Crowns are a type of dental restoration which, when cemented into place, fully covers that portion of a tooth which lies at and above the gum line. In comparison, composite fillings/inlays/onlays are dental restorations that are used to fill in or cover over just a portion of a tooth. Since dental crowns encase the entire visible aspect of a tooth, a dental crown in effect becomes the tooth's new outer surface.
Crowns are used to rebuild broken or decayed teeth, to strengthen teeth, and as a means by which to enhance the cosmetic appearance of teeth. Crowns can be made out of porcelain/ceramic, gold alloy, or a combination of both. Dental crowns are often referred to as "dental caps".