Influence of pressurization on flexural strength distributions of PMMA-based bone cements.

Flexural strength distributions of standard viscosity and low viscosity bone cements based on Polymethylmethacrylate were obtained by testing the materials in four-point bending according to the ISO 5833 protocol. The cement dough was poured into a mold and was allowed to cure at atmospheric pressure. An additional set of specimens of the standard viscosity cement was prepared under pressure while the cement dough was polymerizing in the mold. Following preparation, test specimens were stored in a 37 degrees C water bath for 48 h. The two-parameter Weibull model, which was used to analyze the data, gave a good representation of the fracture loads distribution. Low viscosity cement displayed a higher mean flexural strength and a slightly lower data scatter than standard viscosity cement. The mean flexural strength of the cement increased about 60% when pressure was applied compared with the same material cured at atmospheric pressure. The Weibull modulus, m, characterizes the scattering in the measured values of strength. For the cement prepared at atmospheric pressure the m value was 8.6 while for the cement cured under pressure it was 12.3, which reveals a reduction in the data scatter. The cement tested in four-point bending displayed lower mean flexural strength compared with the cement tested in three-point bending. The influence of the load type upon the mean flexural strength was satisfactory predicted by Weibull model.