I’ve been wanting to write this post for a while but have been collecting the information together. Basically I was watching a good friend of mine performing a molor root canal treatment and i noticed that he was preparing each canal to an ISO size 20 or size 25 with his rotary endodontic system then filling with the thermerfill system. Good results achieved, correct working length, rubber dam etc. brilliant?

The thing was that I thought that you had to prepare up to at least size 30 at the apex.  I’d heard that size 25 was the average canal width and to make sure you had cleared the necrotic pulp you should go a bit wider. We discussed this and both realised we didin’t know what size we should be preparing too. That was about 3 weeks ago and i’ve been tracking down the answer since.

I suppose the short answer is that there is no correct size. Each canal should be gauged individually with a non tapered nickel titanium file. That was what we were taught in dental school and it still holds true now. How often is that the case? you go all round the houses and realise what you first learnt is correct!

When I did look at the evidence for the recommended width of apical preparation, I was amazed how wide they were. The data comes from Lief Tronstad studies from  1977. I’ve found a really neat table of the recommended minium apical preparartion (click on image below) . The values given in Tronstad’s book  “Clinical Endodontics” are actually slightly larger on average (but they reference  his study in this guide)

endodontics

When i look at these values, it all just doesn’t add up. How can the match point system i’m currently using be right? I know there are a hundred rotary systems out there which will make discussion difficult but we use the M2 system and my technique is.

1) Isolate with dam, Access, gain patency with size 10-15 file. coronal flare with Gates gliddens. Use apex locator and radiograph to confirm WL with size 15 file. prepare glide path with hand size 20 file.

2) Use rotary file size 20 6% taper and get to WL

3) Move up systematically to size 30 6% if possible and up to 40 6% if it feels too loose. If still too loose then resort to hand files to apical guage

4) Check match point fits to length. check with master point radiograph

5) Obturate with sealant (tuboseal). fit at least 1 accessory point as best I can and more if possible using cold lateral

6) Apply heat and condense as much as possible

I realise that i’m leaving myself very open to critism here, which i don’t mind at all. I’m not saying this is perfect but i have been getting what i would consider pretty good results and dare i say it better than some practitioners out there.

My issues with the technique are this:

1) I’m not actually guaging the apical stop properly in this way. surely once I’ve got to WL with my rotary, i should go back with a non tapered NITI file and get up to a width closer to those above.

2) The problem with matched points is that they are so much more difficult to compress than ISO master points (due to thickness). This makes cold lateral condensation so much harder and i often feel I’m not getting in enough accessory points down. I’ve been thinking for some time that you would be much better to melt down the matched point with a System B to create an apical stop then back fill with a thermal GP.

Also I sometimes wonder if matched points aren’t a short cut to a long delay. Are they much better than a silver point if we are not condensing them sufficiently with either thermal or lateral condensation. Yes they can look pretty good on an xray but are we really obturating a canal.

The barriers for changing my technique are:

1) Gauging requires a lot of files as you have to try each file in turn to establish when you get an apical stop your happy with. Not a problem when files weren’t disposable but It’ll cost a fortune to do this  on top of the cost of rotary files!

2) If your gauging after you have used your rotary system then the matched point will no longer match. Gutted! The matched points saves you so much time and despite my reservations practically, that is going to make things tricky in practice.

I’m sure there is a way around it though, even if it’s just to accept the change. Accept that there are no short cuts and spend a bit longer. I’m just a bit confused what the best way forward is but I’m determined to work it out. Last week I booked myself on a one day endodontic study day at the Academy Of Clinical Excellence which is in July. In the mean time I’m reading Tronstads excellent book mentioned above and Pathways Of The pulp.

I’d love to hear how other people are completing there root fillings, especially if they are using a rotary system. How do you feel about using matched points and what size are you preparing to?

Finally I would like to say that the above table was from FKG’s Biorace rotary system handbook. That i would like to recommend the following site which gives some good information on apical gauging:

http://www.healthmantra.com/rotary/endo-truth.shendo-booktml

I would also like to recommend the book “Clinical Endodontics” by Tronstad which is really excellent and was new to me.

Also a huge thank you to Dr Whitworth, Newcastle university’s clinical consultant in endodontics for his excellent teaching and for sparing some of his valuable time to point me in the right direction for this blog.

Looking forward to your comments as always

Chris

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