In order to understand exactly what an implant is, you first have to picture a natural tooth, which essentially has two main parts:

1. Crown, which is the part you see in the mouth above the gum line, and

2. Root, which is inside the bone. 

A dental or endosseous implant (“endo” – inside; “osseous” – bone) replaces just the root part of the missing tooth. The implant is then topped by a realistic-looking dental crown.
Definition - A dental implant is an artificial tooth root replacement made of titanium and shaped like a screw. This titanium screw is not like any other screw you buy at the hardware store . Actually it is much more sophisticated. It is produced in a very slow and well monitored process and requires state of the art technology, which results in a very expensive"high techie" looking screw. Dental implants come in different lengths and diameters. Dental implants are made of titanium because (as discovered by Dr. Branemark in 1952) titanium Osseointegrates with the bone which means - it biologically bonds to the bone.