Endodontic therapy, also known as endodontic treatment or root canal therapy, is a treatment sequence for the infected pulp of a tooth which results in the elimination of infection and the protection of the decontaminated tooth from future microbial invasion. Endodontic therapy involves the removal of the dental pulp, the subsequent shaping, cleaning, and decontamination of the hollows with small files and irrigating solutions, and the filling of the decontaminated canals. Filling is typically done with a flexible material such as gutta-percha and an eugenol-based cement.

A tooth is mainly made of a hard material called dentine. Enamel is the surface layer that protects the visible part of the tooth (crown). The part of the tooth that sits beneath the gum line is called the root. The root helps to anchor the tooth into the jaw. Generally, front teeth have only one root, while molars generally have up to three. Within each root, there can be multiple canal spaces.

The hollow centre of a tooth is called the pulp chamber. This area contains the blood vessels, nerves and pulp. The pulp is a sensitive tissue that provides oxygen, nutrients and feeling to the tooth. The pulp extends from the roof of the pulp chamber down into the bottom of each root canal. If it becomes infected, the entire space needs to be disinfected.

The main function of the dental pulp is to regulate the growth and development of the tooth during childhood. Once the tooth is fully formed, nutrition for the tooth comes from the tissues surrounding the root. Therefore, a tooth can function without its pulp and, in most cases, can be kept indefinitely.

A diseased tooth pulp may cause inflammation or infection. The symptoms of a damaged or diseased tooth pulp may include:

• unprovoked or spontaneous pain
• sensitivity to hot and cold drinks and foods
• pain when biting or chewing
• loosening of the tooth
• swelling of the gum near the affected tooth
• oozing of pus surrounding the affected tooth
• facial swelling

Sometimes, tooth pulp may become damaged or diseased without any symptoms. In these cases, the problem is usually diagnosed by special tests or x-rays during a dental check-up or treatment for other dental concerns.

There are many events that can lead to disease or damage to dental pulp. Some of these include:

• deep-seated and untreated tooth decay
• decay beneath a deep filling
• trauma that damages a tooth
• habitual tooth grinding (bruxism)
• long-standing cracks in the teeth
• advanced gum disease

Options are available to manage tooth pulp infection, so it’s important to have this treated when you can to prevent further issues. If tooth pulp infection is left untreated, complications could include:

• spreading infection – once the pulp becomes infected, it loses its ability to fight the spread of the infection. If bacteria find their way into the pulp chamber, the bacteria will multiply. This can cause an infection or an endodontic abscess (a pocket or ‘blister’ of pus) when it spreads into the surrounding bone which can become severe.
• bone loss in the area – the infection may spread around the ends of the infected root canal and erode surrounding jaw bone
• loss of tooth – the tooth may have to be removed, which can affect eating or appearance. Tooth replacement options are available but may be limited if the infection has already caused advanced bone loss.

When a tooth is threatened by an infection of the pulp, a pulpectomy (removal of the pulp tissue) is conducted. If the inflammation is extensive, the tooth can be unroofed to allow drainage and help relieve pressure, the abscess may be drained, antibiotics prescribed, and the treatment continued after the inflammation has been mitigated. The dentist then drills into the pulp chamber and removes the infected pulp. Next, the tissues in the root canal(s) are extracted with long needle-shaped hand instruments known as files (H files and K files). All debris and bacteria have to be completely removed from the empty root canals and from the abscess, if present, in preparation for the tooth to be restored.

This preparation is challenging because the root canals are long and narrow, surrounded by hard tissue (dentin) and they are curved. The root canals are cleaned and widened through manual use of files which are long, thin and flexible, to adjust to the curvature of the root. This cleaning and widening is done as an iterative process in which the filing is alternated with irrigation using antiseptic solutions that wash out debris and kill microorganisms. The procedure usually requires multiple visits over a period of weeks.

Several compositions of irrigant solutions may be used in root canal therapy:

• 5% sodium hypochlorite (NaClO)
• 2% chlorhexidine gluconate
• 17% ethylenediaminetetraacetic acid (EDTA)
• Framycetin sulfate
• Mixture of citric acid, doxycycline, and polysorbate 80 (detergent) (MTAD)

Sodium hypochlorite and chlorhexidine are the most commonly used irrigants and their antimicrobial activity has been verified in vitro. Irrigation is a key component of root canal therapy, not only to clean and sterilize the root canal but also the abscess and fistula, when present.

The root canal(s) can be temporarily filled with calcium hydroxide paste. This strong base is left in for a week or more to disinfect and reduce inflammation in the surrounding tissues.

It may take several visits until the inflation is mitigated and all the infection and debris are removed from the tissues. A temporary filling material is applied to the crown between the visits. Maintaining a coronal seal throughout root canal therapy is important for the success of the treatment.

After all the debris and infected tissue have been removed, the dentist fills each of the root canals and the pulp chamber with an inert material and seals the opening. The standard filling material is gutta-percha, a natural polymer prepared from latex from the percha (Palaquium gutta) tree. Its main characteristics of interest are that this is a fairly rigid yet flexible material and it is highly inert (does not cause reactions) in relation to the body tissues. A cone gutta-percha is inserted into each clean root canal along with a sealing cement. Gutta-percha is radiopaque, allowing for x-ray verification that the root canal passages have been filled without leaving any voids.

Molars and premolars that have had root canal therapy should be protected with a crown that covers the cusps of the tooth. This is because the access made into the root canal system removes a significant amount of tooth structure. Molars and premolars are the primary teeth used in chewing and fracture more frequently after root canal treatment without cuspal coverage. Anterior teeth typically do not require full coverage restorations after a root canal, unless there is extensive tooth loss from decay. Placement of a crown is also recommended because it will best seal the root treated tooth.

After endodontic therapy a tooth is considered dead for not having life cells in it anymore. It should not be considered inert, however. The tooth is still prone to decay and without proper hygiene in can develop caries in its remaining enamel and dentin. This can occur without the patient's knowledge because with the removal of the pulp, the development of new caries does not produce in pain. Caries is the main reason for extraction of teeth after root canal therapy.

Endodontic treatment may fail because of inadequate cleaning of the root canal or incomplete sealing of the crown. In both cases, contamination of the gutta-percha by oral bacteria can reinitiate tooth decay. The contaminated gutta percha would have to be replaced in a retreatment procedure to minimise the risk of failure.

Another potential source of complication is that the dentist may fail to find, clean and fill all of the root canals within a tooth. The number of roots is variable among individuals, such that about half of the maxillary molars have four canals instead of three. An infected canal that is missed during the treatment may later inflame and require treatment.