Over 200,000 total joint replacements are performed yearly in the United States. Although basically succesful, there are reported a significant number of long term failures, many of which involve breakdown of the acrylic bone cement and/or the interface between the bone and the cement. Attempts have been made to improve the cement by removing some of its internal porosity by means of centrifugation during mixing. In our laboratory a partial vacuum mixing bowl has been recently developed which removes even more of the porosity and creates a cement which is superior in mechanical uniaxial tensile and compression strength as well as having much greater tensile fatigue life. A major question remains if the superior properties of the vacuum mixed cement itself will transfer to the cement/bone interface to produce an enhanced mechanical bond. Using long term, low loading cyclic testing modes to produce cement fracture by crack propagation, it is proposed to investigate the feasibility of stronger cements creating better cement/bone bonding. Although well versed in the determination of high load, plastically deforming uniaxial mechanical properties of synthetic dental and medical materials, the principal investigator would have to significantly shift his area of research in order to learn to study the fracture mechanics of low cyclic, elastic loading of complex, multicomponent interfaces. The research plan is to create cement/bone interface specimens, paying great attention to such variables as mixing technique, placement rates and pressures, plus nature and preparation of the cadaveric cancellous bony bed. Then, subject these specimens to interface tests such as lap shear, ring shear, bending and crack propagation. These will be done in 37 C physiologically simulating fluids in both quasi-static and the more clinically relevant long term, low magnitude cyclic dynamic loading in order to evaluate the feasibility of determining the fracture mechanisms and enhancement of the strength of the cement/bone interface.
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