The surface roughness of orthodontic archwires is an essential factor that determines the effectiveness of arch-guided tooth movement. Using the non-destructive techniques of atomic force microscopy (AFM) and of laser specular reflectance, the surface roughness of 11 nickel-titanium orthodontic wires, a stainless steel and a beta-titanium wire was measured. The results were compared with those obtained using surface profilometry. The smoothest wire, stainless steel, had an optical roughness of 0.10 micron, compared with 0.09 micron from AFM and 0.06 from profilometry. The surface roughness for the beta-titanium wire measured by all three methods was approximately 0.21 micron, while that of the NiTi wires ranged from 0.10 to 1.30 microns. As the surface roughness not only affects the effectiveness of sliding mechanics, but also the corrosion behaviour and the aesthetics of orthodontic components, the manufacturers of orthodontic wires should make an effort to improve the surface quality of their products.

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Metals are the most commonly used materials in the construction of orthodontic appliances designed for the correction of malocclusions. Knowledge of the force systems at work is a prerequisite for judging the functionality of these appliances. The elasticity parameters (Young's E-moduli, strain limits) of the alloys employed can be drawn upon to calculate numerically forces and torsional moments. Both tensile tests and bending experiments are used to determine the E-moduli and strain limits of standard steel and highly flexible NiTi wires frequently used in orthodontics. However, parameters obtained by tensile tests are less suited for studying the mechanical properties of orthodontic appliances. Since bending deformation prevails, bending experiments should be preferred method for ascertaining the relevant parameters. This study, therefore, presents a new experimental method for testing the bend ability of highly flexible materials and the determination of the underlying material parameters. A comparison of calculated force systems with direct measurements revealed that bending parameters lead to an appropriate description of forces and moments generated during clinical treatment, whereas calculations based on tensile test parameters differ substantially. The bending test proposed here is, thus, a suitable means for dependably predicting the force systems produced by an orthodontic appliance and the test therefore can contribute to an accurate design of new types of therapeutic devices.

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