Evaluation of Mechanical Properties of Niti and CuNiti Archwires in as Received and After Artificial Aging
Introduction: The archwires for initial alignment stage require a combination of excellent strength, excellent springiness and a long range of action. Metal appliances including orthodontic archwires are prone to corrosion or degradation in the oral environment due to different salivary components, pH levels and thermal fluctuations that may affect their performance. Aim: The purpose of the current in vitro study is to assess the impact of static deflection, thermo-cycling and acidic exposure on load deflection behaviors of nickel titanium and copper nickel titanium archwires. Materials and Methods: Samples of Niti and CuNiti, 0.016 inch, were divided into four groups: 1, as-received; 2, water storage (2 months); 3, thermo-cycling (5000 cycles); 4, acid challenge (pH 2.5). Loading and unloading forces at 0.5mm intervals were measured using modified bending test. One-way ANOVA and independent t-test were applied to compare the means and Tukey's post hoc test used when there was significant difference. Results: At each deflection, Niti archwires have the highest load values compared to CuNiti archwires in both loading and unloading phases. There is a significant difference between Niti and CuNiti archwires regarding plateau gap and hysteresis percentage. No significant difference have been recorded among different conditions for Niti archwire, while there was significant difference for CuNiti archwire. Conclusion: CuNiti archwires have light and more constant force compared to Niti archwires. However Niti archwires are more resistant to in vitro aging compared to CuNiti archwires. Thermo-cycling reduce the hysteresis between loading and unloading phase while acid challenge increase it for CuNiti archwires.