Onlay bone grafts are typically performed to repair defects of the jaws. These defects may arise as a result of traumatic injuries, tumor surgery, or congenital defects. Large defects are repaired using the patient’s own bone. This bone is harvested from a number of different sites depending on the size of the defect. The bone is either obtained from a tissue bank or your own bone is taken from the jaw, hip or tibia (below the knee).