Does long-term intraoral service affect the mechanical properties and elemental composition of multistranded wires of lingual fixed retainers?

Purpose: The aim of this study was to evaluate the elemental and mechanical alterations of stainless steel (SS) multistranded orthodontic wires used in fixed retention after intraoral ageing.

Materials and Methods: Two types of 0.022-inch, seven-stranded wires, Lingual Retainer Wire (LRW) and Tru-Chrome (TCH), from the same manufacturer (Rocky Mountain Orthodontics, Denver, Colo, USA) were tested. Thirty-three samples from LRW group and thirty-seven from TCH were collected, whereas three unused wires from each package were used as controls. The median ageing time for LRW was 7.4 years and 8.4 for TCH. All samples were subjected to scanning electron microscope/X-ray energy dispersive spectroscopy analysis. Three spectra were taken from the surface of each wire and then all samples were used for the assessment of Martens hardness, indentation modulus (EIT), and elastic index (ηIT) with the instrumented indentation testing method (IIT). The intraoral ageing time was statistically compared between the two groups by Mann-Whitney rank sum test and the compositional and mechanical properties were compared by unpaired t-test. The Spearman correlation between elemental content and ageing time was carried out for all elements (a = 0.05).

Results: No significant differences were found for both the elemental content and for the mechanical properties between the wires tested. Spearman analysis revealed no correlation between elemental content and intraoral time while two groups share statistically equal intraoral ageing times (P > 0.05).

Conclusions: Both wires seemed to maintain their mechanical and elemental integrity within a period of 14-year intraoral exposure, whereas no measurable ionic release could be identified.