A dental crown is a tooth-shaped "cap" that is placed over a tooth -- to cover the tooth to restore its shape and size, strength, and improve its appearance.
Crowns, when cemented into place, fully encase the entire visible portion of a tooth that lies at and above the gum line.
A dental crown may be needed in the following situations:
To protect a weak tooth (for instance, from decay) from breaking or to hold together parts of a cracked tooth
To restore an already broken tooth or a tooth that has been severely worn down
To cover and support a tooth with a large filling when there isn't a lot of tooth left
To hold a dental bridge in place
To cover misshapen or severely discoloured teeth
To cover a dental implant
To make a cosmetic modification