Mechanical characterization of bone graft substitute ceramic cements.

The aim of this laboratory work was to study the compressive and flexural characteristics of various commercially available bone graft substitute (BGS) ceramic cements, in their initial as-mixed condition, and compare them to polymethylmethacrylate (PMMA). The tested biomaterials were two different calcium phosphate cements, two different calcium sulphate cements, one nanocrystalline hydroxyapatite and one PMMA cement. All biomaterials were prepared according to manufacturers instructions and the methodology described in ISO 5833 (2002) for acrylic bone cement was followed, as the one closest approaching in vivo requirements. All BGS cements had a brittle behaviour and when subjected to mechanical stress they all failed under sudden crack propagations in their bulk. Both in compression and bending, all BGS cements failed under loads lower than those of PMMA. In compression, the calcium sulphate extra strength cement showed a strength value of approximately 60% of PMMA, the other cements following at a distance. In bending, all BGS cements showed strengths below 22% of PMMA. However, due to limited number and fragility of specimens, calculated bending strengths can only be considered as indicative figures with limited comparative value. The results of this in vitro study showed a varying mechanical performance between tested BGS ceramic cements, whilst all of them exhibited lower compression and bending strength than the selected PMMA. These findings, of course, cannot be directly extrapolated to surgical or clinical implications, since the adopted in vitro context does not necessarily reflect the actual in vivo conditions met by such biomaterials.