Figure 1: Right posterior edentulous mandible with alveolar ridge deficiency.
Figure 2: Decortication and perforation of recipient site in preparation for block grafting.
Figure 3: Harvest of ramus buccal shelf bone.
Figure 4: Autogenous block graft completion of right posterior mandible with screw fixation.
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Achieving Optimal Implant Placement Using Mandibular Block Autografts: A Biological and Biomechanical Approach to Avoid Functional and Esthetic Complications
Michael A. Pikos, DDS
Over the past decade, there has been an increasing interest in not only placement of osseointegrated implants but in restoring proper form and function in the partially edentulous patient. Many patients with edentulous spans require bone augmentation as a prerequisite for implant placement. Proven methods of treatment include sinus grafting1,2 and autogenous block grafting3,4,5,6 for lateral and vertical ridge augmentation. Autogenous bone grafts have been used for many years for ridge augmentation and are still considered to be the gold standard of jaw reconstruction.7 The use of autogenous block grafts with osseointegrated implants was originally discussed by Brånemark et. al.,8 who used the iliac crest as the donor site. For repair of most localized alveolar defects, however, bone grafts from the mandible offer advantages over iliac crest grafts.9 These include the proximity of donor and recipient sites, convenient surgical access, decreased donor site morbidity, and decreased cost (because the surgery can be performed as an outpatient procedure).
Mandibular block grafts for alveolar ridge augmentation have been used extensively with great success and include the symphysis and ramus buccal shelf as donor sites.3,4,5,6,10 This paper focuses on the use of block grafts for alveolar ridge augmentation with osseointegrated implants to avoid functional and esthetic complications, and the biological and biomechanical rationale for their use and success. There appear to be biological advantages for alveolar ridge augmentation with block bone taken from the mandible. Cortical bone contains abundant concentrations of bone morphogenic protein for osteoinduction. In addition, it has been suggested that bone from the maxillofacial skeleton contains growth factors in great concentration that may allow for improved graft incorporation. Studies have shown that block grafts of certain embryologic origin may be responsible for bone healing. Although the majority of bones of the human skeleton are of endochondral origin, mandibular block bone is of a noncartilaginous source (membranous). Research has shown that bone of membranous origin exhibits less resorption than that of endochondral. Early revascularization of cortical membranous grafts has been proposed as a reason for stability of graft morphology. In general, mandibular block grafts resorb minimally, maintain their original bone density, and exhibit excellent incorporation in relatively short healing periods.11
Recipient site development plays a critical role in graft incorporation.11 Decortication of the recipient site followed by drilling of holes to induce increased vascularization and an increased influx of growth factors and platelets allow for incorporation to occur predictably (Figures 1-4).
From a biomechanical perspective, the primary goal of ridge reconstruction with block grafts is to create a sound support for the prosthetic complex of the implant. For posterior ridge augmentation, treatment planning must include solutions to reduce stress. A primary factor is a plan that includes increasing the number of implants. No pontics are used, so one implant per buccal root is the treatment planned for each case. In addition, no cantilevers are allowed. Splinting of all crowns is also indicated for biomechanical force distribution. Occlusal considerations include eliminating lateral interferences during any excursive movements. The final factors involved in decreasing undesirable stress to the implants are interrelated. They include increasing the bone density and maximizing the diameter of implants. These two goals are accomplished with mandibular block grafts. The quality of bone from the ramus buccal shelf is typically Type I, and the symphysis normally exhibits Type II and occasionally Type I quality bone. These mandibular block grafts create areas for the use of larger diameter implants, which increase the surface area over which the stresses of the occlusal forces are distributed.11
For ridge augmentation in the anterior maxilla, esthetics play a larger role in the overall success of implant utilization. A sound hard tissue environment created with mandibular block autografts can produce the desired esthetic and functional result, and in most cases precludes even the use of soft tissue augmentation. Following graft incorporation, bone contouring with use of appropriate burs and precisely fabricated surgical stents can create appropriate crestal bony anatomy including interseptal bone. This in turn results in papilla formation when the edentulous span involves two or more missing teeth. Root anatomy can even be simulated with bone contouring to further enhance the desired esthetic result.
Case studies indicating use of mandibular block grafts harvested from the chin and ramus buccal shelf will demonstrate indications, contraindications, complications, histology and five-year retrospective data. Focus will be on optimal site development from both a biological and biomechanical perspective with block grafts to maximize long-term implant success and predictability.
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