Root Canal Treatment FAQs

Written by the Dental Fear Central Web Team and reviewed by Dr Ikhlas El Karim, a specialist in Restorative Dentistry
Last updated on July 28, 2021

What is root canal treatment?

Root canal treatment (RCT) is basically just a deep filling that goes down your roots and not just into the crown of the tooth which sits above the gum.  During the treatment, the tooth’s inflamed and infected nerve is removed. The inside of the tooth is then cleaned and sealed to prevent further infection and save the tooth.

When is root canal treatment needed?

RCT is needed when the centre of the tooth (also known as pulp or nerve) is infected by bacteria. It can save teeth that would otherwise need to be removed.

The most common cause of the infection is tooth decay, where decay-causing bacteria enter the pulp and cause infection and inflammation. Bacteria can also enter the dental pulp following an injury or if a filling is leaky.

This drawing shows how the pulp can become infected and inflamed:

Drawing of a tooth which needs root canal treatment. If the pulp of the tooth becomes infected, an abscess can form at the the root tip and cause swelling and pain.

The infection can cause a painful abscess, which usually forms at the tip of the root.

What is an abscess, and what causes it?

Here’s a great explanation from our forum, courtesy of Gordon Laurie, BDS:

“Sometimes, due to trauma or decay, the ‘nerve’ inside the tooth dies off. Any passing bacteria find this a source of nourishment and proceed to munch on the dead nerve and have lots of babies. Your body can’t do anything about this infection because, along with the nerve dying, the blood supply to the tooth dies off, too, so the body can’t send in antibacterial cells (white blood cells) to attack the bugs.

Eventually, the bugs start to spill out of the tooth and into the tiny space between the tooth and the jawbone. This starts an abscess: the body reacts to the invasion by pouring in defensive cells. These kill most of the bugs in the area but still can’t get to the source of the problem, which is in the tooth.

If the bugs are hard to kill, the battle rages on for a while, and because the area is very tiny, the pressure becomes high, and it becomes extremely painful. This is called an acute abscess.

Anyway, to sort this mess out, the dentist has two choices:

  • extract the tooth and remove the bugs that way, or
  • do a root treatment.

In a root treatment, the inside of the tooth is cleaned and sterilised, and then a plug is put in to bung up the space inside the tooth and stop more bugs getting in.”

Why can’t the infection just be drained?

If the root source of the infection hasn’t been treated, it will drain into your mouth permanently. This goes on until either the root canal space gets invaded by more aggressive bacteria which could cause a major blow-up with lots of pain and swelling. Or else, your body gets fed up with the constant irritation and walls off the area, causing a cyst to form.

How does RCT work?

This drawing shows a root canal treatment in simplified terms. The front tooth pictured here only has one canal, but back teeth (molars) have 3 or more canals.

Step-by-step illustration of a root canal treatment. First, the pulp is removed with dental files and the empty canal shaped. Then, the canal is filled with gutta percha, and the crown part of the tooth is filled with a dental filling.

The dentist will need to take an x-ray before, during and after the treatment is completed.

  1. The dentist makes an access cavity, using a dental handpiece (drill), to allow access to the canal.
  2. The pulp is removed with dental files, and the empty canal(s) are shaped.
  3. The canals are filled with a pink rubbery material called gutta-percha. The crown part of the tooth is filled with a regular, tooth-coloured dental filling.

Usually, you do root canal treatment over two visits. However, some endodontists do it in one visit.

Is root canal treatment painful?

The short answer is “no”. It may be hard to believe, but the actual root canal treatment really is not that much different from a filling. It takes longer, it’s more boring, and there will be less drilling, but many other steps. Nowadays, with modern techniques, root canal treatment is typically painless. What’s more, it will relieve the pain associated with an abscess.

You may have heard people say that root canal treatment is painful, or you may have had such an experience yourself. Sometimes, a dentist may find it difficult to numb a tooth. You can read why and how to deal with this here: How to numb a hot tooth.

Root canal treatment should be as comfortable as getting a filling. The negative press comes from when people have infected teeth and do not go numb well and yet for some reason treatment proceeds anyway. I personally would not continue in this instance as I feel a patient that is jumpy due to pain won’t get the level of treatment I’d like to provide. Obviously there must be some who have proceeded, possibly because they have tried all other options or at the request of the patient… Who knows?! The point is that for most people it won’t be an issue other than keeping your mouth open for longer than a routine filling!! As is life though we don’t tend to hear about the positive experiences of root canal fillings… They don’t make for such newsworthy stories! 

Jodie Nelson, BDS

Top Tips

  • Root canal treatment should be a pain-free procedure with just local anaesthetic. If you can’t get numb for whatever reason, it’s time to rethink all options including sedation.
  • Specialist endodontists know how to use advanced numbing techniques for hard-to-numb teeth. So if your general dentist can’t get you numb, you might want to see an endodontist instead.
  • It is common practice to be numbed for the second appointment, even though the nerve is likely already gone. It makes work on the surrounding tissue much more comfortable. Besides, it gives longer-lasting relief from any discomfort afterwards.
  • It’s easier to prevent pain than to make it go away once it has started. Take ibuprofen before the local anaesthetic has worn off. Paracetamol is a good alternative if you can’t take ibuprofen because of asthma or other contraindications. Ask your dentist or endodontist which painkiller they recommend.

What are root canals really like?

Our DFC volunteer Brit has written about what root canals are like from a patient’s perspective:

Why am I in pain after root canal treatment?

Pain upon biting down and dull pain are common and recognised side effects of root treatment. The pain should disappear within 48 hours or so, but it can take up to a month for the tooth to fully settle, depending on how good your immune response is. Here’s why you can get pain after root canal treatment, even though the nerve is no longer there:

Basically, when you stick instruments up the root canals, a little bit of the infected material will be pushed out of the end of the canal into the wee space between the tooth and the socket. This sets up a small area of local inflammation and can cause pain upon biting down and a dull pain. – Gordon Laurie, BDS

The pain should be manageable with maybe a little bit of an anti-inflammatory drug like ibuprofen or similar. Contrary to what many websites say, it’s not unusual for pain to last a couple of weeks.

Why do I still feel sensation in my root-treated tooth?

Some sensation in a tooth that’s had root canal treatment does not necessarily mean there’s a problem.

Basically, the tooth has two “nerves”. The first one is the “hot or cold” nerve inside the tooth (the pulp) that has been cleaned, disinfected and sealed in with the root canal treatment.

The second nerve surrounds the tooth and is in what’s called the periodontal ligament. This is the nerve that allows us to pick out a fishbone in our food. It picks up on pressure. The ligament is still alive and will function.

So your root-treated tooth should not feel hot or cold, but it can still feel pressure.

Sometimes, a lingering sensation can relate to clenching or grinding the teeth, so check with your dentist as they might be able to protect it with a splint for example.

Why do root canal teeth need crowns?

Teeth that have had root canal treatment are more brittle. Back teeth usually need a restoration around the tooth (a crown, a three-quarter crown or an onlay) after successful root canal treatment so the tooth will not break. The last thing you want is to pay for root canal treatment and then have the tooth fracture!

Initially, the tooth will be restored with a filling. You then wait until the tooth has completely settled before placing the crown or other restoration.

What can cause sensitivity in a root canal tooth that has recently been crowned?

There is often an innocent explanation. Go back to your dentist to get the bite checked and adjusted if necessary. If the tooth is sensitive to flossing, there may be a bit of cement left that needs removing.

What is an endodontist?

An endodontist is a dentist who specialises in root canal treatment.

When should I see an endodontist?

Success rates are higher when done by a specialist, especially:

• for any tooth behind a premolar

• for any tooth if it’s a re-treatment

• if the roots have difficult anatomy.

However, treatment done by an endodontist is usually more expensive.

How do I get to see an endodontist?

If you are an NHS patient (in the UK), you may be able to get a referral to a specialist endodontist at a hospital from your general dentist.

If you go private, you don’t need a referral to see an endodontist – you can pick your own. But if you trust your dentist, it’s best to get their recommendation for a good endodontist. Otherwise, Google is your friend.

Root canal treatment is not cheap, so make sure you can afford it and find out the cost in advance (check their websites).

Why do root canals fail?

There is no guarantee that root canal treatment will work, but success rates are very high if done properly, in the order of 90% 1.

However, the treatment is technically difficult, and some cases, especially the back teeth, may need a specialist endodontist. Front teeth are easier because:

  • they generally only have one canal (back teeth usually have three or more, and some canals can be hard to find)
  • the canal tends to be quite straight, compared to canals in back teeth
  • they’re easier for the dentist to access because they’re at the front and
  • the canals are wider.

Endodontists have special equipment such as a microscope and advanced training in root canal treatment. Especially for more complex root canal treatments and for re-treatments where a root canal has failed, their chances of success are higher, and in some cases much higher, than those of general dentists.

An operating microscope used by endodontists for root canal treatment
A microscope used by endodontists

This is not to say that general dentists cannot competently carry out root canal treatment. Indeed, many dentists do enjoy it and do additional training in endodontic therapy. But root canal treatment is not everyone’s cup of tea – it’s very intricate and requires time and patience.

So, even with an experienced dentist, you may want to agree up-front that they refer you to an endodontist if there are any unforeseen problems.

What can I do if root canal treatment has failed?

Often, it is possible to redo the treatment. If you’re in any doubt and you’d like to save your tooth, consult with an endodontist. Retreatments are best done by endodontists.

Are there certain people for whom root canals don’t work?

Is it possible for root canals to just not work? I have had two root canals in the past which never settled, and terrified about needing another one. Am I crazy?

A root canal is always a slight compromise. It’s impossible to TOTALLY remove ALL infected material from every single root canal. Some canals have little accessory branches from them, and others have tight kinks and curves in them, which our files and chemicals simply can’t access. Other canals have a sort of delta at the apex rather than a single large (relatively!) opening where the pulp enters. 

Even with the best technique, there are always going to be a few small amounts of bacteria able to colonise these areas.

There is also the question of the seal at the mouth end of the canal. A slightly compromised final restoration of the tooth can allow new bacteria into the canals, and away it all goes again.

HOWEVER, the idea behind root treatment is to reduce the bacterial load to such an extent that the host’s own defences can mop up any bacteria which get out into the space between the tooth and the bone.

There are 2 things which can mess this up: 

1. if the bacteria are particularly aggressive and reproduce quickly enough to overcome the host response and 

2. if the host response is a bit compromised, so the bacteria don’t get killed off quickly enough. 

Or more likely a mixture of the two. 

So that’s a long way of saying that you’re not crazy, but you also can’t assume that every single root canal on all your teeth will be the same!

Gordon Laurie, BDS

Why can’t you root canal a tooth that is cracked below the gumline?

I have been told I have an abscess and the tooth will need to be removed because it has a couple of cracks that extend below the gumline. Why can’t the infection just be drained? And why can’t an apicoectomy be done?

If the root source of the infection can’t be treated, it will drain into your mouth permanently. This will go on until the root canal space is invaded by a more aggressive bacteria, which could cause a major blow-up with lots of pain and swelling. Or else, your body gets fed up with the constant irritation and walls off the area, causing a cyst to form which can cause other issues.

Apicectomy won’t work because the tooth is cracked, allowing more bacteria into the root space so it won’t ever heal.

So the only way to deal with the problem is to remove the tooth.

Questions you may want to ask your dentist

  • What would you do if it was your own tooth?
  • Would you see a specialist, or is it an easy enough job for a general dentist?
  • What is the likely success rate? How long will it last? – If the odds strike you as unacceptably low, or if the answer is something along the lines of “they last about 5 years max”, you may want to ask for a referral to an endodontist.
  • Will you use a rubber dam? – This is the standard of care, and not using a rubber dam is a red flag.
  • Will you be wearing loupes? – Loupes are magnifying glasses that look like binoculars. They allow dentists to carry out much more precise work.
Loupes should be used for fine dental work such as root canal treatment. They look like little binoculars.
  • Is it possible to get an onlay or a three-quarter crown? – If possible, all back teeth that have been root treated should have a crown, a three-quarter crown or an onlay to protect them. The choice of restoration depends on the amount of tooth structure left and what the x-rays show. The most conservative option is an onlay, but if there’s not enough tooth structure left, a full crown will be needed. Nowadays, the trend is to preserve as much tooth structure as possible.

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Further Reading

Sources of Information