Factors Influencing Endodontic Disinfection: Top 10

I gave a lecture at the AAE meeting to about 500 endodontists in Orlando and it was a couple of years ago now. The title of my lecture was the "Factors that Influence Disinfection". So many times when we see, as an example, "up-and-down research"; and what I mean by up-and-down research, somebody can study a device and say it’s terrific, and yet another school can release a paper in another part of the world and it can say that that file is terrible. So, of course, you can quote any article you want to support virtually anything you do, but I might want to just say that the reasons we have up-and-down literature is failure of the researcher to follow clinical protocols, and to control variables as necessary.

So, when we talk about factors influencing disinfection and you think of all the disinfection articles you’ve read and they’ve maybe compared the EndoActivator compared to the Vibringe, or maybe they’re comparing the Vibringe to RinsEndo, or maybe they’re comparing the EndoVac to the PiezoFlow, or maybe they’re comparing photoactivating disinfection to the PlasticEndo file, or maybe they’re comparing the dam brush to perhaps something else... And, you see all this up-and-down literature and it gets confusing.

Here’s why it’s confusing and that’s what the topic is, is to talk about the 10 factors that influence disinfection. I might add, this is not a comprehensive list. This is just some of the more important factors that influence disinfection. When you read your next paper on endodontic disinfection and you’re thinking about the device that’s being studied, ask yourself the following questions.

Here we go:

The first factor that influences disinfection is the anatomy. Obviously if we were working in little straight canals with little conical tubes, it wouldn’t be a job at all and we wouldn’t be talking in a blog format today. We know from looking at the micro CT work, from so many, Frank Paque, Ove Peters, Paul Lambrecht's group, people like this, you begin to see something immediately and that is how complex this anatomy really is. In fact, it’s a little bit sobering sometimes when you’re showing the micro CTs in a large audience and you begin to sense that the audience might feel, you know what these things are so complicated it’s impossible. So, because we have anatomy, it’s going to influence virtually all of subsequent tasks that we do in start-to-finish endodontics. So, that’s a huge variable.

Another variable is the access cavity. This is very easy to explain. If we have incomplete access and we miss an orifice; as an example, we miss a mid-mesial in a mandibular molar, if we miss an MB2 in a maxillary molar, then all bets are off because we’re not debriding and we’re not removing micro-organisms and their byproducts if present. So, we need to have a complete access. A lot of times, when you look at the literature, they decoronate a crown. This always is very curious to me because now we have almost no reservoir to hold our irrigant. And, if you really want to look at disinfection studies, they should be pretty much like our clinical work where we have access preparation through a clinical crown and we have a great reservoir of irrigant up in that access cavity which can exchange potentially deep into the body of the growing preparation as it’s being shaped.

A third variable would be the preparation sequence. There’s been plenty of research that’s shown that you’re going to have a different level of disinfection based on if you do a step-back technique, a crown-down technique, or what I’ve talked about for probably 35 years almost, a pre-enlargement technique. So, each has something to offer. Each has been explained in different ways. And, each is intended to fulfill the disinfecting criteria, but they’re all very different. Based on how you prepare the canal and the sequence used to prepare it, you’re going to have different levels of disinfection.

Glide path is another variable. Is your glide path 1mm short of the full working length? Is it 2mm short? Because obviously our shaping files are designed to follow the glide path and we can only shape what we’ve truly secured with our hand instruments or even the new mechanical glide path instruments like PathFile.

Another variable is the shaping files themselves. What I’m talking about with the shaping files is their exact cross-section. Here’s a simple example: landed instruments work on a principle of burnishing debris into the lateral anatomy and the dentinal tubules and the fins and the cul-de-sacs; whereas a cutting instrument has sharp edges and those edges more cleanly cut dentin and we have more debris in suspension where it can be floated out of the canal in subsequent irrigation procedures. So, even the file you use will have an effect on disinfection.

Another variable would be the canal preparation. What I mean by this is – what do you subscribe to at the full working length? How big do you want to prepare the foramen? Do you keep it as small as practical or do you just needlessly overenlarge it and "cookie cutter it" to a 40 or a 45 or a 50 because you’ve read somewhere that it has to be that big in order to properly exchange irrigants? Then you should ask yourself – is that true?

Another variable that will affect disinfection are the irrigants. We have absolutely no consensus on the concentration, as an example of sodium hypochlorite. Is it 6%? Is it a 50% dilution? Or, is it a tenth of a percent? We have no consensus on what is the optimal temperature of the reagent being introduced into the shaped canal. We have no consensus or agreement on the frequency or the volume. So, you can begin to see how concentration, temperature, frequency and volume all will serve to influence our ability to disinfect a root canal system.

Of course, another variable or factor is the irrigation devices. By this I mean simply – what is the gauge of the canula? Because the gauge of the canula is going to limit the safe depth of insertion of the canula during irrigation procedures. Is it side delivery? Is it end delivery? These are all ideas. Is it stainless steel? Is it nickel titanium?

A ninth factor that would be influencing disinfection is passive irrigation versus active irrigation. Recall, all of us learned when we were in dental school to use a hand-held syringe and we would fill up the pulp chamber and make a big reservoir of reagent and our irrigant just sat there like a pool. So, it was just static and it sat there, and you know, we might run files through that reservoir and by surface tension the instruments can carry reagents sub-orifice level and through studies we can show how this works over time. The key word is ‘time’ and it was a little bit more time consuming to ensure that the reagents could be carried to the full length.

Active irrigation is a concept where we intentionally try to activate through either acoustic streaming, cavitation, microstreaming, these are all ideas to get that solution moving. As an example, if you can fracture a liquid, like a big tsunami, that’s an underwater disturbance. But, if you can activate through vibration, an intracanal reagent you can fracture a liquid and at that fracture interface bubbles are formed and the bubbles are very unstable because of heat and pressure. So, as those bubbles expand, ultimately they’ll implode and here’s what’s really cool. Every single one bubble that implodes sends out 40,000 shock waves. Those shock waves bombard the lateral anatomy and that’s what serves to cleanse deep outside the recesses of the canal where files can ever touch.

Active versus passive, very big concept. In another blog at another time I’ll identify the 10, either to market or emerging, methods that are used to activate your irrigants.

The last one, the last factor that influences disinfection would be the concept of sonics versus ultrasonics. It will require another blog to fully make the critical distinctions between these two technologies, but just understand this is a way, this is a method, sonic or ultrasonics, to activate irrigations. It’s just a question for the colleague on this blog, how do you want to activate your irrigants? If you say piezoelectric, by definition, you’re going to be using stainless steel insert tips or stainless steel canula. Do you really want to vibrate a stainless steel file, as an example, against a well-shaped canal? Now throw in that there are no straight canals... there are straighter canals, but most canals exhibit some curvature and of course many canals exhibit multiplanar curvature. Do we really want to vibrate a file around curvature and risk the chance of a ding... that would be an internal ledge, maybe an apical transportation, when we could use sonics, which by definition can vibrate a soft flexible polymer, that does not cut dentin?

So, these are the 10 factors that influence disinfection and when you look at the papers and you’re looking at the analyses, the various pieces of equipment that are being analyzed as, "Are they efficacious in their ability to disinfect?", look carefully at the methodology and think back about this blog today and the 10 factors that we said influenced disinfection, and you can begin to see how carelessly many of these variables are controlled in formal studies.