Root canals are the commonly used term for the main canals within the dentin of the tooth. These are part of the natural cavity within a tooth that consists of the dental pulp chamber, the main canals, and sometimes more intricate anatomical branches that may connect the root canals to each other or to the root surface of the tooth. Root canals are filled with a highly vascularized, loose connective tissue, the dental pulp. This sometimes becomes infected and inflamed, generally due to caries or tooth fractures that allow microorganisms, mostly bacteria from the oral flora or their by-products, access to the pulp chamber or the root canals; the infected tissue is removed by a surgical intervention known as endodontic therapy and commonly called 'a root canal'.
At the center of a tooth is a hollow area that houses soft tissue, known as pulp. This hollow area contains a relatively wide space towards the chewing surface of the tooth called the pulp chamber. This pulp chamber is connected to the tip of the root of the tooth via thin hollow pipe-like canals—hence, the term "root canal". Human teeth normally have one to four canals, with teeth toward the back of the mouth having the most. These canals run through the centre of the roots like pencil lead runs through the length of a pencil. The tooth receives nutrition through the blood vessels and nerves traversing these canals.
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.
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 are 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 most 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.