Bridge
Bridges are natural-looking dental appliances that can replace a section of missing teeth. Because they are custom-made, bridges are barely noticeable and can restore the natural contour of teeth as well as the proper bite relationship between upper and lower teeth.
There are several types of fixed dental bridges (cannot be removed), including conventional fixed bridges, cantilever bridges and resin-bonded bridges. Some bridges are removable and can be cleaned by the wearer; others need to be removed by a dentist.
Porcelain, gold alloys or combinations of materials are usually used to make bridge appliances.
Appliances called implant bridges are attached to an area below the gum tissue, or the bone.
Implants
Before development of dental implants, dentures were the only alternative to replacing a missing tooth or teeth. 
Implants are synthetic structures that are placed in the area of the tooth normally occupied by the root. Implants are anchored to the jawbone or metal framework on the bone and act as a foundation for an artificial tooth or permanent bridge. In some cases, implants can be used to attach dentures.
Not everyone is a candidate for a dental implant, however. For a successful implant to take hold, a candidate must have proper bone density and have a strong immune system. In all cases, dental 
implants require strict oral hygiene.
Implants are so well designed that they mimic the look and feel of natural teeth. Implants are usually made of a synthetic yet biocompatible material like metal or ceramic.
Surgery is necessary to prepare the area for an implant and place the implant in the mouth. Following the procedure, a period of time is required for the implant to take hold and for bone tissue to build up and anchor the device. In some cases, metal posts are inserted into the implant during a follow-up procedure to connect the tooth.
Because implants require surgery, patients are administered anesthesia and, if necessary, antibiotics to stave off infection following the procedure.
Like any restoration, implants require diligent oral hygiene and proper care to ensure they last a long time.
Sometimes with implants ridge augmentation is required.