A crown is a type of dental restoration which completely caps or encircles a tooth or dental implant to its original shape and size. Crowns are often needed when a large cavity threatens the ongoing health of a tooth. Crowns are typically bonded to the teeth using dental cement, and are used to improve the strength or appearance of teeth. The most popular type of crowns are made of porcelain, though different materials like gold, acrylic resin or a mix of these materials can be used.