The influence of temperature and specimen size on the flexural properties of PMMA bone cement

A three-stage investigation was undertaken to examine the influence of specimen size and polymerization environment on the flexural properties of PMMA. In the first stage, specimens were cut from large pieces of commercially cast acrylic (lucite) and self-curing dental acrylic. The material properties of the cast acrylic as calculated from the results of flexural testing were not influenced by specimen size in the range of 1 X 10 X 30 to 3 X 10 X 60 mm, whereas 1-mm thick dental cement specimens had 12% (p less than 0.001) higher stress and 24% (p less than 0.001) higher strain to failure than 3-mm specimens cut from the same sample. In the second stage, self-curing dental cement and Simplex P bone cement were molded in different thicknesses. These experiments demonstrated that molding thin 1.6-mm specimens resulted in increases of 14% (p less than 0.001) in stress and 30% (p less than 0.001) in strain to failure as compared with 3.2-mm specimens, which were greater differences than those due to the specimen thickness effects alone. In the third stage, temperatures of cement were monitored during polymerization, and cements were molded at different temperatures. These results demonstrated that thicker cement samples reached higher temperatures and that cement samples polymerized at lower temperatures (21 versus 37 degrees C) had 12% (p less than 0.001) greater stress and 105% (p less than 0.001) greater strain to failure.