My endodontic technique: a review

I wanted to revisit endodontics in this blog as since the last posting on the subject and the comments that followed I think I’ve improved my understanding on the subject a little and wanted to share this.

Funnily enough my technique for canal preparation hasn’t changed too much but I now feel far more comfortable why I’m doing it that way and what the alternatives are.

Accessing canals

I still find accessing the canals the hardest part of the operation but there is no easy way around this. On finding canals I have made the following conclusions:

I now routinely remove posterior crowns and large fillings before root filling as without a microscope I just can’t accept the risk of perforation. Removing large amalgams has seen the biggest improvement in results.  You get no loss of orientation and the light penetrates much better. Also these are generally high risk teeth as the amalgam will often have a large base and a very sclerotic pulp which has suffered the long slow death maybe with a lovely ledermix lining to help it!

The only things I’ve found to help safely find canals (apart from scopes, loupes and lights) are endo-Z burs (non end cutting high speed) to help safely access the pulp chamber, DG-16 long stiff probes, to help find the canals and some goose neck burs (which have a long think shank and small steel burr end). Goose neck burs in particular are the best tool I’ve found for picking away at sclerosed canal entrances (which have a cloudy white colour on the pulp foor).  I have used ultrasonic tips to try to find canals but with little success, however I think that because I’ve only tried using scaling tips for this and it’s something I will look into.

The sequence I use goes: access pulp chamber, find canals with DG-16 then introduce size 10 or 15 file. If no luck study the floor of chamber closely (and radiograph) and use goose neck burr to pick away at sclerosed entrance, then DG-16 probe till you can get it to stick in the entrance,  then introduce a size 10 file, sometimes try size 20 as they are stiffer and can help you get in. Repeat until you succeed or cry.

I don’t find it useful to introduce Gates Glidden bur until you have got into the canal.  They are non end cutting burs are not designed for the job and will almost always perforate. The goose neck bur is far more controlled and precise. Also there is no point tunneling deep to find the canal as it becomes harder not easier to find the entrance, you lose the orientation of the canal, are more likely to perforate and weaken the tooth and all the while the canal entrance doesn’t get any wider. You are much better working slowly and patiently near the surface and just try to unroof the canal entrance.

I don’t know if this helps anyone as it is pretty obvious stuff and writing how to do it is far easier than doing it. The good news is that once I get into a canal I’m now 99% confident I’ll get a good root filling in it.  Also let’s be honest in 3/5 root filling the canals are little bleeding gems and easy to find it’s the exception far more than the rule which is a nightmare to find.

So once we get onto the canal we are getting to easy street and it should stay pretty easy unless we mess it up with a ledge, zip, strip perforation or debris. We have control of the canal until we lose it and therefore need to be super careful with it.

Canal preparation

Once you’re in the canal it is pretty much yours to mess up unless it’s really curved.

The first aim is to get control of the whole canal. I used to do this by simply watch winding a size 10 file down the canal. If I got stuck I’d suck air through my teeth and just keep twiddling. The problem with this is that you create a ledge where you’re stuck and this effectively looses your control of the canal which you will have to fight to get back.

In the diagram below you can see how the size 10 is stuck at the curve at the binding point. If we continue to pick and grind at this point then the file could easily create a ledge which will then be very difficult to pass. If instead we accept the binding place and start widening the area of the canal we do have control of we will reduce the effective curve of the canal and increase our chances that our size 10 file can find his way around the curve.  The other thing that will help us is to pre-curve the size 10 file slightly before it goes in.

I’m sure this is why I used to struggle to get patency of some canals previously. It could also lead to a strip perforation if the ledge kept getting bigger and then the file would start to advance and you think you’re getting down the canal. I’ve done this once and I hope never to do it again… I still loose sleep about the subsequent working length radiograph!

So now my protocol is. Size 10 watch wind in the canal as far as it will go and don’t push your luck. Then enter a size 15,20 and 25 file in turn to the same point or wherever they bind (Irrigating between to stop any debris forming). If you then return to a size 10 file you usually find it will go to length but if it doesn’t I just hold back and flare the coronal aspect of the canal and ensure there is straight-line access to the canal.

Coronal flaring

To be honest coronal flaring has caused me a little heartache. I am scared to death of it as I’ve had a couple of perforations flaring coronally and occasionally some ledges. I’ve used both Gates Glidden and orifice shapers and I conclude that both are bloody aggressive instruments to be used with extreme care.

My theory is that the reason I used to have these problems was that the canal I had entered had only been instrumented with a size 10 or 15 file. Then because the gates or orifice shapers are quite thick at the end and rigid they sit in enter the canal but might not follow the canal shape as they bore in. The result is pretty disastrous and for a while I just stopped flaring coronally and just relied on my tapered rotary files to open the orifice. The problem with this was that I was over stressing the instruments as I went to the deeper sections of the canal because I had not reduced the relative curvature of the canal. It never happened much but there was an obvious increase risk of file fracture when I was doing this.

So now I’m using this protocol to get a very careful coronal flare:

After watch winding size 10, 15, 20 and 25 in the coronal portion of the canal as described before (sometimes just to 20 if the canal is easy). Then I introduce a size 20 6% rotary file and introduce in the coronal area of the canal (the first 10mm or so). Size 20 is narrow enough to reduce the stress on the file and you have already widened to 20 hand file so it should enter ok but there will be an appreciable amount of coronal flaring already done when you’re finished. If you use the Protaper system they suggest you use the S1 file for this stage but I think any narrow 6% taper file should do the trick.

Once you have reached this stage you can far more safely introduce your Gates Glidden or orifice shaper and know it will follow the contour of the canal. I slightly prefer the orifice shapers because they keep the coronal aspect tapered and this is harder to create with gates 2 then 3 which you have to blend yourself. Always use your Gates or orifice openers in the speed reducing hand piece by the way as it is far, far more controlled and safer than in the slow handpiece. Obviously it goes without saying you need to irrigate after each file to stop debris blocking your canal.

Working length

Once you’re at this stage it should be pretty simple to get patency and measure your working length (WL). I don’t use an apex locator regularly I just don’t think they are worth the time. If you’ve measured your pre op radiograph, know the average canal length and can feel the apical constriction I just take a WL radiograph and adjust the length from that. I think apex locators are best for checking pin prick perforations when you’re working on a very sclerosed canal system.

Another problem I came across when I started working was that the digital radiographs around a rubber dam can be pretty tricky. You need the small film to have any chance and use bisecting angle technique but at the premolar region it can still be super tricky. I’ve had to remove the dam a couple of times to get a decent picture then replace and re irrigate. I know it’s not perfect but I’d rather do this than continue without a good view of the file at the apex.

Glide path

The glide path creation is essential for using rotary or greater taper instruments. It creates enough space so that the rotary files can work without stress and there tips can follow the path created for them so they stay on course. I typically prepare my glide path to size 20 but more recently to size 25. To do this I watch wind size 10 and 15 files to the working length then use balance force technique to get the size 20 and 25 to length.  This is usually pretty quick and easy once you have done the coronal flaring and is well worth the 2 mins it takes.

Desired shape of the canal

There are two shapes you can aim for in canal preparation and I never used to understand that which was why I was so unsure what master apical file (MAF) size I should go to.

The technique I was taught at university is the apical control zone. Here you prepare the canal to working length with greater taper files (basically anything crown down not 2% taper) with used to use GT hand files. Then once you have this taper you would introduce 2% NITI hand files from 20 to working length until you feel resistance and can cut the seat above the apical constriction.

I don’t really know as I’ve not read up on this enough but I guess the advantages of this technique are that you can guarantee you have removed any necrotic dentine in the critical apical region and that your canal has been prepared wide enough (wider than the apical constriction). The apical area having a large MAF is advantageous because you will get better irrigation in the apical delta area which is hardest to clean, you may also cut away some of these small delta canals. You have also created a seat to obturate to which should in theory stop overfill.

The continuous taper is a lot easier to achieve as you can simply introduce your tapered files to working length and preparation is complete. The difficulty is knowing how wide you should prepare the canal to. Should it end at size 25(6%) file or 40(6%) or even 8% taper? This is why Bio race came up with the below diagram which recommends a size to end at. Protaper also take the decision out of your hands by calling the files s F1 or F2 which you should finish to (anyone know there tip sizes and tapers?).

None of these are very scientific ways to gauge the MAF and for that reason the apical control zone could be considered a better system. It all depends on your view point.

I’m not sure how much it matters. I always prepare using a continuous taper technique and finish at a size 25(6%) file for narrow canals, size 30(6%) for most canals and 40(6%) for large canals like central incisors. I think that it is likely that with the larger tapers like 6% you can irrigate these apical areas well with a small MAF and thus disinfect the canal sufficiently.

There are a lot of advantages to the continuous taper shape too. It is easier and quicker to prepare but also allows you to use match points for obturation which would not fit if you prepare an apical control preparation (in which case you need a matching 2 % taper master point). There is also a natural resistance to the tapered shape of the canal this means that if you have prepared past the working length you may still get a reasonable obturation. You can insert the master match point radiograph how far it is out the apex then trim the point till it fits to working length. This is not the ideal technique but is much better than obliterating the apical constriction entirely trying to get an apical seat with a size 50 hand file.

At the end of the day it’s your choice how you prepare the canal. Clearly both techniques work and have advantages. Personally I think continuous taper is far easier to prepare consistently and with it being so much quicker to prepare and obturate it is the technique I prefer routinely.

Preparing the canal taper

Again there are 3 main techniques you can use to get from glide path to continuous taper:

1)      Sep back

2)      Crown down (small to large)

3)      Crown down (large to small)

The step back method is pretty antiquated now with the advent of NITI files and the subsequent development of greater taper files so I’m not going to discuss it further here. All you really need to know is that it used to used increasingly large stainless steel files to prepare the canal and that as the size of the file increased you would move further coronally from the apex in effect creating a taper.

Crown down (small to large): is a pretty simple technique in which you have found the working length and created a glide path to size 25(2%) you then introduce your rotary files the smallest first. I typically take the 20 (6%() file and slowly introduce it to working length. It is important to remove the file a few times on the way down to clean the flutes and irrigate the canal to prevent debris or ledging but it is usually straightforward to get the file to length. The only place you need to be very careful is near the desired working length where the file can tug through the apex and blow out your apical constriction. I find working very slowly with a firm grip on the handpiece (on 300rpm) helps stop this happening.

You then work up the file sizes to your desired MAF with each file going to working length in turn.  This could be F1 for protaper or 25(6%) for M2 K3 or the designated size for bio race.  It‘s up to you where you finish but I like to typically end on 30 (6%) as I’ve said earlier. Between each file you should irrigate the canal and regain patency with the size 10 file to make sure there is no debris build up

One bit of advice I once got was that if the apical canal is not infected (i.e. the pulp had irreversible pulpitis which is likely to not have infected the apical region) you can prepare to a narrower MAF because it is less critical to get the irrigant to the apex than if you have an apical periodontits and clear infection in the apex area.  Remember a smaller MAF means you have removed less tooth tissue and there is less chance of a fracture later on in the tooth’s life. Alas I have no evidence for this….

Crown down (large to small): is just another way to do the same thing. The basic idea is that after you have created your glide path you introduce a large MAF tapered file. You stop when you reach resistance then continue with a smaller file in sequence until you reach the working length. So for instance with protaper you may start with a size 40 (6%) insert it until you feel resistance then back out. Clean and irrigate the canal and recapitulate working length with a size 10 file. Then you use a 35 (6%) file and go as far as you can with that. You continue this sequence until you are at the working length desired and then work up the files to get the MAF you want to working length.

I personally prefer the small to large technique as I find the whole “wait till you feel resistance thing” slightly unclear and likely to fracture files. I know the theory with “large to small” is that because you are not taking the files to length until you have widened the canal more coronally you are reducing stress on them. I’m sure that is true but at the same time I think you have already flared the coronal region of the canal and have a glide path. Surely there is less stress inserting a small file first than a large one?? You pick your own side to follow, I’m sure there is not much in it I just happen to prefer doing it small to large and as I’ve not had any file fractures so I’m going to keep it up!

Some file systems are designed for the crown down small to large method e.g. M2, Protaper, Biorace. Others are designed for crown down large to small e.g. Profile, Trinity and k3 files. As always it’s better to use the correct technique with the correct system and follow manufacturer’s instructions. So if you want to work a certain way then make sure you buy the right files for you.

Irrigation

I’m afraid I can’t add much information about irrigation because I’m still trying to work out what the best sequence should be. At the moment I just use copious hypochlorite and dry thoroughly before sealing.

I have heard that using EDTA to prepare the dentine and chlorhexidine 2% to irrigate the canal may improve the seal/ disinfection you get but at present I’m just looking into them.

Obturation

There are 5 main obturation techniques I want to talk about and as you will see I’ve used the manufacturers names for some (mainly because I don’t know the scientific names):

1)      Cold lateral condensation

2)      Warm vertical condensation (match point)

3)      Thermafil

4)      Thermal compaction then backfill with obtura

5)      Microseal

Cold lateral condensation: is the gold standard technique. You basically match you MAF with a 2% master point and radiograph to make sure it to the correct length. Then coat the canal with sealer and place a finger spreader to 2mm short of working length. Then place accessory cones (coated with sealer) that match the space left by the finger spreader. Continue until the canal is fully filled and vertically compact the GP.

This technique is very time and technique demanding and often you get thready fills because you have not  managed to fully seat the accessory cones. However if done well the technique manages to compact all but the very tight fitting last 2mm of the canal and the pressure should press some sealer into the lateral canals if present.

Warm vertical condensation: This technique only really works for continuous taper preparations where you can use a match point GP cone to exactly fill the space you prepared in the canal. The aim is insert the cone to WL at which point you should notice some tug back which lets you know you’re not going through the apical constriction.

The other way to do this is to use a 6% tapered feather tipped cone (if you used a 6% taper) and insert it until you feel the tug back of a well fitting cone. You can then measure the length where you feel this tug back. Complete the equation:

length of tip till tugback- working length = amount you need to trim from tip of feather cone

Once you have a well fitting cone you can coat it in sealer and vertically condense with a hot glick instrument and the job is done. The technique gives a good thick fill, the sealer may get slightly compressed into lateral canals but the compaction is worse than lateral condensation especially in the apical region and you are unlikely to force sealer into the lateral canals.  I think of all the techniques this is the least technique sensitive and gives a decent predictable result.

Thermal compaction then backfill with obtura: With this technique you fill the canal as with the warm vertical technique using a matched GP point. Before that though you need to select a system B (or similar) plugger and insert it into the canal. You should mark where the plugger binds and this must not be within 5 mm of the WL, this is your reference point . You can then seal and insert your matched GP point.

Next you cut the end off your matched GP point line the plugger up with its centre heat up to 200 C and insert 3-4 mms from the reference point. Deactivate the heat and continue apical pressure until you are with 1-2mm of reference point and maintain apical pressure for 10 seconds.

Then quickly reactivate the plugger push it to the reference point and immediately withdraw (this is the tricky bit). Once you have done this you can either prepare for a post or simply back fill with obtura or other thermal GP gun.

I like this technique because it has many of the advantages that the vertical condensation technique has but because you are heating and compacting the GP more thoroughly you are bound to get better penetration into lateral canals.  The technique is also good for creating post channels. On the downside the kit is pretty expensive and despite the better compaction you are not really heating the very apical area of the GP because if you did it may extrude. I’d suggest this means you will be getting less penetration of lateral canals in this critical area than you would get with say a cold lateral condensation technique.

NB. You could also use a similar technique to this replacing the system B thermal compactor with a thermomechanical device like a pacmac or gutta condensor.

Thermafil: is a warm GP technique which uses an oven to heat the GP around a plastic carrier. You choose a size matched Thermafil  carrier and insert it into the canal you have prepared. You should place a rubber stop on the carrier when you are 1mm from the WL. You then heat up the carrier in the oven. Add a very small amount of sealer around the coronal aspect of the canal and then insert the carrier to the rubber stop. You should then leave in place for 1 minute to allow the GP to set before cutting off the plastic carrier.

Using this technique allows the warm GP to enter the lateral canals easily and it is a very quick technique. However the technique has some major drawbacks. The worst being that you have very little control of where the GP ends up and it is likely to extrude out of the canal, I suspect burn the periapical tissues and be uncomfortable for the patient.  You also get left with a plastic carrier in your canal which is very difficult to remove and restricts Thermafil to cases that don’t require post preparation.

Microseal: I must confess I don’t know a huge amount about this technique but I wanted to include it for completeness. The basic idea is that you combine the best aspects of the cold lateral and Thermafil techniques. It seems like a pretty tricky technique but maybe that is just because I haven’t tried it yet.

The idea is that you place a 2% tapered match cone into the canal and then laterally condense with a finger spreader at 2mm short of the WL. You then place the microseal compactor which is like a fluted rotary file and rotate to establish its space. You then dip the compactor so it is covered in warm GP and insert again. Hold in place for a few seconds then wind out the compactor slowly leaving the warm GP in place. This GP can then be vertically compacted and hopefully pushed into the lateral canals.

Disclaimer

Written by Chris O’Connor for the Inci-Dental Blog

http://chrisoconnorblog.com

I hope you’ve enjoyed the above waffle/ article. It has been written to help discuss some of my thoughts on endodontics over the past few years and hopefully let others benefit from what I have learned. The opinions stated are those of my own at the time of writing and are liable to change. You will notice there are no references in this article and that is because it has only been researched by what I have read, seen on courses and experienced and as such should be treated with healthy suspicion.

I hope you have found the information useful please feel free to share it widely if you have. That would be great. I will attempt to add and update the techniques as I read on and maybe get some clinical pictures involved so check the blog for updates.

Keep rocking the post to the core

Chris