Bone-bonding behavior of alumina bead composite

Previously we developed an alumina bead composite (ABC) consisting of alumi na bead powder (AL-P) and bisphenol-alpha-glycidyl methacrylate (Bis-GMA)-b ased resin and reported its excellent osteoconductivity in rat tibiae. In t he present study, are evaluated histologically and mechanically the effect of alumina crystallinity on the osteoconductivity and bone-bonding strength of the composite. AL-P was manufactured by fusing crushed alpha-alumina po wder and quenching it. The AL-P was composed mainly of amorphous and delta- crystal phases of alumina. Its average particle size was 3.5 mu m, and it t ook a spherical form. Another composite (alpha ALC), filled with pure alpha -alumina powder (alpha AL-P), was used as a referential material. The propo rtion of powder added to each composite was 70% w/w. Mechanical testing of ABC and alpha ALC indicated that they would be strong enough for use under weight-bearing conditions. The affinity indices for ABC, determined using m ale Wistar rat tibiae, were significantly higher than those for alpha ALC ( p < 0.0001) up to 8 weeks. Composite plates (15 x 10 x 2 mm) that had an un cured surface layer on one side were made in situ in a rectangular mold. On e of the plates was implanted into the proximal metaphysis of the tibia of a male Japanese white rabbit, and the failure load was measured by a detach ing test 10 weeks after implantation. The failure loads for ABC on its uncu red surface [1.91 +/- 1.23 kgf (n = 8)] were significantly higher than thos e for alpha ALC on its uncured surface [0.35 +/- 0.33 kgf (n = 8); (p < 0.0 001)], and they also were significantly higher than those for ABC on the ot her (cured surface) side (p < 0.0001). Histological examinations using rabb it tibiae revealed bone ingrowth into the composite only on the uncured sur face of ABC. This study revealed that the amorphous phase of alumina and fo rmation of an uncured surface layer are needed for the osteoconductive and bone-bonding ability of ABC. ABC shows promise as a basis for the developme nt of a highly osteoconductive and mechanically strong biomaterial. (C) 199 9 John Wiley & Sons, Inc.