A Comparative Analysis of Force Deflection Property of Nickel-Titanium Wires of Four Manufacturers using Five Point Bending Test: An In-vitro Study

Abstract

Introduction: Over the last century, material science has made rapid progress. In orthodontics, not only the materials improved, but also the philosophies have changed. Orthodontic wires, which generate biomechanical forces through brackets for tooth movement, are central to the practice of this profession. Aim: To measure the force deflection properties of Nickel-Titanium (NiTi) wires of four manufacturers, used during orthodontic treatment. Materials and Methods: In this in-vitro study, 480 NiTi wires from four different manufacturers [American Orthodontics (AO), 3M-Unitek (3M), Rabbit Force Orthodontics (RO) and Modern Orthodontics (MO)], of various cross-sections was obtained. Samples of each wire were obtained by cutting the straightest distal portion of an arch wire, thus an approximate length of 5.5 cms was recovered. These wires were subjected to a five point bending test. Five lower anterior stainless steel brackets of tooth number 31, 32, 41, 42 (MBT 0.022” Libral traders Centrino brackets) were fixed with the face of the bracket facing upwards on the acrylic block. Each NiTi wire was placed in the slots of orthodontic brackets and secured with stainless steel ligature wires. These wires were subjected to artificial saliva (Wet Mouth) for 30 days at 37°C. This temperature was regulated by using an incubator. The main assessment criterion was the force deflection property of the wire material. Force deflection was measured using a graph paper where initially the wire was placed and plotted on the graph paper. After the deflection of the wire, it was again placed on the same graph paper such that wire ends coincided and the force deflection at the highest point was measured in millimetres using a digital Vernier Caliper (Mitutoyu). The Design of Experiments (DOE) model was used for analysis and a three-way Analysis of Variance (ANOVA) with wire shape as covariate was used for analysing the variability. Results: A 0.014” NiTi wire showed more mean deflection when compared to 0.016” NiTi wire. When a comparison between 0.016”×0.022” and 0.017”×0.025” NiTi wires was done, mean deflection was almost the same. When round and rectangular wires were compared it showed more mean deflection in round wires. When AO was compared with other three manufacturers. A significant difference (p-value <0.0001) was seen in the mean deflection values of MO and RO. When 3M was compared with the other three manufacturers a significant difference (p-value <0.0001) was seen in the mean deflection values of MO and RO. Three-way ANOVA test with wire shape as co-variate showed a significant amount of difference (p<0.0001) for AO, 3M wires with their counterparts. Conclusion: Round NiTi wires showed more force deflection as compared to rectangular NiTi wires. AO and 3M wires were superior as compared to RO and MO wires. Superelastic wires showed more deflection as compared to conventional and heat- activated NiTi. This can be attributed to the property of the wire. Stiffer the wire, less deflection was seen. Cost of the wire also played a role. Cheaper wires were not able to match the quality and standards of their counterparts.