| PrefaceAlong with the increasing of the magnetism function, rare earth permanent magnet is being applied to the dental prosthetics and ortho-dontics extensively. Among them, magnetic attachment has been ap-plied to clinic extensively because of having different characteristics and advantages with others. Now, the magnetic retainer, which shell was wrapped up with stainless steel, has already been manufactured in abroad, and has further better characteristics than others whether in the decrease of leaking magnetism, or in the function of resistant cor-rosion. The application of dental magnetic retainer in oral becomes more safe.Combining together the domestic and foreign achievements, we develop a same kind of product suiting for the clinical application, and further improve its construction and function, which will promote an extensive application of magnetic retainer in the domestic dental realm. This experiment investigated the biocompatibility of two kinds of special stainless steel materials that will be used in the magnetic re-tainer by MTT - assay for the culture cells in vitro, and compared with pure titanium and cobalt - chrome alloy that are often used in oral, in order to provided a biological basis for the clinical application of the magnetic retainer.Materials and Methods1. The experiment materials were divided into; A set: the medi-cal stainless steel (S1,) , B set; magnetic stainless steel (S2) , C set; pure titanium, D set; Co - Cr alloy, E set: PVC material. A ~ E set materials were made into some cuboids that length, breadth, thickness were respectively 10 mms, 9 mms, 3 mms. After disinfected and ster-ilized, the materials were put into 24 bores culture plate. Then we used the RPMI 1640 culture liquids to prepare the extracting liquids of those materials. We chose the logarithms generate term L -929 cells, and used the RPMI 1640 liquids to prepare the cell suspending liquids which density was roughly 1. 0 x 10 /ml.2. The experiment methods; To take 96 bores culture plates, and add the cell suspending liquids l00#d into each bore. Respectively add the A ~ E set materials extracting liquids l00#l into the group 1 ~ 5 bores, and add RPMI 1640 culture liquids l00#l into group 6 bore, then put them into the culture box. Respectively take out a culture plate after educating 1 ~ 5 day, and observe the changes of cell form by upside down and discrepancy microscope. To add 5mg/ml MTT liquids 20#J into each bore, and take out the plate after educating 4 hours continuously. To suck out the educate liquids and join DMSO 150#l into the each bore. To examine the optical density by automatic enzyme immunoassay analyzer, and calculate the rate of cells relative growth (RGR) and assess the cytotoxic rank of each materials.Results1. The cell's morphological observation; The first day, in the positive control the cells growing on the plate showed fusiform or poly-horn shape, and the suspending cells showed circular or irregularform, and appeared vacuoles or grains in the cytoplasm . The cells of the rest groups all almost grew with attaching on the plate, and with enmorphism and the steady cytoplasm. The fifth day, in the positive control the cells almost shed off, which cytoplasm and cell nucleus concentrated, and even there were many dead cells which plasmale-mma collapsed and karyotheca solved. The ceUs of the rest groups all almost grew with attaching on the plate continuously, and the cell's density creased. There were few suspending degenerate cells or dead cells.2. The results of statistical analysis; There were a significant difference in the optical densities between metal material groups or the negative control and the positive control (P<0.05 orP<0.01). Ac-cording to the rate of cell's relative growth of the four metal material groups, the sequence from big to small was; the pure titanium, S1 stainless steel, S2stainless steel, cobalt - chrome alloy. S1 stainless steel and S2 stainless steel showed slight cytotoxicity ( the RGR de-creased 3% ) , Cobalt...
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