What is the Procedure for a Root Canal?
Root canal is a long procedure- most of the time, dentists will complete the treatment in one to three visits.
Each appointment could be around an hour in length, depending on the situation. If the case is very simple and the tooth only has one canal, then the whole thing may be completed in just one sitting.
On the other hand, if a tooth is heavily infected, extra appointments may be needed in to dress the tooth. Note, dentists in the United States are fans of doing most root canal treatment from start to finish in a single appointment.
The First Appointment
The dentist will begin by diagnosing your problem- identifying which tooth is the culprit and discussing the options, risks and possible consequences for the tooth. An X-ray should be taken as part of this and will let the dentist assess the shapes and number of the roots and ensure the prognosis is a good one.
We will assume that your tooth needs a root canal and you have decided to go ahead with treatment.
Anaesthetic as mentioned previously may not always be needed, but given it is a long procedure and to make you more relaxed, most of the time it makes sense to put some in anyway.
The tooth will then be isolated using rubber dam. A rubber sheet is stretched over your tooth and a small metal clamp is used to hold it in place, forming a water-tight barrier.
This has two purposes:
- To protect you from the materials the dentist is using– we don’t want the dental bleach used to disinfect the canal getting into your mouth or risk any of the small files or materials being swallowed or inhaled.
- To isolate the tooth- keep it dry and prevent any bacteria getting into the canal from your blood or saliva.
Root canal work should ideally always be performed under rubber dam.
- Access to the nerve
It is important that the dentist removes as much caries (decay) and bacteria from the top of the tooth as possible before accessing the pulp (nerve) chamber and they will do this using standard burs and drills.
Remember the key to a successful root canal is removing bacteria and preventing it from getting back in. As I have mentioned previously, different teeth have different numbers of roots and they can have more than one canal in a root.
The dentist knows where the nerve chamber is most likely to be found in a particular tooth and how many canals to look for. On opening the chamber a number of situations may have occurred:
(i) A necrotic nerve– the nerve has been dead for some time.
(ii) Pus– on opening the canal on an abscessed tooth, pus may drain out providing a relief of pressure.
(iii) Hyperaemic nerve– the nerve has been suffering irreversible pulpitis (swelling) and blood from the nerve can pour out.
The dentist will remove any nerve tissue from the top or the pulp chamber- don’t worry it’s numb. They will then locate the canals (sometimes easier said than done) and use something called a barbed broach to remove individual nerves from each of the canals. Nerves rarely come out in one piece- (rather satisfying when they do), so often a bit more filing and washing is necessary.
Depending on the time the dentist has for the appointment, the tooth may be dressed at this point- if this was an emergency appointment this is very likely to be the course of action.
Medicine will be placed into the canal to help kill off any remaining nerve and bacteria, some cotton wool placed in the pulp chamber so the dentist can easily find it again and a temporary filling on top. This will be sufficient to get you out of pain.The most common medicines used are a steroid paste called ledermix which helps to get any inflammation down and non-setting calcium hydroxide- a very alkali paste which kills bacteria in the canals.
- Measuring the canals
The dentist may continue if there was sufficient time and work out the lengths of the canals. This is important because if the measurement is too short, bacteria and infection can remain in the very tip of the canal and if it is too long it can irritate the tissue around your tooth.
There are two ways the dentist can do this; the first and still most reliable is using X-rays. Files will be placed in each canal and an X-ray taken to see how far down they go. They have little rubber stops on the end to allow the dentist to measure the length.
The length will be adjusted accordingly so that the preparation of the canal goes almost to the end. Ideally the root canal will be 1-2mm from the apex (end of the root on the X-ray). This is known as the ‘working distance’ and needs to be calculated for all of the canals in the tooth as their lengths will vary.
The second way is using an apex locator- a high tech instrument that measures ‘electrical impedance’ by placing an electrode in the root canal and sends a signal to the dentist when they are at the end of the canal.This is useful for circumstances when the end of the root on the X-ray is not actually where the apical foramen or constriction is.
Sometimes both methods will be used together for an accurate picture.
- Cleaning the root canals
Now we have established how far down we need to prepare the root canal, we need to clean it and shape it. Cleaning is necessary to remove as much bacteria as possible from the root system, any remnants of nerve tissue and dentine that has been infected. It is this stage that is the most crucial to the success of your root canal treatment.
The cleaning process requires what is known as a ‘chemo-mechanical preparation’. This simply means that it requires chemical action in the form of dental bleach and mechanical action in the form of filing. Because the root canal system in reality is not just one or two main canals but a complex of interconnecting smaller canals, using files alone to prepare the main canals is not enough.
The chemical action of the bleach (sodium hypochlorite) is essential to disinfect the places that the files cannot reach and studies have highlighted how crucial frequent washing of the canal is to success.
Dentists have two main choices when it comes to using root canal files in order to enlarge, shape and smooth the canals.
- Hand files.
- Rotary files.
Nowadays the majority of dentists will use a combination of hand and rotary files.
Hand files are small flexible files that are inserted and twisted around against the walls of the canal. The dentist will start off with a thin file and move up in sequence to progressively thicker files until the sides of the canal are smooth clean and free from soft and infected dentine.
Rotary files look quite similar to hand files except they connect to a special slow handpiece (drill) and take the hard work out of preparing the canal as they do the rotary action automatically.These are a pre-determined sequence of automatic files used in a handpiece.
Think how a normal toothbrush requires you to do little circles and the cleaning action yourself but the electric toothbrush does it for you.
Different systems are available and each has a sequence of progressively larger files to follow. The’ beep beep’ noise you may hear is like a van reversing. It is saying that the file is retreating so as to not exceed the torque and risk fracture.
Lubrication for all files with a special paste that softens the dentine is important and the more bleach to disinfect the better.
After preparing to these distances the dentist may dress the canals with a special medicine, most commonly calcium hydroxide. This paste has a very high PH to kill off remaining bacteria in the canal before you come back to have the root canal filling placed. A temporary filling is then placed to stop bacteria getting in before your next visit.