Chemical and physical properties of nickel-free brackets: An in vitro and ex vivo controlled clinical trial

OBJECTIVE: To evaluate the chemical and dimensional changes of metallic and nickel-free metallic brackets in vitro and ex vivo, regarding oxidation, tie-wing deformation and surface roughness. DESIGN: A split-mouth, in vitro and ex vivo controlled clinical trial. METHODS: A total of 34 adult participants, aged 20-35 years, underwent conventional orthodontic treatment. The right upper central incisor carried the metallic bracket and the left upper central incisor carried the nickel-free metallic bracket. At the 120th day of treatment with a 0.018-inch steel alignment wire, the upper central incisor brackets were removed (ex vivo) and compared with unused brackets (in vitro), distributed into four groups (n = 34): group 1 = in vitro metallic brackets; group 2 = ex vivo metallic brackets; group 3 = in vitro nickel-free metallic brackets; and group 4 = ex vivo nickel-free metallic brackets. Analyses were performed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) to assess slot dimensions and surface irregularity (roughness), respectively, and by energy dispersive spectroscopy (EDS) for oxidation. Analyses were performed with a significance level of 5%. RESULTS: >0.05). Brackets showed no dimensional changes when comparing in vitro and ex vivo conditions. Ex vivo metallic brackets had increased roughness compared to in vitro metallic brackets. CONCLUSIONS: The oral environment promoted corrosion in both metallic and nickel-free brackets. Nickel-free brackets did not have rougher surfaces than metallic brackets, and there were no dimensional changes after use in participants.