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

Abstract

Background: This study presented a cleaning method for orthodontic NiTi‑closed coils and
evaluated its effect on the force characteristics of these coils.
Materials and Methods: 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.
Results: 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).
Conclusion: 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.
Key Words: Autoclave sterilization, cleaning, equipment reuse, hydrochloric acid, sodium
hypochlorite