Shear strength of the cement metal interface--an experimental study

The shear strength of the cement-metal interface using rods with different surface treatments and a clinical standardized cementing technique was studied. Under "dry" conditions, a low interface shear strength can be obtained with polished and smooth CoCrMo surfaces (peak-to-valley height Rt: 1 microm, average 0.2 MPa; 5 microm, 0.38 MPa). Grit-blasted and polymethylmethacrylate (PMMA)-precoated surfaces achieved higher values (PMMA precoat: average 5.16 MPa; CoCrMo peak-to-valley height Rt: 20 microm, average 8.61 MPa: 60 microm, average 7.8 MPa). After immersion in physiological saline solution for 60 days, the PMMA-precoated rods kept their initial stability whereas all the other test rods had lost their stability completely. A microscopic analysis of cross-sections revealed gap formations at the cement-metal interface to varying degrees (1-16 microm). PMMA-precoated rods rarely showed any gap formation at all. The above-mentioned gap formation was seen independently of the porosity at the cement-metal interface and corresponds to the clinical and postmortem observed debonding of the interface.