MECHANICAL-PROPERTIES OF NEW LOW-VISCOSIT Y POLYMETHYL METHACRYLATE BONE CEMENTS - IMPROVEMENT THROUGH VACUUM-MIXING

With the objective of improving mechanical properties by using a new c atalyst, a new bone cement (Sulfix-60) and a new low-viscosity cement with added gentamycin (Allofix-G) were developed. Dynamic weakness was the major disadvantage of the older Sulfix-6 cement, especially in co mparison with high-viscosity bone cement. Although static strength cou ld be improved, investigations into improved fatigue strength and the effect of vaccuum-mixing on the static and fatigue strength had yet to be carried out. To investigate fatigue stability, specimens of the ne w bone cements were tested using loads under wet conditions until brea kage or 20 million cycles. In a first series the cement was hand-mixed , in a second series vacuum-mixed alone, and in a third series vacuum- mixed under pressure. Additionally, the ultimate static bending streng th was investigated using the standard four-point bending test for the three series of bone cement. Vacuum-mixing brought about an improveme nt in the dynamic strength of Sulfix-60 from 6.3 MPa to 9.1 MPa, and f or Allofix-G from 6.3 MPa to 8.2 MPa; additional pressure brought no f urther improvement. A 200% increased fatigue stability was detectable in comparison with the older cement. The ultimate bending strength was also significantly improved by vacuum-mixing for both bone cements.