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Endodontic therapy or root canal therapy is a sequence of treatment 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. Root canals and their associated pulp chamber are the physical hollows within a tooth that are naturally inhabited by nerve tissue, blood vessels and other cellular entities which together constitute the dental pulp. Endodontic therapy involves the ''removal'' of these structures, the subsequent shaping, cleaning, and decontamination of the hollows with small files and irrigating solutions, and the ''obturation'' (filling) of the decontaminated canals with an inert filling such as gutta-percha and typically a eugenol-based cement. Epoxy resin is employed to bind gutta-percha in some root canal procedures.〔 〕 ==Treatment procedure== In the situation that a tooth is considered so threatened (because of decay, cracking, etc.) that future infection is considered likely or inevitable, a pulpectomy, removal of the pulp tissue, is advisable to prevent such infection. Usually, some inflammation and/or infection is already present within or below the tooth. To cure the infection and save the tooth, the dentist drills into the pulp chamber and removes the infected pulp and then drills the nerve out of the root canal(s) with long needle-shaped hand instruments known as files (H files and K files). Starting with a smaller file size (sometimes termed a 'pathfinder'), progressively larger files are used to widen the canals. This process serves to remove debris and infected tissue and facilitates greater penetration of an irrigating solution (see 'irrigants' below). After this is done, the dentist fills each of the root canals and the chamber with an inert material and seals up the opening. This procedure is known as ''root canal therapy''. With the removal of nerves and blood supply from the tooth, it is best that the tooth be fitted with a crown. The standard filling material is gutta-percha, a natural polymer prepared from latex from the percha (Palaquium gutta) tree. The standard endodontic technique involves inserting a gutta-percha cone (a "point") into the cleaned-out root canal along with a sealing cement. Another technique uses melted or heat-softened gutta-percha which is then injected or pressed into the root canal passage(s). However, as gutta-percha shrinks as it cools, thermal techniques can be unreliable and sometimes a combination of techniques is used. Gutta-percha is radiopaque, allowing verification afterwards that the root canal passages have been completely filled, without voids. An alternative filling material was invented in the early 1950s by Angelo Sargenti. It has undergone several formulations over the years (N2, N2 Universal, RC-2B, RC-2B White), but all contain paraformaldehyde. The paraformaldehyde, when placed into the root canal, forms formaldehyde, which penetrates and sterilizes the passage. The formaldehyde is then theoretically transformed to harmless water and carbon dioxide. The outcome is better than a root canal done with gutta-percha according to some investigations. There is however a lack of indisputable, scientifically made studies according to the Swedish Council on Health Technology Assessment. In rare cases, the paste like any other material can be forced past the root tip into the surrounding bone. If this happens, the formaldehyde will immediately be transformed into a harmless substance. The blood normally contains 2 mg formaldehyde per liter and the body regulates this in seconds. The rest of an overfill will be gradually absorbed and the end result is normally good. In 1991 the ADA Council on Dental Therapeutics resolved that the treatment was "not recommended", and it is not taught in any American dental school. Scientific evidence in endodontic therapy was, and still is lacking. The Sargenti technique has its advocates, however, who believe N2 to be less expensive and at least as safe as gutta-percha.〔 Steup, 2001 () Treatment outcome. N2. The collected data indicates that the N2DONTIC Method according to Sargenti is classified as successful method for the evaluated practice.〕 For some patients, root canal therapy is one of the most feared dental procedures, perhaps because of a painful abscess that necessitated the root canal procedure. However, dental professionals assert that modern root canal treatment is relatively painless because the pain can be controlled with a local anesthetic during the procedure and pain control medication can be used before and/or after treatment assuming that the dentist takes the time to administer one. However, in some cases it may be very difficult to achieve pain control before performing a root canal. For example, if a patient has an abscessed tooth, with a swollen area or "fluid-filled gum blister" next to the tooth, the pus in the abscess may contain acids that inactivate any anesthetic injected around the tooth. In this case, the dentist may drain the abscess by cutting it to let the pus drain out. Releasing the pus releases pressure built up around the tooth; this pressure causes the pain. The dentist then prescribes a week of antibiotics such as penicillin, which will reduce the infection and pus, making it easier to anesthetize the tooth when the patient returns one week later. The dentist could also open up the tooth and let the pus drain through the tooth, and could leave the tooth open for a few days to help relieve pressure. A root treated tooth may be eased from the occlusion as a measure to prevent tooth fracture prior to the cementation of a crown or similar restoration. Sometimes the dentist performs preliminary treatment of the tooth by removing all of the infected pulp of the tooth and applying a dressing and temporary filling to the tooth. This is called a pulpectomy. The dentist may also remove just the coronal portion of the dental pulp, which contains 90% of the nerve tissue, and leave intact the pulp in the canals. This procedure, called a "pulpotomy", tends to essentially eliminate all the pain. A pulpotomy may be a relatively definitive treatment for infected primary teeth. The pulpectomy and pulpotomy procedures aim to eliminate pain until the follow-up visit for finishing the root canal. Further occurrences of pain could indicate the presence of continuing infection or retention of vital nerve tissue. After removing as much of the internal pulp as possible, 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 surrounding tissue. The patient may still complain of pain if the dentist left pulp devitalizer over canal thus one visit increased. Ibuprofen taken orally is commonly used before and/or after these procedures to reduce inflammation. The following substances may be used as root canal irrigants during the root canal procedure: * less than 5% sodium hypochlorite (NaOCl) * 6% sodium hypochlorite with surface modifiers for better flow into nooks and crannies * 2% chlorhexidine gluconate * 0.2% chlorhexidine gluconate plus 0.2% cetrimide * 17% ethylenediaminetetraacetic acid (EDTA) * Framycetin sulfate * Mixture of citric acid, doxycycline, and polysorbate 80 (detergent) (MTAD) 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 function, and will almost certainly fracture in the future without cuspal coverage. Anterior teeth typically do not require full coverage restorations after a root canal, unless there is extensive tooth loss from decay or for esthetics or unusual occlusion. Placement of a crown or cusp-protecting cast gold covering is recommended also because these have the best ability to seal the root canaled tooth. If the tooth is not perfectly sealed, the root canal may leak, causing eventual failure of the root canal. Also, many people believe once a tooth has had a root canal treatment it cannot get decay. This is not true. A tooth with a root canal treatment still has the ability to decay, and without proper home care and an adequate fluoride source the tooth structure can become severely decayed (often without the patient's knowledge since the nerve has been removed, leaving the tooth without any pain perception). Thus, non-restorable carious destruction is the main reason for extraction of teeth after root canal therapy, with up to two-thirds of these extractions.〔 Therefore it is very important to have regular X-rays taken of the root canal to ensure that the tooth is not having any problems that the patient would not be aware of. The procedure is often complicated, depending on circumstances, and may involve multiple visits over a period of weeks. The cost is typically high. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Endodontic therapy」の詳細全文を読む スポンサード リンク
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