Abstract
Three types of dense alumina oxide ceramic (Al~2~O~3~) 99.7%, MgO 0.3%; density more than 3.9 g/cm^3^ differing only in their average grain size (5–15μ) and stainless steel (V~4~A) plates were implanted into the left femur of male Wistar rats 6 months old. Light and scanning electron microscopic techniques were used to investigate tissue reaction and the ceramic surface. Both ceramic and stainless steel plates were surrounded by a soft tissue layer that differed greatly depending on the implant type in respect to the fiber/cell ratio. While the body tended to enclose the metal plate with a small more or less avascular tissue mostly composed of fibers and some inactive fibrocytes, around the ceramic implants a highly cellulated soft tissue of mesenchyme character developed with signs of osteoblast and chondrocyte metaplasia. Adjacent to this mesenchyme a dense cuff of newly formed woven bone arose, showing numerous active osteocytes. Both metaplastic tendency of the newly formed messenchyme and osteocyte activity in the surrounding bone did not decrease remarkably towards the end of the experiment (70 weeks after operation), while the tissue around metal implants reached a steady relatively reactive state 12–24 weeks after operation. Intimate ceramic surface‐mesenchyme contacts without foreign body reactions supported the idea that alumina oxide ceramic tends to be incorporated into the body's physiological environment while metals are “excluded” by fibrous tissue layers of low biological activity. Corrosion on the ceramic surface was not detectable.