Bone Grafting Explained
Over a period of time, the jawbone associated with missing teeth atrophies or shrinks. This often leaves a condition in which there is poor quality and quantity of bone suitable for placement of dental implants. In these situations, most patients were previously not candidates for placement of dental implants.
We now have the ability to grow bone where needed. This not only gives us the opportunity to place implants of proper length and width, it also gives us a chance to restore functionality and esthetic appearance. There are a variety of bone grafting procedures which can be done in our office to allow implant placement.
Jawbone and Extraction Site Preservation
When you need to have a tooth or teeth extracted—whether it be due to decay, abscess, gum disease or injury—it is usually in your best interest to do so in a manner which preserves as much of your underlying jawbone as possible. From the time the teeth are removed, significant degeneration of the surrounding bone begins to take place. You have many options to prevent this, and it is important that you consider them BEFORE any teeth are removed. Some of these procedures are best performed at the time the tooth is removed. Dr. Ehsan is an oral and maxillofacial surgeon who specializes in tooth removal, jawbone preservation and dental implant placement.
What happens when a tooth is removed?
There is a special type of bone surrounding your teeth. This bone is called alveolar “ridge” bone, and exists solely to support your teeth. As soon as the tooth is removed, this bone begins to degenerate and “melt away.” This occurs in two dimensions. The first is loss of horizontal width caused by the collapse of the bone surrounding the socket. This makes the remaining ridge narrower than when the tooth was present. The second is a loss of vertical height. This makes the remaining bone less “tall.” This process is faster in areas where you wear a partial or complete denture.
Why is it important to preserve the bone?
You will have several choices of how you can replace the newly missing teeth. All of the options rely on bone support and bone contour for the best function and esthetics. Here is a list of the possible options:
You may choose to replace your missing teeth with dental implants. These are root-shaped supports that hold your replacement teeth. The more bone support you have, the stronger the implant replacements will be. In some cases, the bone can degenerate to a point where implants can no longer be placed without having more complex bone grafting procedures to create the necessary support. Obviously, preventing bone loss is much easier than recreating the bone later.
You may choose to replace the missing teeth with a “fixed bridge.” This is a restoration that is supported by the teeth adjacent to the missing tooth space. The replacement tooth (or pontic) spans across the space. If the bone is deficient, there will be an unsightly space under the pontic that will trap food and affect your speech.
Other replacement alternatives include removable partial or full dentures. These often perform better with more supporting bone.
How can the bone be preserved?
There are two important phases in retaining your alveolar ridge during and after the tooth extraction. Not all extractions are the same—Dr. Ehsan will use the most careful techniques to extract the teeth while preserving as much bone as possible. Second—and key to preventing the collapse of the socket—is the addition of bone replacement material to the extraction socket.
There are several types of bone grafting materials and techniques — Dr. Ehsan will discuss the most appropriate one with you. After the tooth is extracted, the socket will be packed with a bone graft material and covered with a small absorbable plug, membrane or suture. Early on, the grafting material will support the tissue surrounding the socket, and in time will be replaced by new alveolar bone (your own bone). This bone will be an excellent support should you choose later to have dental implant-supported replacement teeth.
Although the bone created by socket grafting supports and preserves the socket, it will not do so indefinitely. Placing dental implants two to six months after the extraction and socket grafting will provide the best long-lasting support for preserving your jawbone and allow you to function as before. Otherwise the graft may “melt away” or resorb over time because bone is maintained in the jawbone when it is under function of tooth or implant.
Sinus Lift Bone Grafting
The maxillary sinuses are behind your cheeks and on top of the upper teeth. Sinuses are like empty rooms that have nothing at all in them. Some of the roots of the natural upper teeth extend up into the maxillary sinuses. When these upper teeth are removed, there is often just an egg shell thin wall of bone separating the maxillary sinus and the mouth. Dental implants need bone to hold them in place so when the sinus wall is very thin, it is impossible to place dental implants in this bone.
This procedure involves elevating the sinus membrane and placing the bone graft onto the sinus floor. This allows implants to be placed in the back part of the upper jaw when teeth have been removed and bone loss has occurred. The implants can often be placed at the time the grafting is performed.
Block Bone Grafting
In severe cases the ridge has been reabsorbed and a bone graft is placed to increase the ridge height and/or width. In these situations, the graft is taken from another area inside your mouth or body. This dental implant bone grafting technique is where a block of bone is cut out of one area and screwed into the area where the dental implants will be placed. Normally, the block bone graft is placed and allowed to integrate into the jaw bone for four to six months before the dental implant is placed.
This office procedure is usually performed using general anesthesia and takes about an hour.
These procedures may be performed separately or together, depending upon the individual's condition. There are several areas of the body which are suitable for attaining bone grafts. In the maxillofacial region, bone grafts can be taken from inside the mouth, in the area of the chin or third molar region or in the upper jaw behind the last tooth. In more extensive situations, a greater quantity of bone can be attained from the hip or the outer aspect of the tibia at the knee.
These surgeries are performed in the out-office surgical suite under IV sedation or general anesthesia. After discharge, bed rest is recommended for one day and limited physical activity for one week.
Many people, including some doctors, incorrectly believe that bone is hard and unbendable. Perhaps this false idea comes from studying dried skeletons. However, living bone is much softer than dried bone. Living bone can be stretched open in certain areas of the jaw. This stretching is called bone expansion.
Bone Expansion Rationale
After an area of bone has had bone expansion, the bone area is much larger than it was before the bone expansion. The bone expansion allows for larger dental implants to be inserted into the bone. Larger implants have a greater surface area to bond to the bone and so have a better long term prognosis. The primary purpose of bone expansion is to allow a larger dental implant to be placed into the recipient area where the bone expansion was successfully performed.
Bone expansion is most often performed in the front of the upper jaw to assist with replacing incisors. However, bone expansion can be done in selected areas anywhere in the mouth.
Bone Expansion Procedure
A small hole is first drilled though the center of the area of the bone to be expanded. Then a series of bone expansion tools are tapped into the hole. As the bone expansion tools get progressively larger, the hole in the bone gets progressively larger and the walls expand. The hole created by the bone expansion can then be filled with bone or an implant can be immediately inserted into the hole. Bone expansion expands or widens the walls of the bone.
The inferior alveolar nerve, which gives feeling to the lower lip and chin, may need to be moved in order to make room for placement of dental implants to the lower jaw.
Immediate Dental Implant placement
In some cases it is possible to actually extract the tooth and place the dental implant at the same time. This is called immediate implantation.
Guided Tissue Regeneration
Soft tissue, such as gum tissue, grows very fast while bone grows very slow. When a surgical hole is created by a surgeon, soft tissue grows into the surgical hole very quickly and blocks out bone from growing into the hole. When bone is needed in an area to place dental implants, uncontrolled gum tissue growth is a problem. A membrane barrier can be used to cover the surgical hole and block out the gum tissue from growing into the area. This allows the more slowly growing bone to fill the surgical hole without any competition.
The membrane barrier guides the gum tissue away from the surgical defect. Gums and bone are both tissues and both are guided by the artful placement of a membrane barrier. Because the bone regenerates in the surgical hole, the technique is called guided tissue regeneration. Some surgeons call it guided bone regeneration because implant surgeons are very concerned about the supporting bone around their dental implants.
Guided tissue regeneration can be used to repair defects around previously placed dental implants or to create additional bone in deficient areas before placing dental implants. The surgical hole can be filled with several different types of materials before covering the area with a protective membrane barrier.
When there is adequate bone height and width and when the density of the bone is acceptable, implant placement and ensuing success is almost a foregone conclusion. However, many of our patients are deficient in bone and in order for the implant placement to be successful, we have to select a means of regenerating this missing bone. While this is not necessarily an easy task, it does have a high degree of success when carried out with skill and knowledge.
Autogenous Bone - Generally considered the best material for bone grafting. In many implant procedures, bone for this purpose can be secured from adjacent sites, the chin, the tuberosity and occasionally from the hip or other areas of the body.
Allografts - They are derived from genetically unrelated members of the same species. This is generally Cadaver bone which has been specifically prepared for this purpose, Freeze dried cortical bone is in this category.
Xenografts - Bone derived from other species such as cows. Bio-Oss (Osteohealth - Shirley, NY) is a popular one at this time. These materials generally work via either Osteoconduction, the formation of new bone from host cells along a framework of a compatible alloplast, or biological material, or Osteoinduction, the formation of new bone from the biomechanically differentiation of the host mesenchymal cells. Bone Morphogenic Protein (BMP) is the material that will stimulate osteoinduction and the research that is currently ongoing gives us great hope of being able to use BMP to predictably and very rapidly induce the growth of bone just about anywhere we want it.
Barrier Membranes - In addition to the grafting materials and BMP, membranes are very often used to guide the generation of new bone. When there is a defect in bone, there is a competition between the bone cells and the epithelial and connective tissue cells to fill up the defect. If left alone, bone usually looses. The membrane allows the bone to win by blocking out the epithelial cells and the connective tissue cells from the site.
Additional Information About Bone Grafting
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