Do they meet? All about canal confluences

Watch out watch out, there’s a confluence about

The confluence of the Taw and the Torridge must bring deep water and strong currents 

(Walking away, Simon armitage)

The confluence of two suggested a deeper and darker aberration 

(Emperor of all Maladies, Siddhartha Mukherjee)

Is not every meanest day the confluence of two eternities

(The French revolution, Thomas Carlyle)

There’s something about confluences, something to beware of. The meeting of two entities often stirs up a sense of foreboding, apprehension, something not quite desired. As in literature, so in endodontics. Confluences look so innocuous and can look so satisfying on the final PA when properly treated, but handled incorrectly they may lead you to “deep water”.

Why do confluences matter?

What we are talking about is canal confluences, where two canals in one root meet before reaching the apical foramen, so they share a single apical canal and foramen.

Browse the Root canal anatomy project, particularly the mandibular and maxillary first molars. It’s surprising how often two separate canals do not always lead to two separate portals of exit (POEs) from the root. Looking at Vertucci’s classic 1984 study of root canal anatomy and his classification of canal configurations where type II represents a confluence of 2 canals into 1 canal (2-1), we can see this occurs in:

Vertucci’s classification of root canal morphology (from Vertucci 2005)

Furthermore, the more canals in one root, the more likely it is there will be a confluence (Furri 2008)

Cleared teeth with multiple confluent canals

So, confluent canal morphology is quite common and you should expect to meet it regularly in everyday practice. At some time, most dentists will have prepared two canals, only to find they were confluent when they tried in their GP. Or, perhaps you remember trying to negotiate a mesial canal in a mandibular first molar, only to find there is an apparent blockage or a “hang up” part way down the canal, at a depth of about 17mm.

Unfortunately, it’s not a good idea to reach the try in of your masterpoints and suddenly think “Oooo ….. that’s interesting those two canals look like they meet before the end of the root”. You really should identify a confluent pair of canals as early as you can in your preparation, preferably before you shape them because:

  1. Where the canals meet there is likely to be a sudden change of direction which may cause an impediment to further progress when you continue to negotiate.
  2. The sudden change of direction, where the canals meet, will cause stress on the file and risk instrument fracture. It would be useful to know if and where this is going to happen.
  3. One of those confluent canals is likely to be the straighter (more direct) canal. Shouldn’t you know which one it is before you start?
  4. Do you really want to go to the trouble and stress of preparing the full length of the second canal, right up to the apex, when you could have just prepared the nice easy coronal non-confluent portion only?
  5. If you have negotiated one of the canals and prepared the common apical portion, do you really want to approach that same common portion again from a different direction and risk further enlargement, such that your master cone wont fit as snugly as it otherwise would have?
  6. Do you really want to fully prepare that common apical portion twice, enlarge it more than you otherwise would and thus weaken the root?
  7. Do you want to have two goes at preparing close to the apical foramen and double the risk tearing it?
  8. Why risk a strip perforation by preparing the root more than you otherwise would have done?

So, how do I identify confluent canals?

First, know your anatomy (see anatomy, above). Study those teeth on the tooth anatomy project. If you suspect a pair of canals may be confluent you need to confirm whether they are before you proceed with shaping.

Second, look at the small SS files you negotiated the canals with. When you withdraw them, they will retain an impression of the canal shape, albeit slightly straightened. Does it look like they bend towards each other to meet?

Third, what do you feel as you negotiate? Does there seem to be a “catch” or a ledge at the level a confluence is likely to be present? Is there a springiness in the file as you slide it past a tight bucco-lingual curve.

Fourth, use this little procedure to formally check for confluence and identify the exact level at which it occurs.

Impression of K file left in GP cone
  1. Prepare the canal that is (or feels) the straightest to the length indicated by your apex locator (the primary canal). This is most likely to be the mesiolingual of a mandibular molar or the mesiobuccal of an maxillary molar.
  2. Negotiate the second canal with a small (10K) file and check the length.
  3. Fit a master cone to length in the first canal, then pass a 10K file along the second canal. If they are confluent, you will probably feel yourself hit the GP shy of full length, rather than pass straight along the canal. Sometimes you will feel the file rub past the GP, leaving a groove in it. Sometimes you can see file moving the GP cone. Remove the file and then the cone.
  4. Look at the cone, preferably under magnification. If the canals are confluent, you will see either a tiny hole where they canals meet or possibly a groove/scratch where the file scraped along the GP.Impression of second file tip on GP in primary canalIf they do not meet, the GP will come out and still look new or with just a few scuffs from abrasion against the canal wall.
  5. Bend the GP cone where the hole is or where the scratches start. Measure the distance from there to the apical end of the cone.
  6. Subtract this from the length you originally measured for the second canal.
  7. Shape the second canal to this length i.e. up to the confluence.

Fifth, you can identify the confluence with an apex locator. Place a file to length in the first canal then advance a file along the second canal and take an apex locator reading. Remove the first file and repeat the reading in the second canal. You have a confluence if the measurement is longer this time, particularly if on the first pass, the reading suddenly jumped to length as the second file “shorted” onto the file already at length in the first canal.

Sixth, CBCT will demonstrate confluences pre-treatment.

My preference, if my suspicions have been aroused by anatomy knowledge, the impression left on the withdrawn hand files or the tactile sensation within the canal, is to use the GP in primary canal technique.

Obturation needs to respect the confluence. If you try to fully obturate one canal first, you risk partially blocking the second canal with set sealer, particularly with warm compaction techniques. In this case you should apply sealer and place the primary GP master cone in the primary canal, then apply sealer and place the GP master cone in the confluent canal. Then, downpack each of them.

So, don’t ignore confluent canals, they are actually quite easy to detect and deal with and, by doing so, you will reduce your chances of all sorts of mishaps. If you are interested, further information is available from this excellent article (Castellucci’s confluence article).


Castellucci, A., 2001, Two canals in a single root: clinical and practical considerations, Endodontic Practice, pp. 17-23. Download from here

Furri, M., 2008, Differences in the confluence of mesial canals in mandibular molar teeth with three or four root canals, International endodontic journal, 41(9), pp. 777-80.

Vertucci, F.J., 1984, Root canal anatomy of the human permanent teeth, Oral Surg Oral Med Oral Pathol, 58(5), pp. 589-99.

Vertucci, F.J., 2005, Root canal morphology and its relationship to endodontic procedures, Endodontic Topics, 10(1), pp. 3-29.

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