What happens during a root canal?

Reviewed by Dr. Samar Fadavi, DDS

Short answer: During a root canal, the dentist freezes the tooth, places a rubber dam, opens the top of the tooth, removes the infected or inflamed pulp, cleans and shapes the canals, disinfects them and fills them with a sealing material. A temporary or permanent filling closes the tooth, and a crown is often placed later. Most people say it feels like a long filling appointment.

Why the root canal has a reputation

Root canal treatment is one of the most feared dental treatments, mostly because of old stories. Today, with modern freezing and careful technique, most patients feel pressure and vibration but little discomfort during treatment. In fact, root canal treatment is done to relieve the pain of an infected or inflamed nerve, not to cause it.

This guide explains what a root canal is, why it is needed, what happens step by step on the day, how you may feel afterwards and how to protect the tooth. It is general information for patients in Scarborough, the Danforth and East Toronto. Our root canal treatment page explains how we provide this care at our clinic.

What is inside a tooth

A tooth has three main layers. The outer enamel is the hardest substance in the body. Under it is dentin, a softer layer with tiny tubes that can carry sensations. At the centre is the pulp, soft tissue containing nerves and blood vessels. The pulp runs from the crown of the tooth down through narrow channels in each root, called root canals. Front teeth usually have one canal, while molars often have three or four.

Why a root canal is needed

A root canal is suggested when the pulp is inflamed or infected and cannot heal on its own. Common causes include:

• Deep decay that reaches the pulp.
• A crack or chip that exposes the pulp.
• Repeated dental work on the same tooth.
• A blow to the tooth, even without a visible break.
• Infection that has spread from the pulp to the bone at the tip of the root, called an abscess.

Signs you may need one

• Lingering pain to hot or cold that lasts after the trigger is gone.
• Throbbing pain that wakes you at night.
• Pain when biting or touching the tooth.
• Swelling of the gum or face.
• A small pimple on the gum that may leak fluid.
• A tooth that has darkened in colour.

Sometimes there are no symptoms at all and the problem is found on an x-ray. Our guide on different types of tooth pain explains what different pains can mean.

Before the appointment

The dentist examines the tooth, takes x-rays and may do simple tests, such as touching the tooth with something cold or tapping it gently, to see how the nerve responds. In some cases, CBCT 3D imaging is used to see the shape of the canals or the extent of infection. The dentist explains the diagnosis, the treatment, other options such as extraction, and what is likely to follow, such as a crown.

Tell the dentist about your medical history and medicines. If you are anxious, say so. Our guide on dental anxiety has tips for feeling calmer.

What happens during a root canal, step by step

1. Freezing. The dentist applies a numbing gel and then gives a local anesthetic to freeze the tooth and surrounding area. If the tooth is very inflamed, extra freezing may be needed. Our guide on dental anesthesia explains how freezing works.
2. Rubber dam. A thin sheet of rubber or non-latex material is placed around the tooth on a small clamp. It keeps the tooth dry and clean and stops tiny instruments and rinsing solutions from going into your mouth. Our guide to the rubber dam explains why it matters.
3. Opening the tooth. A small opening is made in the top of a back tooth or the back of a front tooth to reach the pulp chamber.
4. Finding the canals. The dentist locates each canal, often with magnification and a bright light.
5. Measuring the length. The length of each canal is measured with a small electronic device and x-rays so cleaning reaches the tip of the root.
6. Cleaning and shaping. Fine flexible files remove the pulp tissue and bacteria and shape the canals. Throughout this step, the canals are rinsed with disinfecting solutions.
7. Medication, if needed. If there is a lot of infection, the dentist may place medicine inside the tooth and finish at a second visit.
8. Filling the canals. The cleaned canals are dried and filled with a rubber-like material called gutta-percha and a sealer, which seals them against bacteria.
9. Sealing the top. A temporary or permanent filling closes the opening.
10. Final x-ray. An x-ray checks that the canals are filled to the right length.

How long it takes

A root canal on a front tooth may take about an hour. A molar with several canals can take longer and sometimes needs two visits. Complex cases, such as curved or narrow canals, may take extra time.

What it feels like

With good freezing, most people feel pressure, vibration and the sensation of the dentist working, but not sharp pain. If you feel any discomfort, raise your hand and the dentist can give more freezing. Many patients listen to music or podcasts with headphones. Your jaw may feel tired from staying open, and short breaks can be taken.

After the root canal

The first few days

The tooth and gum may feel tender for a few days, especially when biting. This is normal as the tissue around the root settles. Most people manage with over-the-counter pain relief as advised by the dentist or pharmacist. Swelling should go down, not up.

Eating

Wait until the freezing wears off before eating so you do not bite your cheek or tongue. Chew on the other side until the tooth has its final filling or crown, because a tooth with a temporary filling can break.

Cleaning

Brush and floss normally, being gentle around the tooth for the first day or two.

Why a crown is often needed

After a root canal, a tooth no longer has its blood supply and can become more brittle, especially back teeth that take heavy chewing forces. Many back teeth need a crown to protect them from cracking. Front teeth with little damage may only need a filling. Our guide on what affects the cost of a crown explains crowns and coverage.

Root canal or extraction?

When a tooth has an infected nerve, the two main options are root canal treatment or removing the tooth. Keeping the natural tooth with a root canal usually means you keep normal chewing and avoid the gap, shifting teeth and the need to replace the tooth later. Extraction may be suggested if the tooth is cracked through the root, has very little structure left, or has advanced gum disease. The dentist will explain the outlook for your tooth before you decide.

Is it safe?

Root canal treatment is a common, well-studied procedure. Old claims that root canal treated teeth cause illness elsewhere in the body are not supported by current evidence. Like any treatment, there are some risks, such as a small chance the tooth needs retreatment if bacteria remain or return, or a crack that develops later. Our guide on risks with dental treatments explains how risks are reduced.

What to avoid

• Do not wait for pain to go away on its own. Pain that stops can mean the nerve has died, while infection continues.
• Do not chew hard foods on the tooth until it has its final filling or crown.
• Do not skip the crown if one is recommended. Untreated back teeth can crack after a root canal.
• Do not use leftover antibiotics from a past illness. Antibiotics alone do not fix an infected nerve.
• Do not miss follow-up x-rays if the dentist wants to check healing.

Signs of healing and warning signs

After a root canal, the tooth should feel a little better each day. Normal signs include mild tenderness when biting, a slightly sore gum where the clamp sat and some jaw stiffness from keeping your mouth open. These usually ease within a few days.

Call the clinic if you notice:

• Pain that gets worse after the second or third day instead of better.
• Swelling inside the mouth or on the face that is growing.
• A rash, itching or other signs of a reaction to a medicine.
• The temporary filling coming out completely.
• Your bite feeling uneven, as if the tooth hits first when you close.
• Symptoms you had before treatment coming back.

Root canal treatment for children

Baby teeth have nerves too, and deep decay can reach them. In children, a smaller procedure called a pulpotomy is often used. It removes the inflamed nerve tissue from the top of the tooth and leaves the healthy tissue in the roots. The tooth is then usually covered with a stainless steel crown. Keeping a baby tooth until it falls out naturally helps hold space for the adult tooth. Young adult teeth with an injured nerve may also be treated in special ways that allow the root to keep developing. Our children’s dentistry page explains care for kids.

When a root canal needs another look

Most root canal treated teeth do well for many years. Occasionally, a tooth that had a root canal becomes sore again months or years later. This can happen if a canal was very narrow or curved, if bacteria leaked in under an old filling or crown, or if a new crack has formed. Options then include retreatment, where the old filling material is removed and the canals are cleaned and sealed again, or a small procedure at the tip of the root called an apicoectomy. If the tooth cannot be saved, extraction and replacement are discussed. Prompt attention gives the tooth a much better chance of being saved.

Preventing the need for a root canal

• Treat cavities while they are small. Our guide on how dentists find cavities early explains early detection.
• Wear a mouthguard for contact sports.
• Wear a night guard if you grind your teeth.
• Avoid chewing ice, hard candy and pens.
• Keep regular check-ups so small cracks and leaks are caught early.

When to see a dentist

Book a visit if:

• You have tooth pain that lingers after hot or cold, or wakes you at night.
• A tooth hurts when you bite.
• You notice swelling or a pimple on the gum.
• A tooth has darkened after an injury.

Swelling of the face, fever or trouble swallowing needs same-day care. Our guide on dental abscess signs and what to do explains these warning signs. Our emergency dentist page explains same-day visits, and our root canal treatment page explains treatment at our clinic.

Questions about root canals

Does a root canal hurt?

Most people feel pressure but little discomfort with good freezing. The tooth may be tender for a few days afterwards.

How many visits does a root canal take?

Often one, sometimes two, especially for molars or teeth with heavy infection.

Can I go to work after a root canal?

Most people return to work or school the same day once the freezing wears off.

Will my tooth still be alive?

No. The nerve is removed, but the tooth stays in place and is nourished by the surrounding tissues.

Why do I need a crown afterwards?

Back teeth can become brittle after a root canal. A crown protects them from cracking when you chew.

Can a root canal fail?

Occasionally bacteria remain or return. Retreatment or a minor surgical procedure at the root tip can often still save the tooth.

Is extraction a simpler choice?

It is quicker on the day, but it leaves a gap that often needs an implant, bridge or denture later. Keeping a healthy root is usually preferred.

Can I drive home after a root canal?

Yes, with local freezing alone most people drive themselves home. If you take a medicine to relax, arrange a ride.

What if I am pregnant and need a root canal?

Root canal treatment can usually be done safely during pregnancy, often in the second trimester. Tell the dentist you are pregnant so freezing, x-rays and medicines are planned with care.