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 Table of Contents  
Year : 2020  |  Volume : 7  |  Issue : 2  |  Page : 75-85

Effect of additives to sodium hypochlorite on pulp tissue dissolution and physico-mechanical effects on root canal dentin: A systematic review

Department of Conservative Dentistry and Endodontics, Dr. D. Y. Patil Dental College and Hospital, D. Y. Patil Vidyapeeth, Pune, Maharashtra, India

Date of Submission22-Jan-2020
Date of Decision28-Feb-2020
Date of Acceptance11-Feb-2020
Date of Web Publication20-Jun-2020

Correspondence Address:
Shalini D Aggarwal
Department of Conservative Dentistry and Endodontics, Dr. D. Y. Patil Dental College and Hospital, Sant Tukaram Nagar, Pimpri, Pune - 411 018, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jdrr.jdrr_4_20

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Background: It is widely accepted now that; additives to sodium hypochlorite helps in better pulp tissue dissolution. However, due to proprietary concerns, the available literature is unable to clarify exactly how the modified NaOCl is better than unaltered NaOCl. This review evaluates the effect of additives on sodium hypochlorite on pulp tissue dissolution and physicomechanical effects on dentin. Methods: A systematic search was conducted using Medline PubMed, Ebscohost, Scopus, Google Scholar up to and including September 31, 2018, to identify relevant studies. All cross-reference lists of the selected studies were also screened. The inclusion criteria were articles in English or those having a detailed summary in English, published between January 2009 and September 2018. Articles were providing information about sodium hypochlorite, surfactants, and etidronic acid. Articles were providing information about in vitro studies, in which effect on root dentin was evaluated. Review, case reports, abstracts, letters to editors, and editorials were excluded. In vivo studies were excluded from this systematic review. Results: A total of 195 articles were examined, of which 11 articles were selected for the final synthesis. Most of the articles concluded that additives to sodium hypochlorite led to better pulp tissue dissolution and reduced the hardness of root canal dentin. Conclusion: This systematic review was able to garner adequate information stating that additives to sodium hypochlorite performed better pulp tissue dissolution. It was also able to evaluate successfully the physicomechanical effects of these solutions on root canal dentin.

Keywords: Etidronic acid, pulp tissue dissolution, root canal dentin, sodium hypochlorite, surfactants

How to cite this article:
Kurtarkar P, Aggarwal SD, Ahmed I, Khadtare S, Digholkar R. Effect of additives to sodium hypochlorite on pulp tissue dissolution and physico-mechanical effects on root canal dentin: A systematic review. J Dent Res Rev 2020;7:75-85

How to cite this URL:
Kurtarkar P, Aggarwal SD, Ahmed I, Khadtare S, Digholkar R. Effect of additives to sodium hypochlorite on pulp tissue dissolution and physico-mechanical effects on root canal dentin: A systematic review. J Dent Res Rev [serial online] 2020 [cited 2022 Oct 2];7:75-85. Available from: https://www.jdrr.org/text.asp?2020/7/2/75/287337

  Introduction Top

NaOCl was first used in 1915 by Henry Dakin to debride fresh wounds during the first World War and subsequently, in 1920, it was used by Crane in Endodontics for root canal debridement. Since then, NaOCl remains the cornerstone of disinfection and cleansing of the root canal systems. Despite its most obvious flaws like untrammeled destruction of tissues and its inability to clear away debris after tissue dissolution, it remains the perennial favorite, as the irrigant of choice to debride the root canal system.[1]

The key to the superior action of NaOCl lies in the fact that when NaOCl reacts with the proteins in the tissue, it leads to the formation of nitrogen, formaldehyde, and acetaldehyde.[1] Peptide links get broken down leading to protein dissolution. Further, hypochlorous acid is formed which leads to chloramination reaction causing amino acid degradation and hydrolysis. A variation in the concentration, temperature, agitation, and time of contact of NaOCl has shown varying degrees of tissue dissolution.

Despite being biocidal, the action of NaOCl on biofilms is known to be woefully inadequate. NaOCl shows some disruptive effects on biofilms at concentration of 1% and 3%. A precursor to biofilm formation is the smear layer which is generated after the shaping of root canals. To ensure complete cleanliness of the root canal systems, the clinician needs to use a chelating agent like 17% ethylene diamine tetraacetic acid (EDTA) or 10% citric acid as the final rinse.

When modifiers are added to NaOCl in the form of surfactants or etidronic acid, they did in the elimination of the dentinal smear layer and other debris along with pulp dissolution.[2] The first recorded incidence of modifiers with NaOCl was by an Australian company that made available a commercially available solution called hypochlor (1% and 4%).[2]

Another desirable addition to NaOCl is etidronic acid hydroxyethylidene diphosphonic acid (HEDP) and peracetic acid. Even on being mixed, NaOCl and HEDP retain their chemical properties and are used in the cleansing and shaping of root canals. The use of NaOCl and HEDP together leads to the dissolution of pulp debris and the elimination of microbes. The use of this combination also prevents the formation of the smear layer and may thus render a final rinse with EDTA nonessential.

Etidronic acid (also known as HEDP) is a chelating agent with biocompatible properties and can be combined with NaOCl, without either chemical losing any potency in the short-term evaluation.[3]

Various studies have been conducted to evaluate for the effect of additives on NaOCl. The properties evaluated range from soft-tissue dissolution, elimination of smear layer, and effect on the physical properties of dentin. The purpose of this systematic review was to analyze if modified sodium hypochlorite solutions could be used successfully in root canal irrigation protocols.

Focused question

What is the effect of modified sodium hypochlorite on pulp dissolution and root canal dentin when used in freshly extracted human, bovine, or porcine teeth?

  Methods Top

Eligibility criteria

Articles in English or those having detailed summary in English, studies published between January 1, 2009, and September 31, 2018,in vitro histological studies done on human extracted teeth and bovine and porcine tissue and studies comparing effects of additives to sodium hypochlorite on pulp tissue dissolution and physicomechanical effects on root canal dentin, are included in this systematic review.

Review, case reports, abstracts, letters to editors, editorials, andin vivo studies were excluded.

In the PICOS guidelines that were selected, population included freshly extracted human teeth and bovine and porcine tissue, intervention was sodium hypochlorite, the comparison was made with additives to sodium hypochlorite and the outcome was pulp tissue dissolution and physicomechanical effects on root dentin inin vitro studies.

Information sources

A comprehensive search of the literature was undertaken. A date restriction from January 1, 2009 to September 30, 2018, and language restriction of English were put while undertaking the electronic search. PubMed, Google Scholar, Research Gate, and institutional library were used to complete the search for all full-text articles available. The search was done till September 30, 2018.


The following databases were searched on: PubMed (The limits used were all full-text articles in English dated from January 1, 2009, to September 30, 2018, and Google scholar. For the electronic search strategy, the following terms were used as keywords in several combinations.

Study selection process

In vitro and comparative studies were selected. However, only articles that included conventional sodium hypochlorite and its modifications such as sodium hypochlorite with surfactants or etidronic acid were included. Using different search strategies from the above-mentioned keywords and the combinations, various electronic databases were searched. Preliminary screening consisted of a total of 194 articles that were identified through the database searching. After a thorough screening of 194 articles, 162 articles were excluded. Further, these records were assessed for any duplicates which were removed. Further, 15 articles were screened for abstracts. Four articles were then excluded after reviewing of abstracts. Eleven articles were screened for full texts finally synthesized in this systematic review.

  Results Top

The summary and characteristics of the included articles is presented in [Table 1] and [Table 2].
Table 1: Data extraction sheet - Pulp dissolution

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Table 2: Data extraction sheet - Root canal dentin

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  Discussion Top

Sodium hypochlorite is a much-revered irrigant when it comes to the shaping and subsequent disinfection of the root canals. However, just like every other gold standard, it comes with its own set of flaws, namely:

Sodium hypochlorite cannot dissolve smear layer/accumulated hard tissue debris; it is buffered by dentin and is toxic to host tissues.

In an effort to overcome the afore discussed points, additives are incorporated into standard sodium hypochlorite solutions. Some of these additives could be surfactants that are added to solutions of sodium hypochlorite in an effort to buffer their toxic effect leading to lesser tissue damage while not disrupting its tissue dissolution capability inside the root canal, owing to its steadily tapering chlorine availability.

Recently, authors have recommended that weak acids such as peracetic acid and etidronic acid, have been incorporated into sodium hypochlorite to provide support in getting cleaner root canal lumens and dentinal tubules.

Both categories of these additives ultimately constitute in making the cleaning ability of sodium hypochlorite far superior to the cleaning ability of sodium hypochlorite alone.

This translates into:

  1. Elimination of smear layer
  2. A simpler irrigation protocol as the need for follow-up irrigants such as EDTA or citric acid is eliminated
  3. Better pulp dissolution
  4. Deeper lateral penetration of the sealer into the dentinal tubules radiating out from the root canal lumen, thereby effecting a better seal.

NaOCl displays increased efficacy when it is diluted less, heated, or agitated. Adding a surface-active agent leads to a reduction of the contact angle between NaOCl and the dentin.[4]

The data were evaluated under the following headings:

  1. Effect of modified sodium hypochlorite on pulp dissolution
  2. Effect of modified sodium hypochlorite on root canal dentin.

Summary of evidence

Effect of modified Sodium hypochlorite on pulp dissolution

Stojicic et al.[4] evaluated and compared conventional NaOCl to a NaOCl solution having a surface-active agent.

The tissues on which the dissolution was demonstrated were sourced from bovine muscle tissue, rabbit liver, porcine muscle tissue, pig palatal mucosa, bovine pulp, and rat connective tissue. The rationale of this was to achieve a controlled surface area and quality of tissue, which would not have been possible when pulpal tissue was used.

They also from this study concluded that NaOCl to which a surface-active agent had been added, showed the maximum tissue dissolution and further that the heated sodium hypochlorite can remain for up to 4 h and 10 s after being heated to 37°C. As all the solutions, irrespective of the concentrations, would generate an optimum quantity of available chlorine for 60 min between 45°C and 60°C. Stojicic et al. finished all the experiments within an hour. Thus, they concluded that the addition of surfactants to NaOCl led to a discernible improvement in tissue dissolution.

On a confrontational note, in a later publication Clarkson et al.,[2] disputed these findings of Stojicic et al., even though they were in accordance with the findings of Jungbluth et al.[5] Clarkson claimed inaccuracies in the study done by Stojicic et al. on the basis that their surfactant content was vague and that also that they did not independently measure the available chlorine. In addition, Clarkson also objected to the varying osmolarity of solutions and the measurement of weight loss to assess tissue dissolution. The results achieved by Stojicic et al. could well have been different if these factors had been uniform. Clarkson et al. in 2012 conducted a study to investigate the pulp dissolution capability of 2 hypochlor solutions (1% and 4%), with and without surfactant.[2]

They derived from their study that the mere addition of surfactants did not contribute to an increased rate of tissue dissolution of dental pulp tissues. Their study could be a better measure of actual pulp dissolution, because the pulp was meticulously harvested from the lower incisors of pigs after slaughter. The four solutions were stirred for the same number of circuits; although these were not timed. The dissolution was timed with a stopwatch and the nominal active chlorine was used as a covariate. Any reduction in the production of the hypochlorous ion (Ocl-) leads to a lower dissolution ability.[2]

de Almeida et al.[6] measured the tissue dissolution capacity of NaOCl, after the addition of cetrimide and polypropylene glycol. They concluded that the tissue dissolution was directly proportional to the concentration of the solutions and the time of exposure.

They postulated that NaOCl at varying concentrations ranging from 0.5% to 5.25%, and when surfactants such as polypropylene glycol and cetrimide were added, significantly increased tissue dissolution capability.

Tartari et al. (2015)[7] evaluated the tissue dissolution effect of NaOCl individually and when combined with HEDP. They used 5% NaOCl and 18% Etidronic acid mixed in 50:50 ratio to give a solution of 9% HEDP and 2.5% NaOCl.

In their study, this mixture was found to be effective in the dissolution of the organic matter (bovine muscle tissue). HEDP and NaOCl do not interfere with each other's chemical properties[7] and Zehnder et al. in 2005 stated that the HEDP had no effect on the antibacterial properties of NaOCl.[8]

Peña López et al.[9] calculated the dissolution of porcine palatal mucosa by NaOCl with and without the addition of glycocholic acid and a mix of various surfactants (Keratobacter).

The composition of keratobacter is 29% glycocholic acid which is added for demineralization and lysis of organic matter. Also added to this, are a mixture of surfactants which also have benzalkonium chloride.

Ulusoy et al.[10] checked the efficacy of NaOCl and HEBP that had been activated ultrasonically. They combined this with an XP endo finisher to eliminate organic tissue from simulated internal root resorption cavities and found it to be an effective irrigation regimen.

Given the lack of interaction between HEBP and NaOCl, it has been proposed that they are used as a single irrigant in the biomechanical preparation of root canals.[7],[8] Tartari et al. reported that a mixture of etidronate and sodium hypochlorite was able to dissolve organic tissue in a similar way to that of NaOCl alone. Furthermore, this combination has been reported to achieve the smear layer and hard tissue debris removal in the root canals.[7]

Ulusoy et al. also stated that they did not use the same volume of irrigating solutions, which is an important parameter. Therefore, this could have been a limitation of this study.[10]

Patil et al.[3] conducted a study to do a comparative evaluation of HEBP based irrigants versus others in the apical one-third for their ability to remove the smear layer. They established that using sodium hypochlorite in the concentration of 5.25% with surf followed by a wash of 17% EDTA with surfactant was the best.

Chloroquick was the second-best in smear layer elimination in the root canal apex.

Palazzi et al. showed that solution modified with surfactants had significantly lower surface tension than its normal composition, thereby increasing their adaptation to dentin and penetration into the dentinal tubules.[3],[11]

18% etidronic acid is a weak chelating agent than 17% EDTA and citric acid solution studied and quoted by Tartari et al.[3],[7] and De-Deus et al. According to De-Deus et al., this combination required approximately 300 s to completely remove the smear layer due to its slow and weak action on inorganic contents.[3],[12]

Effect of modified Sodium hypochlorite on root canal dentin

A reduced contact angle ensures unfettered access by the NaOCl to the radicular dentin, presumably leading to lesser smear layer.

Lottanti et al.[13] investigated how EDTA, HEDP and peracetic acid, when used as irrigants affected root canal dentin and smear layer. Their chief objective was to examine the decalcifying effects of these chemicals. They further concluded that these decalcifying agents could remove or prevent the formation of the smear layer. Though their patterns of dentinal wall erosion were found to be entirely different.

This protocol can be simplified as follows:

  1. Use a noninterfering decalcifying agent
  2. Use a decalcifying agent that is also a string disinfectant for the final rinse
  3. A combination of sodium hypochlorite-etidronic acid should be used during and after shaping, hence disallowing smear layer formation.

Lottanti et al.[13] stated that the reduction in the smear layer of instrumented shaped canals was possible with protocols using HEBP in the same manner as 17% EDTA.

The efficacy of HEBP has been known to drop from coronal to apical one third from the root canals. The data elicited by the backscatter analysis for the detection of apparent decalcifications was accurate.

The smear layer removing capability with these additives proved to be vastly superior to NaOCl. However, this ability has to be outweighed by the effect that they displayed at the dentinal wall.

If there is a substantial decrease in the microhardness of the root canal dentin due to these irrigating solutions, iatrogenic errors such as perforation and canal deviations may result.[13]

Tartari et al.[14] also studied the reduction in root dentin microhardness when various irrigation protocols were used. Their study demonstrated a reduction in the root canal dentin microhardness with each protocol, except when normal saline was used.

NaOCl can cause protein dissolution and hence when used after a chelator leads to optimal adhesions. This happens because of its reactions to the mineral phase of dentin. Further, the use of NaOCl does not permit the adhesion of bacteria to expose collagen.

Garcia et al.[15] conducted a study for the comparative evaluation for the effect of 3 formulations of NaOCl on the physical properties of radicular dentin, coronally, and apically.

The tissue dissolution capability of NaOCl on the collagen of radicular dentin causes a reduction of dentin microhardness.

Concentration and time of action of NaOCl on dentin interfered with its microhardness. The location of the indentation in the dentin also affected the results.

Other researchers, too have observed a reduction in the dentinal hardness for the same period. In their studies, concentrations of the irrigants had no bearing on the outcomes.

They demonstrated that 5.5% NaOCl gel and Chlor-Xtra caused a decrease in dentin microhardness as did 2.5% NaOCl.

An irrigant while demonstrating superior disinfecting and cleaning properties, should not at any juncture lead to a decrease in the strengths of the radicular dentin. Even if near disinfection is achieved, the overall prognosis gets compromised if the structural integrity of the remaining tooth structure is collapsible.

Tartari et al.[16] conducted a study to observe how NaOCl and HEBP, affected radicular dentin roughness when used in varying protocols. They have demonstrated through their study that irrigation regimens using chelators alter the surface roughness of radicular dentin. This study was done using a surface profilometer. There is a substantial rise in the smoothness of radicular dentin post the use of Citric acid or EDTA and HEBP. The surface topography showed major changes when a chelating agent had been used.

With an increase in the surface roughness, there could be a definitive clinical advantage as this roughened surface promotes micro-mechanical bonding with root canal sealers. Since radicular dentin has more peaks and valleys, it increases the surface area of contact and penetration. The other side of the coin, however, is that increased roughness could provide safe havens for the bacteria, thus facilitating biofilm formation at a latter stage.

Inspite of the fact that different root thirds have different structures, both at the macroscopic and microscopic levels, all the irrigants in the different protocols used exhibited a similar set of behaviors when they came in direct contact with the root surface.

The limitation of this systematic review is that there was a lack of standardization of the tissue specimens used; hence, meta-analysis cannot be carried out. The articles, in which human teeth have been used do not specify the exact extra-oral time. Furthermore, the time taken for dissolution is not mentioned and there is no grading of smear layer done.

  Conclusion Top

In the absence of specific quantitative data, it is unclear about the quantum, by which additives improve the dissolution of various living tissues. This systematic review was able to garner adequate information stating that additives to sodium hypochlorite performed better pulp tissue dissolution and is effective when used as a single irrigant. This review was evaluated that additives to sodium hypochlorite increased the surface roughness and decreased the microhardness of root canal dentin.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Basrani B, Haapasalo M. Update on endodontic irrigating solutions. Endod Top 2012;27:74-102.  Back to cited text no. 1
Clarkson RM, Kidd B, Evans GE, Moule AJ. The effect of surfactant on the dissolution of porcine pulpal tissue by sodium hypochlorite solutions. J Endod 2012;38:1257-60.  Back to cited text no. 2
Patil PH, Gulve MN, Kolhe SJ, Samuel RM, Aher GB. Efficacy of new irrigating solution on smear layer removal in apical third of root canal: A scanning electron microscope study. J Conserv Dent 2018;21:190-3.  Back to cited text no. 3
[PUBMED]  [Full text]  
Stojicic S, Zivkovic S, Qian W, Zhang H, Haapasalo M. Tissue dissolution by sodium hypochlorite: Effect of concentration, temperature, agitation, and surfactant. J Endod 2010;36:1558-62.  Back to cited text no. 4
Jungbluth H, Peters C, Peters O, Sener B, Zehnder M. Physicochemical and pulp tissue dissolution properties of some household bleach brands compared with a dental sodium hypochlorite solution. J Endod 2012;38:372-5.  Back to cited text no. 5
de Almeida LH, Leonardo NG, Gomes AP, Giardino L, Souza EM, Pappen FG. Pulp tissue dissolution capacity of sodium hypochlorite combined with cetrimide and polypropylene glycol. Braz Dent J 2013;24:477-81.  Back to cited text no. 6
Tartari T, Guimarães BM, Amoras LS, Duarte MA, Silva e Souza PA, Bramante CM. Etidronate causes minimal changes in the ability of sodium hypochlorite to dissolve organic matter. Int Endod J 2015;48:399-404.  Back to cited text no. 7
Zehnder M, Schmidlin P, Sener B, Waltimo T. Chelation in root canal therapy reconsidered. J Endod 2005;31:817-20.  Back to cited text no. 8
Peña López A, Conde AJ, Estevez R, Valencia de Pablo O, Rossi-Fedele G, Cisneros R. Sodium hypochlorite and a preparation containing glycocholic acid and surfactants have a synergistic action on organic tissue dissolution in vitro. J Endod 2018;44:813-5.  Back to cited text no. 9
Ulusoy ÖI, Savur IG, Alaçam T, Çelik B. The effectiveness of various irrigation protocols on organic tissue removal from simulated internal resorption defects. Int Endod J 2018;51:1030-6.  Back to cited text no. 10
Palazzi F, Blasi A, Mohammadi Z, Del Fabbro M, Estrela C. Penetration of Sodium hypochlorite modified with surfactants into root canal dentin. Braz Dent J 2016;27:208-16.  Back to cited text no. 11
De-Deus G, Zehnder M, Reis C, Fidel S, Fidel RA, Galan J Jr., et al. Longitudinal co-site optical microscopy study on the chelating ability of etidronate and EDTA using a comparative single-tooth model. J Endod 2008;34:71-5.  Back to cited text no. 12
Lottanti S, Gautschi H, Sener B, Zehnder M. Effects of ethylenediaminetetraacetic, etidronic and peracetic acid irrigation on human root dentine and the smear layer. Int Endod J 2009;42:335-43.  Back to cited text no. 13
Tartari T, Vila Nova de Almeida B, Carrera Silva Júnior JO, Facíola Pessoa O. A new weak chelator in endodontics: effects of different irrigation regimens with etidronate on root dentin microhardness. International Journal of Dentistry 2013;2013.  Back to cited text no. 14
Garcia AJ, Kuga MC, Palma-Dibb RG, Só MV, Matsumoto MA, Faria G, et al. Effect of sodium hypochlorite under several formulations on root canal dentin microhardness. J Investig Clin Dent 2013;4:229-32.  Back to cited text no. 15
Tartari T, Duarte Junior AP, Silva Júnior JO, Klautau EB, Silva E Souza Junior MH, Silva E Souza Junior Pde A. Etidronate from medicine to endodontics: effects of different irrigation regimes on root dentin roughness. J Appl Oral Sci 2013;21:409-15.  Back to cited text no. 16


  [Table 1], [Table 2]


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