Dental implants are artificial devices used by dentists to replace missing teeth. Implants come in many different sizes and shapes. Implants which rest on top of the bone are called subperiosteal implants. There are also very narrow implants which are placed within the bone, and are called blade implants. Those implants which resemble the root of the tooth are called root form implants, and they are placed into the bone to act as support for a prosthetic crown.