Ridge Expansion / Ridge Augmentation

When teeth are lost and not replaced with implants soon after, the bone in the area tends to shrink away, making it less esthetic or difficult to place implants. In severe cases, the ridge has been reabsorbed and a bone graft is placed to increase ridge height and/or width. This is a technique used to restore the lost bone dimension when the jaw ridge gets too thin to place conventional implants. In this procedure, the bony ridge of the jaw are literally expanded by mechanical means. Bone graft material can be placed and matured for a few months before placing the implant. This causes slight discomfort and can be easily managed with ibuprofen.

http://www.perio.org/consumer/ridge.htm

When there is too little bone to place an implant which is shown in the first diagram