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| IMC Wiki | Chelators and solutions for irrigation

Chelators and solutions for irrigation

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Use of chelators during root canal preparation

Chelates are stable circular complexes of metals with organic compounds.

In endodontics, edetic acid (EDTA; ethylenediaminetetraacetic acid) is used
  • as a lubricant to support mechanical root canal preparation with rotary nickel-titanium instruments,
  • for the removal of the preparation-associated smear layer, and
  • under certain circumstances for the exposure of calcified and obliterated root canals.
Liquid chelator preparations usually contain approx. 15 - 17 % EDTA and sodium hydroxide.
On the other hand, gel-like preparations contain approx. 15 % EDTA and 10 % urea peroxide.

Use of chelators as lubricants

According to reports, the use of a chelator during mechanical root canal preparation using nickel-titanium instruments is clearly advisable.
Among other things, the chelator serves as a lubricant for the instruments and will thus reduce snagging and eventually fracturing of instruments inside the root canal. While the manufacturers recommend use of a paste, current studies indicate that liquid preparations should be used instead.
Since EDTA also reduces dentine hardness, this preparation results in increased reduction of the dentine during any mechanical root canal manipulation using root canal instruments.

Use of a chelator to remove the preparation-associated smear layer

It is generally accepted that preparations containing EDTA are extremely useful for removing the preparation-associated smear layer.
The smear layer of approx. 1 - 5 µm forms only in the areas of the canal wall that were subject to direct manipulation using root canal instruments; there will be no smear layer on areas of the wall that have not been manipulated.
The layer consists of ground dentine, remnants of pulp tissue, odontoblast processes, remnants of the solution used for irrigation and, in case of infected root canals, also of bacterial components.
It will obturate the dentine tubules to a depth of approx. 6 – 40 µm. Intensive irrigation of the root canal with EDTA following root canal preparation ensures a significant reduction of the remaining smear layer. The cleansing effect of the preparation is optimised and the result is that the filling will adhere better to the wall of the root canal.

Use of a chelator to expose calcified and obliterated root canals

Occasionally, EDTA is recommended to enable easier penetration of calcified or obliterated root canals due to its decalcifying effect. However, the efficiency of dentine demineralisation of EDTA preparations is questionable. The large chelator molecule EDTA can merely bind one calcium ion, ie all molecules will be bound quickly and the process of demineralisation will come to a standstill. 0.02 ml EDTA will decalcify no more than 0.35 mm2 dentine.
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Root canal irrigation

Please also refer to the official DGZMK and DDZ statements (in German): Root canal irrigation

Clinical studies from Scandinavia by Byström and Sundqvist (1981 - 1987) demonstrate clear evidence that root canal irrigation using disinfectants is essential to reduce bacterial contamination of the endodontium as much as possible.
The endodontium is a three-dimensional, very complex and at the same time open system (it connects the oral cavity, desmodontium and endodontium via dentine tubules, lateral and accessory canals, apical ramifications and furcation canals); #pic# chemical measures to reduce contamination must be adopted.

Therefore, root canal preparation is always a chemo-mechanical treatment. In addition to the use of various mechanical instruments in the root canal, irrigation is the obligatory chemical component.

Root canal irrigation aims at the following:
  • reduction of bacterial contamination and bacterial toxins in the canal (especially lipopolysaccharides),
  • dissolution and removal of remaining pulp tissue,
  • support of mechanical preparation, and
  • transport of dentine shavings resulting from manipulation with root canal instruments.
Based on these objectives, a solution for irrigation must meet the following requirements: a disinfecting effect, biological tolerability and a tissue-dissolving effect.

Solutions for irrigation are differentiated as follows:
  • solutions for irrigation used for disinfection of the endodontium
  • solutions for irrigation used to enable removal of the preparation-associated smear layer
  • solutions for irrigation used to dry the root canal following preparation.

Solutions for irrigation used for disinfection

Always bear in mind that the irrigating effect is limited to an area of no more than 3-4 mm apically from the tip of the irrigation cannula.

As the thinnest available cannula for irrigation has a diameter of 0,3 mm, it can be concluded that for the first session for root canal preparation, even in case of an emergency, an ISO size 30, or rather 35, must always be used. Otherwise it cannot be ensured that irrigation in the apical root canal section has had a disinfecting effect.

It should be ensured clinically that the irrigation cannula on the one hand is inserted far enough into the root canal and on the other that it is inserted without producing any friction, so as to avoid excessive pressure at the time of insertion of the irrigation solution in the apical tissue possibly resulting in damage to the tissue, severe pain and the formation of gas emphysema.

Sodium hypochlorite (NaOCl)

The antimicrobial effect of the solution for irrigation against the majority of all bacteria relevant in endodontics is very good; it is able to dissolve necrotic and vital pulp tissue and is the only solution for irrigation that can be used to neutralise lipopolysaccharides. NaOCl in a concentration between 0.5 - 5 % is the irrigation solution of choice.

Minimum contact of 30 minutes is recommended to dissolve the biofilm in infected root canals.

The tissue-dissolving effect of sodium hypochlorite increases with increasing concentration and temperature. The sodium hypochlorite should thus be heated immediately before use.

Activation of NaOCl using ultrasound significantly enhances the cleansing and antimicrobial efficacy.

Hydrogen peroxide (H2O2)

This solution has hardly any antimicrobial effect in the concentration usually used of 3 - 5 %.

Alternating irrigation using sodium hypochlorite and hydrogen peroxide is often recommended but is not advisable as - due to the following chemical reaction - it results in a strong reduction of the desired tissue-dissolving and antimicrobial effect of sodium hypochlorite:
H2O2 + NaOCl H2O + NaCl + O2.

Chlorhexidine (CHX)

CHX should be used in endodontics in a 2 % concentration.
The substantial effect of CHX on dentine resulting in a longer-term antimicrobial effect, ie not only during the irrigation process, is an advantage.

The antimicrobial effect is very good, especially against gram-positive bacteria, such as enterococci and fungi that are frequently found during revision, and may be resistant to NaOCl and/or Ca(OH)2.

Therefore, CHX should be considered as an essential component of the irrigation protocol, especially for revision treatment.
Sodium hypochlorite cannot be considered appropriate to replace CHX as a standard irrigation solution as it is neither able to neutralise lipopolysaccharides nor has a tissue-dissolving effect.

CHX should not come into contact with sodium hypochlorite as this will result in the precipitation of CHX crystals.

Phenol- and formaldehyde-containing substances

These substances are non-specifically toxic, ie toxic also for the body's own healthy tissue. They can also cause peri-apical inflammation. Nowadays, these solutions are considered clearly obsolete.

Iodine-potassium-iodide (IPI) solution

IPI has very good anti-microbial properties associated with minimal toxicity and is recommended for additional irrigation during revision.
Use in patients who are allergic to iodine is contraindicated.

Solutions for irrigation for removal of the smear layer

Edetic acid (EDTA)

The concentration used most often is 15 - 17 %. In this concentration, EDTA is very effective for removing the smear layer (also refer to the 'Chelators' section). If EDTA comes into direct contact with NaOCl, the effects of both solutions are increased.

Citric acid

Concentrations of up to 40 % are recommended. Citric acid quickly and reliably removes the smear layer. It must be considered, however, that higher concentrations will not only remove the smear layer but also partially dissolve the peri-tubular dentine.

Solution for irrigation used to dry the canal

Highly concentrated alcohol penetrates the lateral canals due to its low surface tension and results in a dry endodontium. Therefore, alcohol is recommended by some authors for the final irrigation immediately before root canal filling.

Irrigation protocol

Summarising these aspects of the various solutions for irrigation, the following irrigation protocol can be recommended for clinical use: #pic#

Novel solution for irrigation

MTAD is a novel solution for irrigation; its properties have not been proved sufficiently by independent scientific studies so far.

MT are the developer's initials (Mahmoud Torabinejad),
T also stands for tetracycline (doxycycline),
A stands for an acid (citric acid), and
D stands for a detergent (Tween 80) that is supposed to reduce surface tension.
The pH value of this solution is 2.15. The acid will remove the smear layer as a prerequisite for the broad-spectrum antibiotic to penetrate into dentine canals in the presence of the detergent.
Tetracycline has been selected as an antibiotic because of its comparably high potency. The results obtained so far are very promising. Though MTAD will not be able to replace sodium hypochlorite, it seems to have significant potential if combined with the latter. Further studies with this substance must be expected before a final recommendation is possible.