Influence of temperature and vacuum mixing on bone cement properties

To analyze the influence of varying viscosity and mixing temperature (22 degrees C and 6 degrees C) on macro- and microporosity, density, and compressive strength in vacuum mixed bone cement, high, medium, and low viscosity cement were mixed in 2 vacuum mixing systems and compared with bowl mixing at atmospheric pressure. At 22 degrees C, vacuum mixing significantly reduced void volume to less than approximately 3 per mill. The reduction was most pronounced in low viscosity cement. Microporosity also was reduced in all cements by vacuum mixing and to highest degree in low viscosity cement. At 6 degrees C the reduction of micropores was more pronounced in high viscosity cement. In medium and especially low viscosity cement, the prechilling gave an increased number of micropores. Cement density also was significantly reduced in low viscosity cement at 6 degrees C. Vacuum mixing significantly increased compressive strength by approximately 15% in all cement types (30 days). The temperature did not significantly influence compressive strength, but low viscosity cement generally was stronger when mixed at 22 degrees C. It is concluded that vacuum mixing improves cement quality. However, the temperature influences the final result; in particular, low viscosity cement should not be mixed after prechilling to 6 degrees C.