When a tooth is lost, the surrounding bone shrinks, or resorbs, as a natural physiological response. Over a period of time, the jawbone associated with missing teeth atrophies or is reabsorbed. 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 are not candidates for placement of dental implants.
Today, we 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 aesthetic appearance.
Bone grafting can repair implant sites with inadequate bone structure due to previous extractions, gum disease or injuries. The bone is either obtained from a tissue bank or your own bone is taken from the jaw, hip or tibia (below the knee). Sinus bone grafts are also performed to replace bone in the posterior upper jaw. In addition, special membranes may be utilized that are placed under the gums to protect the bone graft and encourage bone regeneration. This is called guided bone or guided tissue regeneration.
For smaller defects, the bone is obtained from an outside artificial source. Synthetic materials are often used to stimulate bone formation. In some cases, we can use allograft material to implement bone grafting for dental implants. This bone is prepared from cadavers or from a bovine source and used to promote the patients own bone to grow into the repair site. During the preparation of the graft, strict, aseptic sterilization techniques are employed and approved by the FDA to ensure that there are no transmissible agents in the grafts. The material is devoid of proteinaceous matter and only contains the minerals from the donors. It is very effective and very safe. The latest advancements in tissue engineering technology has allowed the use of concentrated bone forming proteins (known as BMPs) to allow predictable and abundant bone regeneration. The technology comes at a high cost, therefore, is only reserved for complex and difficult clinical situations.
These procedures may be performed separately or together with implant placement, depending upon the individual’s overall condition of the native bone at the site. As stated earlier, there are several areas of the body that are suitable for obtaining bone grafts. In the facial 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. When we use the patient’s own bone for repairs, we generally get the best results. However, due to the morbidity of a second surgical site, this is reserved for larger defects.
Major bone grafts are typically performed to repair defects of the jaws. These defects may arise as a result of traumatic injuries, tumor surgery, or congenital defects. Large defects are repaired using the patient’s own bone. This bone is harvested from a number of different sites depending on the size of the defect. The skull (cranium), hip (iliac crest), and lateral knee (tibia), are common donor sites. These procedures are routinely performed in an operating room and require a hospital stay.
Sinus Lift Procedure
The maxillary sinuses are behind your cheeks and on top of the upper teeth. Sinuses are empty air filled spaces lined by a tissue thin membrane. 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 a thin wall of bone separating the maxillary sinus and the mouth. Dental implants need bone to hold them in place. When the sinus wall is very thin, it is impossible to place dental implants in this bone.
The solution is called a sinus graft or sinus lift graft. The dental implant surgeon enters the sinus from where the upper teeth used to be. The sinus membrane is then lifted upward and donor bone is inserted into the floor of the sinus. Keep in mind that the floor of the sinus is the roof of the upper jaw. After several months of healing, the bone becomes part of the patient’s jaw and dental implants can be inserted and stabilized in this new sinus bone. The sinus graft makes it possible for many patients to have dental implants when years ago there was no other option other than wearing loose dentures.
If enough bone between the upper jaw ridge and the bottom of the sinus is available to stabilize the implant, sinus augmentations and implant placement can sometimes be performed as a single procedure. If not enough bone is available, the sinus augmentation will have to be performed first, then the graft will have to mature for several months. Once the graft has fully healed, the implants can be placed.
In severe cases, the ridge has been reabsorbed and a bone graft is placed to increase ridge height and/or width. This is a technique used to restore the lost bone dimension when the jaw ridge gets too thin to place conventional implants. In this procedure, the bony ridge of the jaw is literally expanded by mechanical means. Bone graft material can be placed and matured for a few months before placing the implant.
Onlay Block Grafting
When there is inadequate volume of bone (either width or height), an onlay block graft can be used to secure a solid block of bone obtained from either the back of the lower jaw or the chin area to the area where the future implant will be placed. The block is secured with temporary screws and allowed to heal for six to nine months prior to placement of implants, at which time the screws will be removed. This clinical scenario is ideal in younger patients with congenitally missing teeth and retained wisdom teeth. The block graft can be obtained from the site of the wisdom teeth and repositioned to the site of the future implants. This essentially combines two surgeries into one with an extremely predictable result.
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 in the lower jaw. This procedure is limited to the lower jaw and indicated when teeth are missing in the area of the two back molars and/or and second premolar. Since this procedure is considered a very aggressive approach (there is almost always some postoperative numbness of the lower lip and jaw area, which dissipates only very slowly, if ever), usually other less aggressive options are considered first.
Soft Tissue Grafting
When teeth are lost, along with atrophy of the bone, shrinking of the soft tissue and gums also occur. When implants are placed in the esthetic zone, i.e. front teeth, grafting of deficient gum tissue might be required to achieve a natural, healthy smile around the implant and crown. This could potentially require a mucosal (gum) graft from your palate to the region around the implant and crown. If needed, this would occur later in the treatment sequence after the bone graft and implants have completely healed. Your surgeon will make the recommendation of when or if this procedure will be needed throughout the course of your treatment.
Distraction osteogenesis refers the slow movement (distraction) of two bony segments in a manner such that new bone is allowed to fill in the gap created by the separating bony segments. It was initially used to treat defects of the oral and facial region in 1990s. Since then, the surgical and technological advances made in the field of distraction osteogenesis have provided oral surgeons with a safe and predictable method to treat selected deformities of the oral and facial skeleton without the potential complications of grafting. This means faster recovery and no need for a secondary donor site.
Recent advances in technology have provided the oral and maxillofacial surgeon with an easy to place and use distraction device that can be used to slowly grow bone in selected areas of bone loss that has occurred in the upper and lower jaws. The newly formed bone can then serve as an excellent foundation for dental implants.
Distraction osteogenesis does have some disadvantages. It requires the patient to return to the surgeon’s office frequently during the initial two weeks after surgery. This is necessary because in this time frame the surgeon will need to closely monitor the patient for any infection and the patient needs to be informed how to activate the appliance, which needs to occur daily. Also, a second minor office surgical procedure is necessary to remove the distraction appliance.