Load‑deflection characteristics of coated and noncoated nickel‑titanium wires in self‑ligating brackets using a modified bending test: An in vitro study

Abstract

Background: To determine and compare the force‑deflection values of different types of nickel‑titanium (NiTi) wires during unloading phase at varying deflections, that is 1 mm, 1.5 mm, 2 mm, and 2.5 mm, with the use of self‑ligating ceramic brackets using modified bending test on a typodont under controlled temperature conditions.

Materials and Methods: In this in vitro study total of 45 wires of ovoid shape of three different NiTi wires – pseudoelastic NiTi (Group I), heat activated NiTi (Group II), and esthetic coated NiTi (Group III) for maxillary arch were tested after insertion in ceramic self‑ligating brackets bonded to plastic teeth of phantom jaw . The maxillary left lateral incisor was removed to simulate a malpositioned tooth which acted as the load site, and load‑deflection characteristics were measured during unloading using Instron and data analyzed statically by two-way analysis of variance ,Tukey’s post hoc test, intraclass correlation coefficientand Pearson correlation coefficient,. A two‑sided (α = 2) P < 0.05 was considered statistically significant.

Results: When wires were compared at each deflection statistically significant difference was observed between the three groups of wires (Group I > Group II > Group III) at all the four levels of deflection except for Group II versus Group III at 1 mm, 1.5 mm, and 2 mm of deflection. Statistically significant difference was noted in mean load values for comparisons made at different deflections for each wire except for the comparison made at 1.5 versus 2 mm for Group II and Group III.

Conclusion: Overall comparison showed esthetic coated Ni‑Ti wires gave significantly lower mean load values, followed by heat activated and pseudoelastic NiTi wires. Thus, heat activated NiTi wires are best suited in patients with severe malpositions/periodontitis, while for esthetically conscious patients esthetic coated NiTi can be used.

Key Words: Nickel titanium, testing, unloading, wires