielded mixed findings due to various conditions. It’s unclear if etidronate in combination with NaOCl actually slows down organic tissue dissolution.

Antimicrobial activity

All research on the antibacterial effects of continuous chelation have used E. faecalis, with the exception of a clinical study by Ballal et al.²¹

a) Solana et al. evaluated the antibacterial activity of alkaline EDTA, it was found that 5 % or 10% Na₄ EDTA-2.5% NaOCl was as effective on 3-week biofilms as 2.5 % NaOCl. Colony counting and the adenosine triphosphate test were used as techniques. The result was the same when 0.2% cetrimide was added to the mixture. As a result, using a detergent may be unnecessary.²²

b) Zehnder et al. studied initial antimicrobial testing of etidronate in continuous chelation with a planktonic suspension containing 3.5% etidronate and 0.5% mixes, as well as a 1/10 and 1/100 dilution. Continuous chelation was reported to be as effective as 0.5% NaOCl, but this needs to be verified. The study however indicated that 3.5% etidronate was not antibacterial after 15 minutes of testing.⁴

c) Tartari et al. evaluated the biofilm for the potential of reinfection following irrigation using a two-hour growth time for E. faecalis and a live/dead approach for C. albicans. When 9% HEDP-2.5% NaOCl was employed instead of the conventional 2.5% NaOCl/17% EDTA, fewer viable E. faecalis were attached.²³

d) Etidronate was used to disinfect 5-7 day biofilms in in -vitro studies, with just one study reporting a 4-week biofilm growth period. ^{9, 10, 25,26,27} The level of disinfection happening in the dentinal tubules was assessed in all of the in-vitro biofilm tests using live/ dead staining.

e) Ballal et al. assessed, the antibacterial activity of continuous chelation with 9% HEDP-2.5% NaOCl was compared to irrigation with 2.5% NaOCl.²¹, Intracanal bacteria were collected using paper points. Single and multirooted teeth were included, although multirooted teeth only had roots with single canals. The goal of the study was to see if adding etidronate to NaOCl changed its action or caused any negative effects, therefore a comparison to a typical sequence was ruled out. Despite the study’s small sample size, intracanal sampling revealed that the etidronate mixture and plain NaOCl both resulted in bacteria-free canals in 50% and 40% of the instances, respectively. On the other hand, the discrepancy between the two protocols was unimportant. A comparison to a conventional endodontic irrigating sequence seems logical.

Detrimental effects on dentine

There have been few studies on the potential negative effects of chelator-NaOCl combinations on dentine.

Tartari et al. evaluated combinations of 5% Na₄ EDTA and 2.5% NaOCl on dentine for 5 or 10 minutes .The amide III/phosphate ratio remained stable, and collagen dissolution was balanced by demineralization, according to the findings. ²⁸However, this does not suggest that dentine thickness was preserved. The ratio of 9% HEDP to 2.5% NaOCl was found to be decreased in the same study. As a result, demineralization was less than collagen dissolution. This is because etidronate’s ligand stability is lower than that of EDTA, and thus more demineralization is required with HEDP than with Na₄ EDTA.

Lottanti et al., investigated the duration of demineralization zones caused by mixtures of 9% HEDP-1% NaOCl over 18 minutes.¹⁴ They used dentine discs under SEM and found no erosive effects for the mixture, but erosion was observed in dentine treated with 1% NaOCl for 15 minutes and then 17% EDTA for 3 minutes.

Domnguez et al. found that irrigation with the sequence 2.5% NaOCl/17% EDTA induced less mechanical strength changes than irrigation with 9% HEDP2.5% NaOCl.²⁹ The fracture resistance to compressive force was lower in the sequence than in the continuous chelation mixture.

2) Safety:

Ballal et al. examined cell viability in vitro using the tetrazolium dye MTT (3-(4,5-dimethylthiazol2-yl)-2,5-diphenyltetrazolium bromide) and the clonogenic assay, as well as a micronucleus test to measure genotoxicity.³⁰ In all tests, the etidronateNaOCl mixture had no effect. Ballal et al. examined postoperative pain at 24 hours and levels of matrix metallopeptidase immediately after therapy and at 1 week in a similar in vivo clinical experiment to report safety outcomes for continuous chelation (HEDP-NaOCl mixture).²¹ The MMP9 level was reduced with minimal postoperative pain after 24 hours, suggesting a decrease in the inflammatory response.

3) Bond strength:

Endodontic material binding strength to dentine is known to be affected by irrigation regimens. Three investigations compared the strength of the pushout bond after irrigation with HEDP-NaOCl mixtures to the sequence 2.5% NaOCl/17% EDTA. The pushout bond strengths were stronger when irrigation was done with the etidronate combination rather than the sequence, whether bonding occurred to Biodentine®31, AH Plus32, or Resilon/Epiphany¹⁵. While bond strengths should improve when the smear layer is removed, the improved outcome for the etidronate mixture in the AH Plus research was attributed to better bonding to collagen and sealer penetration in the dentine. The poorer result for Biodentine was assumed to be related to EDTAinduced drying of the cement.

Gaps in literature on continuous chelation

• The impact of temperature on NaOCl stability in continuous chelation mixtures,

• Novel chelator mixtures, such as Clodronate, must be checked for efficacy, which may lead to an irrigant with a wider therapeutic window. It’s unclear whether etidronate interferes with NaOCl’s tissue dissolving effects.

• Live/dead staining has been used extensively in antimicrobial testing of continuous chelation combinations. To confirm the existing antibacterial finding for etidronate combinations with NaOCl and to test novel mixes, different antimicrobial evaluation approaches are required.

• The physico-chemical changes in root dentine tissue after exposure to a continuous chelating irrigating procedure using a combination of novel chelators.

Conclusion

Continuous chelation, in which a chelator is combined with NaOCl for antibacterial and proteolytic activities as well as the capacity to remove the smear layer, has shown promise, with its biological and mechanical properties outperforming those of standard sequence. Continuous chelation is currently being studied as a means for clinicians to save time. The best outcome of future studies will be to prove biological benefits for endodontic patients.

Conflicts of Interest

None