Influence of Ni²⁺ from nickel-chromium alloy on H₂O₂ from S.oralis

Objectives: In order to decide whether restoration made from nickel-chromium alloy can interfere with subgingival homeostasis of microorganisms, this research investigated the influence of nickel ions (Ni²⁺) released from this material on the ability of producing H₂O₂ by Streptococcus oralis (S.oralis). Methods: S.oralis was culitvated in substrates with nickel ions of different concentions: 3.75 ppm, 7.5 ppm, 15 ppm, 30 ppm, 60 ppm and 120 ppm. After 24hrs, bacteria were collected and separated into two parts. One was tested for the concentration of bacterial protein with Bradford Method, while the other one was tested for the amount of H₂O₂ produced by S.oralis with ABTS-HRP Method. Then ability of H₂O₂ production by S.oralis was calculated. Finally, difference of this ability before and after adding Ni²⁺ was tested with one-way ANOVA. Results: The amount of H₂O₂ produced by S.oralis descended with the increasing of Ni²⁺ concentration. S.oralis could produce 342.15nmol/mg H₂O₂ without Ni²⁺. The concentration of H₂O₂ declined to 8.11nmol/mg when the concentration of Ni²⁺ added reached 120ppm. The production of H₂O₂ decreased dramatically in the region between 3.75ppm and 30ppm Ni²⁺ concentration. When this concentration became higher than 60ppm, the H₂O₂ production ability of S.oralis is significantly inhibited by Ni²⁺ (P<0.05). Conclusions: Ni²⁺ can inhibit the H₂O₂ producing ability of S.oralis and decrease the amount of H₂O₂ in gingival crevice. Since H₂O₂ is an important beneficial factor for the antibacterial effect of S.oralis, the inhibitory effect of nickel ions may cause dysbacteriosis and then lead to periodontitis around the margin of prosthesis made of nickel-chromium alloys.