A natural tooth consists of a crown (the part you see above the gum), and the root (the part hidden under the gum, within the jawbone).  It is the root that actually holds the natural tooth in place.
When a person is missing a tooth, the dentist must decide how to re-create the crown portion, and he must choose the best method to hold it in place.  Dental Implants were created for this purpose.
Dental Implants are titanium cylinders that are placed into the jawbone and serve as replacement roots for missing teeth. The replacement teeth that are later attached to the Implants, look, feel, and function like natural teeth.

Titanium is the most compatible with human biology, it is also used in the manufacture of orthopedic appliances such as hips, knees, wrists, and elbows. Thanks to the process of osseointegration, the jawbone fuses to the titanium Implants, creating anchors for new, prosthetic teeth.
Dental Implant-supported teeth consist of 3 basic components:

Implant: A titanium post, inserted in the jawbone, which functions as an artificial root. It will become the foundation for the new, prosthetic teeth. Once the new bone grows around them, Implants become permanent. More than 4 decades of research in Sweden and the United States has recognized titanium for its biological compatibility with the human body. Studies show that the earliest patients treated with titanium osseointegrated Implants continue to have good dental function.

Abutment: An extension to the Implant, it screws onto the implant and holds the artificial tooth. It may be positioned slightly above or even below the gumline.

Crown: is usually made of ceramic, with a core structure made of metal, ceramic or zirconium.

Crowns are custom-designed and shaded so that they look like natural teeth.