Histological and microradiographic appearances of Silicon Nitride and Aluminum Oxide in a rabbit femur implantation model*

Silicon nitride (Si₃N₄) is a ceramic known for its high performance characterized by fracture toughness, high wear resistance and low coefficient of friction. It has therefore been considered as a biomaterial especially for orthopaedic and dental indications. There is a controversy concerning the biocompatibility among the limited number of authors dealing with this material. Own investigations, applying the L929‐fibroblast cell culture model revealed good biocompatibilty. The aim of this study is to verify these findings in the animal model. 36 cylinders of Si₃N₄ and the established biomaterial aluminum oxide (Al₂O₃) were implanted “press fit” into the lateral condyli of the femurs of 6 New Zealand white male rabbits (three implants per condylus, materials randomized). The right femur of each animal was prepared for microradiographs and grounded sections, the left for histological sections, respectively. Animals were divided into 2 groups with 3 rabbits each. One group was sacrificed after a period of 4 weeks and the other after 8 weeks. Morphometric assessment of bone‐implant attachment was performed using a digital image analyzing system. Percentages of bone‐implant attachment ranged from 44 to 82 %. There was no statistically different percentage of bone‐implant attachment between Al₂O₃ and Si₃N₄ after 4 and 8 weeks, except in the histological section after 8 weeks of implantation. During the period of 4 to 8 weeks after implantation there was no significant decrease of bone‐implant contact except for Al₂O₃ in the histological sections. No local or generalized immuno‐inflammatory reactions were observed. The lamellar bone in direct contact to the materials showed no histological evidence of round cell infiltration or giant cell reactions. Our investigations suggest that Si₃N₄ shows good biocompatibility and presumably even better osseointegration than Al₂O₃.