The purpose of a dental crown is to protect your tooth. It can be used for tooth restoration and cosmetic purposes, but the goal is to prevent further damage to a weakened tooth.
The crown covers the entire tooth, although there are variations of inlays and onlays. It seals the tooth off from external forces and allows it to function normally.
A dental crown prevents debris and bacteria from re-entering a heavily decayed tooth or a split tooth. It is used after a root canal because it covers the hole the endodontist drilled to remove the infection.

All dental crowns are customized for each patient. This means three things for the patient.