The Air Bubble / Air-Lock Assertion & Controversy

The controversy that I’d like to address today is the reported, mythical air bubble or air-lock assertion.  Before I get into this discussion though, I’d like to tell you about a meeting I recently attended in July of 2010 in Washington, DC.  Dentsply Tulsa Dental annually holds an opinion leader forum.  This is a hot ticket and attendance is strictly limited to 100 doctors.  If you looked around the room to see who was present, you would have seen about 25-30 academicians.  These are department chairman of both undergraduate and post-graduate endodontics.  You would’ve seen some of the most important researchers we have in the field today.  And, finally, some of the best clinicians that endodontics has to offer. 

The congress was focused on two or three different topics but the topic I want to talk about is the day that was spent on endodontic disinfection.  There were some lively presentations.  Each person in the audience had a handheld device and they could vote on questions that were proposed to them by the speaker.  It was very interesting to see immediately the feedback displayed on the screens.  On a percentage basis, we could see which portion of the audience, as an example, might have voted for answer A, B, C, D or combinations of above.  We could very rapidly begin to understand that there was a lot of ambiguity, a lot of misinformation, a lot of misconceptions and, sadly, this all perpetuates endodontic myths. 

As an example, when this was all done, there was a very lively question and answer period.  People in the audience would go to the microphone and ask a general question that sometimes would then be responded to by other members in the audience, or the panel.  What we found out is one doctor went to the mic and said that it was very difficult to exchange endodontic irrigation in the apical one-third of a root because of the air bubble.  This made me a little bit uncomfortable because I had wanted to talk about this air bubble thing now for quite some time and now suddenly we have people speaking about it as if it was gospel truth.  So, that’s why today we’re going to talk about this mythical air bubble or air-lock assertion, which has been described as a serious and limiting factor in restricting an intracanal irrigant from reaching the most apical extent of the canal preparation. 

In fact, the air bubble baloney has led to an entire marketing campaign to sell a product.  The product I speak of can pull irrigant from the pulp chamber reservoir along the length of the canal and effectively exchange this reagent at the full working length.  Never mind that clinicians will at times be required to needlessly over prepare certain foramina in order to accommodate the canula which needs to extend to about 1 mm short of the full working length. 

So this conversation doesn’t get needlessly mysterious, the product that I’m speaking about is the EndoVac System.  The EndoVac System is in fact an excellent product, but it has nothing to do with a bubble phenomenon or an air-lock assertion. 

I’ll first describe the three things the EndoVac can do quite well.  The EndoVac improves the volume of reagent exchange in the apical one-third of a well prepared canal as compared to traditional syringe-held devices.  The second advantage of the EndoVac is it's reported that it reduces sharply sodium hypochlorite accidents.  Then again, how many sodium hypochlorite accidents are reportedly globally in any given year?  It has to be a low single digit number. 

This infrequent occurrence absolutely needs to be understood to be related to and attributable to operator error, 100% of the time.  Perhaps in another blog I can go over sodium hypochlorite accidents, the proper use of hand held devices and just a few little clinical tips on how to 100% eliminate this disparaging result.

Finally, the EndoVac improves exchange of irrigant.  This is logical and one would expect it because of the great volume of exchange, it should lead to improvement in disinfection. 

Word of caution about the EndoVac, the available research today demonstrates that the EndoVac works almost exclusively within the confines of the prepared portion of a canal.  It does very little, if anything in the deep lateral anatomy. 

So, to summarize, my problem is not with the EndoVac device, rather and this is most important, it’s with the air bubble assertion and how the air bubble assertion has been a theory that’s been promoted to sell the EndoVac.  So, regardless of whether you use the EndoVac, are interested in the EndoVac, or have dismissed the EndoVac as a disinfecting device, let’s go back to the air bubble assertion.

In other words, is there an air bubble at the apical extent of the preparation that prevents the effective exchange of an irrigant?  First, nobody needs to get defensive because both sides of the air bubble argument can be right.  In fact, nobody has to be wrong regardless of whether you think there is a bubble or you think there is not a bubble.  The problem again with the entire air bubble assertion is trying to sell a device to remedy a non-existent problem. 

Well, whether you get an air bubble or you don’t has everything to do with your canal preparation concepts. That is, the apical diameter that you prepare a canal to, the apical one-third taper that the canal is expanded to, your concept of the working length, in other words, the vertical extent of treatment, and, if you use small sized flexible patency files to clear the foramen and to prevent the accumulation of debris. 

Those that tirelessly promote the air bubble dilemma like to show an in vitro plastic model with a sealed, hear blocked, canal apically.  This is the antithesis to my concepts of cleaning and shaping and preparing a canal.  We never want to have a canal that is blocked or shelved-out or a Washington monument some distance from the actual foramina.  The air block people like to demonstrate that throughout the canal preparation and when they are intentionally working short, and during the increase in the apical size of the preparation to a minimum size 30 file, they like to show the air bubble forms and then they like to show how this air bubble prevents the exchange of irrigant. 

Of course, their solution for this self-imposed and needless problem is to use the EndoVac.  Fortunately there has been an enormous amount of international research published in peer review journals that totally refutes the air bubble dilemma. 

I know I sound pretty tough on these air bubble people, but I’m hearing it more and more and it is absolutely not true.  If you just use common sense canal preparation objectives.  Like the objectives that were first reported in 1974 in Dental Clinics of North America by Dr. Herb Schilder.  In this famous article, the most frequently quoted article on canal preparation in the international literature, he proposed five mechanical objectives for preparing canals.  One of the objectives was a smooth flowing preparation from the orifice to the full working length.  The canal was not obstructed apically.  It was not ledged.  There was not a seat made to confine gutta-percha.  There was no intention whatsoever to have an obstructed canal.  Schilder talked about the importance of taking a small flexible patency file and carrying to the radiographic terminus and recognizing that this file was minutely long, but importantly, he and his students repeatedly demonstrated that irrigant could be exchanged to the full working length. 

Let me explain this just a little bit more.  Subsequent to his article and in the years ahead, many of his students performed research that can be found at the Boston University’s Library of Medicine and they used a radiopaque dye called hypaque.  What Schilder showed was that in a pre-enlarged canal, this is important… in a pre-enlarged shaped canal, by the time the colleague first carried a 10 file to the full working length, followed by a 15 file that 100% of all clinical cases done in vivo had reagent to the radiographic terminus of the canal.  Although this visualization of hypaque to the full working length does not imply that the canal was disinfected, it absolutely implies that reagent is exchanged and this gives us a pretty good glimpse clinically into the dynamics of fluid hydrodynamics.  How fluids move, when they can achieve full length, what kind of shape has to be present in order for this reagent to achieve length.

So, it’s now important to state to the audience that’s listening, that even though we know quite a bit about fluid exchange and it’s been reported many times in the literature, and there is no air-lock; regarding the actual disinfection, the histological cleanliness of a canal, many studies have been published emphasizing through micro CT, clear section analysis, SEM and other modalities, that we can get reagent to the full working length in clinical cases on a routine basis if we do nothing more than use a patency clearing file. 

So, is there an air bubble?  Is there a mysterious air lock at length?  Yes.  If you work short in an apically blocked canal, there will be an air bubble.   On the contrary, if you work intentionally, deliberately and minutely through the foramen and maintain patency with a size 10 file, there will be no air bubble and irrigant will exchange to length.