14.3. Root Canal Therapy

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.

Diagnostic and preparation

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.

Filling the root canal

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.

Final restoration

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.

Success of the treatment

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.

Alternatives

If extensive loss of tooth structure occurs, extraction may be the only treatment option. It is also conducted when the treatment needs to be completed in a single session or when the endodontic equipment or expertise are not available. Following tooth extraction, options for prosthetic replacement may include dental implants, a fixed partial denture (bridge), or a removable denture.

Summary

Root canal treatment is conducted when the pulp is infected or otherwise compromised. The crown is opened with a drill and the pulp is removed. Removal of the pulp from the roots and widening of the canal is done manually with flexible files because the roots are long, thin and curved. This is done in conjunction with antiseptic irrigation that washes out the debris and sterilizes the canal. All roots of the tooth are treated and filled with gutta-percha. Permanent restoration of posterior teeth requires a prosthetic crown to reduce the risk of tooth fracture. The alternative treatment to root canal therapy is dental extraction.

Key terms

Endodontic treatment, gutta-percha, dental cement, eugenol, endodontic file, dental file, abscess, fistula, irrigant, sodium hypochlorite, chlorhexidine gluconate, calcium, hydroxide, root canal filling, restoration, dental extraction.

Figure credits

Figure 1 by Original version by Jeremy Kemp; SVG conversion by Jellocube27. - Root Canal Illustration with Molars by Jeremy Kemp (2005-03-22) using Adobe Illustrator; converted to SVG by Jellocube27 (2007-01-07); based on information from illustrations at www.animated-teeth.com., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1550875

Figure 2 by DRosenbach at en.Wikipedia - http://en.wikipedia.org/wiki/File:Pulpandbroach.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=17087977

Figure 3 by DRosenbach at English Wikipedia - Transferred from en.wikipedia to Commons by Masur using CommonsHelper., Public Domain, https://commons.wikimedia.org/w/index.php?curid=7231479

Figure 4 by BruceBlaus. When using this image in external sources it can be cited as:Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=28909222

Figure 5 by Dr.mohan m.muthal - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=41893850