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In vitro Evaluation of Corrosion and Cytotoxicity of Orthodontic Brackets

¹ Graduate Program in Orthodontics, School of Dentistry,
² Immunology Section, Institute of Tropical Pathology and Public Health, Federal University of Goiás–Goiânia-Goiás, Brazil; and
³ Nuclear and Energy Research Institute (IPEN/CNEN-SP), São Paulo–SP, Brazil;

View larger version (102K): [in this window] [in a new window]   Figure 1. Scanning electron micrographs of brackets, before and after artificial saliva exposure. (A) AISI 304 stainless steel brackets before and (B) after 63-day saliva exposure. In (C), low-nickel steel brackets prior to and (D) after 63-day exposure. AISI 304 stainless steel bracket surface (B), with irregular areas suggestive of corrosive attack, and low-nickel steel bracket surface (D), presenting regular and less-altered surfaces after artificial saliva exposure.

View larger version (18K): [in this window] [in a new window]   Figure 2. AISI 304 stainless steel brackets’ cytotoxic-corrosion extracts. L929 cells cultured (3.5 x 104 cells/100 µL of medium) to obtain a cell monolayer. After 24 hrs (37°C, 5% CO2), 20 µL of control saliva, low-nickel steel or AISI 304 stainless steel-bracket extracts, obtained after 42 days of incubation, were added to the culture separately. After a 48-hour exposure period (37°C, 5% CO2), crystal violet (A) and MTT (B) assays were performed as described in MATERIALS & METHODS. Data represent mean ± SEM (n = 6). *p < 0.05.

View larger version (48K): [in this window] [in a new window]   Figure 3. L929 cell culture nickel sulfate cytotoxicity. L929 cells were cultured (3.5 x 104 cells/100 µL of medium) for 24 hrs (37°C, 5% CO2) to obtain a monolayer, after which different nickel sulfate concentrations were added. After a 48-hour incubation period (37°C, 5% CO2), the cytotoxicity was assessed by crystal violet and MTT assays, as described in MATERIALS & METHODS. The data represent optical density (OD), mean ± SEM (n = 6), obtained at 620 nm (crystal violet assay) and 550 nm (MTT assay). In parentheses are percentages of extract cytotoxicity. Light-microscopic images of the L929-cell monolayer after exposure to different nickel sulfate concentrations are depicted (A,B,C,D) (scale bar: 100 µm) (magnification x 400). *p < 0.05 (medium vs. NiSO4).