Because most people lose bone after a tooth is removed, bone grafting is often necessary. In most cases dental implants need at least 6 millimeters (1/4 inch) of bone. The average dental implant is 4.0 mm (3/16 inch). When you start with 6 mm of bone, after site preparation it leaves only one millimeter of bone on the front and the back sides of the implant. One millimeter (1/32 inch) is very little bone remaining around the implant. Ideally, 8 mm (5/16 inch) is much better. One of the most common mistakes in implant dentistry is when the dentist attempts to put the implant into inadequate bone.
Many dentists who perform dental implant treatment do not perform bone grafting. Frequently, they do not recognize those sites that require bone grafting. When an implant is placed in a site with inadequate bone the outcome is almost always compromised. An implant in the back of the mouth with compromised bone may be considered a success while an implant in the front of the mouth that has compromised bone is almost always a train wreck. Rarely can these situations be rectified without implant removal. When an implant is removed it is a very traumatic procedure for the bone, further compromising the site.
Sadly, these situations can usually be avoided with proper planning and execution. The key to success is to find an implant dentist with the best credentials and the most experience. While at a dental implant consultation, ask to see as many outcomes as you time will allow. If a dentist cannot show you a dozen of his or her cases as an example of what you can expect you should seek additional consultation(s). Ask to speak to former patients. Search the internet for complaints against the dentist.
Once a dental implant is improperly placed in the bone it is very difficult to fix. Dentists work in a very small space and good outcomes have a very small tolerance for error. It really needs to be done properly the first time.
Bone grafting can be done in a variety of different ways with a variety of different materials. A bone graft can be completed at the time of the tooth extraction. This is called a “socket preservation bone graft”. The intent is to increase bone volume as the bone remodels after the extraction. Human bank bone or demineralized cow bone is placed in the boney socket after the tooth/root is removed. A small white membrane is then sutured over the bone graft material. This membrane is non-resorbable which means it must be removed in 21-28 days. It then takes between 4 and 6 months for the body to convert the bone graft material into mature bone ready for an implant.
An “onlay bone graft” is done when an existing site, without a tooth, has inadequate bone for a dental implant. Again, human bone or cow bone can be used. Cow bone typically converts much more slowly than human bone. This is a much more invasive procedure. The tissue around the site must be raised away from the bone to be able to add bone to the deficient site. Because some of the bone graft volume is lost during healing, a strong attempt to over build the site is made. Meaning we try to add 30% more bone than will be needed after healing. Some tissue will not accommodate this volume. The usual healing time after an onlay bone graft is 6 months.
Growth factors such as PRP (platelet rich plasma) and BMP (bone morphogenic protein) are two examples of materials commonly used to enhance or promote better and faster bone healing. There is some debate as to whether the net increase in bone volume can justify the significant increase in the cost of the procedure.
There are techniques that implant dentists can use to avoid bone grafts. See our Alternatives to Bone Grafts Section in the FAQs.