The dental implant used by most dentists and dental specialists are root-form implants. This basically means that they are replacement, or substitute tooth roots. They are used to replace natural tooth roots in areas of the mouth where teeth are missing
The reason it is so important to replace the tooth root as well as the visible part of the tooth (crown) is that natural tooth roots are embedded in the bone. In essence, the bone holds the tooth roots in place, which in turn helps preserve the bone from deteriorating.
When teeth are missing, the bone that previously supported those teeth melts away or deteriorates. This process is called bone resorption. The bone can be preserved by replacing missing tooth roots with dental implants. Since the bone actually forms a strong bond to the implants, they can serve the same functions as natural tooth roots: a strong foundation for biting and chewing and to provide stimulation for the bone to hold the implants in place.