Apical Size Matters: Unnecessarily Over-Preparing the Foramen

I’d like to get into a topic right now that obviously is controversial and there is no international agreement, but it has to do with apical size. I would like to just weigh in on this because there’s so much banter on the internet and chat rooms, in articles and point / counter point, at the AAE meeting. You can go on and on and there is no consensus on this topic, but just a few thoughts from Cliff Ruddle.

If you look at the literature and you talk to people, why do some schools or advocates preach, if you will, that we need to have a 40 file, or equivalent, at the full working length? Of course, some of these same people would say that it’d even be better in their minds if you could have a 50 file at the full working length.

Well, if you just look at the micro CTs, you’ll have a problem with this concept immediately because if you look at the micro anatomy and the undisturbed anatomy, it’s really obvious that the turns, the curvatures, the divisions at this level are not going to be amenable to these large diameters whether it’s stainless steel, nickel titanium, M-wire or any of the new innovations in metallurgy that's thrown at us.

So, why do we make them big?  And why is there such controversy about… some people say, "Keep them as small as practical" and some people say, "Make them big"?  So, we have the two camps, make them big so we can do what?  So we can make them round.  Then, these same advocates will say, "Make them big so we can exchange irrigant".

Is it true?  Do we have to make them big to make them round and do we have to make them big to exchange irrigant?  In other blogs that I’ve talked about, I’ve talked about you can move reagents with a 29 gauge needle 7mm apical to the needle. So, we can get reagents to the terminus even in foramina that are prepared to 20 or 25mm file. So, in other words, a quarter of a millimeter, 0.25 or 0.20. So, a 20 or 25 file is often my last file, pretty much at the RT, in posterior teeth.

So, Baumgartner, one of our most brilliant researchers in endodontics, recently retired. He was up at the University of Oregon, Health Science Center. He was Department Chairman of Post Doctoral Endodontics... a prolific researcher... a very respected man. He said in his article in 2004, June, Journal of Endodontics that if we just look at disinfection and cleanliness that a 40/06 preparation is no cleaner than a 20/10 preparation. So, 40/06 means the file is 0.4 of a millimeter at D0 and it has a 6% taper. So, if you aspire to taking a 40 file to length, that’s 6% tapered and you’re making it a 40 because you’ve been told it has to be big to exchange irrigant and it has to be big to make them round, then you need to understand that if you took a 20 to the full working length and it had a 10% taper, the two preparations would be deemed and the research reported, they were absolutely equivalent in their cleanliness. So, when we talk about disinfection, I’m talking about debridement, I’m talking about smear layer management, and I’m talking about removing microorganisms.  All right?

Well, so we know we don’t have to make them big and make them this size to exchange the irrigant. So, what about making them round? This may surprise you but it’s been advocated to make them big so that we can include all the thinning and eccentricities off the rounder part of the foramen that our files actually shape. If you think about it, we’ll have to go back to Craig Baumgartner and look again at his article that appeared in 1987, the April issue of the Journal of Endodontics. At the full working length, he noted that the uninstrumented portions of the foramen were cleaner than the instrumented portions.

Now, this just sounded like, probably, heresy for a lot of you because you’re wondering how could that possibly be?  But, it has to do with our old friend the smear layer. In other words, when you take a file to the full working length, that part of the instrument that’s engaging dentin, the by product is mud and that mud is getting burnished into the tubules at that level or other lateral anatomy. If you think then about the uninstrumented portions, the file never reached these areas, therefore there was no smear layer and it was the reagent that actually cleaned this aspect of the preparation.

So, again, the old adage that we set from the 70s, files shape a root canal but irrigants clean a root canal system. So, you don’t need to make them big to make them round because you don’t need to try to include all the foramen. Let your reagents do this important job. It’s very safe, it’s very three-dimensional in the cleaning outcomes, and you’ll notice that you’ll have more peaceful patients.

Again, trying to carry large, less flexible instruments to the full working length promotes rips, tears, blocks, ledges, and transportations, and all of these have serious clinical issues and oftentimes can condemn a case and oftentimes a case will not succeed because we might not be able to overcome these deficiencies in nonsurgical retreatment. So, that means that we might actually commit the patient to a surgical procedure or an extraction.

So, keep your foramen as small as practical. I’m frequently misquoted; I did not say "as small as possible"... that’s a pink 06, but "as a small as practical". When you find a file that is snug at length, that file is only snug at length if every successively larger instrument uniformly backs out of the canal. Then you can go to the black board and you can draw that shape for your patient, and you know that you have a file at length that could be touching circumferential dentin, but let’s be honest, when you tap on a file and you're saying it’s snug at length, it could be touching two-wall dentin, but remember those uninstrumented portions are cleaner than the instrumented portions.

I hope this adds a little bit of insight to what you’re dealing with every day in the clinic and maybe this will create a little bit more opportunity for you when you can stay away from post-operative flare-ups, have more control, better hydraulics during compaction, and good things show up radiographically when we have these kinds of shapes.