Implant Placement & Bone Block Reconstruction
Bone grafting techniques are widely used in the restoration of atrophic maxillary bone prior to placement of dental implants.
The reduction in bone volume has many etiologies. The most common are a result of: Periodontal disease, pneumatization of the maxillary sinus, long term ill-fitting dentures, and the general progression of osteoporosis with aging. Initially, malposition or short implants were used in areas of deficient bone volume. This often resulted in compromised prosthetic design and poor long term treatment outcomes. Today’s treatment plans first consider the prosthesis options. This necessitates reconstruction and modifications of the pre-existing anatomy provide the ideal environment needed for optimal implant placement.
The rehabilitation of large bone defects can be achieved with various types of grafting materials and may be natural or synthetic. The use of autologous grafts exhibits the highest success rate, and autogenous block grafts are considered the gold standard because their osteogenic, osteoinductive, and osteoconductive properties maximize the success of graft incorporation. Nevertheless, the use of autogenous bone grafts also presents considerable drawbacks, including high morbidity at the donor site, limited quantity of bone, unpredictable quality of bone, increased blood loss, increased operative time, and infection at the donor site.
Although autogenous bone grafts remain the preferred reconstructive method, there has been an increased use of fresh frozen bone allografts in oral and maxillofacial surgery. The advantages of using fresh frozen bone allografts include decreased operative trauma for the patient, a nearly unlimited supply of reconstructive material, decreased blood loss, absence of donor-site morbidity.
The treatment planning sequence for implant dentistry begins with the design of the final prosthesis. After the determination of the type of restoration, number and position of teeth to be restored and the patients force factors are then evaluated. The bone density in the region of the implant placement is then considered. The key implant positions and the number and ideal implant sizes are then selected. Finally the available bone volume is evaluated for implant placement according to the proposed treatment plan.
Dental implants function to transfer occlusal loads to the surrounding biological tissues. If occlusal loads are within the bone physiologic tolerance zone, osseointegration will be maintained. On the other hand, if occlusal loads are excessive and beyond the bone physiologic tolerance limit, bone will ultimately resorb and failure of osseointegration result. Thus, as a general rule the goal of treatment planning should be to minimize and evenly distribute the mechanical stress in the implant system and the surrounding bone.