Root canal irrigation in modern Endodontics. Part one: the routine
Why do we irrigate?
Successful endodontic treatment, in agreement with what Prof. Schilder, the father of modern endodontics, enunciated, depends on the ability of the operator to mechanically and chemically clean the root canal system and subsequently obturate it three dimensionally.1
The endodontium consists of a space that is easily accessible to rotary and manual instruments (principal canals) and, as has been confirmed by numerous clinical and histological studies, there are spaces that are difficult to access or completely inaccessible (deltas, loops, isthmi, lateral and accessory canals, and dentinal tubules).
In particular lateral and accessory canals are found with significant frequency especially in the apical third of the root and in molar bifurcations.
Canal shaping is unable to reach some areas and they remain untouched by the instruments, no matter what technique is used; thus about half of the endodontium remains untreated.2
The complexity of the endodontium could, however, be one of the determining factors in failure of root canal treatment even in properly treated teeth, due to irregular and sometimes unpredictable spaces that characterize root canals.3-4
In the light of the above one of the most exciting challenges of modern endodontics is represented by the biochemical debridement of the endodontium (accessible and non accessible).
When debridement is performed according to the state of the art (three dimensional) cleaning, the endodontium can then be filled and sealed with cement and gutta-percha at the time of obturation.
Irrigation, therefore, plays a crucial role in determining the outcome of root canal treatment.
What irrigants should be used? A choice based on scientific evidence.
I remember back in my university days, I once took my father to his dentist, a general practitioner, as he had to have root canal treatment. I was particularly struck by the frenetic rinsing with a sodium chloride solution alternated with hydrogen peroxide and asked why this procedure was performed.
He answered that they had been taught to do it this way, without critically motivating his choice.
In every field of medicine, the clinical practitioner must follow logic and must be supported by literature.
Therefore, to rationally choose an irrigant you must first answer the question: “What do we want to remove from the canal?”
The answer is simple; we want to eliminate the organic tissue (pulp), bacteria and toxins, as well as organic and inorganic debris that our rotary and manual instruments inevitably produce.
At this point the choice is easy and natural.
Literature has highlighted sodium hypochlorite in a concentration of 6% as the irrigant of choice inasmuch as it is able to dissolve organic substances and eliminate the bacterial presence and the biofilm from inside the canal.5-10
Complete debridement is achieved by combining a substance capable of eliminating the inorganic component created after the instrumentation. It is
necessary to use a chelating agent namely 17% EDTA or 10% Citric Acid.11-14
A 2% Chlorhexidine aqueous solution has been suggested as an irrigant for the root canal system. This has an antibacterial action but lacks the ability to dissolve the organic and inorganic material.15-16
Furthermore mixing sodium hypochlorite and chlorohexidine generates a toxic and cancerous compound, parachloroanaline and its use as an irrigant is not recommended.17
How do we irrigate the canals?
Unfortunately even today biochemical debridement is the most underestimated phase of root canal treatment and this is proven by
the fact that many colleagues, mainly general practitioners, still irrigate using the same needles and syringes as those used for intra muscular injections. (Figure 1)
Figure 1: Many still irrigate like this…
Considering the large gauge of the needles, they can reach no further than the canal opening and therefore irrigation is reduced to a simple change
of the irrigant in the pulp chamber.
On the contrary the irrigant solution should penetrate the entire root canal system and it is essential that it cleanses those areas that our instruments cannot reach.
By doing this, the gutta percha, which becomes plastic due to the heat, is able to fill those spaces opened by the irrigants during the obturation phase.
We should treat the entire root canal system in the same way as a surgeon removes entire areas of infection and inflammation; the irrigants are, therefore, an extension of our hands and our instruments.
If we acknowledge the importance of irrigation we have to acknowledge that it is not something that can be improvised and necessitates dedicated
technologically advanced instruments.
There is basically a choice between two approaches.
The first is based on the traditional system of positive pressure that pushes the irrigant into the canal by means of dedicated syringes and needles
of varying designs.18
The second, on the contrary, employs a new system of negative pressure in which the irrigant placed in the pulp chamber is drawn down inside the canal to be aspirated by a micro-cannula.
The micro-cannula is the key to the negative apical pressure approach. It gently recovers the hypochlorite that the assistant deposits in the pulp chamber by creating aspiration (negative pressure) at the apex (apical pressure). The hypochlorite therefore passes through the entire canal before
being aspirated at the apical foramen.19-21
Whichever technique is used, the closer to the apical foramen the irrigant is deposited, the better the debridement will be.
How long should we irrigate for?
The irrigation time line is a topic of significant clinical relevance and has considerable implications for ergonomics in dental practice.
With the arrival of Ni-Ti in endodontics it is now possible to shape a canal in a very short time but this does not mean that the canals are ready for obturation and anyone who hurriedly obturates at the end of shaping, bypassing the irrigation phase or doing it for insufficient time, is making an error.
Numerous recent failures are paradoxically due to the speed of shaping, after which irrigation is carried out for insufficient time.
On the contrary is reasonable and profitable to invest the time saved with the rapid shaping carried out with nickel-titanium instruments, in biochemical debridement procedures that will raise the quality of the root canal treatment.
Most probably due to the multiple variables related to the operator, canal anatomy and physical-chemical properties of the irrigant, there are no precise indications in literature on how much time to dedicate to canal irrigation.22
It is rather the opinions of brilliant clinicians that guide us.
Doctor Buchanan reminds us that: “Efficacy with these solutions (NaOCl) currently requires direct contact with all the walls of the shaped canal for a significant time period, 20 to 40 minutes, in order to disinfect and dissolve organic tissue.”23
In conclusion I would like to repeat this concept: even on a Friday afternoon when you are treating the last patient and your mind is on the coming weekend and the shaping was particularly easy and fast, resist the temptation to immediately obturate the canals if you have not irrigated them sufficiently.
Therefore walk around the practice, do some stretching, have a coffee or why not phone a colleague or friends, answer your e-mail… and rest assured that the irrigants are working for you inside the canals!
We Learn from Our Failures
Ten years ago one of my best friends developed a severe pain localized around the upper right lateral incisor and so I treated him for the emergency in my practice.
Acute peri-apical periodontitis was diagnosed and a radiograph evidenced a previous incongruous root canal treatment that barely reached half way up the root with a small peri-apical radiolucency.
We decided to schedule treatment for the following day.
Right from the beginning I realized that the canal was very large and fortunately patent under the root filling, so determining the correct working length and shaping the whole canal was very easy and fast.
This case was probably the easiest I had treated up until then, so I hastily irrigated with sodium hypochlorite, convinced (wrongly) that in a large canal like this one, the irrigant would also exert its disinfecting action rapidly.
After this I obturated the canal with warm vertical compaction using gutta percha and cement.
Six years later my friend came to the practice with a swollen face and pain due to an abscess of the same lateral incisor. The radiograph examination
revealed a radiolucency 5 times greater than the one present at the time of my treatment. (Figure 2)
Figure 2: Pre-operative radiograph which, notwithstanding the obturation appearing to be correctly completed, highlights a large periapical lesion which is larger than it was 6 years before.
Notwithstanding the fact that my root canal filling was perfectly positioned apically, the case had miserably failed. So what could have happened
Too little irrigation time?
Insufficient penetration of the irrigant to the apical third?
Profoundly disillusioned and sorry, I prescribed antibiotics and a week later I performed a second retreatment on the tooth.
After removal of the gutta percha I saw that my rotary instruments had removed grey colored debris from the canal walls which showed the inadequate debridement of my previous treatment. (Figure 3)
This debris probably prevented the cement and gutta percha from filling the canal three dimensionally.
Figure 3: GT 40-.08 rotary file with grooves filled with infected debris.
Considering the previous experience, this time I dedicated most of the retreatment time to biochemical debridement but above all conveyed and renewed the irrigant up to the apical foramen thanks to an aspirating micro-cannula positioned at the full working length and thus performed an irrigation
technique using negative pressure. (Figure 4)
This type of irrigation technique is carried out by placing the irrigant solution in the pulp chamber which is then drawn down by the micro-cannula inside the canal all the way to the tip of the micro-cannula.
Figure 4: Determining the working length. I used a steel micro-cannula as a verifier (being hollow it is less radio opaque than a K-file in the x-ray) to demonstrate that the irrigation was carried out safely up to the apical foramen, because it is a negative pressure technique.
Then I performed warm vertical obturation. (Figures 5-7)
Figure 6: Check up at one year: definite improvement with reduction of the radiolucency.
Figure 7: Check up at three years: the case with complete resolution.
This case shows that allowing sufficient time for canal irrigation, as well as the importance of enriching your endodontic equipment with new technology dedicated to irrigation, is an intelligent strategy.
How do we improve irrigation? Seeking the ideal instrument
Literature demonstrates that if 6% hypochlorite is placed directly in contact with the pulp for sufficient time and in sufficient volume, it will completely digest it. The same occurs with bacteria (even if it is in the form a biofilm),
viruses and spores, destroying them.
Similarly a calcium chelating agent such as EDTA 17% shows that it is perfectly capable of removing the inorganic component of the smear layer coating canal walls after dentin is cut during shaping.
So then why should we potentiate the irrigant?
The technique of potentiating with ultrasonic or subsonic instruments is often suggested by some clinicians and researchers firstly to accelerate and improve the biochemical reaction between the irrigant and the substrate and secondly to mobilize the irrigant because they are afraid that it might not penetrate the whole canal surface including the endodontium that cannot be probed.
Instruments dedicated to cleansing, like thin flexible needles or aspirating micro-cannulas, are now available so distributing the irrigant solutions throughout the canals should no longer be considered a problem; the question that needs resolving is another one.
The intimate contact between the canal walls and the irrigant is prevented by a film of debris that remains on the walls after the shaping carried out
by our instruments.
Before coming into direct contact with the canal walls the irrigants have to “do a large amount of work” to dissolve this layer of debris and so if
there was an instrument that could rapidly detach it then our irrigants would immediately act at the surface level of the canal walls which are now “naked”.
This instrument should, amongst other things, act at the level of the canal walls without producing further debris.
I would like to make a quick digression.
A glaring example of ergonomics can be described by tasks facing housewives, many which have to be carried out, done well and as quickly as possible. One of the things they have to do is to remove the grease from dirty dishes and pots. To do this they don’t just use washing up liquid, but scrub the surface with a sponge and brushes so that it is more effective.
Similarly endodontists must not just deposit the hypochlorite in the canals expecting it to miraculously remove the layer of debris from the canal walls, disinfect them and even penetrate inside the lateral canals, the apical delta and the dentinal tubules!
This is why in my daily practice I felt the need to introduce my own canal brushes constructed by using irrigant needles (Figure 8) with bristles which i attach specifically to these comfortable silicon handles identical to those used for K-files in order to have improved control. (Figures 9-11)
At the end of the shaping, during the irrigation with hypochlorite and EDTA, I move these self-made brushes up and down in a scrubbing motion to detach the debris from the canal walls.
From a clinical point of view this gives me great satisfaction because I noticed that the irrigant becomes cloudy after this brushing, showing that the debris is released and how effective this method is.
Figure 8: Dedicated irrigation needle with bristles: using a laboratory disk I remove the last two mm without bristles as well as the plastic attachment, and then I fit a silicon handle.
Figure 10: Detail of the bristles used to free the debris spread on the canal walls.
Figure 11: The brush has a steel core so it can be bent.
The difficulty with endodontics is generally the last few millimeters of the canal, in other words the apical third where more than 90% of the portals of exit are located.
The apical third is by nature narrow and deep and so it has to be adequately rinsed with the irrigant solutions.
However, this is not all.
One of the imperatives of endodontic irrigation is the renewal of the irrigant in the deeper portion of the canal, the apical third.
Indeed, because of the significant buffering capacity of dentine, the irrigant loses its effectiveness after a while and it has to be renewed.
Having identified the necessary of not only reaching but also renewing the irrigant in the apical third, to complicate matters we also have the canal anatomy.
The canal anatomy limits every part of the root canal treatment, including irrigation. Indeed the difficulty is compounded if the apical third is found at the end of a long or narrow canal or worse still after a curve, in other words with anatomy like this, where shaping and obturation are both difficult, irrigation is difficult too.
Successful treatment of these cases really depends on the operator’s ability to shape, cleanse and obturate the entire root canal even if the canal is curved, narrow or long. (Figures 12-19)
Figure 12: Lower molar bridge abutment with acute apical periodontitis; you can see the peri-apical radiolucency.
Figure 13: The distal root has an unexpected curve in the last 3 mm. The apical third was, therefore, shaped using manual instruments alone: firstly K-files and then GT hand files bent with the EndoBender pliers used to bend the files without damaging the blades.
Figure 15: Irrigation needles, like other root canal instruments, can also be bent to follow the curves in cases with a complex anatomy, in order to deposit the irrigant in areas which are otherwise hard to reach.
In this case an aspirating micro-cannula was bent so that it could be placed at the foramen. The negative pressure draws the irrigant solution down past the curve up to the apex without the risk of the dangerous extrusion of the irrigant into the tissues.
Figure 16: Radiograph of micro-cannula at the apex in the distal root. You can see how much the last few mm is curved.
Figure 18: Check up at 1 year, oblique projection, the case has healed.
Figure 19: Check up at 1 year, straight projection, no radiolucency noted.
Predictable Irrigation Protocol
1- Before introducing an instrument into the canals and therefore after opening the pulp chamber, rinse with 6% sodium hypochlorite.
2- Remove excess hypochlorite and place EDTA gel in the pulp chamber to act as a lubricant and to facilitate manual instrumentation. Another important function is to prevent the pulp tissue from forming a plug in the canal due to it being compacted by the downward movement of the instruments.
3- Copious irrigation with sodium hypochlorite after use of each rotary instrument.
4- At the end of the shaping, dry and proceed by rinsing with liquid EDTA 17% for 5 minutes (renewing every 2 minutes).
5- Dry and perform final abundant rinsing with hypochlorite renewing frequently in the deeper areas.
6- Take note of the clinical signs that would indicate a need to increase the irrigation time. The development of bubbles on the inside of the hypochlorite solution could indicate “digestive” action on the organic residue still taking place and would require an increase in the time that the irrigant should be left in the canal.
Similarly if, during the drying phase, you should see small red marks on the paper points, it is an indication of “lateral” bleeding due to pulp still being present in the non-probable endodontium and it would be useful to increase the irrigation time. (Figures 20-25)
Figure 20: Upper canine with pulpitis.
Figure 21: A 0.20 K-file at full working length.
Figure 22: Paper point marked laterally with blood at the end of treatment made me suspect the presence of lateral canals and suggested that I should increase the irrigation time.
Figure 23: Warm gutta percha and cement fill the entire root canal system confirming the complexity of the anatomy and the presence of a lateral canal.
Figure 24: Back-packing.
Figure 25: Check up at 6 months, no radiolucency noted.
7- Before drying the root canals I carry out a technique of intracanal heating with the aim of speeding up the digestion of the organic residue
that may be present.24
I heat the hypochlorite for 3 seconds at 200°using the finest System-B heat plugger, trying not to touch the root canal walls. I do this four to five times while my assistant aspirates the vapor.
I consider this technique particularly useful to digest the organic debris that could remain after root canal treatment where the canals merge and in the irregularities of a complex C-shaped anatomy.
8- Rinse with pure alcohol and dry with paper points to dehydrate the root canal.
Scrupulous and patient debridement raises the quality of the whole treatment and lays a solid base for ultimate successful root canal treatment.
The biochemical debridement of the large areas that are not accessible to instrumentation, such as an anastomosis, is the test of efficacy of this protocol. Indeed these large junctions between canals, which are full of organic residues and bacteria before treatment, are completely emptied
by the action of the irrigants. Then the subsequent phase of warm vertical obturation provides a three dimensional filling with gutta percha and cement (Figures 26-29)
Figure 26: Second lower molar treated for pulpitis. The x-ray shows a large anastomosis between the mesial and distal part of the c-shaped canal.
Figure 27: First upper premolar treated for pulpitis. The x-ray shows anastomosis in the middle and apical third.
Figure 28: Re-treatment of a second upper premolar for acute apical periodontitis. The x-ray shows anastomosis in the middle and apical third and an irregular anatomy.
Figure 29: The x-ray shows a second lower molar with long anastomosis between its mesial and distal part.