Objective: To test the hypothesis that there is no difference between the action of at-home and in-office vital bleaching on the shear bond strength of metallic brackets bonded with composite resin 24 hours after bleaching. Materials and Methods: Forty-five human upper premolars were randomly divided into three groups: (1) control, (2) 10% carbamide peroxide at-home bleached, and (3) 35% hydrogen peroxide in-office bleached. Twenty-four hours after bleaching the teeth were pumiced, bonded with metallic brackets, and stored in distilled water. One day after bonding the shear bond strength of the brackets was determined. Results: The mean shear bond strength of Group 1 (control) and Group 2 (carbamide peroxide bleached) were not statistically different. Group 3 (hydrogen peroxide bleached) had a significantly lower mean shear bond strength than Group 1 and Group 2. Conclusions: The hypothesis is rejected. Use of 10% carbamide peroxide bleaching does not significantly alter shear bond strength values. On the other hand, use of 35% hydrogen peroxide bleaching significantly reduces these values and diminishes the amount of resin remnant on the tooth surface after bracket debonding. (Angle Orthod. 2009;79:122-126.)
The corrosion resistance of AISI 304 stainless steel (AISI 304 SS) and manganese stainless steel (low-nickel SS) brackets in artificial saliva was investigated. The cytotoxic effects of their corrosion products on L929 cell culture were compared by two assays, crystal violet, to evaluate cell viability, and MTT (3-[4,5-dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide), for cell metabolism and proliferation. The atomic absorption spectroscopic analysis of the corrosion products demonstrated that nickel and manganese ion concentrations were higher for the AISI 304 SS-bracket immersion solution as compared with the low-nickel SS brackets. Scanning electron microscopy and energy-dispersive spectroscopy demonstrated less corrosion resistance for the AISI 304 SS brackets. Although none of the bracket extracts altered L929 cell viability or morphology, the AISI 304 SS-bracket extracts decreased cellular metabolism slightly. The results indicated that the low-nickel SS presents better in vitro biocompatibility than AISI 304 SS brackets. Abbreviations used: AISI, American Iron and Steel Institute; EDS, energy-dispersive spectroscopy; OD, optical density; ISO, International Organization for Standardization; MTT, (3-{4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; NiSO(4), nickel sulfate; SEM, standard error of the mean; WHO, World Health Organization; and TNF, tumor necrosis factor.
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