ABSTRACT
BACKGROUND: Nickel-titanium archwires have unique mechanical properties that make them the archwire of choice during the first phase of orthodontic treatment. However, during its clinical use when subjected to oral conditions, these properties can undergo great changes. MATERIALS AND METHODS: A sample of 24 randomly chosen superelastic NiTi orthodontic archwires (12 TE and 12 PSE) with a 0.014-inch round section from the same manufacturer were distributed into four groups of six archwires each. The first two groups were new wires (as-received), which were used as controls (T0), and the other two were collected after 3 months of clinical usage (as-retrieved) in orthodontic patients (T1). Mechanical properties were measured by mechanical tensile testing and three-point bending tests under the same experimental and temperature conditions (36°C) in a universal testing machine. Comparisons between the groups at T0 and T1 were performed with t-tests and Mann-Whitney U tests. A paired t-test and Wilcoxon signed rank sum test were used for intragroup comparisons (T1-T0). RESULTS: At baseline, PSE wires presented significantly (P < 0.05) higher load at fracture, range, ultimate tensile strength (UTS), yield strength, springback, maximum tension and flexural ultimate strength (FUS) than those of TE wires. At T1, a significant decrease in load at fracture and UTS in PSE wires and in FUS in TE wires was found. After 3 months of clinical usage, the changes (T1-T0) in the mechanical properties of both alloys were similar. CONCLUSIONS: After 3 months of clinical usage, wires lost some of their mechanical properties and had less resistance to breakage. However, the as-received differences between both wires were maintained after clinical usage.
