Do not wait for the appointment if

Ring 999 or go to an emergency department

You are finding it hard to breathe, speak or swallow
Your eye is swollen or painful, or your eyesight has changed
There is a lot of swelling inside your mouth, or under your tongue
You cannot open your mouth properly

Do not drive yourself. Ask somebody to take you, or ring an ambulance.

Ring a dentist today — or 111 if you cannot get through

Swelling of the gum, cheek, jaw or neck, however small it starts
A temperature, shivering, or feeling unwell with the tooth
Pain getting rapidly worse, or no longer held by paracetamol
Anything clearly worse than when the appointment was booked

A GP cannot treat this. An infected tooth can spread into the tissues around it, and that can move within hours — a booked appointment next week is not the answer to a swelling that is growing today. Where to go when it will not wait

What this appointment is for

Inside every tooth is a soft core of nerve and blood vessels — the pulp. When decay, a crack or an injury lets bacteria reach it, the pulp becomes infected and dies. It cannot recover, and it cannot be cleaned out by antibiotics, because there is no blood supply left to carry them in.

That leaves two options: take the tooth out, or take the pulp out and keep the tooth. Root canal treatment is the second one.

The point of it is not the filling at the end. The point is that the space the pulp occupied — narrow, curved, branching, and running the whole length of each root — is cleaned, shaped and sealed, so there is nowhere left for an infection to live.

What actually happens

NHS guidance puts it at two or more appointments, each of which may run one to two hours or longer. That is not a sign of difficulty; it is the normal shape of the treatment.

The tooth is numbed. Properly — this is the step everything else depends on, and a dentist will test it before starting.
A rubber dam goes on. A small sheet of rubber clipped around the tooth, isolating it. It is not optional practice here: it keeps your saliva out of a canal that is about to be sealed, and keeps the cleaning solutions out of your mouth. It also means you can swallow normally throughout, which surprises people.
An opening is made through the top of the tooth.
The pulp is removed, and the canals are cleaned with fine instruments and rinsed with disinfecting solution. This is most of the appointment.
The canals are measured, usually electronically and with an X-ray, because they have to be cleaned and sealed to their full length and not beyond it.
A temporary filling seals the tooth between visits.
At the last visit the canals are filled permanently, and the tooth is sealed.

Then the tooth needs rebuilding properly, and this is the part people do not expect. See below — it matters more than anything else on this page.

The bit nobody mentions: the tooth still needs restoring

A root-treated tooth has had a hole made in the top of it, has lost its blood supply, and is usually a tooth that was already heavily broken down. It is more brittle than it was.

So the root treatment is half the job. The other half is a permanent restoration — a substantial filling, an onlay, or a crown. NHS guidance notes a crown may be needed where the tooth was badly infected, and for back teeth it is common.

Ask at the start what the plan is, and what it will cost. A tooth that is root treated and then left under a temporary filling for months can split, and a tooth that splits below the gum usually cannot be saved — which means losing the tooth anyway, after all of this.

Does it hurt?

The honest answer is that the reputation belongs to the toothache, not to the treatment.

Most people arrive for a root canal in pain, because that is what sends them. The appointment is what stops it. Done under proper anaesthetic, it should feel like a long filling: pressure, a lot of fiddling, no sharpness.

Two honest qualifications:

A hot, acutely infected tooth can be harder to numb. Inflamed nerve tissue is genuinely less responsive to local anaesthetic. There are ways around it — more anaesthetic, different injections, placing it inside the tooth itself. If you feel anything sharp, raise a hand and say so. Pushing on is not bravery and it makes the next appointment worse.
The jaw ache is real. Mouth open, same position, over an hour. Ask for a break; people rarely do.

How long it takes

Expect a long appointment rather than a short one, and expect more than one. How many depends on which tooth: a front tooth has one canal, an upper back molar often has four, sometimes one of them curved like a hook. Nobody can give you a number without looking at the X-ray.

Before you come

Eat beforehand. It is a long appointment and you will be numb afterwards.
Take your medicines as normal, and bring a list.
Say what you take and what you have. Bring the list, and say it out loud rather than assuming it is on file: any blood thinner; bisphosphonates, denosumab or any other bone or osteoporosis medicine; steroids; anything that affects your immune system; diabetes; a heart valve problem or replacement, or endocarditis in the past; pregnancy or breastfeeding; any allergy, including latex and penicillin; and any hospital treatment in the last few months. None of it necessarily changes the appointment. All of it changes whether the decision is made with the full picture.
Take a painkiller before you come if the tooth is already hurting. Paracetamol. If you take a blood thinner — warfarin, apixaban, dabigatran, rivaroxaban, edoxaban, clopidogrel, prasugrel, ticagrelor, dipyridamole, or aspirin a doctor put you on — take paracetamol and not ibuprofen, aspirin, naproxen or diclofenac. They raise the bleeding risk alongside those medicines whether or not there is a wound to bleed from, so the rule does not relax. If your medicine is not on that list and you are not sure which kind it is, ask a pharmacist. If you are not on one, ibuprofen is an option if you normally take it safely. Follow the packet. Arriving comfortable makes it easier to numb.
Finish any antibiotics you were given, and say if you are still taking them. Antibiotics settle the swelling; they do not treat the tooth, which is why this appointment still exists.
Say if you cannot lie flat for long, or have a sensitive gag reflex, or will struggle with your mouth open. All three are manageable, and only if mentioned.
Bring headphones if noise is what bothers you. Most practices do not mind at all.

Worth asking

What is the plan for restoring the tooth afterwards, and what will it cost? The most important question on this page.
How many appointments, and how far apart?
What are the chances it works, for this tooth? It varies with the tooth, the infection and how much tooth is left. A general figure is not much use to you; their assessment of yours is.
What are the alternatives? Usually extraction, and then the question of whether to replace the gap. Worth hearing before you start, not after.

Afterwards

Tender for a few days, and one instruction that matters more than the rest: do not chew on it until it has been properly rebuilt.

→ After root canal treatment

Your dentist’s instructions come first

The instructions you are given by the dentist who is treating you take precedence over anything on this page. They know your tooth, your history and their plan; this page does not.

Sources

Root canal treatment — NHS, last reviewed 3 October 2025
Extirpation aftercare advice — Guy’s and St Thomas' NHS Foundation Trust, reviewed June 2025
Having root canal treatment — Wirral Community Health and Care NHS Foundation Trust