This diagram demonstrate the "workings" a single tooth implant crown.  The center picture compares a natural tooth to an implant restored with a crown.  The small ligaments attached to the tooth make is slightly "spongy" in the bone that holds it.  Conversely, the implant is very rigidly attached to that bone with no "give" or movement.  Because implants are very rigidly held by the bone, it is very important that your bite is designed to function in close harmony with your other teeth, so it will not be overloaded with by your bite forces. 

This diagram demonstrates the difference between a natural tooth restored with a crown, and a single implant restored with a crown. Both of these treatment modalities should function and esthetically present very similarly.  At this point in time, a single tooth implant is the closest replacement to that which only nature can provide. 

Another example which demonstrates the use of implant crowns and an implant bridge.