When your tooth has been badly damaged by a cavity, it may leave an opening where the nerve of the tooth is irritated from the bacteria in the cavity. If the area where the nerve is affected is small enough, and the symptoms with the tooth are mild (very short response to cold temperature), the tooth has a chance to recover.
However, if the area affected is large, the nerve will start to die. This will cause spontaneous, prolonged, sharp pain due to temperature or pressure or occasionally it may be a constant dull ache from an infection, or abscess that has developed. Once a nerve dies, this is an irreversible process; the nerve will not get better and eventually will lead to infection.
At this point, a decision must be made on how to remove the dying nerve so pain and infection may be removed or avoided. Either the tooth must be removed with the dying nerve inside, or a root canal must be done to remove the dead nerve from inside the tooth.
When a tooth is extracted, a hole will be left inside the gums and bone where the tooth base or roots were placed. This area will take months to completely heal, ultimately leaving a smooth surface and contour to the bone and gums remaining. However within a week or so, the area will appear to be filled in, and normal eating and function should return.
Pain after an extraction depends on the difficulty of removing the tooth; however with a standard extraction, it should peak within a day after the extraction and resolve quickly. If pain seems minimal immediately after the extraction, but several days later seems to increase, you may be experiencing a "dry socket". This is an exposure of the bone to the air and oral fluids, because the blood clot formed during healing has been lost. To avoid a "dry socket", it is advised to avoid sucking on straws, spitting forcefully or smoking for at least 48 hours. Caution should be used when eating—a soft diet is advised for a couple days following an extraction.
When a root canal is performed, a small opening is made to the outer surface of the tooth entering down into the area where the nerve of the tooth is located. The dead or dying nerve is removed with small instruments and the area is cleaned to eliminate any bacteria living in this space. The area is then filled down into the root of the tooth with a rubbery material that will seal it completely. This will prevent bacteria from infiltrating the space and causing an infection in the future. This process should be pain free, due to the use of local anesthesia. Occasionally, an antibiotic may need to be taken prior to a root canal procedure to allow the anesthetic to work optimally.
After a root canal, the top portion of the tooth is then repaired with either a filling or a crown. A crown is advised on any "broken down" teeth or posterior teeth, such as the molars or premolars. This will help prevent fracture of these teeth that after a root canal. They tend to become brittle due to the removal of the nerve and blood supply to the tooth. The investment of money placed in a root canal should be considered when deciding on placing a crown afterwards. It would be a shame to lose a tooth to fracture after money had been previously invested in a root canal!