In the case of the dental implants, the jaw bone may not have enough bone mass to support an implanted post and will cause the implant to fail. The upper jaw is more succeptible to the need of a bone graft than the lower. Think of it like nailing something into the thinnest end of an extremely thin board. What happens? The board splits. The bone graft helps bulk up the area of the jaw that needs treatment by fusing the osseous tissue of the graft and of the bone already present and allowing it to heal together. It may take anywhere from 4 to 6 months for the grafted area to be ready for treatment depending on the type of dental implant you use.