Crowns, or better known as "caps," are needed on teeth for various reasons. Some of the reasons crowns are needed are to restore broken and unaesthetic teeth.
Teeth are often restored with fillings of silver or composite plastics. These materials can often accomplish the aim of replacing the part of the tooth that has been lost, in a strong and good-looking manner.
However, there comes a point where the damage to the tooth has removed too much structure to hold a filling. The restoration must be done by a technique that will attach to the remaining tooth, stand up under heavier use and meet more elaborate cosmetic requirements.