Biomechanical evaluation of polymethyl methacrylate with the addition of various doses of cefazolin, vancomycin, gentamicin, and silver microparticles.

Objectives: Numerous studies have examined the biomechanics of polymethyl methacrylate (PMMA) with added antibiotics, but direct comparison between studies is difficult. Our purpose was to evaluate the effects of the addition of antibiotic drugs and silver on compressive and bending strength of PMMA. Our null hypothesis was that there would be no significant difference in the compressive strength or bending strength of PMMA with the addition of silver or varying amounts of antibiotic drugs.

Methods: Polymethyl methacrylate was mixed with cefazolin, gentamicin, vancomycin, or silver; the control was PMMA alone. Antibiotic groups contained 20 g PMMA and 0.5 g, 1 g, 2 g, or 3 g of antibiotic. Silver groups had 0.25 g silver powder alone added to 20 g PMMA or silver with PMMA and 0, 0.5 g or 1 g of antibiotic. Samples underwent four-point bending and compression testing in air at room temperature and prevailing humidity. Pairwise comparisons between groups and to the ASTM and ISO standards were performed.

Results: Compression: All antibiotic and silver groups were weaker than the control. Samples with cefazolin tended to be stronger than other antibiotic groups with equivalent doses of antibiotic. All groups were above the ASTM standard, except 3 g vancomycin. Four-point bending: The addition of antibiotics did not significantly affect bending strength in groups with lower doses of antibiotics. The silver + PMMA group was weaker than the control. No groups were significantly below the ISO standard except the 3 g vancomycin group.

Clinical Significance: The addition of antibiotic or silver decreased the biomechanical strength in all samples, but not below the ASTM or ISO standard for most groups. The addition of cefazolin appears to affect strength the least, while high doses of vancomycin alter strength the most.