Endodontic Microbes. Who needs them?

OK so a patient has come to see you complaining of toothache. It’s root canal time. You open up the lower right first molar and find a necrotic pulp. You’ve isolated well and done a nice endodontic preparation. Length is good and you’re happy with the sizes of your apical preps. You’ve been irrigating with plenty of sodium hypochlorite and used a final rinse of EDTA. Job done right?

Think again. In the vast majority of teeth, canals are not round, and as such there are going to be vast areas that are still harbouring debris and microbes. Just take a look at some of the microCT produced by Paque et al after preparation with rotary Ni Ti (Paque at al. 2010). It’s quite clear in these images that a good proportion of the original canal space remains untouched by our instruments.

So, hopefully, our irrigant is managing to get into these nooks and crannies? Well it will, but even after irrigation, there is still going to be significant debris from preparation (mushed up dentine, bacteria, necrotic pulp remnants) hiding away in fins, apical delta and especially in isthmuses.

I recommend you check out the work by Burleson and colleagues for some nice images on what can be left behind (Burleson et al. 2007). These guys conducted a randomised controlled trial (nice and high on the level of evidence) and compared preparation and irrigation alone, or with the addition of 1min of passive ultrasonic irrigation (PUI). They used the mesial roots of infected lower molars and then extracted the teeth to examine how much debris was left behind. Check out the table below to see the results on cleanliness of the canals at various levels from the apex. The isthmus especially is full of debris without PUI.

Cleanliness of Canals at various levels from the apex. Pay special attention to the number in the isthmus.

Interesting right? It’s even better when you see the images in their article and realise just how much is being left behind when you only rely on irrigation.

I know what you’re thinking though. It’s bacteria that we’re concerned about, not debris. Well, Burleson’s colleagues thought of this, and conducted a separate study, I assume on the same teeth, using microbiological sampling to see what they could find (Carver et al. 2010). They concluded that PUI resulted in a significant reduction in colony forming units and positive cultures. In fact PUI was, “7 times more likely to yield a negative culture”.

So, it seems that PUI is something worth doing, and it’s certainly part of my routine. If you haven’t heard of it, I’ll explain what it is. PUI is simply the placement of an ultrasonically activated file into the canal filled with irrigant. There is some debate over how it works exactly, but acoustic streaming seems to be the key. This basically means moving the solution around so that fresh sodium hypochlorite gets into areas that needles won’t push it. The important point here is that the ultasonic file has to be loose in the canal. Touch the canal wall and acoustic streaming stops.

Personally, I use the Irrisafe from VDW because it’s easy. Just screw it on to your US unit and place it in the canal. The irrisafe is “smooth” i.e. it doesn’t have the sharp cutting edges that files do, so it is safer in the canal (Hence the name – smart huh). Here are my three keys to PUI:

1.     Use a low power setting as recommended by the manufacturer. You risk fracturing the ultrasonic file otherwise;

2.     Keep the file loose in the canal and don’t push it too deep;

3.     Replenish your sodium hypochlorite as you go.

The Irrisafe. Attach it to your ultrasonic and kill more bugs.

Acoustic Streaming in Action

I generally have my DA using a syringe to supply sodium hypochlorite and suction while I run the ultrasonic in the canals. If you don’t have a stand alone ultrasonic unit where you can easily control the power, then I wouldn’t risk using an ultrasonic file. You can achieve the same result by just holding a normal scalar tip against a size 10 stainless steel file. This is obviously much cheaper as well. Just be careful not to put the file too deep into the canal or you might actually damage the canal walls and ruin your nice preparation.

There are other methods for activating irrigant such as the Endoactivator and the Endovac. These work slightly differently. The Endoactivator is a sonic machine and has disposible polymer inserts. It seems very safe to me, but there isn’t much in the literature indicating that it is better at killing bugs than other methods (Huffaker at al. 2010), and it is not as effective as PUI at removing calcium hydroxide from canals (Wiseman et al. 2010).

This is just part of the Endovac system

The Endovac shows promise. It relies on a vacuum to remove irrigant that is being supplied by a needle deep in the canal. That means there is no positive pressure. One clinical trial showed that post-op pain was reduced after using the Endovac compared to needle irrigation (Gondim et al 2010). It is a bit of a contraption though and I have enough machines clogging up my surgery. I am waiting to see some studies comparing PUI directly to Endovac and Endoactivator before I give up my proven method of cleaning the canals.

Next time you finish a prep, grab your ultrasonic and give the canal a bit of a shake up. It’s impressive to see how much more debris you can get out when you irrigate again.

References:

BURLESON A, NUSSTEIN J, READER A, BECK M. 2007. The in vivo evaluation of hand/rotary/ultrasound instrumentation in necrotic, human mandibular molars. J Endod. 33: 782-787

GONDIM E, SETZER F, BERTELLI C, KIM S. 2010. Postoperative Pain after the Application of Two Different Irrigation Devices in a Prospective Randomized Clinical Trial. J Endod. 36:1295–1301

HUFFAKER S, SAFAVI K, SPANGBERG L, KAUFMAN B. 2010. Influence of a Passive Sonic Irrigation System on the Elimination of Bacteria from Root Canal Systems: A Clinical Study. J Endod. 36:1315–1318

PAQUE F, BALMER M, ATTIN T, PETERS OA. 2010. Preparation of oval-shaped root canals in mandibular molars using nickel-titanium rotary instruments: a micro-computed tomography study. J Endod. 36(4): 703-7

WISEMAN A, COX C, PARANJPE A, FLAKE N, COHENCA N, JOHNSON J. 2011.  Efficacy of Sonic and Ultrasonic Activation for Removal of Calcium Hydroxide from Mesial Canals. J Endod. 37:235– 238