Osseointegration of alumina with a bioactive coating under load-bearing and unloaded conditions

The aim of the study was to evaluate the osseointegration of Al2O3 coated with a bioactive glass ceramic (Bioverit®I), in a load-bearing implant model in sheep in comparison to uncoated Al2O3 and to a minimally loaded situation. Both types of implants were inserted into the proximal tibia (load-bearing model) and in a drill hole defect into the tibia diaphysis (minimally loaded model). Under load-bearing conditions, the coating resulted in significantly higher interfacial shear strength and a high amount of mineralized bone in direct contact to the implant surface. In contrast, the uncoated Al2O3 was surrounded by a thick connective tissue layer corresponding to low interfacial shear strength. In the minimally loaded model, however, there was rather a tendency of lower interfacial shear strength in the case of the coated implants. This finding corresponds to the histological results, which showed mineralized bone in the interface of uncoated Al2O3, whereas in the case of the coated implants a thin layer of osteoid was observed. It was suggested that the osseointegration of Al2O3 could be improved by the coating under load-bearing conditions, under which uncoated Al2O3 ceramics cannot directly bind to bone.