Bone formation over partially exposed implants using guided tissue generation

This pilot study tested whether a semipermeable expanded polytetrafluoroethylene (e-PTFE) membrane could be used to induce new bone to cover the partially exposed surface of titanium and hydroxylapatite (HA)-coated endosseous implants. Twenty threaded titanium and 10 HA-coated implants were placed in the tibia of five mongrel dogs. The implants were placed in a manner that left the cervical 2 to 3 mm exposed. Fifteen implants were used as controls and the rest were covered with an e-PTFE membrane. Animals were killed at 6, 8, and 12 weeks. Those implants covered by the membrane showed a progressive formation of bone on the exposed portion. The threaded titanium control implants showed reactive periosteal bone formation in the adjacent area, but no new bone formation on the exposed threads. The HA-coated controls, however, showed progressive bone formation on the exposed portion. Membrane position appeared to have an effect on the quantity of bone that formed, as those test sites in which there was a collapse of the membrane against the implant showed less new bone than those in which a protected space was created. This study showed that guided tissue generation may be used to induce new bone to form over the exposed portion of an implant, that the amount of new bone is influenced by the width of the space between membrane and implant, and that new bone forms on an exposed HA-coated implant even in the absence of a guiding membrane.