Rectangular NiTi Research Articles

Effect of Fluoride Prophylactic Agents on the Mechanical Properties of Nickel-Titanium Wires: An in vitro Study

Titanium-based alloys have high corrosion resistance because they form a thin, stable oxide layer. Nevertheless, fluoride prophylactic agents can cause corrosion and associated discoloration of titanium-based orthodontic wires. Objective: The purpose of this investigation was to study the effects of fluoride prophylactic agents on the mechanical properties of nickeltitanium (NiTi) and copper-nickel-titanium (Cu-NiTi) orthodontic archwires. Materials and methods: Preformed rectangular NiTi and Cu-NiTi wires were immersed in either an acidulated fluoride agent, a neutral fluoride agent, or distilled water (control) for 1.5 hours at 37°C. After immersion, the loading and unloading elastic modulus and yield strength of the wires were measured with a 3-point bend test in a water bath at 37°C, in accordance with the criteria in the current American National Standard/ American Dental Association Specification No. 32 for Orthodontic Wires (2000). Scanning electron microscopy was also used to characterize the effects of the fluoride treatment on the wire topography. Results: The results showed that unloading mechanical properties of both the NiTi orthodontic wires were significantly decreased after exposure to both fluoride agents [one-way analysis of variance (ANOVA) and Dunnett’s post-hoc,  = 0.05]; corrosive changes in surface topography were observed for both wires, with Phos-Flur gel creating more detrimental effects. Conclusion: The results suggest that using topical fluoride agents with NiTi wire could decrease the functional unloading mechanical properties of the wire and contribute to prolonged orthodontic treatment.

How does temperature influence the properties of rectangular nickel-titanium wires?

Thermodynamic nickel-titanium (NiTi) wires have become increasingly popular. The relationship between the temperature variation within the mouth and the force level delivered is, however, far from elucidated. The aim of this study was to evaluate the influence of possible intraoral temperature differences on the forces exerted by seven commercially available 0.019 x 0.025 inch NiTi archwires. As mouth temperature ranges from 33 to 37 degrees C most of the time, all wires were tested at five different temperatures between 30 and 40 degrees C in an orthodontic wire-testing device, a so-called Force System Identification (FSI) apparatus, placed in a climate chamber. In the FSI a two-bracket system using self-ligating Damon brackets simulated first order displacements up to 4 mm. At each temperature five samples of each archwire brand were tested. The following variables from the activation/deactivation curves were calculated: force and displacement at the yield point, maximum force level, total energy up to maximum displacement, energy loss after deactivation, force and displacement at the beginning and at the finish of the plateau, and the slope of the plateau. Any statistically significant differences in these variables for the different brands and temperature levels were analysed using one-way analysis of variance. The results showed that: (1) The behaviour of all wires was different. (2) Copper NiTi40 showed the lowest and the most constant force level, followed by NeoSentalloy 200 g. On the other hand, these wires may not work properly in mouth breathers as no forces were exerted below 35 degrees C. (3) If the use of superelastic characteristics and low force levels are the reasons for utilizing rectangular NiTi wires, austenitic NiTi wires should be avoided.

Effect of fluoride prophylactic agents on the mechanical properties of nickel-titanium-based orthodontic wires

Titanium-based alloys have high corrosion resistance because they form a thin, stable oxide layer. Nevertheless, fluoride prophylactic agents can cause corrosion and associated discoloration of titanium-based orthodontic wires. The purpose of this investigation was to study the effects of fluoride prophylactic agents on the mechanical properties of nickel-titanium (Ni-Ti) and copper-nickel-titanium (Cu-Ni-Ti) orthodontic archwires. Preformed rectangular Ni-Ti and Cu-Ni-Ti wires were immersed in either an acidulated fluoride agent, a neutral fluoride agent, or distilled water (control) for 1.5 hours at 37 degrees C. After immersion, the loading and unloading elastic modulus and yield strength of the wires were measured with a 3-point bend test in a water bath at 37 degrees C, in accordance with the criteria in the current American National Standard/American Dental Association Specification No. 32 for Orthodontic Wires (2000). Scanning electron microscopy was also used to characterize the effects of the fluoride treatment on the wire topography. Unloading mechanical properties of Ni-Ti orthodontic wires were significantly decreased after exposure to both fluoride agents (1-way analysis of variance [ANOVA] and Dunnett's post hoc, alpha =.05); however, Cu-Ni-Ti wire mechanical properties were not significantly affected by either fluoride agent (1-way ANOVA, alpha =.05). Corrosive changes in surface topography were observed for both wires, with Cu-Ni-Ti appearing to be more severely affected. The results suggest that using topical fluoride agents with Ni-Ti wire could decrease the functional unloading mechanical properties of the wire and contribute to prolonged orthodontic treatment.

Torsional elastic property measurements of selected orthodontic archwires

A method for quantifying the torsional elastic properties of orthodontic archwires was investigated using three different alloys: stainless steel [SS], beta titanium [βTi], and nickel titanium [NiTi]. The shear moduli (G) were determined dynamically using a torsion pendulum. Aftera clamping correction was applied, the values of ( G equalled 11.0–11.3, 4.3–4.4, and 2.3–3.0 Msi for SS, βTi, and NiTi wires respectively. Using a 10% energy loss criterion in a static test, the torsional yield strengths (τ ys) were all nearly 100 ksi except for the 0.018″ SS (51 ksi) and rectangular NiTi (13–17 ksi). The latter exhibited some pseudoelastic behaviour which could only be accommodated by the Johnson Elastic Limit (JEL). Having determined G, T ys, and the wire dimensions, the three basic torsional elastic properties (stiffness, strength, range) were calculated for each of the wires. The NiTi wires displayed the greatest range and the least stiffness, whereas SS wires showed the greatest stiffness and the least range. As predicted in earlierwork, the properties of βTi were intermediate.