Introduction: Bone grafts are widely used in periodontal surgery, such as periodontal regeneration, socket preservation, peri-implant defects, and alveolar bone augmentation. The possibility to reconstruct an infrabony periodontal defect or a resorbed edentulous ridge, or to prevent the resorption of the extraction socket, represents a significant improvement in the treatment of clinical conditions. An ideal bone graft material should be biocompatible, biosafe, non-allergenic, non-toxic, and no risk of disease transmission. It should also have enough mechanical strength for space maintenance and be easy to manipulate during surgical phases. Magnesium alloys are presently investigated as potential implant materials for their good biocompatibility, osteogenesis and biodegradability[1]. More importantly, magnesium has been reported to have antibacterial activity and could therefore be used to prevent implant infections. Degradation of magnesium alloys in the body can locally produce alkaline environment to kill bacteria. But the body fluid will soon neutralize the alkaline and thus reduce the antibacterial effect. Hence a novel Mg-Cu alloy is designed to combine the favorable properties of magnesium with the well-known antibacterial performance of copper ions[3]. Porphyromonas gingivalis is one of the most important periodontal pathogen bacteria. Periodontal doctors can only rely on a large number of antibiotics to prevent postoperative infections[2]. However, the abuse of antibiotics has become a worldwide problem. Therefore, Mg-Cu alloy as a new type of antibacterial bone graft has great research value. In this study, three Mg-Cu alloys with different Cu content, Mg-0.05Cu, Mg-0.2Cu and Mg-0.5Cu, respectively, were studied in order to provide relevant experimental evidence for future application.
Methods: Materials: Material extract solution was made according to ISO10993-5. Mg-Cu alloys were immersed separately in brain-heart infusion broth (BHI) for 3h, 6h, 12h, 24h and 48h, and then the alloy extract solution was obtained.
Antibacterial test: The strain used in this study was Porphyromonas gingivalis ATCC33277. Bacterial suspension (1×109CFU/ml) was added to material extract solution in a proportion of 1:100, and the mixture was incubated anaerobically for 24h. Then the cell suspension was cultivated on a BHI agar plate. The bacteria cells were enumerated after incubation for 7-10 days. Real-time quantitative PCR (qPCR) analysis was performed to enumerate the definitive qualification of bacteria DNA, and then to calculate the concentration of bacteria in the material extract solution through the standard curve.
Results: The antimicrobial activities of Mg-Cu alloys were compared with pure Mg (Fig 1). The 3h extract solution of Mg-Cu alloy showed fast killing rate, and the 24h extract solution achieved nearly 100% killing. While the 12h extract solution of pure Mg showed fast killing rate. In the study of the inhibitory abilities of Mg-Cu alloy and Mg through Real-time PCR, the bacterial concentration through standard curve was calculated (Fig 2). The results showed that the ability of Mg-Cu alloy to inhibit bacteria growth was much stronger than that of pure Mg. But the difference among three Mg-Cu alloys was not much obvious.
Conclusion: Mg-Cu alloy has stronger antiseptic effect to Porphyromonas gingivalis than pure Mg, which will have more value in dental application.
References:
[1] Chaya A, Yoshizawa S, Verdelis K, et al. In vivo study of magnesium plate and screw degradation and bone fracture healing. Acta Biomater, 2015 , 18(5): 262-269.
[2] Davies D. Understanding biofilm resistance to antibacterial agents. Nat Rev Drug Discov, 2003, 2(2): 114–122.
[3] Prado J V, Esparza M M, Vidal A R,et al. Adherence to copper and stainless steel metal coupons of common nosocomial bacterial strains. Rev Med Chil, 2013, 141(3): 291-297.