To fully understand a root canal, one should understand normal tooth anatomy.
A tooth may need a root canal under the following circumstances:A tooth has fractured and exposed the pulp (often called “the nerve”). A tooth has received a physical trauma, which has created an inflammatory reaction in the pulp tissue causing a quick or slow death of the pulp tissue by the strangulation theory of pulp necrosis. A severe blow to the tooth can sever the blood vessels entering the root leading to pulp necrosis. The tooth has a recent or old deep filling which has created an inflammatory reaction in the pulp tissue.
Bacterial decay has progressed deeply towards the pulp and is either very close to the pulp chamber or has infected the pulp chamber.
The end result of irreversible inflammation of the pulp is a pulp necrosis: the tissue inside the root no longer has a blood supply, and the tissue dies. Bacteria quickly infect dead tissue and the bacteria grows and multiplies creating pressure and pain.
To use an analogy, lets say a person receives a good blow to a finger. A bruise develops, the finger swells and blood rushes into the finger to try to repair the damaged tissue. The same amount of blood entering into the finger must leave the finger and return to the body. The skin surrounding the tissues of the finger is elastic and expands allowing blood to enter and swell the finger. A tooth’s skin is not elastic like the finger but the actual hard part of the tooth and root itself. Any injury, be it extreme cold or hot, bacteria from decay or the trauma of a blow or deep drilling into the tooth causes an inflammatory reaction in the tooth pulp. Extra blood rushes into the tooth to try and repair the inflamed tissue. The same amount of blood entering the tooth must leave the tooth and because the tooth’s skin (the hard outer enamel of the tooth) cannot swell, blood begins to pool inside the tooth. Blood no longer flows easily in and out of the tooth, the blood vessels in the pulp eventually strangle off, i.e. break down and the pulp tissue dies.
Bacteria quickly infect the dead pulp tissue and the bacterium grows and multiplies creating pressure and pain in the tooth.
Continuing the analogy with the finger, if the tissue in the finger was all dead, then the finger should be amputated before gangrene infection spreads throughout the hand, arm and body. Unfortunately, taxidermy of a finger is not possible because the skin needs a blood supply, which no longer exists. In the case of the dead tooth, the bacteria infected tissue inside the tooth can escape the root and infect the jaw creating an abscess. The tooth must extracted from the mouth. Alternatively, the dead tissue inside the tooth could be removed and the space filled with a biocompatible substance. This taxidermy of a tooth is possible because the skin of the tooth, the enamel, dentin and cementum, once fully formed, no longer need a blood supply for its survival. This called a root canal.
A root canal is the removal of the pulp tissue inside a tooth, sterilization of the empty space created and the sealing or plugging of that space with a biocompatible substance.