SCANNING ELECTRON MICROSCOPY-ELECTRON PROBE MICROANALYSIS STUDY OF THE INTERFACE BETWEEN APATITE AND WOLLASTONITE-CONTAINING GLASS-CERAMIC AND RABBIT TIBIA UNDER LOAD-BEARING CONDITIONS AFTER LONG-TERM IMPLANTATION

Glass-ceramic implants containing oxy- and fluoroapatite [Ca-10(PO4)(6 )(O, F-2)] and beta-wollastonite (CaSiO3) were studied under load-bear ing conditions in a segmental replacement model in the tibia of the ra bbit. A 16-mm segment of the middle of the tibial shaft was resected a t a point distal to the junction of the tibia and the fibula. The defe ct was replaced by a 15 mm-long hollow, cylindrical implant that was f ixed by intramedullary nailing using Kirschner wire. The implants were 9 mm in diameter and 15 mm long bearing a central hole 3.05 mm in dia meter. The rabbits used were killed 6 months, 1 year, 18 months, and 2 years after implantation. The interface between the bone and the glas s-ceramic was investigated by scanning electron microscopy-electron-pr obe microanalysis (SEM-EPMA). None of the glass-ceramic implants broke , and the glass-ceramic had bonded directly to the bone tissue without any intervening soft tissue. A calcium-phosphorus layer (Ca-P layer) was observed at the glass-ceramic/bone interface. This layer was 30-10 0 mu m thick at 6 months after implantation, 60-110 mu m thick at 1 ye ar after implantation, 80-200 mu m thick at 18 months, and 120-350 mu m thick at 2 years. At the lateral surface of the glass-ceramic uncove red by the bone, the calcium-phosphorus layer was 50-80 mu m thick at 6 months after implantation, 250-450 mu m thick at 1 year, 300 similar to 400 mu m thick at 18 months, and 300 mu m thick at 2 years. The th ickness of the calcium-phosphorus layer increased moderately after lon g-term implantation. However, it was difficult to estimate the rate of increase in the thickness of calcium-phosphorus layer.