Effects of laminations and blood entrapment on the strength of acrylic bone cement.

The tensile and shear strengths of surgically mixed acrylic bone cement were measured for intact specimens and for special two-part cylindrical specimens containing single laminations perpendicular to their longitudinal axes. Laminations were formed at times ranging from 3 1/2 to 6 1/2 minutes after initial mixing of the powder and liquid for dry interfaces and for interfaces containing fresh blood at the time of lamination formation. In additon, special tests were conducted to measure the bond strength between freshly mixed and pre-polymerized acrylic. The tensile and shear strengths at the lamination interface decreased significantly when the laminations were formed late in the working life of the acrylic. The presence of blood at the interface further weakened the bond to approximately 25 per cent (tension) and 36 per cent (shear) of the virgin strengths of the material. These results support early acrylic placement with dry surgical fields. The bonding of fresh acrylic to pre-polymerized material was most effective when the material was poured into the mold before dough stage. This technique would have practical application in special cases for re-cementing revision prostheses without removing the old acrylic from within the bone.