In the middle of each healthy tooth there is a pulp, a living tissue that makes the tooth susceptible to heat, cold, pressure and pain. If the pulp dies, the tooth dies, too.
The pulp may die from a tooth decay or caries, and sometimes even after a tooth damage. However, in some cases, there is no apparent cause. No symptoms will alert you to the tooth decay (except for the cessation of pain in the tooth that is decaying), so you may not know that you have a dead tooth until your dentist tells you (during the chekup). After a while, the dead teeth turn grey.
What to do?
Once you discover a dead tooth, the dentist may treat it. There is a danger, especially after caries, that poisonous substances and bacteria penetrate from the dead pulp through the root and cause abscess.
Since the dead tooth can still effectively perform the function it is intended for, there is usually no reason to take it out if it is not decayed. The dentist usually opens the tooth, cleanses it, disinfects it, and fills the pulp chamber and the root canal; this is commonly referred to as root canal treatment. All cavities in the dental crown are sealed by the usual procedure.