Why is irrigant agitation necessary?
Passively “squirting” the irrigant into the canal and expecting it to intimately contact the whole canal surface is misguided because:
- Surface tension prevents irrigant penetrating all the fine tributaries (isthmuses, lateral canals, apical delta, fins) in the canal system.
- A vapour lock may form in the canal, which is a small gas bubble that either remains trapped, or forms at the apex (Senia et al. 1971). If it does, the bubble prevents irrigant contacting the canal surface and exerting its desirable properties in what is the most critical part of the canal.
- Even if there is no vapour lock, if you don’t (or can’t) place the needle sufficiently deep (see part 1), there may be a “dead zone” some distance apical to the needle tip beyond which exchange of fresh irrigant for old fluid will not occur (see diagram, below) . The depth of the start of the dead zone (the stagnation plane) will depend on, among other things; the needle type used, depth of needle insertion, pressure of irrigation and physical properties of the fluid used. Although an open ended needle will irrigate much deeper apically than a side or slot vented needle, we use side or slot vented needles to reduce the risk of apical extrusion.
Irrigant activation overcomes these problems. A handy analogy for irrigant agitation is to think of cleaning a tall vacuum flask which contained a thick soup (hopefully not bacterial soup!). If you simply fill the flask with water and empty it (passive irrigation), it won’t clean very well. But, if you fill it with water AND shake it vigorously (agitate or activate it), the cleaning will be much more effective. Well, we can’t pick up our patients and give them a good shake (much as we want to sometimes) but there are various approaches and devices we can use to introduce the necessary energy into the canal to agitate the irrigant, and increase its penetration throughout the entire canal system.
Although it is an obvious solution, increasing irrigant penetration by the simple expedient of pressing the syringe plunger harder to squirt the irrigant in faster and under higher pressure should be avoided because it increases the risk of apical irrigant extrusion (see diagram, above). There are many options for penetrating the vapour lock or agitating the irrigant and this is one area where new devices appear regularly. The most frequently encountered options are:
Simple agitation. Moving the needle within the canal as irrigant is delivered with a very brief insertion to length will displace an apical vapour lock if present (Boutsioukis et al. 2013).
Patency filing Vapour lock can be overcome by penetrating the apical bubble. Although intended to prevent blockage of the apical foramen, patency filing, where a small (10K) file is gently inserted through the apical foramen by 1mm, can disperse the apical vapour lock and mixes fresh with old irrigant in the dead zone beyond the stagnation plane (Gulabivala et al. 2010). So, recapitulation with a size 10 file after every file insertion not only maintains apical patency, but also increases penetration of irrigant solutions.
Manual dynamic irrigation (MDA) with a gutta percha cone. Although MDA is also referred to as GP pumping, this is poor terminology as it implies a vigorous pumping of the GP in and out, an action that may cause apical extrusion of irrigant, and increased post treatment pain.
To minimise extrusion, use a well fitting tapered GP cone (matching the last file used) and repeatedly gently insert it to length then withdraw rapidly approximately 50-100 times, in approximately 2-3mm amplitude strokes. Think of performing a pulling action, rather than a pumping or pushing action. A tapered preparation and cone is necessary because the action of seating a tapered cone to length in a tapered canal does not form a tight apical fit of the cone in the canal until the cone reaches length, so it does not act like a syringe plunger. As the GP slides to length it displaces any apical bubble and, as the GP is withdrawn , it safely draws (or sucks) the irrigant apically to the canal terminus to achieve improved irrigant penetration. The withdrawal can be viewed as a manual apical negative pressure irrigation.
MDA has been shown to be effective (Huang et al. 2007). MDA also increases sheer stresses on the canal wall which increase the displacement of infected debris from the canal wall.
MDA is very simple to do, only takes a minute and is a very cost-effective option. If you do not practise irrigant activation already, it should probably be your first port of call for irrigant activation. After all, you already have the equipment (GP and fingers!) to start tomorrow, but make sure you don’t pump.
Ultrasonic activation Passive ultrasonic irrigation (PUI) is generally regarded as the gold standard in irrigant agitation. PUI is the use of an ultrasonically (20-30kHz) activated file passively in the canal. Passive means there should be no contact of the activated file with the canal wall when activated as this may damage/gouge the canal. There is extensive literature available to support its effectiveness. Being ultrasonic, greater energy is imparted to the solution than by other methods, with acoustic streaming and cavitation occurring within the irrigant (Ahmad et al. 1987). Acoustic streaming and cavitation also increase the mobilisation of debris into the irrigant, propel irrigant through the entire canal system and increase the irrigant temperature.
Irrisafetm tips are widely available. They are a non-cutting (i.e. safe) tip, which is inserted upu to 1-2mm short of the canal length and activated on a low to medium ultrasonic setting for about 1 minute. They must be free to vibrate freely in the canal.
Their disadvantages are the high cost of the dedicated files, the risk of it becoming non-passive (and shaping/damaging the canal wall), limited effectiveness in curved canals and the risk of file tip separation.
Sonic or mechanical activation There are a number of sonic or mechanical devices available. The most prevalent is probably the endoactivatortm (EA) and there is some research available into its effectiveness. This battery operated hand piece vibrates a flexible polymer tip at approximately 166Hz. Being flexible polymer, gouging of the canal wall and tip separation are not a problem.
The technique is to choose the largest tip that fits loosely at length-2mm, insert to this depth and activate for 30-60 secs. while using 2-3mm amplitude vertical movements then flush debris laden irrigant away.
This is not an exhaustive list of devices and I have restricted discussion to current techniques, widely available in dental practices. In particular I have not discussed PIPS, PAD and ANP agitation which may well form the basis of future posts. So, which is the best method to use? Investigations into the relative merits of each particular technique have been contradictory. On balance, it is likely that the most effective is PUI although it is costly and technique sensitive. What stands out above all in the studies is that any activation removes debris and distributes the fresh irrigant more effectively than no activation. In assessing any new devices, bear in mind the need for critical appraisal of the device and of any literature supporting its use, because irrigant agitation is an area that has seen many unproven products come and go over the years.
The message is clear; whatever you do, do not rely on passive irrigation, get energy into the irrigant (Caron et al. 2010). Move the needle, use an apical patency file and activate the irrigant with something … shake the flask!
Our irrigants are used in quick succession and consequently mixed in the root canal. Some combinations may cause toxic by products or may interact antagonistically and deactivate the intended effect. The patient’s tooth is not the place to run your chemistry experiments, so knowledge of these reactions and which combinations are unfavourable is important (Rossi-Fedele et al. 2012).
NaOCl and EDTA. EDTA is an acid and the decrease in pH caused by mixing it with NaOCl reduces the freely available chlorine from the NaOCl. Therefore, do not mix EDTA and NaOCl in the canal. When going from EDTA to NaOCl, use a copious flush of NaOCl to remove all traces of EDTA. Do not repeatedly alternate NaOCl with EDTA in your irrigation regime as this cycles through waves of demineralisation by EDTA (exposing of collagen) and dissolving exposed collagen by NaOCl, which leads to excessive dentine erosion, weakening the root. It also prolongs the period of reduced feely available chlorine (due to their interaction). EDTA is not deactivated by NaOCl, so a flush with EDTA when there is NaOCl in the canal will not cause a problem.
NaOCl and chlorhexidine (CHX). These two interact to produce a brown/orange precipitate of parachloraniline (PCA) (Basrani et al. 2007). PCA is toxic and a likely carcinogen so this interaction needs to be avoided. The precipitate also reduces dentine permeability and may even block the lumen of a fine canal with a chemical sludge. So, if you wish to use CHX after NaOCl (or vice versa) use an interim flush of EDTA or saline to clear the canal of the other reactant.
CHX and EDTA. Do not mix well but a white harmless precipitate (a salt) forms, which is probably safe.
CHX and CA. No interaction
Up to now, I have explained the how of irrigation with reference largely to “the irrigant” rather than a specific irrigant. Remember what was said at the start in part 1, that there is no single ideal irrigant so we need a multi-irrigant protocol. This section describes the currently recommended irrigant protocol and, as before, the discussion is limited to widely available irrigants which have a wide evidence base for their use with an emphasis on a pragmatic guide for clinical practice.
Vital canals – There is no intracanal infection yet, so the primary aim is to remove any organic material from the canal.
- Organic material is dissolved by NaOCl, so during preparation refresh the NaOCl after each preparation file and use a patency file. Do not use EDTA.
- After preparation is complete, the smear layer will be buttered over the internal surface of the canal, so this needs to be removed using EDTA 17% for 1 minute (no longer than 1 minute as continued EDTA erosion will weaken the dentine). Use irrigant agitation to disperse the fresh irrigant and to penetrate any apical vapour lock.
- After the EDTA flush, the smear layer will have been removed but the surface of the canal will also have been minutely demineralised, which leaves a thin layer of collagen fibrils. This is a poor substrate to place sealer against and forms a substrate for future bacterial contaminants, so it needs to be removed with a final flush of NaOCl for 1 minute. Use irrigant agitation to disperse the fresh irrigant and penetrate any apical vapour lock.
- If you intend to use resin bonding in the canal there is one final step. Matrix metalloproteinases (MMPs) are released from the dentine by the preparation which, over time will slowly degrade the bond/resin hybrid layer formed during bonding procedures. MMPs are deactivated by CHX. We must not mix NaOCl and CHX in the canal, so we need to flush with saline or alcohol and then finally CHX 2% for 1 minute to inactivate the MMPs.
Necrotic canals – As well as the need to remove organic material there is a need to kill bacteria harboured within the canal and its various microscopic ramifications. The bacteria may be free (planktonic) or protected in their biofilm in clumps within the canal lumen or on the canal surface. The protocol is the same as vital canals, but now there is a greater need for effective irrigant agitation to disperse the irrigant into all the ramifications as well as penetrate vapour lock and mix fresh irrigant with the dead zone. PUI is probably the best option but, if not available MDA or sonic/mechanical agitation should be used.
Retreatments – Retreatment cases are more likely to contain the more resistant bacteria (e.g. Enterococcus faecalis) or fungi which are resistant to NaOCl. As well as seriously considering a multi-visit approach with an interim medication of Ca(OH)2, the protocol should be supplemented with a 10 minute irrigation with CHX 2% (with appropriate intermediate saline or alcohol flush) before final obturation or IKI before the final NaOCl flush.
Ahmad, M., Pitt Ford, T.J. & Crum, L.A., 1987, Ultrasonic debridement of root canals: acoustic streaming and its possible role, Journal of endodontics, 13(10), pp. 490-9.
Basrani, B.R., Manek, S., Sodhi, R.N., Fillery, E. & Manzur, A., 2007, Interaction between sodium hypochlorite and chlorhexidine gluconate, Journal of endodontics, 33(8), pp. 966-9.
Boutsioukis, C., Kastrinakis, E., Lambrianidis, T., Verhaagen, B., Versluis, M. & van der Sluis, L.W., 2013, Formation and removal of apical vapor lock during syringe irrigation: a combined experimental and Computational Fluid Dynamics approach, International endodontic journal.
Caron, G., Nham, K., Bronnec, F. & Machtou, P., 2010, Effectiveness of different final irrigant activation protocols on smear layer removal in curved canals, Journal of endodontics, 36(8), pp. 1361-6.
Gulabivala, K., Ng, Y.L., Gilbertson, M. & Eames, I., 2010, The fluid mechanics of root canal irrigation, Physiol Meas, 31(12), pp. R49-84.
Huang, T.Y., Gulabivala, K. & Ng, Y.L., 2008, A bio-molecular film ex-vivo model to evaluate the influence of canal dimensions and irrigation variables on the efficacy of irrigation, International endodontic journal, 41(1), pp. 60-71.
Prado, M., Santos Júnior, H.M., Rezende, C.M., Pinto, A.C., Faria, R.B., Simão, R.A. & Gomes, B.P., 2013, Interactions between Irrigants Commonly Used in Endodontic Practice: A Chemical Analysis, Journal of endodontics, 39(4), pp. 505-10.
Rossi-Fedele, G., Doğramaci, E.J., Guastalli, A.R., Steier, L. & de Figueiredo, J.A., 2012, Antagonistic interactions between sodium hypochlorite, chlorhexidine, EDTA, and citric acid, Journal of endodontics, 38(4), pp. 426-31.
Senia, E.S., Marshall, F.J. & Rosen, S., 1971, The solvent action of sodium hypochlorite on pulp tissue of extracted teeth, Oral Surg Oral Med Oral Pathol, 31(1), pp. 96-103.