Jawbone usually gets reabsorbed if it is not used (this happens when teeth are missing). Sometimes before an implant can be placed, bone needs to be added to the site and allowed to regenerate. This bone graft acts as a scaffold for your own bone to grow across, regenerate and calcify. As the new bone matures, the bone graft material gets reabsorbed. Most of the time, a membrane is used to guide the graft to grow the proper way. A bone graft may or may not be done at the same time an implant is placed, this depends on each individual situation. If it is determined that this needs to be performed during separate visits, the length of time between each appointment is normally 4 to 8 months, again depending on what type of bone the graft is put in.