Augmentation of the mandible with GTR and onlay cortical bone grafting. An experimental study in the rat.

The aim of the present study was to evaluate the effect of augmenting the mandible with onlay mandibular bone grafts that were covered with e-PTFE membranes according to the principle of guided tissue regeneration (GTR). The experiment was carried out in 30 rats. The inferior border of the mandible and parts of the mandibular body were exposed on both sides. On one side, an autogenous bone graft that was harvested from the angle of the mandible was placed on the inferior border of the mandible and was fixed with a titanium microimplant. Subsequently, the graft was covered with an e-PTFE membrane. The contralateral side, serving as control, was treated the same way except for the placement of the membrane. Groups of six animals were sacrificed 15, 30, 60, 120 and 180 days following surgery, and specimens that were prepared from the experimental and control sites were analyzed histologically. The bone graft underneath the membrane initially presented superficial resorption but, subsequently, the space that was created by the membrane gradually became filled with bone. After 180 days, the area underneath the membrane was completely filled with bone and it was impossible to distinguish between the bone graft and the newly formed bone. Generally, the bone grafts at the control sides were characterized by a gradual resorption during the entire experimental period. At 180 days after transplantation, only a few grafts at the control sites had retained their height, and there was frequently a lack of continuity between the bone graft and the underlying mandibular bone. It can be concluded that onlay mandibular bone grafts combined with GTR may improve the predictability of mandibular augmentation, in comparison to bone grafting alone.