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No treatment procedure can claim a 100% success rate and the same is true for root canal treatment as well. In this article, we will take a look at how successful root canal treatment actually is and what are some reasons why it may fail.

Root canal treatment may be required for a number of reasons including decay, fracture, severe sensitivity, or to prepare for a prosthetic restoration. The exact procedure of root canal treatment can vary according to the kind of tooth being treated but it is a blind procedure where the dentist is trying to disinfect the pulp chamber, filling it, and then putting a cap on top of the tooth to hopefully extend its life [1].

Can root canal treatment go wrong? It can. Lets us see why it can happen and how often it ends up happening.

RCT Failure rate

Studies have estimated that the success rate of root canal treatment can vary from 86-98% but that figure is quite malleable [2]. This is because the definition of success can change quite dramatically from study to study [3]. Is RCT treatment considered a success if it lasts five years? Ten years? What if the patient does not have symptoms but the tooth starts to develop radiographic symptoms?

These are questions that should be left to the academics. Successful root canal treatment from a patient’s point of view should be a tooth that has been successfully disinfected, is pain-free, and has been restored for functional use in the mouth.   

The reality is that with more and more root canal treatment procedures being performed around the world, the number of failure cases is also rising, even if the percentage remains the same [4].

Why does RCT failure occur?

There are several reasons why a root canal treated tooth can fail.

Improper debridement

If the canals are not cleaned sufficiently then some amount of infected material can get left behind on the walls and be a cause for re-infection down the line [5]. With the improvement in instruments available to the dentists and the speed with which a rotary root canal can be performed, insufficient cleaning is quite rare.

Insufficient irrigation

Once the canal has been cleaned and shaped by the use of physical instruments, the root canals must be cleaned and disinfected by the use of chemical irrigants. A failure to use a sufficient amount of irrigant or to not use the proper technique while doing so is also one reason why root canal failure can take place [6].

Once again, this is not something that should occur at the hands of a well-trained and experienced dentist.

Missed Canal

Teeth vary wildly from one another and can have extra canals, canals in unexpected locations, or even extra roots. This variation from the mean can sometimes be missed by a dentist who is not trained to look for it [7].

Dentists that do not make a big enough opening into the tooth can sometimes miss the extra canals. As a result, a reservoir of infected canals remains inside the tooth and then causes problems once the rest of the treatment has been completed [8].

Tooth Fracture

This is perhaps the most common reason for the failure of root canal treated teeth. The procedure of performing root canal treatment involves drilling deep inside the tooth and basically making it hollow. This remaining tooth structure is like a shell which can crack if it is not protected by an adequate protective covering.

A lot of the times patients get relief from pain after the root canal treatment and then do not get a cap on top. This must be avoided at all costs. Root canal treatment technically finishes only when the tooth has been replaced with the cap [9].

If a root canal treated tooth fractures and becomes non-restorable then there is no option but to have it extracted.

Instrument fracture

The instruments that are used to clean and shape the root canal are extremely fine. They can sometimes be subjected to more stresses than they are designed to handle as in the case of an extremely curved tooth.

In such a case the instrument can fracture inside the tooth. This in itself is not a cause for concern because the instrument is sterilized and will stay lodged inside the tooth much like a filling would. The instrument, however, does prevent the root canal from being completely cleaned and could allow some amount of bacterial infection to remain inside.

The stage of cleaning and shaping at which the instrument fractures makes a very big difference to its contribution to RCT failure [10].  

Underfilled or Overfilled root canal

The filling material used to fill (obturate) the root canal must ideally end exactly at the tip of the root. In some cases, this material can actually extend out from the canal or be very short from it. Both the situations are not ideal but the material extending out from the canal is much worse [11].

Thankfully, though, a simple X-ray taken after the completion of the filling procedure can help identify and rectify this mistake at the same time.


Root canal failures are bound to happen in some cases even if everything else seems to be perfect. There is nothing that can be done about that. Cases where a Clear mistake has been made, however, must be avoided and rectified if possible.

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