Effect of bioactive filler content on mechanical properties and osteoconductivity of bioactive bone cement

We took three types of bioactive bone cement (designated AWC, HAC, and TCPC ), each with a different bioactive filler, and evaluated the influence of e ach filler on the mechanical properties and osteoconductivity of the cement . The cements consisted of bisphenol-a-glycidyl methacrylate-based (Bis-GMA based) monomers as an organic matrix, with a bioactive filler of apatite/w ollastonite containing glass-ceramic (AW-GC) or sintered hydroxyapatite (HA ) or beta-tricalcium phosphate (beta-TCP) powder. Each filler was mixed wit h the monomers in proportions of 50, 70, and 80% (w/w), giving a total of n ine cement subgroups. The nine subgroups were designated AWC50, AWC70, AWC8 0, HAC50, HAC70, HAC80, TCPC50, TCPC70, and TCPC80. The compressive and ben ding strengths of AWC were found to be higher than those of HAC and TCPC fo r all bioactive filler contents. We also evaluated the cements in vivo by p acking them into the intramedullary canals of rat tibiae. To compare the os teoconductivity of the cements, an affinity index was calculated for each c ement; it equaled the length of bone in direct apposition to the cement, ex pressed as a percentage of the total length of the cement surface. Microrad iographic examination up to 26 weeks after implantation revealed that AWC s howed a higher affinity index than HAC and TCPC for each filler content alt hough the affinity indices of all nine subgroups (especially the AWC and HA C subgroups) increased with time. New bone had formed along the AWC surface within 4 weeks, even in the cement containing AW-GC filler at only 50% (w/ w); observation of the cement-bone interfaces using a scanning electron mic roscope showed that all the cements had directly contacted the bone. At 4 w eeks the AWC had bonded to the bone via a 10 mu m-thick reactive layer; the width of the layer, in which partly degraded AW-GC particles were seen, be came slightly thicker with time. On the other hand, in the HAC and TCPC-imp lanted tibiae, some particles on the cement surface were surrounded by new bone and partly absorbed or degraded. The results suggest that the stronger bonding between the inorganic filler and the organic matrix in the AWC cem ents gave them better mechanical properties. The results also indicate that the higher osteoconductivity of AWC was caused by the higher reactivity of the AW-GC powder on the cement surface. (C) 1999 John Wiley & Sons, Inc.