[The porosity of bone cement (author's transl)].

This paper describes a method of measuring the porosity, shape, distribution and formation of cavities in acrylic cement. We distinguish between big spherical cavities greater than 60 mu and small cavities less than 60 mu which form a variable "basic porosity" with a large number, but a minor volume of bubbles. The bubbles are formed in two different ways. The first is through introduction of air bubbles in the mixing phase by stirring the cement before the working time. These bubbles expand little by temperature rise. The second method of formation is through neoformation of bubbles by evaporation of the monomer at about 100 degrees C. This neoformation of porosity expands the cement. The rise of volume through the neoformation and expansion of bubbles is able to compensate the shrinking of cement due to the polymerization. This effect, however, cannot be currently controlled. Cement strength is influenced by the degree of porosity.