Endodontic therapy

# Overview
Endodontic therapy is a sequence of treatment for the pulp of a tooth whose end result is the elimination of infection and protection of the decontaminated tooth from future microbial invasion.  Although this set of procedures is commonly referred to as a root canal, this term is imprecise; root canals and their associated pulp chamber are the anatomical hollows within a tooth which are naturally inhabited by nerve tissue, blood vessels and a number of other cellular entities, whereas endodontic therapy includes the complete removal of these structures, the subsequent cleaning, shaping and decontamination of these hollows with the use of tiny files and irrigating solutions and the obturation, or filling, of the decontaminated root canals with an inert filling, such as gutta percha and a usually eugenol-based cement. After the surgery the tooth will be "dead", and if the infection is spread at apex - root end surgery is required.
Although the procedure is relatively painless when done properly, the root canal remains the stereotypical fearsome dental operation, and in the United States, a common response to an unpleasant proposal is, "I'd rather have a root canal."

# Root canal treatment
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 it. 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 by scraping it out of the root canals. Once this is done, the dentist fills the cavity with an inert material and seals up the opening. This procedure is known as root canal therapy. If enough of the tooth has been damaged, or removed as a result of the treatment, a crown may be required.
The standard filling material is gutta-percha, a natural thermoplastic polymer of isoprene, which is melted and injected to fill the root canal passages. Barium is added to the isoprene so the material will be opaque to X-rays, allowing verification afterwards that the passages have been properly completely filled in, without voids.
For patients, root canal therapy is one of the most feared procedures in all of dentistry; however, dental professionals assert that modern root canal treatment is relatively painless because the pain can be controlled. Lidocaine is a commonly used local anesthetic. Pain control medication may be used either before or after treatment. 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, it is best for the dentist to 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 much 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.
At this first visit, the dentist must ensure that the patient is not biting into the tooth, which could also trigger pain. 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 eliminate almost all pain until the follow-up visit for finishing the root canal. But if the pain returns, it means any of three things: the patient is biting into the tooth, there is still a significant amount of sensitive nerve material left in the tooth, or there is still more pus building up inside and around the infected tooth; all of these cause pain.
After removing as much of the internal pulp as possible, the root canals can be temporarily filled with calcium hydroxide paste. This strong alkaline base is left in for a week or more to disinfect and reduce inflammation in surrounding tissue. Ibuprofen taken orally is commonly used before and/or after these procedures to reduce inflammation.
After receiving a root canal, the tooth should be protected with a crown that covers the cusps of the tooth. Otherwise, over the years the tooth will almost certainly fracture, since root canals remove tooth structure from the tooth and undermine the tooth's structural integrity. Also, root canal teeth tend to be more brittle than teeth not treated with a root canal. This is commonly due to the fact that the blood supply to the tooth, which nourishes and hydrates the tooth structure, is removed during the root canal procedure, leaving the tooth without a source of moisture replenishment. 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 it cannot get decay. This is not true. A tooth with a root canal still has the ability to decay, and without proper home care and an adequate fluoride source the tooth structure can become severely decayed  without the patient's knowledge since the nerve has been removed, leaving the tooth without any pain perception. 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 high, by local standards. In the United States, it would typically cost US$400-1,000though exceeded by the even more expensive related crown procedure, typically around US$500-1,500 with usually only 50% being covered by the dental insurer (DMO or DPO). In India, the root canal procedure would typically cost INR 1,500-4,500 (US$35-110), when performed by an endodontist  and the crown procedure, for a ceramic crown, would cost around INR 2,000-5,000 (US$50-125).  In Argentina mostly all medical insurance services offer full coverage for the endodontic therapy.  Without dental insurance, the average cost for an endodontic therapy, done by a qualified endodontist, is around ARP 140 or USD 44 (March, 2008).  This procedure does not include the ceramic crown which, without dental insurance, is around ARP 540 or USD 170 (March, 2008)

# Innovation
In the last ten to twenty years, there have been great innovations in the art and science of root canal therapy. Dentists now must be educated on the current concepts in order to optimally perform a root canal. Root canal therapy has become more automated and can be performed faster, thanks to advances in automated mechanical instrumentation of teeth and more advanced root canal filling methods. Dentists also possess newer technologies that allow more efficient, scientific measurements to be taken of the dimensions of the root canal that must be filled. Many dentists use microscopes to perform root canals, and the consensus is that root canals performed using microscopes or other forms of magnification are more likely to succeed than those performed without them. Although general dentists are becoming versed in these advanced technologies, they are still more likely to be used by specialist root canal doctors (known as endodontists). Dr. Arnaldo Castellucci, an Italian dentist, has recently authored a three-volume treatise on endodontics which thoroughly covers these modern concepts.
Laser root canal procedures are a controversial innovation. Lasers may be fast but have not been shown to thoroughly disinfect the whole tooth, and may cause damage.

# Failure
Root canal treatments can fail. Patients should be educated on some of the reasons why root canals may fail. They may fail if the dentist does not find, clean and fill all of the root canals within a tooth. For example, on a top molar tooth, there is a more than 50% chance that the tooth has four canals instead of just three. But the fourth canal, often called a "mesio-buccal 2", tends to be very difficult to see and often requires special instruments and magnification in order to see it. So it may be missed, and this infected canal may cause a continued infection or "flare up" of the tooth. Any tooth may have more than one canal, which may be missed while performing the root canal. Sometimes the canal may be unusually shaped, making it impossible to fill it completely, so that some infected material is still left in the canal. Sometimes the canal filling does not extend deeply enough into the canal, or it does not fill the canal as much as it should. Sometimes a tooth root may be perforated while the root canal is being performed, making it difficult to fill the tooth. The hole may be filled with a material derived from natural cement called "MTA", although usually a specialist would perform this procedure. Fortunately, a specialist can often re-treat and definitively heal up these teeth, often years after the initial root canal procedure.
Sometimes a tool can break while it is in the tooth.  If the tip of a spiral metal file used by the doctor breaks off during the procedure, it is usually left behind and not extracted, leaving the patient with a small amount of retained metal.  The occurrence of this event is proportional to the narrowness, curvature, length, and number of roots on the tooth being treated.  Complications resulting from retained metal are not well studied, but the occurrence of tool breakage is well documented .

# Systemic issues
An infected tooth may endanger other parts of the body. People with special vulnerabilities, such as prosthetic joint replacement or mitral valve prolapse, may need to take antibiotics to protect from infection spreading during dental procedures. Both endodontic therapy and tooth extraction can lead to subsequent jaw bone infection.  The American Dental Association (ADA) asserts that any risks can be adequately controlled.
Recent studies indicate that substances commonly used to clean the interior of the tooth provide a low overall chance of succeeding in completely sterilizing a tooth internally; however, a properly restored tooth following root canal therapy yields long-term success rates near 97% in this study large scale Delta Dental Study of over 1.6 million patients who had root canal therapy, 97% had retained their teeth 8 years following the procedure.
There is no scientific evidence that root canal therapy has any adverse affects on the over all health of the individual. Effective root canal therapy performed by adequately trained clinicians results in very high success rates with no systemic relationship to the patient's overall health.

# List of root canal irrigants
The following substances are used as root canal irrigants during the root canal procedure:
- 5.25% sodium hypochlorite (NaOCl)
- 6% sodium hypochlorite (NaOCl) with Surface modifiers for better flow into nooks and crannys
- 2% chlorhexidine gluconate
- 0.2% chlorhexidine gluconate plus 0.2% cetrimide (Cetrexidin)
- 17% Ethylenediaminetetraacetic acid (EDTA)
- framycetin sulfate (Septomixine)