Mechanical strength of the cement-bone interface is greater in shear than in tension

The objective of this study was to determine the relative mechanical proper ties of the cement-bone interface due to tensile or shear loading. Mechanic al tests were performed on cement-bone specimens in tensile (n = 51) or she ar (n = 55) test jigs under the displacement control at 1 mm/min until comp lete failure. Before testing, the quantity of bone interdigitated with the cement was determined and served as a covariate in the study. The apparent strength of the cement-bone interface was significantly higher (p < 0.0001) for the interface when loaded in shear (2.25 MPa) when compared to tensile loading (1.35 MPa). Significantly higher energies to failure (p < 0.0001) and displacement before failure (p < 0.01) were also determined for the she ar specimens. The post-yield softening response was not different for the t wo test directions. The data obtained herein suggests that cement-bone inte rfaces with equal amountsof tensile and shear stress would be more likely t o fail under tensile loading. (C) 1999 Elsevier Science Ltd. All rights res erved.