Guided bone regeneration : the influence of barrier membranes on bone grafts and bone defects

Guided bone regeneration (GBR) can be described as the use of a barrier membrane to provide a space available for new bone formation in a bony defect. The barrier membrane protects the defect from in-growth of soft tissue cells and allows bone progenitor cells to develop bone within a blood clot that is formed beneath the barrier membrane. Furthermore, the membrane excludes inhibiting factors from outside the defect and preserves bone growth factors inside. GBR was developed in the 1950s and 1960s and has been applied in trauma and reconstructive surgery. In the 1980s, clinicians started to use barrier membranes in implant dentistry. The membranes were applied to reconstruct small bony defects prior to implantation or to cover dehiscences or fenestrations around dental implants. In large defects a bone graft is frequently necessary. The bone graft serves as a scaffold and carrier for living cells. However, bone grafting is not always successful because of graft resorption or insufficient graft incorporation. To enhance the predictability of bone augmentation procedures, in the mid1990s grafts were covered with barrier membranes in an attempt to prevent bone graft resorption. A barrier membrane would prevent graft resorption and possibly would enhance graft incorporation by keeping the osteoinductive substances in place and secluding the grafted area from inhibiting factors and connective tissue cells. The overlying barrier membrane would maintain space in remaining crevices for bone regeneration. Although most studies have been uncontrolled, the application of barrier membranes to cover bone grafts is now widespread among clinicians because the reported results were promising. However, in maxillofacial surgery and implant dentistry a continuing debate exists as to whether a barrier membrane should be applied to cover autologous onlay bone block grafts when augmenting the jaw. It is desirable that this question is answered because the use of barrier membrane may have adverse effects and is rather expensive. Numerous membranes have been developed throughout the years. Although the standard reference materials, i.e., a porcine bilayer collagen membrane for biodegradable membranes and a synthetic expanded polytetrafluoroethylene (ePTFE) membrane for non-degradable membranes, have been established as being successful in covering defects, there are some disadvantages to their application. Collagen has poor space making properties in wet conditions and its composition of animal derived collagen may possibly lead to disease transmission from animal to people, at least theoretically. The ePTFE is non-degradable and therefore must be removed in an additional surgical procedure. Furthermore, the membrane has to be removed when exposed to the oral cavity to resolve an inflammatory reaction that occurs. The 'ideal' barrier membrane for alveolar ridge augmentation is thus not yet applied in clinical practice. The 'ideal' membrane should be both biodegradable and synthetic. A recently developed Vivosorb® membrane composed of poly(DL-lactide-Ecaprolactone) (PDLLCL) is biodegradable and synthetic and might have the required properties of an 'ideal' barrier membrane. The first aim of this thesis was to study the preventive effect of barrier membranes on bone resorption of autologous