Bone volume after tooth loss

I read about dental bone graft recently. I know about inserting a screw into the jaw to later get a tooth fixed on it. But what I didn't know was that when a tooth comes off, the gap where the tooth was remains in the jaw and this gap has to be filled first before a screw can be inserted. The filling of the gap is called dental bone graft and can be done using either one of these methods:

1. Using your own bone from hip or chin. 
2. Using a cadaver's bone which has been sterilized.
3. Using cow's bone which has been sterilized.
4. Using a chemical substance which resembles bone.

There is a chance of rejection using options 2 and 3. By the way, I typed this out from memory from what I read  few days ago. Please refer to reliable sources for detailed information.

Anyway, here is something interesting. When a tooth is removed, the bone decreases in volume. This image I found on a dental website will give you a an idea of what exactly happens when teeth is lost and why old people look the way they do:

Image source