Evaluation & Comparison of load- deflection characteristics of super elastic Nickel Titanium orthodontic arch wires

Ni-Ti alloys are widely used in orthodontics. The aim of this study was to evaluate & compare the load- deflection properties of Ni-Ti wires. In this experimental study, 65 Ni-Ti round wire (0. 014 inch) from 13 different brands were subjected to a 3-bracket bending test at 37ºc using an upper central bracket attached to rod in a manner the distance between the midpoint of brackets was 15. 5mm. For each wire, the average force was determined at 1, 1. 5, 2 & 2. 5 deflections in unloading area. Then, SEM equipped with EDX system was used to asses element composition of each brand of wire. The drawing graphs had the overall shape of superelastic graphs; however, the amount of force applied by different wires at different deflections were significantly different, so 13 wires was divided to 4 categories according to their force delivary: high force (orthoforce), moderate force (Proflex، ORG، Ortho technology، IMD، GAC & Force I), Low force (Smart،Nitanium،Nitinol SE،SE NITI،Rematitan Lite) & very low force (Imagination). Additionally it was revealed that wires belong to one manufactory doesn’t act similarly. The maximum & minimum Coefficient of Vriation belonged to Ortho Force & ORG, respectively. In element analysis, the ratio of Ni/Ti was not similar in different wire brands. It seemed likely that wires with higher Ti atomic percentage show lower load- deflection rate. It is revealed by this study that although studied wires almost showed superelastic graphs, the slope of the graph showed significant difference among the wires. So in this regard, the manufacturers’ propagations are not reliable completely. The general recommendation is application of caution & precision in wire selection and attention to study results, element analysis & amount of crowding.