Bone Augmentation and Nerve Repositioning
For dental implants to be successful, the jawbone must have enough bone to support them. Tooth loss often leads to more loss of bone over time. The tooth loss may be caused by:
- Periodontal (gum) disease
- Dental caries (cavities) and infection
- Injury or trauma
- A defect in development
If the bone under your gum is not tall enough, not wide enough or both, you will need a procedure to add bone to your jaw before implants can be placed.
Bone augmentation is a term that describes a variety of procedures used to "build" bone so that dental implants can be placed. These procedures typically involve grafting (adding) bone or bonelike materials to the jaw. The graft can be your own bone or be processed bone (off the shelf) obtained from a cadaver. After grafting, you have to wait several months for the grafted material to fuse with the existing bone. "Off–the-shelf" grafted materials either cause surrounding bone to grow into the graft or cause cells around the graft to change into bone. A graft from your own bone transplants bone cells or a block of bone that fuses to the jaw.
Several different procedures can be used for bone augmentation. Your dentist will select one depending on the type, location and number of implants to be used. If you need a bone graft, it is important that you and your dentist discuss all of the options available to you.
After bone augmentation, dentists usually wait four to nine months before placing implants.
Where Does the Bone Come From?
Most bone augmentation procedures involve the use of bone grafts. An excellent choice for a bone graft is your own bone. This most likely will come from your chin or ramus (the back part of your lower jaw). If your dentist cannot get enough bone from these areas, he or she may need to get bone from your hip or shin bone (tibia) instead. The hip is considered to be a better source because the hip bone can provide a large amount of bone. The marrow from either the hip or shin (tibia) contains bone-forming cells. However bone taken from your hip requires a hospital stay and general anesthesia.
If you don't like the idea of having bone removed from your body to be placed in your jaw, other excellent options are available. Your dentist can use materials made from the bone of human cadavers or cows. Synthetic materials also can be used for bone grafting. Newer products, such as bone morphogenetic protein-2 (BMP-2), also are available. BMP-2 stimulates certain body cells to turn into bone, without grafting. This protein occurs naturally in the body. The dental material is produced using DNA technology. You should discuss your options and their risks and benefits with your dentist before any procedures are done.
A Typical Bone-Augmentation Procedure
In a typical situation, a patient has lost a single tooth and wants to have it replaced with a crown supported by a dental implant. However, the tooth has been missing for several years and there is not enough bone to support the implant.
In this case, bone taken from the patient's chin or from a cadaver can be used to "rebuild" the lost bone so that it can support an implant. This type of procedure is done in the surgeon's office under intravenous (IV) sedation. Before the procedure, you will need to have a cone-beam computed tomography (CT) scan. This provides a 3-D image of your bone.
Local anesthesia will be used to numb the area where the bone augmentation is needed (recipient site) as well as the area from where bone will be removed (donor site). An incision (cut) in the gum where the implant will be placed is made to determine how much and what type of bone is needed.
If the bone is taken from the chin, then the surgeon will make a cut in the gum below the lower front teeth to expose the chin bone. A block of bone will be removed from the chin along with any bone marrow. Many dentists fill the spot where the bone was removed with another type of bone-graft material. They may cover this with a thin film of tissue to keep gum tissue from filling the space as it heals. The incision is then closed with stitches.
The block of bone that was removed from the chin will be anchored in place with small titanium screws. A mixture of your bone marrow and some other bone-graft material may then be placed around the edges of bone block. Finally, the surgeon may place a membrane over the graft and close the incision.
After a bone augmentation procedure, you will be given antibiotics, pain medicine and an antibacterial mouthwash. You will be asked to avoid certain foods. You also will be told how to avoid putting pressure on the area while it heals. If you wear a denture, you may not be able to wear it for a month or longer while the area heals. If you have natural teeth near the bone graft, your dentist may make a temporary removable bridge or denture to help protect the area.
The bone graft will take about six to nine months to heal before dental implants can be placed. At that time, the titanium screws used to anchor the bone block in place will be removed before the implant is placed.
Building Up Bone for Several Implants
Many people are missing several teeth and need several implants. If bone needs to be built up to support several implants, a lot more bone graft material will be needed than if a single implant is being placed. If you are having several implants placed and choose to use your own bone for a bone graft procedure, the bone may be taken from your hip, shin or another site. This type of procedure is done in the hospital under general anesthesia.
You may spend one or two nights in the hospital if you have bone harvested from the hip. A bone graft from the hip is really taken from the ilium, which is above the hip joint. This does not increase your risk of hip fracture.
Some surgeons will remove bone from the shin in their office. You will be given a shot to numb the area (local anesthesia) and medicine through a vein to make you drowsy (intravenous sedation). Many surgeons may also use bone from a cadaver in the office, without removing any of your own bone.
Success of Bone Grafting
The success rate for bone grafts in the jaws for the purpose of placing dental implants is very high. However, there is always a chance that the bone graft will fail, even if your own bone was used. Bone grafts are not rejected like organ transplants. Dentists don't know why some bone grafts fail. They do know that certain people—such as those who smoke and those with certain medical conditions—have higher risks of graft failure than others do.
A failed graft will be removed. Once the area has healed, your dentist may choose to place a second graft.
Other Types of Bone-Augmentation Procedures
In addition to bone grafting, many other types of procedures can be used to build bone for placement of implants.
One procedure is called a sinus lift (or elevation). It increases the height of your upper jaw by filling part of your maxillary sinus with bone. The maxillary sinus is the area above your jaw on either side of your nose above the back teeth. This is done when the back part of the upper jaw does not have enough bone to allow implants to be placed.
A ridge expansion is a type of bone graft that can be done when the jaw is not wide enough to support implants. Your dentist uses a special saw to split the jaw along the top (ridge) and packs graft material into the newly created space. Some dentists will place implants directly after this procedure. Others will wait several months for the ridge to heal. This procedure, called a split ridge technique, can be done in the dental office under local anesthesia.
A bone augmentation procedure that is performed less often is called distraction osteogenesis. It is used most often to increase the height of bone that is too short. This procedure originally was used for lengthening the bones of people with abnormally short legs. It now has been adapted for use in the mouth.
A surgeon makes cuts in your jawbone to separate a piece of bone from the rest of the jaw. A titanium device inserted with pins or screws holds the piece of bone apart from the rest of the jawbone. Each day, you unscrew the device a small amount. Over time, this makes the space between the piece of bone and the jawbone taller. The area between the pieces gradually fills in with bone.
"Distraction" refers to the process of separating the two pieces of bone. "Osteogenesis" refers to the forming of new bone. Distraction osteogenesis is used more often to make the jawbone taller, but it can be used to increase the bone in any direction. The procedure is becoming more common.
A nerve called the inferior alveolar nerve runs through the lower jaw. This nerve gives feeling to the lower lip and chin. In patients who have lost significant amounts of lower jawbone, it may not be possible to place implants without damaging this nerve. To address this problem, an oral surgeon can drill a small window in the bone and move the nerve to one side. The implants then can be placed through the bony canal previously filled by the nerve. This technique is not used very often because it is possible to damage the nerve just by moving it.
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