Crowns are needed if a significant portion of the tooth is missing. Crowns are usually either made of gold or porcelain. When a tooth is prepared for a crown only a few millimeters of the tooth structure is taken away to allow enough room for the crown to fit over the tooth. An implant replaces the root portion of the missing tooth. The abutment is a metal collar that attaches to the top of the implant and is the base for a crown as shown above.