Abstract
ObjectiveTo test the null hypothesis that the aging process in self-ligating brackets is not higher than in conventional brackets.MethodsTwenty-five conventional (GN-3M/Unitek; GE-GAC; VE-Aditek) and 25 self-ligating (SCs-3M/Unitek; INs-GAC; ECs-Aditek) metal brackets from three manufacturers (n = 150) were submitted to aging process in 0.9% NaCl solution at a constant temperature of 37 ± 1ºC for 21 days. The content of nickel, chromium and iron ions in the solution collected at intervals of 7, 14 and 21 days was quantified by atomic absorption spectrophotometry. After the aging process, the brackets were analyzed by scanning electron microscopy (SEM) under 22X and 1,000X magnifications.ResultsComparison of metal release in self-ligating and conventional brackets from the same manufacturer proved that the SCs group released more nickel (p < 0.05) than the GN group after 7 and 14 days, but less chromium (p < 0.05) after 14 days and less iron (p < 0.05) at the three experimental time intervals. The INs group released less iron (p < 0.05) than the GE group after 7 days and less nickel, chromium and iron (p < 0.05) after 14 and 21 days. The ECs group released more nickel, chromium and iron (p < 0.05) than the VE group after 14 days, but released less nickel and chromium (p < 0.05) after 7 days and less chromium and iron (p < 0.05) after 21 days. The SEM analysis revealed alterations on surface topography of conventional and self-ligating brackets.ConclusionsThe aging process in self-ligating brackets was not greater than in conventional brackets from the same manufacturer. The null hypothesis was accepted.
Highlights
During the experimental period, the release of nickel, chromium and iron metal ions was observed in all groups, except for nickel ion in the GN group, which was not detected at any of the time intervals (Tables 2, 3 and 4)
The experimental groups revealed a trend towards increasing release of ions, such as chromium and iron, from the first to the third week of the experiment (p < 0.05)
A corroded bracket often presents a more irregular surface and can accumulate products resulting from corrosion (Fig 4)
Summary
To test the null hypothesis that the aging process in self-ligating brackets is not higher than in conventional brackets. Results: Comparison of metal release in self-ligating and conventional brackets from the same manufacturer proved that the SCs group released more nickel (p < 0.05) than the GN group after 7 and 14 days, but less chromium (p < 0.05) after 14 days and less iron (p < 0.05) at the three experimental time intervals. These alloys are made of austenitic stainless steel,[1,2] such as AISI 303, 304 and 316L,3 and have nickel, chromium and iron in their composition. The null hypothesis assumed that the aging process in self-ligating brackets is not greater than in conventional brackets
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