Effect of hydrochloric acid, sodium hypochlorite, and autoclave sterilization on the force characteristics of orthodontic NiTi‑closed coils

This study presented a cleaning method for orthodontic NiTi‑closed coils and evaluated its effect on the force characteristics of these coils.

In this in vitro study, 160 orthodontic NiTi‑closed coils, 160 orthodontic NiTi‑closed coils (9 mm) from two brands G and H and DB, randomly assigned into four groups. Group 1: Three times of immersion in the 10% hydrochloric acid (HCI) solution for 1 min followed by the immersion in 5.25% sodium hypochlorite solution for 5 min. Group 2: Three times autoclave sterilization. Group 3: Three times of immersion in 10% HCI solution for 1 min, followed by the immersion in 5.25% sodium hypochlorite solution for 5 min and autoclave sterilization. Group 4: No immersion and no sterilization. The forces of coils were measured at 25, 23, 21, 19, and 17 mm extension. To measure the force characteristics of coils, an electromechanical universal testing machine was used. For the statistical analysis, Kolmogorov–Smirnov, Kruskal–Wallis, and Mann– Whitney U‑tests were used at 0.05 significance level.

In G and H coils, no significant differences between the mean forces of different groups were found in any extensions. In DB coils, only in 25 mm extension, there were no significant differences between the groups (P = 0.144). In 17‑, 19‑, and 21‑mm extensions, significant differences (P < 0.001) were found like in 23 mm extension (P = 0.05). In both brands, more extension makes significant more forces statistically (P < 0.01). In all extensions, G and H coils have significant less forces (P < 0.001).

Immersion in HCl, 10% for 1 min followed by the immersion in NaOCl, 5.25% for 5 min followed by autoclave sterilization, even three times repeating of this process, did not result in significant changes in the force characteristics of A‑NiTi‑closed coils.