How many roots and root canals does your tooth have?

- What are the usual numbers? - by tooth type.  |  Root and canal variations.  |  Methods dentist use to identify additional root canals.

Roots, root canals and root canal treatment.

The number of roots and root canals that a tooth has is an important detail when it comes to performing its endodontic therapy because so many factors associated with this work are influenced by this tally.

For example, the level of difficulty of the tooth's procedure, how long or how many visits it will take to complete and even how much it will cost are all substantially influenced by the number of both.

How many roots and root canals do teeth have?

For teeth in general, there's no set number of either. Instead it varies by way of tooth type.

Our table below lists what your dentist generally expects to find. But variation is a key theme when it comes to these details.

What your dentist actually discovers, and therefore must ultimately treat when performing your endodontic therapy, can vary, even substantially, from what's stated below.

Kind of Tooth # of Roots # of Root Canals
Upper Incisors 1 1
Upper Canines 1 1
Upper 1st Premolars 2 2
Upper 2nd Premolars 1 or 2 1 or 2
Upper Molars 3 3 or more
Lower Incisors 1 1
Lower Canines 1 1
Lower Premolars 1 1
Lower Molars 2 3 or more

Your dentist must assume that every tooth displays variation.

As stated above, while the numbers in our table are common and usual, the bottom line is that when performing your root canal work your dentist must look for what's expected, and then expect to find variation.

That's because a tooth's root canal therapy won't be successful unless the dentist treats the tooth's entire root canal system. Any aspect that's overlooked can be expected to result in treatment failure.

Forms of anatomical variation your dentist is likely to discover.
  • Additional tooth roots - While its always possible that your tooth has a greater number of roots than most teeth of its type, as compared to variations in a tooth's number of root canals, this type of deviation is less common.

    A primary exception to this rule would be upper premolars where from a statistical standpoint the presence of either just one or two roots runs practically neck and neck. (Al-Ghananeem 2014, Chaparro 1999) [page references]

  • Fused tooth roots - More common than the occurrence of extra roots is the issue of multi-rooted teeth (premolars, molars) having fused roots.

    This issue alone doesn't necessarily increase the complexity of a root canal case. But it's not uncommon that teeth with fused roots display wider variation in root canal number and configuration, which would tend to do so. (Ahmad 2016)

  • Additional root canals - Discovering a tooth that has a greater number of canals than what's listed in our table above isn't uncommon at all.

    Certain types of teeth (lower incisors, upper premolars, molars) and even specific tooth roots (mesiobuccal roots of upper first molars, distal roots of lower 1st molars) are well known for having the potential to have additional canals.

Ways a dentist identifies all of a tooth's roots and root canals.

If the variations in number of roots and canals mentioned above are so common, and so important for the dentist performing the tooth's endodontic treatment to know about, then how do they discover them all?

The three primary ways they do so are:


a) Taking x-rays.

Long before your dentist ever begins performing your tooth's actual root canal work, they'll have taken dental x-rays. And these pictures can give them a substantial amount of information about the number of roots and root canals that your tooth has.

1) Two-dimensional pictures.

The common type of x-ray that a general dentist takes, and probably the only type you've ever seen, is like the one shown in our graphic. It's a flat picture of your three-dimensional tooth.

What your dentist can learn from this type of film.

An x-ray like the one shown below can reveal a lot of information. Here are some of the details a dentist would notice: (The tooth is a lower first molar.)

X-ray of a lower first molar.
  • Running down the length of root "B" you can see the clear outline of two root canals.

    Actually, that's to be expected. This root (the mesial root) of a lower 1st molar usually does have two canals.

  • In contrast to root "B," when you look at root "A" you just see one canal. And actually, for this root (the distal root) that's the most common form.
  • We'll also point out that from this picture it's clear that this tooth has two distinct roots (as opposed to them being fused together), which once again is the most common form for this type of tooth.

So, just from the simple act of taking a radiograph, and long before they have taken any instruments to your tooth at all, it's possible for them to have quite a bit of information about it. And with this particular tooth, so far everything seems common about its roots and canals.

What your dentist can't always tell from a two-dimensional x-ray.

As informative as traditional x-rays can be, there are times when what they show can be difficult to interpret. To give you some insight into what your dentist must deal with, here are some unclear points about this same radiograph.

    X-ray of a lower first molar.
  • Root "B"'s two canals are obvious at the level of the arrow. But notice how down around the tooth's tip they aren't so clear?

    What's the real story, are there two full-length canals or do they possibly merge into a single one down low?

    While the dentist won't know for sure until they start to perform this tooth's work, it's most likely that due to the angle at which this film was taken that one canal is simply hidden behind the other, thus giving the appearance of one.

  • To this same point, root "A" looks like it just has a single canal but its not uncommon for a first molar's distal root to have two.

    Once again, the angle at which this picture was taken may have resulted in overlapping the two canals so they just look like one.

    But as opposed to root "B" where the dentist always knew to look for two canals, on root "A," despite that they have no warning, the dentist must keep an eye out for a second canal when they perform their work, just in case one exists.

2) Three-dimensional radiographs.

Over the past decade the use of Cone Beam Computed Tomography (CBCT) has become more and more common in dentistry.

With this type of imaging, the dentist can create a 3D representation of your tooth that can answer many of the uncertainties about roots and canals posed above.

Due to the expense of these units however, most general practitioners don't have CBCT capability. It's use with root canal work is typically limited to the offices of endodontists (root canal specialists).

b) Searching for root canals via visual inspection.

Once your dentist has begun the process of performing your tooth's endodontic therapy, visual inspection is a vitally important way by which they determine how many root canals it has.

Pulpal floor of lower first molar.

The pulpal floor of a lower first molar.

This picture shows the inside of a lower first molar (the same type of tooth as in our example above). This is what the dentist sees after creating the access cavity through which they'll perform their work.

  • What you see is the floor of the tooth's pulp chamber (its "pulpal floor").
  • The openings you see (the two faint lines inside the tooth) are literally the openings (orifices) of each of the tooth's root canals where they connect with the tooth's pulp chamber.

When examining this picture, a dentist would notice:

  • Just like described above, the mesial root (which lies underneath the portion of the tooth at the top of our picture) appears to have two separate canals. (You can see the two small round openings at each end of the faint dark line).
  • And just like above but in contrast to the mesial root, the distal root (which lies underneath the portion of the tooth at the bottom of our picture) seems to have just one broad slit-like canal.

    The dentist will need to investigate further to confirm that this is in fact just a single canal.

Using a surgical microscope during root canal treatment.

An endodontist using an operating microscope.

Inspection via microscope.

Visual inspection is such an important discovery tool that it's common for root canal specialist to use a surgical microscope when they evaluate a tooth's pulpal floor.

An example from research.

Stropko (1999) evaluated the pulpal floor of upper first molars in the region of their mesiobuccal root (a root that frequently has a very minute second canal). They did this first by normal visual inspection and then again with the aid of an operating microscope.

Initially 73% of teeth were identified as having a second canal in this root. However, with the aid of a microscope it was determined that a second canal was actually present in 93% of cases.

This type of discovery is important because missing (not treating) a canal, even one this small, can be expected to lead to root canal failure. In fact, a study by Hoen [2002] suggests that 42% of failed cases involve missed canals.

c) Tactile discovery of root canals during your procedure.

Using a root canal file inside a tooth.

Working a root canal file inside a tooth.

Another important way by which a tooth's total number of root canals is ultimately ascertained is by tactile discovery during the process of performing its endodontic work.

Dentists clean and shape the nerve space within a tooth via the use of root canal files.

And the paths these files tend to follow as they are worked up and down inside the tooth's root canal system gives the dentist a good idea of its overall anatomy.


Configurations your dentist may discover.

It's possible for a dentist to determine a number of features about a tooth's canal system as they work.

A branched root canal.
  • The canal may be branched. - A single canal sometimes divides into two separate ones.

    With our distal root example above, that was the concern. And as the dentist performs the tooth's work, they would need to investigate whether what looks like the opening to a single canal is in fact that. Or if instead it branches into two separate ones lower on down in the root.

  • Two canals may coalesce into one. - We mentioned the possibility of this configuration in our mesial root example above. It's possible that what is two obviously separate canals at the tooth's pulpal floor combine to form a single one lower on down in the root.

    Now with the kind of tooth in our example above that's unlikely. But the dentist must confirm this fact as they perform their work.

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So now you know ...

  • The issue of how many roots a tooth has does vary for some kinds of teeth. But with others is practically a non issue.
  • A tooth's usual number of root canals can also vary, with some types of teeth, or even some specific tooth roots, especially noted for variation.
  • And because discovering and treating all canals is so vitally important for the success of a tooth's endodontic work, dentists place great emphasis on searching for and identifying them using the methods described on this page.