The problem with tooth loss is that the bone that previously held the
tooth begins to "dissolve" once the tooth is removed.  The loss of bone takes place from the top of the jaw, often resulting in a dip in the area where the teeth have been extracted.

Dental researchers have worked for years to find ways to keep bone
from shrinking because bone loss can cause loose dentures (which can
lead to sore spots, leading to need for dental adhesives).  Loss of significant bone can lead to facial structure collapse and even
painful dentures when the denture rests on the nerve in the lower jaw.

Today, we have a well-researched solution that prevents the loss of bone and allows for highly retentive permanent restorations.  This is known as a dental implant, an artificial tooth root that actually replaces
your tooth root in the bone.

The dental implant is placed in the area where the extraction occurred and is held in place by bone just like the roots of the original tooth.  
One of the major benefits of having implants placed following extractions is that the placement of implants reduces or eliminates the loss of bone.