Why Are Root Canals So Controversial? What the Evidence Actually Shows
The short answer: Root canals are controversial because two things are true at once, and the debate usually picks only one of them. On one side, a well-performed root canal on a suitable tooth is a safe, successful treatment, and the claim that every root-treated tooth poisons the body is not supported by good evidence. On the other side, research does show something worth taking seriously: when infection persists in a root canal system, that lingering infection, known as apical periodontitis, has been associated in studies with raised markers of inflammation elsewhere in the body. The key word is persistent infection, not root canals in general, and the key word is associated, not proven to cause. The controversy comes from one camp ignoring the first truth and the other ignoring the second. An honest, biological view holds both: respect the success of good endodontics, and take silent, persistent infection seriously rather than assuming a tooth is fine simply because it does not hurt.
Where the controversy comes from
Few treatments divide opinion like root canals. Mainstream dentistry points, correctly, to high success rates and decades of saved teeth. A louder online narrative claims root canals are “toxic” and cause disease throughout the body, a strong claim that good evidence does not support.
Caught between the two, patients are understandably confused. The way out is not to pick a side, but to look at what the research actually investigates, because the interesting science is not about the procedure itself. It is about what happens when infection persists after treatment.
What the research actually looks at
Here is the distinction that resolves most of the confusion. The studies that raise real biological questions are not about healthy, well-sealed root-treated teeth. They are about teeth where infection lingers at the root tip, a condition called apical periodontitis. Three studies are worth knowing, described for what they do and do not show.
1. Can bacteria survive inside a treated root canal? Using molecular techniques, Siqueira and Rôças (2004) analysed teeth with failed endodontic treatment and documented bacteria persisting in the canal system despite treatment. The honest reading: in teeth where treatment has not fully succeeded, microorganisms can survive deep in the anatomy where instruments and disinfectants do not reach. This is about failed or persistent cases, not every root canal.
2. Is persistent infection linked to inflammation elsewhere? A 2013 systematic review and meta-analysis examined whether apical periodontitis is associated with systemic inflammatory markers, and found that it is: people with this persistent infection tended to show higher levels of inflammatory mediators in the blood. The honest reading: a localised, chronic infection can be associated with measurable signals elsewhere in the body. Association is not proof of cause, but it is not nothing either.
3. What about bacterial endotoxins? Research by Gomes and colleagues (2017/2018) reported that higher endotoxin levels in root canals were associated with chronic apical periodontitis, with markers of oxidative and nitrosative stress, and with measures of depression and a lower quality of life. The honest reading: this is an association study, not evidence that root canals cause depression. But it points to a biological relationship between persistent endodontic infection and the wider body that is worth investigating, not dismissing.
Notice the thread running through all three: the concern is persistent infection, not the existence of a root canal. A quiet, well-healed root-treated tooth is a very different situation from one carrying a chronic, often painless lesion.
“But where is the evidence?” Both questions are fair
Two challenges are often thrown across this debate, and both deserve an honest answer.
To those who say there is no proof root canals harm the body: that is largely correct for healthy, well-treated teeth, and the sweeping “all root canals are toxic” claim is not supported. But “no proof of systemic disease” is not the same as “no biological questions worth asking,” and the research above shows there are real questions around persistent infection.
To those who say any lingering concern is fear-mongering: the studies on apical periodontitis are real, published and measured. Taking persistent infection seriously is not fringe. It is simply good medicine to treat a chronic, silent source of inflammation as something that matters.
Why the pain-free part matters most
The most important practical point is that a failing root canal is usually painless. The tooth has no living nerve, so a chronic lesion at the root tip can sit quietly for years, invisible on a normal flat X-ray and causing no symptoms. “It does not hurt” is therefore not the same as “it is healthy.”
This is why a biological approach relies on looking properly, rather than waiting for pain. A CBCT 3D scan shows the root tip in three dimensions and reveals a chronic lesion that a flat image can miss entirely. The aim is not to find reasons to remove teeth, but to know what is actually there before making any decision.
What this does and does not mean for you
It does not mean healthy, symptom-free root-treated teeth should be removed on principle. That is overtreatment, not biological dentistry, and it is as wrong as dismissing the concern entirely.
It does mean that a root-treated tooth deserves honest assessment rather than assumption. A comfortable tooth with a clean root tip on 3D imaging can simply be monitored. One with a chronic lesion, repeated problems, or a history of failed treatment deserves proper evaluation and an individual decision, which may be retreatment, or removal and replacement, depending entirely on the tooth and the patient.
This is what a biological perspective adds: not a slogan in either direction, but a wider lens that treats the mouth as part of the whole body and takes persistent infection seriously, while respecting what good endodontics achieves.
Frequently asked questions
Are root canals actually dangerous? For most patients, a well-performed root canal on a suitable tooth is safe and successful, and the claim that all root canals cause systemic disease is not supported by good evidence. The genuine concern is persistent infection in teeth where treatment has not fully succeeded, which research associates with wider inflammation. The safety of a root canal depends on how well it is done and whether infection remains.
Do the studies prove root canals cause illness? No. The studies on apical periodontitis show associations between persistent endodontic infection and systemic markers of inflammation, not proof of cause and effect. They are a reason to take lingering infection seriously and investigate it, not a reason to panic or to remove healthy teeth.
What is apical periodontitis? It is persistent inflammation and infection at the tip of a tooth’s root, often following a root canal that has not fully resolved the infection. It can be completely painless and invisible on a standard X-ray, which is why 3D imaging matters.
My root canal does not hurt. Should I be concerned? Not necessarily, but do not assume it is healthy just because it is comfortable. A failing root canal is usually painless. A root-treated tooth that shows a clean root tip on a 3D scan can be monitored; one with a chronic lesion deserves evaluation.
Should I have my root canals removed? Not on principle. Healthy, symptom-free root-treated teeth do not need removing. Removal is considered only when a tooth has a chronic infection or symptoms that cannot be resolved, and each tooth is assessed individually, ideally with 3D imaging.
What does a biological dentist do differently? The biological approach does not reject endodontics, and it does not remove healthy teeth out of fear. It assesses root-treated teeth honestly, uses 3D imaging to find silent infection, takes persistent inflammation seriously in the context of overall health, and individualises the decision for each patient and each tooth.
References
1. Siqueira JF Jr, Rôças IN. Polymerase chain reaction-based analysis of microorganisms associated with failed endodontic treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2004;97(1):85-94. doi:10.1016/s1079-2104(03)00353-6
2. Gomes MS, Blattner TC, Sant’Ana Filho M, Grecca FS, Hugo FN, Fouad AF, Reynolds MA. Can apical periodontitis modify systemic levels of inflammatory markers? A systematic review and meta-analysis. J Endod. 2013;39(10):1205-1217. doi:10.1016/j.joen.2013.06.014
3. Gomes C, Martinho FC, Barbosa DS, Antunes LS, Póvoa HCC, Baltus THL, Morelli NR, Vargas HO, Nunes SOV, Anderson G, Maes M. Increased root canal endotoxin levels are associated with chronic apical periodontitis, increased oxidative and nitrosative stress, major depression, severity of depression, and a lowered quality of life. Mol Neurobiol. 2018;55(4):2814-2827. doi:10.1007/s12035-017-0545-z
Note: these studies report associations, not proof of causation, and concern persistent infection (apical periodontitis) rather than all root-treated teeth.
Dr. Tomasz Zaranski is a certified biological dentist and ceramic implant specialist practising at Dr. Joy Dental Clinic in Dubai. He is SMART certified (IAOMT), trained in the Swiss BioHealth concept, and listed in the Global BGS Directory. He holds Diplomate status with the ICOI and DGOI, an MSc in Esthetic Dentistry from Goethe University Frankfurt, and has over 21 years of clinical experience.
This article is for educational purposes only and does not replace an individual dental consultation. Diagnosis, treatment options, risks and expected outcomes should always be discussed with a DHA licensed dentist after clinical examination and appropriate imaging.
