Why would a doc have to do a bone graft while removing wisdom teeth?

Large defect: Sometimes its necessary to place a bone graft when removing teeth to protect the nerve in the jaw but usually to preserve bone on the back side of the 2nd molar which could cause more tooth loss.

Wisdom and Graft.: The answer to this is "sometimes". It depends on the position of the wisdom tooth. If the wisdom tooth makes the lower jaw very thin after removal, it is possible to be prone to get a broken jaw. The bone graft can help fill the area in and speed up healing. It could also be placed if dental implants are planned in the future.

Bone loss: It is possible there was a large cyst that required bone grafting to replace the bone that was destroyed. Also there may have been a significant amount of bone loss around the distal (back part) of the 2nd molar and he was trying to salvage it.

To prevent bone loss: Wisdom tooth removal on adults can lead to loss of bone behind the 2nd molar (the tooth in front of the wisdom tooth). To minimize this bone loss which can be significant, a bone graft is placed in the extraction socket.