Following on from Part 1 on access cavities and locating root canals, part 2 of our endodontics revision series takes us through the steps once we’ve found the root canals!
Preparing the root canals. 2>
Okay so you have found all your root canals, you have the perfect access cavity, you have straight line access to the first curve of the canal, right? Of course we have, what could go wrong?!
Shaping coronal 2/3rds
Once you’ve found the canals, you don’t want to lose them! We’ll need to open up the orifice so you can repeatedly and reliably find them again and again.
First, pop a size 10K file in as far as it will go and shape this area by circumferential filing (That’s just pulling it up and down around the wall of the canal). Remember to keep irrigating the canals to prevent anything getting stuck in the root canals. Progress to a size 15K file, again with circumferential filing to open up the canal orifice.
To further open the root canal, you can use gates gliddens drill sequentially. Some practitioners start with smaller GG heads and progressively increase the size. Alternatively, you can start big, and create more space for smaller heads to go further along the canal.
Reaching Working Length
Now you’re happy that you’ve sufficiently flared the canal orifices and your files start to get sucked into the canals without you spending hours on end finding each entrance, you can start negotiating down to the estimated working length.
Start with the size 10 K file with a watch-winding action (3/4 turn clockwise, 1/4 turn anticlockwise, pull, repeat), remember to pull your file out and clear the flutes, irrigate the canal, to stop anything getting stuck. Progress your way to a size 15 to the working length.
You want to get at least a size 15 to the estimated working length, this is because a size 10 may not be picked up on the check X-ray. In teeth with several root canals, you can use different sizes of K files, OR you can use different types of files like a Hedstrom file, just so you can differentiate between the two on the radiograph.
Take a check x-ray. Check that you are in the right canals, and how close/far you are from the apex. After you’ve taken your x-rays with the file in situ, move the rubber stop to your reference point, take the file out and measure it again. If you are long on the x-ray by 2mm, take 2mm of this measurement, if you are short, add to it. This is your final working length
The aim of shaping in the final third is to create a 6-8% taper with a size 25 at the apex which you can obturate against. Remember that standard K-files have a 2% taper, which is why you use a step-back technique to create the intended 6-8%. Some hand files, like Pro-Taper, or rotary endo systems have files that create the 6% taper for us, which makes things easier, but obviously these aren’t readily available in dental school!
What you are looking for is that the size 25 file binds at the apex only, with tug back just at the end. The file should drop passively to working length, if it is difficult to get down to working length then you need to do more shaping.
To do the step-back technique, once you have got to this point, just pick up the next size K-file, take 1mm off the length, and file until you get the same tugback. then repeat until the largest file isn’t binding anymore.
Now it’s time for the root filling. You have a check x-ray to say you have prepared the root to the right working length, you want to fill it up with Gutta Percha.
We will talk about cold lateral condensation, which is the gold standard in predictability and prognosis. Sure, there are other systems available, most use heat, but these aren’t the ones taught at undergraduate level.
Your master cone should drop effortlessly to length, bob a bit of ZoE sealer on the final third of the GP point and push it into the canal. Keep pressure on for at least 10 seconds so that it doesn’t “bounce” back.
Using the thinnest finger spreader, pop this to working length and keep pressure on for another 10 seconds to deform the original GP point. You DON’T need to waggle the finger spreader from side to side to get the “lateral condensation”. The apical force in the tapered canal causes displacement forces laterally, this does the condensing for us.
Once you are satisfied you have enough GP in the apical third, you can start obturating with larger accessory points in the coronal 2/3rds.
At the end, remember to cut the GP RIGHT BACK into the canal system. GP has no place in the pulp chamber and just interferes with the final restoration!
This article was put together using tips given by Ian Cross BDS MDentSci MRDRCS, Specialist Endodontist and Prosthodontist of Bramhope Dental Clinic.