A crown may be all ceramic, metal ceramic, gold, acrylic resin or composite resin. Ceramic crowns most closely mimic the optical value of natural teeth. For that reason they are primarily used to restore teeth in the front part of either upper or lower jaw. Metal ceramic crowns are used to restore teeth toward the back of the mouth where strength of the bite requires more stress resistant materials. The1-2 millimeters thick porcelain coating is supported by the cast gold-alloy metal structure of the crown. Acrylic resin and composite resin crowns are intended for temporary use, typically for several week but may be need for up to 6 months.
Teeth restored with crowns should be cleaned in exactly the same manner as natural teeth. If a crown comes loose that is an indication that it has lost it's cement seal and bacteria-continuing saliva have probably been bathing the tooth structure inside the crown. The tooth should be checked for decay before the crown can be re-cemented. Implant crowns are immune to decay.