Irrigation – how should I irrigate? Part 1: properties and delivery of irrigants

This two part post looks at the irrigation of root canal systems. I’ll start in this post with the ‘why’ and then in the next post move on to the ‘how’ of irrigation, concentrating the practicalities of the clinical implementation of effective irrigation in general dental practice. So, part 1 deals with the why of irrigation, properties of irrigants and delivery of irrigants into the root canal. Part 2 will discuss irrigant activation and recommended irrigant protocols.

First, why irrigation?

Pulpal and endodontic disease are caused by microbial infection of the canal system (Kakehashi et al 1965). Root canals may be infected by a variety of microrganisms cocci, filaments, spirochaetes, rods, fungi and even viruses. The infection is a complex polymicrobial ecosystem (Sundqvist 1992) with the microorganisms mostly organised into biofilms, making them much more resistant to disinfectants than planktonic (free-floating) organisms (Svensater & Bergenholtz 2004). There are differences between primary and secondary infections and, although they are both polymicrobial, secondary infections tend to be simpler, albeit with more problematic species such as entoroccoccus faecalis sp.

No matter which microorganisms are in the canal, part of our aim in providing root canal treatment is to remove them. Unfortunately, you cannot manage canals by mechanical means alone for a number of reasons:

  • Large parts of canal systems (e.g. isthmuses, apical deltas, fins, lateral canals, accessory canals, within dentinal tubules, internal resorptive cavities and parts of C-shaped canals) are inaccessible to current mechanical instrumentation techniques.
µ-CT of lower molar root canal system demonstrating isthmus and fin (courtesy of The Root Canal Anatomy Project)
  • Peters et al. (2001) showed that 35% or more of the canal surface is not touched by rotary instruments.
µ-CT of prepared root canal system prepared with rotary instruments. Green indicates areas untouched by the instrumentation (Hübscher et al. 2003)

Non-vital, immature UL1

  • Sometimes, mechanical preparation must be avoided because it will weaken already thin canal walls. For example, you wouldn’t want to remove any more dentine from this immature tooth, would you?
Immature UL1
  • When a root canal is prepared with hand files or rotary instruments a smear layer forms on its surface:
SEM showing smear layer remaining on canal wall after preparation (Ritter and Swift 2003)

The smear layer is a mix of dentine debris, pulpal tissue remnants and bacteria which is ‘buttered’ onto the canal wall by the mechanical instruments and can’t be removed mechanically. Clearly, as it is infected material, this is not something you want left in the root canal. Furthermore, it acts as a ‘greasy’ barrier preventing disinfectants from acting on the canal wall and into tubules.  Eventually, when you obturate the canal, it will prevent effective adaptation and adhesion of sealants and filling materials to the canal walls.

These problems may be overcome with an effective chemical irrigation and disinfection protocol. Hence, the concept of chemo-mechanical disinfection has developed, where the aim of mechanical instrumentation is to create a shape that allows efficient removal of debris and facilitates the introduction of chemical disinfectant along the full length of the canal, right up to the apical foramen. In short, the aim of root canal preparation is not to grind out all the infected material, but to ‘wash, wash, wash and wash’ the whole root canal with disinfectant.

What are the desirable properties of the irrigant?

Lists of the ideal properties of root canal irrigants have evolved as various benefits and disadvantages of individual irrigants have become apparent:

  • Bactericidal and fungicidal
  • Inactivate endotoxin
  • Dissolve organic tissue
  • Dissolve inorganic tissue
  • Remove smear layer
  • Penetrate and disrupt biofilm
  • Penetrate dentine tubules
  • Remove debris (flush the canal)
  • Lubricate intrumentation
  • Cost effective
  • No adverse effects on dentine properties
  • Not cause discolouration of tooth
  • No adverse effect on sealers used in obturation
  • Non-toxic
  • Non-carcinogenic
  • Non-allergenic

The first (bolded) properties in the list are the critical biological properties and no single irrigant has all these desirable properties, so we need to use a multi-irrigant protocol to give our patients the best possible prognosis. Note that local anaesthetic, saline, distilled water and various mouthwashes do not come anywhere near these critical properties and therefore do not have any place as a primary irrigant in root canal irrigation.

Currently, the primary irrigant most frequently used by endodontists (Mello et al. 2016) and the accepted “gold-standard” is sodium hypochlorite 1%-5% (NaOCl) because it satisfies more of the desired properties than any others. It has excellent bactericidal properties (Bystrom & Sundqvist 1983), dissolves organic matter (both vital pulpal material and necrotic material) and is cost effective (Zehnder 2006). However, it has little effect on non-organic material or the smear layer, so a chelating agent is also required, commonly ethylenediaminetetraacetic acid 17% (EDTA), but citric acid is also effective. As these posts aim to be a practical guide to irrigation, I will concentrate on the widely accepted NaOCl/EDTA combination, but many other irrigants with diverse properties have been used and could form the basis of another post in the future.

Above, SEM of dentine surface after preparation and NaOCl irrigation. Below, after irrigation with NaOCl then EDTA. Notice the removal of smear layer exposing open dentinal tubules which will allow intimate irrigant exchange and adaptation of obturation materials (from Metzger et al. 2013)
Sodium hypochlorite (3%) and EDTA (17%)

Unfortunately, NaOCl is far from ideal with respect to some of the adverse properties towards the bottom of the above list, although this can be overcome with a clinical protocol which avoids apical extrusion by safely manipulating it within the canal.

Trying to mitigate the problems associated with NaOCl by using chlorhexidine (CHX) is ill-advised and misguided. Although more active than saline or local anaesthetic (which is not difficult!), it is not acceptable as the primary irrigant because:

  • CHX does not have the antibacterial activity of NaOCl.
  • CHX does not have any tissue dissolving properties, so infected necrotic tissue will remain in the canal.
  • CHX is normally only available in dental practice as 0.2% Corsodyltm whereas studies of CHX effectiveness use 2% CHX.
  • CHX has a detrimental interaction with NaOCl if they are mixed in the canal.

However, there is a part to played by CHX when correctly used as an adjunctive irrigant as part of a multi-irrigant regime which also includes NaOCl (see part 2). Also, if the patient has a hypersensitivity to NaOCl then CHX may be an appropriate, although compromised, second choice primary irrigant.

How do you achieve safe and effective irrigation?

Effective irrigation requires using the correct solutions, applied to the whole root canal system, for sufficient time, without extrusion into the periapical tissues or inadvertently depositing the irrigant in the mouth or on the patient’s clothes. Achieving this is not as simple as picking up whichever syringe happens to be available, inserting it part-way into the canal and squirting the irrigant around. If you want your irrigant to exert all those beneficial properties on the whole internal surface of the canal, particularly the apical few millimetres, you need to be precise with your technique. The following practical tips will maximise the effectiveness of your irrigation.

Use rubber dam Unfortunately, up to 60% to 70% of dentists admit to not routinely using rubber dam for endodontic treatment (Ahmad 2009). As you need to use NaOCl as part of your irrigation protocol, if you are not using rubber dam you need to start using it properly so that you don’t have to worry about getting NaOCl in your patient’s mouth. If you are not using NaOCl because you are not using rubber dam, you need to start using rubber dam! Not only does rubber dam prevent NaOCl from entering the patient’s mouth, correctly used, it also prevents the NaOCl coming into contact with the lips and peri-oral skin where it may cause a chemical burn.

Use a caulking compound Without a perfect peripeheral seal round the tooth, the interface of dam and tooth can (and will!) leak. Use a caulking compound (such as Orasealtm) to effectively seal the rubber dam where it meets the tooth and prevent NaOCl from seeping under the dam into the mouth or onto the patient’s face. The rubber dam provides airway protection, retraction and improved visibility whereas the peripheral seal isolates the tooth from saliva and controls the irrigants.

Oraseal around tooth to ensure an effective rubber dam seal

Use an effective barrier over the patients clothes, the average square dental bib is not good enough. No matter how careful you are, NaOCl drops always seems end up where you don’t want them to go, particularly if your patient is wearing a Jaeger suit! In our surgery, we staple together two standard square plastic backed disposable bibs to lay over both of the patient’s shoulders AND over the top of that, place a large disposable plastic-backed disposable bib which ties round their neck.

Large plastic backed patient bib over two dental bibs stapled together.

Use the correct syringes, needles and technique The irrigation solution needs to reach the full canal length, right into the apical area. Poking a needle part way into a canal and squirting it around is NOT adequate. Sedgely et al. (2005) showed that getting irrigant within 1mm is crucial. So, you need a technique that uses a small enough needle to reach a sufficient depth, safely enough to achieve this whilst not risking extruding irrigant through the apical foramen under pressure – a hypochlorite accident.

Use a Luer Lock syringe. The needle needs to lock (screw) onto the syringe to prevent inadvertent loosening of the needle leading to irrigant escape over the patient’s face or clothes.

5ml Luer Lock syringe, note the screw lock for the needle

Smaller (around 5ml) syringes are best as they are easier to hold and manipulate. The larger syringes tend to be more sticky and unpredictable when you squeeze the plunger. They are also too large for most of us to comfortably use the appropriate hand grip (see photo later in post).

Label your syringes so you don’t make mistakes! I label my syringes (both sides as they lie on the work surface) with an indelible pen, blue for bleach and red for EDTA.

Labelled syringes

Use a fine (ideally 30G) needle. Do not use those large diameter needles, already rattling around in the surgery drawers, which you use for periodontal pocket irrigation; at 27G or larger, the needle diameter (0.41mm) is too large to place it close enough to full canal length in most canals for effective endodontic irrigation. A 30G needle has a tip diameter of 0.31mm. If you have prepared your root canal to size 25 with taper of 4% or more the 30G needle will easily be able to loosely reach 2mm short of working length in a straight canal.

Use a safe tipped endodontic irrigation needle. There are various side-vented or slotted tip designs which reduce the chance of inadvertent extrusion beyond the apical foramen.

Examples of safe ended endodontic needles designs (from Boutsioukis et al. 2010)

Place the needle 2mm short of the working length. If the needle is not placed sufficiently deep into the canal, a dead zone will form apical to the needle tip where the fresh irrigant does not exchange with the fluid already in the canal.

Computer generated model of irrigant flow within a canal from a side-vented needle demonstrating a dead zone apical to the needle tip where there is no exchange of fresh irrigant with the canal contents (from Boutsiakouis 2010)

Some elegant research (Boutsioukis et al. 2010) on different needle types, flow pressures and needle depths has demonstrated that the most reasonable compromise between effective irrigation and prevention of extrusion, is to place the needle 2mm short of working length.

Mark the length of the needle with a stop or by bending the needle at length-2mm to make sure you don’t irrigate ineffectively short or risk irrigant extrusion.

Mark the correct irrigation depth on the needle

Introduce irrigant as passively as possible. Only use light forefinger pressure (not thumb pressure) when introducing irrigant into the canal.

Light finger pressure only

Do not wedge the needle in the canal and risk extruding irrigant under pressure beyond the apical foramen. Keep the needle moving gently in and out whilst irrigating to ensure you don’t inadvertently push it too far and wedge it.

Do not abuse the tip of the needle. The tip of endodontic safe-ended needles is delicate, particularly the slotted types. I have found quality control for some types is quite poor and you may have a needle with a very thin tip which can easily be bent and fracture off in the canal, particularly in curved canals. 

Above, fractured needle tip being recovered from canal and below, recovered tip

Although, if this happens, it shouldn’t be tightly wedged in and should be removable with a micro-opener, H file or a little judicious irrigation , this is not the kind of headache you want just as you are about to finish.

Check your needle tips before use for dangerously thin “safe” ends! These two needles are from the same batch and have very different slot dimensions.

Be sure you are in the canal before introducing irrigant. Knowledge of anatomy and a reliable electronic apex locator reading should be enough to be certain you are in the canal, but if there is any doubt take a PA before introducing irrigant.

Open apex/immature cases To avoid extrusion, exercise caution with the above advice, keep the pressure to a minimum, use low pressure on the plunger and measure accurately.

In summary If possible, place the irrigation needle tip 2mm short of the working length. Early in the canal shaping process, the canal diameter will be too small to place the needle at length-2mm, in which case it should be placed as deeply as possible. Do not allow the needle to wedge in the canal, it should be just loose. If it does wedge pull back until it is free. Correct position of the needle is usually simple in a straight canal but can be difficult in curved canals, where it may help to prebend the needle to match the canal curvature. Once positioned, apply gentle finger pressure whilst keeping the needle gently moving up and down in a 1-2mm amplitude movement whilst the assistant collects used irrigant with high volume suction.

So, having introduced your irrigant correctly and safely into the canal in a manner that maximises its penetration within the canal, you still need to ensure it then penetrates all the microscopic ramifications that exist beyond the main canal (fins, isthmuses, lateral canals, apical delta, accessory canals and dentinal tubules). This is achieved with a combination of irrrigant agitation and following an effective irrigation protocol, both of which will be covered in part 2.

References

Ahmad, I.A., 2009. Rubber dam usage for endodontic treatment: a review. International endodontic journal, 42(11), pp.963-972

Boutsioukis, C., Verhaagen, B., Versluis, M., Kastrinakis, E., Wesselink, P.R. & van der Sluis, L.W., 2010, Evaluation of irrigant flow in the root canal using different needle types by an unsteady computational fluid dynamics model, Journal of endodontics, 36(5), pp. 875-9

Byström, A. & Sundqvist, G., 1983, Bacteriologic evaluation of the effect of 0.5 percent sodium hypochlorite in endodontic therapy, Oral Surg Oral Med Oral Pathol, 55(3), pp. 307-12.

Hübscher, W., Barbakow, F. and Peters, O.A., 2003. Root‐canal preparation with FlexMaster: canal shapes analysed by micro‐computed tomography. International Endodontic Journal36(11), pp.740-747

Kakehashi, S., Stanley, H.R. & Fitzgerald, R.J., 1965, The effects of surgical exposures of dental pulps in germ-free and conventional laboratory rats, Oral Surgery, Oral Medicine, Oral Pathology, 20(3), pp. 340-9

Mello I., Cunha, R.S., Schönwetter, D.J., 2016, Current clinical practices in root canal irrigation among canadian endodontists, Oral Health, (May11).  http://www.oralhealthgroup.com/features/current-clinical-practices-root-canal-irrigation-among-canadian-endodontists/ 

Metzger, Z., Solomonov, M. & Kfir, A., 2013, The role of mechanical instrumentation in the cleaning of root canals, Endodontic Topics, 29(1), pp. 87-109

Peters, O.A., Schönenberger, K. & Laib, A., 2001, Effects of four Ni–Ti preparation techniques on root canal geometry assessed by micro computed tomography, International endodontic journal, 34(3), pp. 221-30

Ritter, A.V. and Swift, E.J., 2003. Current restorative concepts of pulp protection. Endodontic topics5(1), pp.41-48

Sedgley, C.M., Nagel, A.C., Hall, D. and Applegate, B., 2005. Influence of irrigant needle depth in removing bioluminescent bacteria inoculated into instrumented root canals using real‐time imaging in vitro. International endodontic journal, 38(2), pp.97-104

Sundqvist, G., 1992, Ecology of the root canal flora, Journal of endodontics, 18(9), pp. 427-30

Svensater, G. & Bergenholtz, G., 2004, Biofilms in endodontic infections, Endodontic Topics, 9, pp. 27-36

Zehnder, M., 2006, Root canal irrigants, Journal of endodontics, 32(5), pp. 389-98

Leave a Reply

Your email address will not be published. Required fields are marked *