The bone graft procedures are referred to as:

Sinus lift procedure
This procedure involves elevating the sinus membrane and placing the bone graft onto the sinus floor, allowing implants to be placed in the back part of the upper jaw.

Socket-Preservation
After a tooth is extracted, a void is left where the tooth was previously.  A bone graft may be placed into the extraction socket to help preserve bone height and width to facilitate implant placement at a future date.  The bone graft is then left to heal for 3-6 months before an implant is placed.

Ridge-augmentation
In severe cases the jaw ridge may be inadequate for dental implants. A bone graft is placed to increase the ridge height and/or width.