Chemical irrigation is used throughout the treatment. A luer-lock 27-30G side-vented needle prevents irrigants being pushed through the apex, and the needle being separated from the syringe. Files can be used to aid chemical preparation as well as mechanically prepare the canal.
Features of an ideal irrigant for root canal treatments include:
- Dissolves pupal tissue
- Removes the smear layer*
- Easy to use
- Low surface tension
- Non-cytotoxic, compatible with dentine and tissue friendly
- Non-corrosive to instruments
- Cheap and has a long shelf life
Chemical Irrigants for Root Canal Treatments
The irrigant of choice for general practitioners in primary care is often sodium hypochlorite. This has the advantages of being antimicrobial and dissolving residual organic matter. Free chlorine ions break down bacterial proteins into amino acids. The high pH helps denature proteins and the hypochlorite anion damages bacterial DNA and the lipid membrane.
However, it cannot satisfy all the properties of an ideal irrigant and is toxic, non-substantive, can discolour the tooth, corrodes instruments, has an unpleasant odour and is ineffective in removing the smear layer. The recommended concentration is 0.5-3%, with a lower concentration still being bactericidal, and a higher concentration being more effective against E. faecalis, a bacteria usually present in persistent endodontic infections. Although a higher concentration would increase the irritants capacity to dissolve tissue, it is more likely to be a problem if extruded through the apex, and there would be a higher risk of it acting like an irritant. The highest concentration available is 5.25%.
Another irrigant is chlorhexidine, usually available between 0.12-2%. This is not the irrigant of choice as it has a very low level of tissue toxicity, although allergic reaction is rare- it is possible. The reversible reaction of uptake and release of chlorhexidine results in antibacterial activity, with a substantivity lasting up to 12 hours. Chlorhexidine is also more effective against the gram-negative E. faecalis, but it can’t dissolve organic matter or necrotic pulps, and it has no action on the smear layer. It also forms a carcinogenic precipitate when used with sodium hypochlorite and can block canals, so irrigation is no longer possible.
Ethylene-Diamine-Tetra-Acetic acid or EDTA is another type of irrigant used at about 17%. It has the advantage of being a chelating agent at about pH 7. It removes the smear layer and provides canal lubrication. It is often useful at negotiating sclerotic canals, however, use for too long can weaken the tooth. The other disadvantage is that it has no antibacterial effect but works very effectively with sodium hypochlorite (which is antibacterial) to effectively remove the entire smear layer and bacteria. The EDTA interacts with and reduces the antimicrobial effect of sodium hypochlorite, therefore copious amounts should be used. Note that the final wash-out should be with sodium hypochlorite.
Iodine or potassium iodide is used as an irrigant at 2.5%, and it can penetrate deep into the dentine, and clear E.faecalis and C.albicans (another canal bacteria) as well as having antiviral effects. Allergies to iodine are not unheard of, and therefore use is often not first-line.
Citric acid of 10-50% can remove the smear layer, but interacts with sodium hypochlorite, reducing the chloride ions available.
*The smear layer is a layer of organic and inorganic material that contains bacteria and their by-products. Leaving the smear layer slows bacterial invasion and keeps difficult to clean dentinal tubules blocked, whereas removing the smear layer accesses bacterial removal, allowing irrigants to reach lateral canals.
A summary of irrigants for root canal treatments
|Antimicrobial and bactericidal even at low concentrations
Ineffective in removing the smear layer
|Antibacterial substantivity lasting up to 12 hours
|Doesn’t dissolve smear or organic matter,
|Chelating, removes smear, lubrication
|No antibacterial effect
|Penetrate deep, antiviral and antibacterial
|Interacts with sodium hypochlorite
Useful Links & Recommended Reading
- Pre-op assessment for root canal treatments
- Cohen S, Burns RC, Walton R, Torabenijad M. Pathways of the Pulp (1). Learning. 1998;30(10).
- Abbaszadegan A, Khayat A, Motamedifar M. Comparison of antimicrobial efficacy of IKI and NaOCl irrigants in infected root canals: An in vivo study. Iranian endodontic journal. 2010;5(3):101.
- Walton, R.E. and Torabinejad, M., 1996. Principles and practice of endodontics. 2-nd ed. Phiadelphia: WB Saunders Co, pp.214-215.
- Endodontics: Principles and Practice
- Single Best Answer Questions for Dentistry
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