The terms dental crowns and caps are synonymous. Crowns are typically used to restore a tooth's function and appearance following a restorative procedure such as a root canal. When decay in a tooth has become so advanced that large portions of the tooth must be removed, crowns are often used to restore the tooth. Crowns are also used to attach bridges, cover implants, prevent a cracked tooth from becoming worse, or an existing filling is in jeopardy of becoming loose or dislocated. Crowns also serve an aesthetic use, and are applied when a discolored or stained tooth needs to be restored to its natural appearance. Crowns are fabricated in a laboratory and are made either of porcelain baked onto a metal substrate, all-porcelain, or many of the new ceramic materials that have been developed.