The bone-bonding behavior of three kinds of bioactive ceramics coated on titanium alloy by the plasma-spray technique was investigated. Titanium alloy (Ti-6A1-4V) coated with BioglassR (45S5), apatite-wollastonite containing glass ceramic (AW), or beta-tricalcium phosphate (TCP) was prepared, and rectangular specimens were implanted into the tibial bones of mature male rabbits, which were sacrificed 8 or 24 weeks after implantation. The tibiae containing the implants were dissected out and subjected to detachment tests to measure the failure load. The bone-implant interface was investigated by Giemsa surface staining, contact microradiography, and scanning electron microscopy-electron probe microanalysis (SEM-EPMA). Eight weeks after implantation, the failure loads for implants coated with BioglassR, AW, and TCP were 1.04 +/- 0.94, 2.03 +/- 1.17, and 3.91 +/- 1.51 kg, respectively, and 24 weeks after implantation, the respective failure loads were 2.72 +/- 1.33, 2.39 +/- 1.30, and 4.23 +/- 1.34 kg. Failure loads of AW- and TCP-coated implants did not increase significantly with time. After the detachment test, breakage of the coating layer was observed. Bioactive ceramics can act as stimulants that induce bonding between bone and metal implants. However, failure load of metal implants coated with the bioactive ceramics was lower than that of bulk AW or TCP. It appears impossible to obtain a higher failure load using a bioactive-ceramic coating on titanium alloy. Histologically, the coating layer was found to become detached from the metal implant and the bone tissue bonded to the coating layer. SEM-EPMA observation revealed breakage of the coating layer, although bonding between bone and the coating layer was evident. A Ca-P-rich layer was observed at the interface between bone and the AW coating, and a Ca-P-rich and a Si-rich layer were observed at the interface between bone and the BioglassR coating. For clinical application, it would seem better to use coated metal implants for short-term implantation. However, there is a possibility of breakage of the coating layer because of both dissolution of the bioactive ceramic and mechanical weakness at the interface between the coating layer and the metal implant.

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W e have developed a bioactive bone cement (BA cement) consisting of Bis-GMA resin and bioactive glass powder. It has high compressive and tensile strengths, a low curing temperature and its bioactivity allows it to bond directly with bone.We operated on the 18 femora of nine mongrel dogs for intercalary replacement of part of the bone by a metal prosthesis using either PMMA cement or BA cement for fixation. Three dogs were killed at each of 4, 12 and 26 weeks after surgery for the evaluation of fixation strength by a push-out test and for histological examination by Giemsa surface staining and SEM.Fixation strengths with PMMA cement at 4, 12 and 26 weeks after surgery were 46.8 ± 18.9, 50.0 ± 24.7, and 58.2 ± 28.9 kgf (mean ±SD), respectively. Those with BA cement were 56.8 ± 26.1, 67.2 ± 19.2, and 72.8 ± 22.2 kgf, respectively. Fibrous tissue intervened between bone and PMMA cement but BA cement had bonded directly to bone at 12 and 26 weeks. This suggests that BA cement will be useful in providing long-lasting fixation of implants to bone under weight-bearing conditions.

Alumina ceramic with a porous surface coated with glass-ceramic containing apatite and wollastonite (AW-GC) was implanted in a state of press-fit under load-bearing conditions in the femoral condylus of the mongrel dog and compared with a non-glass-ceramic-coated alumina ceramic. A trapezoid alumina ceramic implant (7 x 10 x 5 mm) with a lateral recess (0.9 mm deep) coated with alumina ceramic beads (mean diameter, 750 microns) in a single layer was prepared. The alumina ceramic beads were bonded to the alumina ceramic substratum using an identical alumina binder. The thickness of coating was 10-50 microns (mean, 30 microns). The surface of the beads and the substratum of the alumina implant were coated with AW-GC. A pull-out test and histologic examination were performed at 4, 8, and 24 weeks after implantation. The interfacial shear load was significantly increased from 8 to 24 weeks in both groups. The shear load of the glass-ceramic-coated implant was significantly greater than that of the noncoated implant at every stage. The interface shear load of the noncoated implant was 12.13 +/- 2.76 kg at 4 weeks, 13.92 +/- 4.18 kg at 8 weeks, and 24.17 +/- 5.17 kg at 24 weeks after implantation. The interface shear load of the glass-ceramic-coated implant was 17.96 +/- 2.81 kg at 4 weeks, 24.92 +/- 9.87 kg at 8 weeks, and 34.83 +/- 4.12 kg at 24 weeks after implantation. Histologic examination showed more ingrown bone tissue in the glass-ceramic-coated implants. It is suggested that AW-GC stimulated the bone ingrowth.(ABSTRACT TRUNCATED AT 250 WORDS)

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