Irrigation Beliefs & Methods: Effect of Needle Insertion Depth

Today I’m going to talk about the effect of needle insertion depth on irrigant flow in the root canal.

There have been countless articles published over decades describing the exchange of irrigant based on how deep the needle is inside a shaped root canal. In fact, there’s a lot of controversy and so we have to step back just a little bit so we can better appreciate irrigant exchange.

First of all, irrigants have been dispensed through typically large diameter stainless steel needles. In recent years, we’ve been able to use nickel titanium canula which are much more flexible and we’ve been able to use gauges anywhere from 29, 30 and 31. In a well-shaped canal, this type of a gauged needle will easily work itself through curvatures and into the apical one-third of a well-shaped canal.

The thing I want to talk about is typically, probably, controversial because there’s misinformation and, because there’s such a diversity of opinions, we have different speakers and journal articles and textbooks all reporting things that are quite confusing. Let me explain. It has been reported repeatedly that we can only really irrigate about 1-2 mm apical to the level of the needle in the canal.

I’d like you to think about this and ask yourself, "Is that true?" Because if you assume that that’s true, then lots of things will happen procedurally based on those belief systems.

The side bended needles need to be discussed, just briefly. There’s a lot of different canula and gauges as I have mentioned. There’s different thoughts regarding – Do you have side port delivery, or do you have a flat 90° angle to the long axis of the canula in the irrigator? Or, do you side irrigate? Most people have traditionally used a beveled needle and irrigated through the very terminal end of the canula; however, because of the concern with sodium hypochlorite accidents, manufacturers have produced side port irrigation devices, presumably so that you can’t irrigate through the apical end, the most distal extent of the canula, but rather the irrigant has to move laterally.

Well, pretty much if you want to exchange irrigant in a well-shaped canal, you do not want lateral, side port delivery. This is very, very ineffective. Although you could argue that it would reduce the potential for sodium hypochlorite accidents. So now I have to digress further and say that we can pretty much eliminate sodium hypochlorite accidents if we simply do two things. One, keep your hand moving as you progressively dispense reagent into the shaped canal. If the hand is moving, the needle then can never be locked up inside a shaped canal where the canal becomes an extension of the canula. This will clearly invite or promote driving reagent through the foramen and this can cause quite an upset, such as the reported sodium hypochlorite accident.

The other thing to be aware of when you’re irrigating is – move the plunger slow. Slow plunger speed equates to a very sustained gentle type of irrigation where we’re not trying to hydraulically drive irrigant deeper than the canula. So, keep your hand moving and dispense the reagent in a slow rate... that means mLs per seconds of time. Your office can figure out what’s appropriate for you.

So, back to our question – How deep do we deliver reagent apical to the canula? You can begin to see it’s based on the shape of the canal; it’s based on the gauge of the canula itself. It has to do further – Is it side port or is it end delivery? What I want to say is – the articles are largely talking about ‘end delivery’. They’re largely talking about shapes that are quite large apically so that you can get the canula deep into the canal. But, let’s just cut to the chase. The articles will say that you can only effectively exchange irrigant 1 or 2mm apical to the level of the canula in the shaped canal. I totally disagree with this, but yet article, after article, after article continue to make these assertions.

Here’s what I would like you to do: The way they conducted their methodology would explain their results. So, in other words, their results are honest, their results are accurate and there are big limitations based on how they irrigate. What they are basically doing is pressing on the plunger and moving reagent through a canula and they’re looking at different fluid dynamic models to assess fluid movement. In most instances, these magazines will report that like a side bended needle can achieve replacement to working length only if the needle is 1mm short of the full working length. Whereas, they’ll say an open ended needle that’s flat on the end, it can be a little further back at the 2mm level and still you’ll see fluid exchanged in that apical 2mm.

I’m going to talk to you about a way that you can exchange irrigant 6-7mm apical to the level of your canula if you just think outside the box. So, so often in endodontics, we write articles, we have clinical observations and then we talk to colleagues, we go to classes and what we read is who we become and what we see is who we are. So, we pretty much are locked in as a specialty that we don’t effectively irrigate more than 1 or 2mm apical to our canula.

This is because most people, now think carefully, you could be driving your car today as you listen to this. You could be on a treadmill. So, you’re going to have to fanaticize just briefly how you held an anesthetic syringe. The way dentists hold an anesthetic syringe is they use their index finger and their middle finger on the wings of the body of the syringe and they put their thumb on the plunger and that’s how we would administer, as an example, anesthetic into the vestibule.

Well, most dentists pick up an irrigating syringe when their doing endodontics and they hold the syringe, the irrigating syringe exactly like they held the anesthetic syringe. Again, to be redundant, they have their index finger and their middle finger on the wings of the syringe and they use that to support the pressure movement of the thumb pushing the plunger down through the tube.

Okay, what if we held the syringe differently? So, now you’re chairside. The assistant passes you over a 3cc syringe, a 5cc syringe, it doesn’t really matter, whatever you’re using, and rather than putting your index finger and your middle finger on the wings, why don’t you put only your thumb on the wing and then you can use your index finger, and your middle finger on the actual plunger and you can pull and push. So, you use your thumb to pull on the wing, when you pull you’re irrigating. When you push on the wing, you’re vacuuming. If you go to a plastic block, as an example, you’ll notice that you can exchange irrigant 6-7mm apical to the level of the canula and that means even around curvatures where your canula never gets.

So, I bring you good news today. If you would like to irrigate further away from the foramen safely and exchange 6-7mm apical to your canula, just think of a new way of holding the hand-held irrigating syringe. Okay? I’ll probably have more information about this visually on my website in the weeks ahead because I know many of you are very intrigued by this method. I’ve been talking about this method for many years because I’ve been very interested in root canal system anatomy and we know that we’re not going to get our instruments into all the ramifications so really it’s the reagent that’s going to clean a root canal system.

So, we’ve always said – file shape a canal, but irrigants clean a root canal system. I welcome you to push-pull, push-pull and concomitantly irrigate-vacuum, irrigate-vacuum, and you can watch your solutions with methylene blue or with some Chinese red dye… in a plastic block, very carefully look at the power of this method of irrigation.

Thanks.