A crown is an artificial restoration that fits over the remaining part of a prepared tooth, making it strong and giving it the shape of a natural tooth.
A crown is sometimes known as a ‘cap’. Crowns are an ideal restoration for teeth that have been broken, or have been weakened by decay or a very large filling.
A crown could be used for a number of other reasons, for instance:
you may have discoloured fillings and would like to improve the appearance of the tooth
you may have had a root filling which will need a crown to protect it
it may help hold a bridge or denture firmly in place.