Severe pain on a tooth which lasts for several seconds to minutes after a stimulus such as cold drink or chewing can be indicative of irreversible changes to the nerve/blood supply(pulp) of the tooth. This may happen if there is a long-standing cavity on the tooth or can result from a fractured tooth among other reasons. See your dentist immediately if you have any similar symptoms.
A tooth that is severely decayed or infected can be saved, rather than be removed, through a procedure commonly known as a root canal treatment.
The typical tooth has around one to three roots. Each of these roots has one or two canals that essentially go from the top of your tooth to the bottom. Within these canals is a soft, living tissue called pulp, which consists of nerves and blood vessels. When a root canal is done, the pulp is removed, your tooth's canals are disinfected, and a special dental filler (plant extract) is used to seal them off. Your tooth will receive a temporary or permanent filling after the root canal procedure. The final step in the process will be to place a permanent covering, such as a crown, over the treated tooth.
Root canals today are generally painless procedures thanks to the effectiveness of local anesthetic and advances in dental technology.