Healthy natural teeth stimulate the jawbone through chewing. When teeth are lost or missing, the alveolar bone, the portion of the bone immediately surrounding the tooth root, no longer receives the necessary stimulation and begins to shrink or “resorb.” Over a period of time, as the jawbone associated with missing teeth atrophies or is reabsorbed, the lip support can be lost and the bite can change. This often leaves a condition in which there is poor quality and insufficient quantity of bone suitable for placement of dental implants. In these situations, bone grafting can be done prior to implant placement to restore the original contours of the jaw bone. Other common causes of dental alveolar bone loss include chronic periodontal disease (gum inflammation and infection), dentures (false teeth) which place compressive forces on the crest of the jawbone and bridgework where underlying areas are shielded from normal physiologic stress.
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.
The most common grafts are:
Socket preservation graft
The ‘socket graft’ is the most common bone grafting procedure used to preserve the height and width of bone associated with a single extraction site. The socket graft is most effectively placed when a tooth is extracted in preparation for implant placement. It is important when removing a tooth in an area of future implant placement to remove it with great care to maintain the maximum bone volume. Minimally invasive dental alveolar surgical ‘MIDAS’ techniques are used to insure the best bone height and width with the least amount of post operative swelling and pain along with the shortest recovery time. This is why you want the procedure to be performed by an oral surgeon experienced in preservation, grafting techniques, as well as the extraction of teeth. In addition to tooth removal with bone preservation, it is also important to graft the extraction site with bone to provide a scaffold for bone growth within the socket which helps to preserve the bone width and height.
Sinus Lift / Sinus floor elevation graft
When upper posterior teeth are removed and no preservation grafting techniques are used the ridge height can decrease. This usually occurs in combination with pneumatization (downward expansion) of the sinus cavity. Over time the remaining bone height can shrink requiring bone grafting prior to implant placement. The sinus lift graft involves elevating the sinus membrane and placing the bone graft onto the sinus floor and then allowing 4 to 6 months for the graft material to be converted to host bone. Once the graft is mature, implants can be placed in the back part of the upper jaw.
In patients where the ridge has been reabsorbed a bone graft can be placed to restore the ridge shape and increase the ridge height and/or width.
When teeth are removed following a dental infection or extraction sites that have been left unrestored for years the bone width and height can diminish over time. The extent of this bone loss is often best evaluated using a volumetric cone beam or “CT scan.” (If an area is determined to be deficient in bone volume; an onlay graft, or “tunnel” graft may be appropriate)
In the lower jaw occasions arise where the extreme bone resorption along with the position of the inferior alveolar nerve (IAN) combine to create a situation where implants can not be placed without first repositioning the neurovascular bundle. A CT scan is needed to properly treatment plan this type of surgery. The inferior alveolar nerve, which supplies feeling to the lower lip and chin, can need to be moved in order to make room for placement of dental implants in the back portions of the lower jaw.
Guided Tissue Regeneration
Often when grafting procedures are being performed a special membrane is utilized to protect the bone graft and to encourage bone regeneration. These membranes can be made from collagen, which dissolve under the gums or from synthetic materials (i.e. Teflon), which are removed several months later.
Types of graft materials
Block Bone Graft
Bone grafting can repair and restore implant sites with inadequate bone structure due to previous extractions, gum disease or traumatic injuries. These grafting procedures and implant placement may be performed separately or together, depending upon the individual’s condition. There are several areas of the body which are suitable for harvesting bone grafts. Autogenous grafts, also know as “autografts” are harvested from a patients own body to improve bone quality and quantity in another area. Autogenous grafts are most frequently harvested from an intra-oral site such as the ramus, chin, and third molar regions.
The advantages of autogenous grafts are that the graft material is live bone, which contains living cellular elements that enhance bone growth. One disadvantage of an “autograft” is that it requires a second surgical procedure to harvest the bone from elsewhere in your body. This secondary location is known as the donor site. 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.
Allogenic bone, or an “allograft” is dead bone harvested from a cadaver (human donor). The use of allograft bone greatly reduces the trauma of bone harvesting. Allografts have been a preferred material used successfully for decades in conjunction with oral surgery and dental implants.
Xenogenic bone is derived from non-living bone of another species, usually cow. Like allogenic grafts, xenogenic grafts serve as a framework for bone from the surrounding area to grow to fill the defect. Both xenogenic and allogenic grafts lack bone-forming properties found in autografts and therefore regeneration may take longer and may have a less predictable outcome.
Special collagen membranes are placed under the gums and normally dissolve within several weeks. They are utilized to protect the bone raft from soft tissue migration, thus encouraging bone regeneration. This process is “guided bone and tissue regenerations.”
Often these surgeries are performed in the office surgical suite under I.V. Sedation or general anesthesia. After discharge, bed rest is recommended for one day and physical activity is to be limited for one week.
Preserving Jaw bone volume
When one or more teeth are missing, it can lead to loss of jawbone at the site of the gap. This chronic loss of bone may take years to become severe and often has direct relationship to conditions such as osteoporosis which can result from a systemic decrease in calcium absorption.
Bone Morphogenic Proteins
Bone Morphogenic Proteins (BMP) are naturally occurring proteins that promote, stimulate and support bone formation and maturation. Many of today’s bone grafting materials have Bone Morphogenic Proteins added to them to improve the bone quality and quantity in the final outcome.