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Why does a root canal fail?



Junior member
Feb 28, 2018
Hi, I would be grateful if anyone can help answer some questions that I cannot seem to get a proper answer to. Why does a root canal fail? If you go to an endodontist who specialises in this treatment and carries it out under a microscope with all the most up to date equipment and says it was a success, then why does it fail? I know I may be naive here and, due to my chronic dental phobia I don't have much experience, but I simply don't know anyone (other than the lovely fellow forum posters here) who has spent thousands on a procedure to then be told it hasn't worked (even though everything looks perfect on x-rays) and all that stress and money was for nothing!

I have had a root canal retreated. It was originally done 20 years ago, crowned and never gave me an ounce of trouble. Suddenly it started hurting. Nobody can give me a proper explanation as to why this happens. Suddenly after 20 years it fails? Retreatment done, endo happy, all a success, temp crown on, and still the pain persists. Horrendous taste in my mouth. Extraction next step they say. Really? Nothing can be done? I just feel like the explanation as to what has failed is missing. No explanation to the bad taste either. Is this infection? Surely if someone charges you thousands and then says "sorry, it hasn't worked", that is not enough?

Some posters in the forum say to wait. That root canal teeth can take weeks to settle and suddenly improve. Is this sensible? If there is pain can it be anything other than infection if there are no fractures? Is a CBCT scan worth the risk and the cost to see if anything else can be revealed?

Sorry for so many questions but I would be grateful for answers as I am frustrated and feel helpess not getting proper explanations from either the endo or the dentist and don't know anyone who has been though anything similar. Thank you.


Staff member
Verified dentist
Oct 25, 2005
Because they do.

I'm sorry but when you're dealing with a very complex biological system, sometimes things can happen in ways that we can't predict and can't account for.

I've already gone over this in a different thread, but a RCT cannot completely seal up the canal system of a tooth, the bugs can still find ways to get past the sealant. The whole objective is to try to seal the canal space enough that the minimal number of bugs can get out into the spaces beyond and cause mischief.

Bear in mind also that for a tooth to need RCT in the first place, it's already heavily compromised due to decay, the structure has been damaged badly and there are loads of bacteria in the microscopic spaces in the dentine tubules etc. Because of this, bacteria will almost always find ways back into the canal spaces and from there into the danger zone around the apexes of the roots.

There's also a massive difference in people's immune systems' response to any bugs that manage to get into the apex system, probably even in the same person but at different times the response varies.

In short, as dentists, we don't like the situation any more than you patients do, probably worse actually, most dentists are terrible at self-flagellation when things don't go as we hope, but there really is nothing we can do about it at the current state of our knowledge.

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