How many roots and root canals does your tooth have?

- What are the usual numbers? - According to tooth type.  |  How common are variations? - Examples. |  Methods dentist use to identify additional root canals.

Knowing these numbers is an important detail.

The number of roots and root canals that a tooth has is an important factor when it comes to performing its endodontic therapy. That's because so many issues associated with this treatment are influenced by the tally of both.

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?

There's no set number of either. Instead, what's found varies by way of tooth type. But even then, there are no absolute rules.

The exception would be the general axiom that "a root always contains a canal" (Torabinejad). (A canal may be very tiny and therefore difficult to locate but there is always at least one in each root.)

What's usually found?

Our table below lists what your dentist generally expects to find when evaluating different types of teeth. But variation is a key theme when it comes to these numbers.

How many your dentist actually discovers, and therefore must ultimately treat when performing your endodontic therapy, can vary, even substantially, from that which is stated below.

Section references - Torabinejad

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

Section references - Ingle

Your dentist must assume that every tooth displays variation in the number of canals, and possibly roots too.

As stated above, while the numbers in our table are common and usual, the bottom line is that when performing your tooth's endodontic 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 portion that's overlooked, and therefore is not treated, 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 other teeth of its type, as compared to variations in the 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, Chaparro)

  • 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)

  • 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.

Section references - Al-Ghananeem, Chaparro, Ahmad

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 taking conventional x-rays can be, there can be 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 the same radiograph shown above.

X-ray of a lower first molar.
Do root "B"'s canals merge?

Root "B"'s two separate canals are obvious at the level of the arrow. But notice how down around the tooth's tip they aren't so distinct?

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

It's most likely that due to the angle at which this film was taken that one canal simply overlaps the other (the two are superimposed), thus giving the appearance of just one.

Why dentists take multiple x-rays.

Actually, your dentist has a technique they can use that can help to clarify things. That's simply taking an additional x-ray(s) from a slightly different angle (like plus or minus 20 degrees) and comparing them.

When that's done, what actually exists is more likely to be revealed. And for this reason, it's commonplace and should be expected that your dentist will take multiple (two or more) pre-operative x-rays of your tooth.

Does root "A" have one or two canals?

This same type of inconclusiveness exists with root "A". It looks like it just has a single canal but its not uncommon for a first molar's distal root to have two. (About one-third of cases have two. Ingle - linked above.)

Once again, the angle at which this picture was taken may have resulted in superimposing the two canals. And also just like above, taking additional radiographs from different angles may help to clarify what actually 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.

This is 3D imaging, and the view that it gives can answer many uncertainties about a tooth's roots and canals, including the types of example difficulties discussed 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.

A study by Stropko 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 suggests that 42% of failed cases involve missed canals.

Section references - Stropko


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.

 

 


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.
 
 
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