Table of Contents
Bone Grafting 2
Real World Consequences of Bone Resorption
Whenever a tooth is extracted, and no interventions are planned to preserve the bone, approximately 25% of the bone height above the base of the socket may be lost within the first year. Within the first three years, as much as 63% of the bone height will be resorbed. The final height of the remaining ridge depends upon the depth of the original socket, and the presence of adjacent teeth. If there are adjacent teeth present, less bone will be lost. On the other hand, if multiple teeth are lost, then, over a period of years, bone will be lost down to the depth of the of the original socket, and even beyond, since the cortical bone will eventually remodel.
The images above are drawn by hand, but they show the real effect of the loss of the teeth. The image to the left shows the profile of a middle age woman with a full set of teeth. The center image shows what the patient would look like immediately after the extraction of her teeth. The image to the right shows the what the patient would look like at the same age if the teeth had been removed about ten years before. If you have ever ridden the subway in any large city, you have seen people with this type of deformity. They were not born that way. They have simply lost all their teeth. Visit my page on dentures to see several more images of patients who have lost their teeth. Click on the image above to go to the website of the International Congress of Oral Implantologists for more on this subject.
(For dental professionals and students)
Guided tissue regeneration–Technically, the term “guided tissue regeneration” applies to the use of resorbable or non resorbable membranes to allow for the rebuilding of bone around periodontally involved teeth. The same term can be applied to the use of resorbable or non resorbable membranes with a bone graft material to prevent epithelial migration into a socket during any form of socket preservation procedure.
Both the bone graft and the membrane act as barriers to epithelial migration, however, the bone graft is secondary to the membrane in this respect, and in cases in which the membrane is sufficiently supported by the patient’s surrounding natural bone, the bone graft material may not even be necessary. This applies mainly to small residual spaces surrounding an implant that is placed directly into a socket immediately after an extraction.
The reason that guided tissue regeneration works is outlined below
After a tooth is extracted, the socket fills with blood. The blood clots, and acts as a kind of scaffold for somatic (from the body) cells to begin the work of healing the wound. There are essentially three types of cells that concern us here. Epithelial cells from the gingiva (the gums), begin to creep down over and into the clot, or over the exposed bone of the socket if the clot is not well adhered to the socket bone. These epithelial cells come from the top down, and begin creating a new “skin” to heal over the socket. From the bone deep inside the socket, two other types of cells begin working their way into the deep layers of the clot to reshape the remaining bone, and to build new bone within the clot. Osteoclasts are cells who’s job is to break down existing bone so that it can be rebuilt to better conform to the newly toothless environment that the bone will occupy when healed. Osteoblasts are cells which build new bone in the socket.
Thus, when a tooth is extracted, a sort of race begins to see which process “wins”. The osteoblasts and osteoclasts work from the bottom up to reshape and rebuild bone in the socket, while the epithelial cells work their way from the top down into the socket displacing the clot and producing a soft tissue “scar”. Bone building is called osteogenesis, while the process of epithelial cells migrating down the walls of the socket is called epithelialization. Under the epithelialized layer, another process begins to form tiny blood vessels and collagen fibers throughout the blood clot. This granulation tissue then becomes a soft tissue scar which prevents bone from fully filling the extraction socket. Because the body builds soft tissue much faster than bone (about a mm per day as opposed to a mm per month), the process of epithelialization and granulation often wins out, filling the socket from half to two thirds full of epithelialized collagen scar tissue. If the patient gets a
dry socket, the socket may end up as an epithelialized hole in the surrounding bone. Some patients are lucky and build more bone in their sockets, but many do not.
Dentists have discovered that they can prevent the epithelialization process by filling the socket with a material which can prevent epithelial cells from migrating into the socket, and then covering the socket with a membrane. Ideally, these materials should be resorbable themselves, and replaced by the body’s own bone. There are essentially three ways of doing this. These three techniques have the added advantage of preventing dry sockets after the extraction