If the nerve inside the tooth is damaged, whether by immediate trauma such as a blow to the tooth or longer-term damage caused by decay and fillings, it can die.
Dying can be a very painful process if it happens over a short time, but teeth can also die quite silently over a longer timescale. Whichever happens, a tooth with a dead nerve will almost always become infected by germs from the neck of the tooth, through the local lymphatic system.
When germs find a dead nerve, they colonise it, and the lack of oxygen inside the tooth selects for those bacteria that cannot live in the presence of oxygen. Such bacteria are usually disease-causers. Living happily in the space where the nerve used to be in a dead tooth, the bacteria grow and divide and rapidly fill the space. Further divisions cause a mass of germs to be pushed back out of the tooth through the hole at the tip of the root that they went in through, which is where the nerve used to get its blood, lymphatic, and nerve supply.
The sudden emergence of these germs causes a dramatic response by the body which sends white blood cells to eat the germs and sets up inflammation at the site. The white blood cells die in huge numbers creating a rapidly enlarging pool of pus at the tip of the tooth root. Combined with the local inflammation, the effect is to create pressure which tries to force the tooth up and out of its socket. To you, the tooth feels raised and very tender to touch, and there is rapidly increasing and very serious throbbing pain below it. This is an acute dental abscess.
If left untreated the pain rises to a peak over one or two days and then quickly subsides when the pressure of the pus manages to force it through the bone and out into the soft tissues. When that happens the pain goes because the pressure has gone, and the soft tissues in the area swell from the presence of the pus, and from inflammation caused by the presence of the pus. Eventually, the pus will break through the soft tissues as well and discharge. When that happens the soft tissue swelling returns to normal, the tooth becomes comfortable to bite on, and there is a small hole left discharging the new, slow production of pus from the infection under the tooth. This is a chronic dental abscess. Although it is pain-free, it is not a healthy situation as there is a chronic area of infection remaining within the jawbone. It can become acute and painful again at any time, especially at times of stress such as holidays or Christmas, and could even cause a very serious infection of your jawbone.
The options for treatment are to remove the tooth with the loss of stability and function that causes, or to have the tooth root-filled.
Working inside the tooth to clean out the root canals and to fill them with a permanent filling material that will last well and stop germs re-colonising the tooth is the business of Endodontics or root-filling (in America, “root canal”).
Root-filling – how it’s done
To root-fill a tooth the dentist must first gain access to the nerve chamber within the tooth, usually by drilling through the tooth to create an access hole. If the tooth is dead this is quite painless and can be done without any anaesthetic since a tooth without a nerve is as dead as your hair or fingernails.
Next he has to locate the entrances to each and all of the root canals. This can be very difficult because the root canals are irregular in their disposition and numbers. It requires considerable experience and an operating microscope to have a good chance of finding any small or hidden canals, but if any canal is left unfilled, then the treatment is likely to fail and cause the tooth to be removed. Even with the aid of a microscope, it can be difficult to find all the canals, and even when found it may not be possible to prepare every canal in the tooth.
For this reason, Endodontics does not come with a guarantee of success, any more than any other form of surgery. Nevertheless, using experience, taking the time and care, maximises the chances of success. Success rates for well-performed Endodontics are very high and can enable you to save a tooth, maintain the stability and function of your mouth, and save the costs of replacing a lost tooth.
A root-treated tooth becomes weaker over time because the root-filling dries out the inside of the tooth and makes it brittle. To counteract the later loss of the tooth due to fracture, such teeth are often crowned, both to strengthen them, and because too much tooth may have been lost to allow the use of a lesser restoration.
Despite this… The combined cost of root filling and restoring a back tooth is usually about half of the cost of replacing it if it is lost.