Bone cement improved by vacuum mixing and chilling.

Two mixing methods, hand and vacuum mixing, were compared using high viscosity, high molecular, antibiotic containing polymethylmethacrylate kept at two different temperatures, 4 degrees C and 21 degrees C, prior to mixing. The mechanical properties, i.e., fracture strength, maximum deflection, modulus of elasticity and hardness, were improved by vacuum mixing when compared with hand mixing at both temperatures. The fatigue life was 10 times longer after vacuum mixing. Chilling prior to mixing made the mixing easier and improved the handling characteristics. Vacuum mixing delayed the setting time by 1 minute, but also decreased the peak temperature. Radiographic analysis showed that vacuum mixing mainly reduced the microporosity, but also the macroporosity. The mechanical properties deteriorated slightly after 2 months in Ringer's solution, but the differences between the mixing procedures remained unchanged.