Why would a tooth need a root canal?

Teeth have nerves and blood vessels in their hollow center, which is known as the pulp chamber. The pulp chamber extends down the length of the roots through the root canals. If the tissue inside this pulp chamber dies or becomes infected, an infection (called an abscess) develops and the tooth will be lost. Teeth are a unique structure in the human body because the blood supply and immune system have very limited access to the tissue inside of them. The only access that blood vessels have into a tooth is through tiny openings in the tips of the roots, which prevents the immune system from stopping bacterial infection. Once dead, the tissue inside the tooth becomes a food source for bacteria, and the bacteria and dead tissue seep out the tips of the roots, creating an abscess around the root tips. Once this happens, the infected tooth will never get better and the abscess will eventually destroy enough bone around the tooth that it will become loose and be lost. Placing people on antibiotics is a temporary fix; the infection will continue as long as there is dead tissue within the tooth. We can prevent this tooth loss by performing Root Canal Therapy on the tooth. It is the dead tissue inside an infected tooth which is removed when a root canal is done. Once all the dead and infected tissue is removed, the inside of the tooth is filled up to prevent subsequent infections.

How do teeth become infected?

This tissue inside teeth can die and become infected different ways. The most common is from tooth decay. Cavities are caused by bacteria, and when a cavity gets deep enough and the bacteria gets into the pulp chamber, pulpal infection and tissue death follow.

Trauma can also cause the pulpal tissues to die. Trauma is defined as anything which is irritating to the pulpal tissues and includes cavities, injury (biting on something hard, being hit by something), cracks or fractures, and dental work. Trauma causes inflammation and swelling of the pulpal tissues. If the swelling becomes too intense, it can cut off the blood supply to the pulpal tissues and cause tissue death. Since dental work is traumatic to teeth it is very important to identify and treat decay as soon as possible. The deeper we have to go inside a tooth to remove decay, the more trauma we introduce to the tooth. It is also important to keep the size of a restoration as minimal as possible, which is why we use white composite fillings instead of silver amalgam and inlays and onlays instead of crowns whenever possible.

How is a root canal done?

There are two basic steps to a root canal, cleaning the inside of the tooth (called "shaping") and filling the inside of the tooth. After the tooth is numbed, a hole is opened up into the pulp chamber. Once inside the pulp chamber, the openings to the canals (one to four depending on the tooth) are located and cleaned out using instruments called files. The files ream out the inside of the canals, removing dead tissue and opening up the canals so we can rinse them out with an antibacterial solution. Once the canals are fully cleansed, the canals are dried and filled with a rubbery material which seals up the little hole at the tip of the root so nothing can ever get back inside your tooth. If there is a large abscess present, we sometimes place the patient on antibiotics for a week before filling the canals. This is done so we do not trap any bacteria inside our root canal filling. You can tell if a tooth has had a root canal by looking at the x-ray and seeing the white filling material down the length of the roots. We may place a post inside one of the canals before placing a crown to help strengthen the tooth. We may refer a patient to a root canal specialist, called an Endodontist, if there are any unusual circumstances such as curved roots, extra roots or extremely small canals.

X-ray of a completed root canal.

Why does a tooth with a root canal need a crown?

Once a tooth has had a root canal, a crown quickly needs to be placed on it. Now that the tooth has been hollowed out, it is fairly fragile and prone to fracturing. Unlike fillings, inlays and onlays, crowns cover the entire tooth and are the only acceptable restoration for a tooth which has had a root canal. If you are not planning on placing a crown on your tooth after a root canal, you may as well have skipped the root canal and had the tooth extracted. We cannot stress enough that a tooth which has had a root canal and does not have a crown placed is doomed to develop a serious fracture which will require extraction of the tooth. It may not happen right away, but eventually it will and we cannot predict how long that will be.

How long will it last?

This really depends on how much tooth is left, the condition it is in, and where it is in the mouth. A tooth with a root canal and a crown can eventually develop a root fracture, which is the end of the line for a tooth. In general, most teeth which have had root canals will last for twenty years or so. This is an average, so some last a lifetime and some only a few years. Teeth which were severely broken down prior to the root canal and crown are most likely to fracture, although we get surprised all the time by teeth which appear to be in decent shape developing root fractures. Teeth which are farther back in the mouth are also more at risk since they are constantly under extremely heavy chewing forces. Teeth have a lot of anatomical variation, and teeth with thinner roots are more susceptible to fractures. Root fractures are when the root of the tooth splits apart below the gumline. They are un-repairable and the only treatment for them is extraction. With this in mind, it is sometimes wiser to remove a severly broken down tooth with a poor long-term prognosis and replace it with a predictable and long lasting implant.

Here is a link to the patient education section of our website which you may find helpful. There is a lot of information there for you to browse through and to answer any questions you may have, and was designed by a dental education company whose tools are used in our office to help our patients understand their treatment options. Some of the information there may be a bit outdated because the dental field is always evolving, but the general concepts of dentistry are nicely described and illustrated.

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