Root Canal Side Effects, and the One That Is Not Real
The short-term effects published sources describe are soreness, sensitivity and a tooth that is easier to break until it is restored. The long-term one you will find most often online — that root canals make you ill — comes from a theory the research has discredited.
What is actually described
Two things, and they are both short-term. The American Dental Association's patient page says the tooth and the area around it "may feel sensitive for a few days". The American Association of Endodontists says the tooth "may feel slightly sore for a few days after your endodontic treatment is completed while the area heals", and that symptoms improve within three to five days in most cases.
A third is structural rather than a sensation: a tooth that has had its pulp removed has also had a hole made in the top of it and has less material left than it started with. Until it is properly restored, it is easier to break. That is why the ADA describes a temporary filling going in and being replaced later by a regular filling or a crown, and it is why the restoration is a separate procedure code at a separate fee on every schedule we read.
The claim that root canals cause illness
This is the thing most people are actually asking about, so it deserves a direct answer rather than a careful one.
The claim traces back to what is called focal infection theory, an idea from the early twentieth century that a treated tooth seeds disease elsewhere in the body. The AAE's page addressing root canal myths puts it this way: "The belief that root canals cause systemic disease stems largely from the early 1900s 'focal infection theory'... Contemporary peer-reviewed research has discredited these claims."
Two honest caveats about that quotation. The AAE is the endodontists' own professional association, so it has an obvious interest in the answer. And its page does not cite the research it refers to in a form we could open and read, which is why you will not find a percentage or a study name on this site attached to it. We are telling you where the claim came from and what the relevant professional body says about it, and we are not dressing a trade association's summary up as a literature review.
What we will not do is repeat the figures that circulate alongside this argument in either direction. The AAE's own pages carry a claim about cancer risk and a success rate above ninety per cent; neither arrives with a study we could open, so neither appears here. An unsourced percentage reads exactly like a citation, and that is the problem with it.
What a treated tooth is and is not
It helps to know what is left. The AAE describes the pulp as the soft tissue beneath the enamel and dentine containing "blood vessels, nerves and connective tissue, which help grow the root of your tooth during its development" — and says plainly that "a fully developed tooth can survive without the pulp because the tooth continues to be nourished by the tissues surrounding it".
So the tooth is not dead in the sense of being a foreign object sitting in your jaw. It is a tooth without its nerve supply, held and fed by the tissues around it, sealed with what the AAE calls "a rubber-like material called gutta-percha". It also cannot tell you when something is going wrong, which is the genuine trade-off and the reason the follow-up appointments exist.
The side effect nobody lists: it can go quiet
Losing the nerve means losing the alarm. A tooth that has been treated does not generate the kind of pain that sent you to a dentist in the first place, which means a problem underneath it can develop without producing a symptom you would notice.
That is not an argument against the treatment. It is an argument for the X-rays at the review appointments, and for not deciding on your own that a tooth is fine because it does not hurt.
When a side effect is not a side effect
Some things people find after treatment are not the treatment settling down. From the NHS page on dental abscess, reviewed on 18 March 2026, these belong to infection rather than to healing: a swollen face or jaw, swollen glands in the neck, a high temperature, a bad taste in the mouth, difficulty opening the mouth and chewing.
And the list that stops being a dental question at all — call 999 or go to A&E in the UK, 911 or an emergency department in the US: hard to breathe, speak or swallow; a swollen or painful eye or sudden problems with eyesight; a lot of swelling in the mouth; difficulty opening the mouth.
The AAE is blunt about why this matters: "If left untreated, the localized infection in the tooth can progress into an abscess and spread to adjacent tissues, and in some cases can even be life threatening."
What to do with all of this
Very little, until something happens. Soreness that is fading is behaving the way the sources describe. Soreness that is severe, or that is not fading after a few days, is what the AAE says to ring about. Swelling and fever are not a waiting game. And a treated tooth without its final restoration is an unfinished job, not a finished one.
If the reason the restoration has not happened is money, the honest figures are on our page about what root canal treatment and the crown after it cost on three fee schedules — the crown is roughly half the total on the schedules that price both, which is not a small thing to be told after the fact.
When treatment does not settle at all, there is a specific path for that, and it has its own chapter: what a failed root canal means and what retreatment involves.
Questions about after-effects
Do root canals cause illness or disease?
The idea comes from focal infection theory, an early-twentieth-century hypothesis. The American Association of Endodontists states that contemporary peer-reviewed research has discredited the claim. It is their own professional body and its page does not cite the research in a form we could open, so we report what they say and attribute it to them rather than presenting it as our own finding. What we would say independently is that the numbers circulating on both sides of this argument are almost all unsourced, and we print none of them.
Is a root-canal-treated tooth a dead tooth?
It no longer has its pulp — the nerve and blood supply inside it — but the AAE's own description is that a fully developed tooth survives without the pulp because it continues to be nourished by the tissues around it. The practical consequence is not that the tooth rots in place; it is that the tooth can no longer warn you, which is why review X-rays exist.
Will the tooth go darker?
We could not find a sourced statement about how often that happens or by how much, so we print none. It is a reasonable thing to ask the dentist about before treatment if the tooth is at the front of your mouth, because it affects what restoration makes sense and what it costs.
How long do the side effects last?
The published descriptions are a few days of soreness or sensitivity, with the AAE saying symptoms improve within three to five days in the majority of cases. Anything severe, anything involving pressure, or anything still going after a few days is the point at which the AAE says to call — and swelling or a temperature is not a side effect at all, it is a reason to be seen today.
Can a treated tooth get infected again?
Yes, and that is a documented situation with its own procedure codes: two of the three schedules we read price retreatment explicitly, and both price it higher than the original treatment. It is not a rare, unmentionable outcome. It is a line item.
Carry on
The prices behind all of this are on what a root canal costs on three fee schedules.
Anaesthetic and Sedation for a Root Canal
Local anaesthetic is the default and is included in the procedure — it has no separate line on any schedule we read. Sedation is a different thing entirely, billed by the quarter hour, and it is worth knowing what that costs before you say yes.
Do You Need a Crown After a Root Canal?
On the schedules that price both, the crown is roughly half of the total bill — and the endodontists' own guidance says it depends mostly on which tooth it is. Back teeth generally get one; front teeth often do not.