The Research Of Influence Produced By Nickel Ions From Nickel-chromium Alloys On Subgingival Microbes

Nickel-chromium alloys are widely used in crowns and bridges for repairing damaged or lost teeth, for its favorable mechanical properties and low cost. But in clinic, hyperplasia and swelling of the gingiva around the cervical part of the prosthesis are usually occurred. Accompanying with it, gingival fluid increases and gingival indexes elevate. Although a lot of scholars have brought forward different kinds of possible mechanisms to explain these phenomena, there is still no convincing proof provided. This research aims to examine the influences produced by nickel (II) ions on the growth and metabolisms of Streptococcus oralis (S. oralis) and Porphyromonas gingivalis (P. gingival is). And futher analysis of the molecular mechanisms of these changes in order to illuminate the reasons for post-prosthodontic damage in periodontal tissues is needed.This research confirmed the inhibitory effect of nickel ion on the growth of S. oralis and P. gingivalis by liquid-dilution method; observed the changes in morphology and permeability of cell membrane by scanning electronic microscope (SEM) and X-ray energy dispersion spectrum(EDS); detected the influence of nickel ions on the antibacterial or pathogenic abilities by liquid scintillation method and micro-plate method; investigated the alteration in genotype of P. gingivalis by PCR extension and sequencing analysis.The research showed:1. Nickel ions could exert inhibitiory effects on the growth of S. oralis and P. gingivalis. When the concentration of nickel ions was 120 ppm, thegrowth of P. gingivalis was totally inhibited. When the concentration dropped to 3.75ppm, there was no difference between the tested groups and the positive ones. The results got from cloning forming unit (CFU) counting method were consistent with those from liquid-dilution method.2. When the nickel ions' concentration was 120ppm, the morphology of S.oralis changed from ovid to rod-shape, meanwhile the length of the chain formed became shorter. The morphology of P.gingivalis altered obviously at the concentration of 60ppm, which was manifested by the sharpness of border and depression on the surface. There were no observable abnormity at other concentrations.3. The results of X-ray energy dispersion spectrum showed that, after the treatment of nickel ions, the values of Na, Ca on cell membrane of S. oralis of augmented and the P peak dropped. While all the Na, Ca and P peak descended on the surface of P. gingivalis. Even disappearance of P peak can be seen when the concentration was higher than 15 ppm.4. Nickel ions produced inhibitory effects on the ability of adhesion and producing H₂O₂ of S.oralis But no such effects on the extracellular and intracellular trypsin-like proteinase (TLP) of P. gingivalis could be observed.5. There would be changes in genotype when the Porphyromonas gingivalis was incubated in the environment with the nickel concentration at 60ppm. Both the fimA gene and prtC gene showed mutation in sequence. The former was mainly point mutation while the latter mainly manifested as base absence. The 5' terminal of fimA was a sensitive domain, among which 12 bases changed and 1 base lost. When the concentration of nickel ions was 7.5ppm, double peaks appeared in DNA380, indicating some bases of this spot might have changed from T to G. The prtC gene showed 3 bases missing and 2 point mutation after incubation with nickel ions.The results indicted:1. Nickel ions can interfere with the growth, morphology and metabolic activities of subgingival microorganisms, mainly manifested as inhibitory effects.2. There were changes of constitution and permeability on cell mebmbrane after treated by nickel ions. This may be one of mechanisms for explaining inhibitory effects. What's more, the mechanisms of such effect maybe varied in different microbes.3. Nickel ions can also produced different effects on the metabolic activities of S. oralis and P. gingivalis. This may lead to the decrease in number of beneficial microorganisms and accumulation of toxic products. The elevation of amount and metabolic products of P. gingivalis will break down collagens in periodontal tissues. As a result of it, the microecologic balance in subgingival environment was interrupted and the periodontal disease may occur.4. There would be gene sequence changes of P. gingivalis incubated in the high-nickel-concentration environment. The alteration in genotype may lead to shift of reading frame, in turn influence the synthesis of fimbriae and collagenase. As a result the virulence of P. gingivalis may tone up or fall down.5. Nickel ions liberating from nickel-chromium alloys can influence the structure, metabolic activities and genotype of subgingival microbes, and then lead to injury of periodontal tissue. Thus, considering the microecologic balance after prosthodontic treatments, we should choose a more stable material in clinic, in order to avoid such damage caused by the corrosive products from prosthodontic alloys.This research observed changes in antibacterial properties or pathogenic abilities of two representive subgingival bacteria caused by nickel ions, investigated the reasons of such changes from morphologic level, protein synthesis and molecular point of view, and discovered a portion of molecular biologic mechanisms. Considering the complexities of oral cavity and periodontal environment, coordinative and antagonistic effects among bacteria in dental plaque and intercross influence among the corrosive products of alloys, futher and deeper study on this topic is necessary.