An in vitro assessment of the mechanical characteristics of nickel-titanium orthodontic wires in Fluoride solutions with different acidities

OBJECTIVES The aim was to evaluate the in vitro effects of fluoride solutions with different acidities on load-deflection characteristics of nickel-titanium (NiTi) orthodontic wires. MATERIALS AND METHODS In this study, which lasted 30 days, 36 (3 cm long, 0.016 × 0.022 inches, SENT 1622, G & H wire Company, Greenwood, Indiana, USA) NiTi wires, were divided into three experimental groups of 12 each. Two groups were subjected to 0.05 topical fluoride mouthwash with different acidities (G1, pH 4; G2, pH 6.6) for 90 s, twice a day, and kept in normal saline after that. The third group (G3, the control group) was kept in normal saline only. Load and unload forces were measured with three bracket bending test in a universal testing machine (Testometric Co, Rochdale, UK). Loading and unloading plateaus and hysteresis were also recorded. Data were then analyzed using analysis of variance and honestly significant difference Tukey at P < 0.05. RESULTS During the loading phase, there was a significant difference between deflections (P < 0.001); but there was no interaction effect (P = 0.191) and no significant difference among three groups (P = 0.268). In the unloading phase, there was a significant difference between deflections (P < 0.001) and an interaction effect was also observed (P = 0.008). Further, significant differences noted among three groups (P = 0.037). Only in the unloading phase, at deflections of 2.2 through 0.2 mm, significant differences between the mean force values of the G1 and G3 groups were observed (P = 0.037). CONCLUSION Based on this in-vitro study, compared to neutral fluoride solution, daily mouthwash with a fluoride solution with more acidic pH of 4 affected the NiTi wires load-deflection characteristics during the unloading phase. This finding may have clinical implications and can be further validated by in-vivo studies.