Corrosion resistance of iron–platinum magnets

Objectives. The objective of this study was to investigate the corrosion resistance of the prototype iron–platinum (FePt) magnets and non-encapsulated neodymium–iron–boron (NdFeB) magnets in three different pH environments. Methods. The corrosion resistance of the magnets was studied using a corrosion indicator, the breakaway force. The breakaway forces of the magnets after immersion in three media, namely 1% lactic acid solution (pH=2.7), 0.1% sodium sulphide solution (pH=12) and adjusted artificial saliva (pH=6.8) were compared after 28 and 60-day periods. Results. By day 7, all NdFeB magnets dissolved completely in the acid medium, and they showed significantly lower breakaway forces at day 28 and day 60 in artificial saliva (90%, 69%) and in alkaline medium (67%, 42%). In contrast, the FePt magnets did not show a drop in the breakaway forces after immersion in acid or artificial saliva, although approximately half of the original breakaway forces were recorded at day 28 and day 60 after immersion in strong alkali. Conclusions. The new iron–platinum magnets, which require no yoke assembly or protective casing, has good corrosion resistance for the oral environment. If its retentive force can be improved without increasing its thickness (0.3 mm), then it will have distinct advantages for clinical use.