In order to save a tooth that may be in serious condition, you will need a root canal treatment. The condition may result from decay that has gone farther into the tooth than a normal cavity or from some physical injury. The procedure itself is known as endodontic treatment.

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As noted in the video, those who perform such procedures are endodontists, which are essentially dentists with some extra training and skills.
The video further noted than an endodontist will use some of the same and some specialized equipment and techniques. Among the familiar techniques is the use of a local anesthetic to protect the patient from excessive pain. Root canal treatment goes beyond the filling of a cavity, however, and instead involves the removal of the pulp, the soft area within the tooth that itself contains blood vessels, nerves, and additional tissue.
Following the removal of the pulp, the endodontist will clean and shape the canal areas, then seal them with a special material. The final step in the procedure will probably involve the placement of a crown atop the affected tooth. In addition to the relief from pain, the patient will have a tooth that looks new.