Load-deflection characteristics and plastic deformation of NiTi closed coil springs / 대한치과교정학회지

OBJECTIVE: NiTi closed coil springs were reported to have relatively constant unloading forces. However, the characteristics of NiTi closed coil springs from various manufacturers have not been elucidated. The purpose of this study was to compare load-deflection characteristics of various NiTi closed coil springs and to find out the optimal range of extension. METHODS: Seven kinds of NiTi closed coil springs from five manufacturers were tested. Load deflection curves were obtained at extension ranges from 2 mm to 30 mm. Also, springs were kept extended during a 4 week period, and then load deflection curves were obtained again. RESULTS: Sentalloy (Tomy) and Jinsung blue (Jinsung) showed superelasticity in every extension ranges tested and showed plastic deformation of less than 1 mm. Ni-Ti (Ormco) showed superelasticity only after the springs were extended at or more than 10 mm, thereby meaning that clinicians should extend these springs at or more than 10 mm to utilize the superelasticity. Orthonol (RMO) and Nitanium (Ortho Organizers) did not show superelasticity. After 4 weeks of extension, all springs showed plastic deformation less than 1 mm when the extension was at or under 25 mm. CONCLUSIONS: The superelastic behavior of NiTi closed springs were different among various NiTi spring products, and some NiTi closed springs failed to show superelasticity.

Effects of heat treatment on the load-deflection properties of nickel-titanium wire / 대한치과교정학회지

OBJECTIVE: Nickel-titanium alloy wire possesses excellent spring-back properties, shape memory and super-elasticity. In order to adapt this wire to clinical use, it is necessary to bend as well as to control its super-elastic force. The purpose of this study is to evaluate the effects of heat treatment on the load-deflection properties and transitional temperature range (TTR) of nickel-titanium wires. METHODS: Nickel-titanium wires of different diameters (0.016" x 0.022", 0.018" x 0.025" and 0.0215" x 0.028") were used. The samples were divided into 4 groups as follows: group 1 , posterior segment of archwire (24 mm) without heat treatment; group 2, posterior segment of archwire (24 mm) with heat treatment only; group 3, anterior segment with bending and heat treatment; group 4, anterior segment with bending and 1 sec over heat treatment. Three point bending test was used to evaluate the change in load-deflection curve and obtained DSC (different scanning calorimetry) to check changes in Af temperature. RESULTS: In the three point bending test, nickel-titanium wires with heat treatment only had higher load-deflection curve and loading and unloading plateau than nickel-titanium wires without heat treatment. Nickel-titanium wires with heat treatment had lower Af temperature than nickel-titanium wires without heat treatment. Nickel-titanium wires with heat treatment and bending had higher load-deflection curve than nickel-titanium wires with heat treatment and nickel-titanium wires without heat treatment. Nickel-titanium with heat treatment of over 1 sec and bending had the highest load-deflection curve. Nickel-titanium wires with heat treatment and bending had lower Af temperature, Nickel-titanium wires with heat treatment of over 1 sec and bending had the lowest Af temperature. CONCLUSION: From the results of this study, it can be stated that heat treatment for bending of Nickel-titanium wires does not deprive the superelastic property but can cause increased force magnitude due to a higher load-deflection curve.

A study on the changes of the elastic properties in looped wires by variable factors / 대한치과교정학회지

The purpose of this study was to evaluate and compare the effect of the variable factors of wire on the elastic properties of looped rectangular wire. Five variable factors were presented - material(Hi-T, blue Elgiloy), wire size(.016" x .022", .018" x .025"), loop length(15mm, 20mm), loop configuration(open loop, closed loop), gabling (non-gable, gable). So, the total 256 specimens were divided into 32 groups, and each of those was pulled on Instron testing machine. The load-deflection curve of each wire was obtained, from which force, range in elastic limit, and stiffness were computed and analyzed statistically. The results were obtained as follows: 1. All of the variable factors - wire material, size, loop length, loop configuration, and gabling - took a significant effect on load-deflection rate of looped wire. 2. The force at elastic limit was the smallest in the group of Hi-T, .0l6"x.022", 20mm loop length, open loop, non-gable, and the largest in the group of blue Elgiloy, .018"x.025", 15mm loop length, closed loop, non-gable. 3. The range at elastic limit was the smallest in the group of Hi-T, .0l8"x.025", 15mm loop length, open loop, non-gable, and the largest in the group of HI-T, .016"x.022", 20mm loop length, closed loop, gable. 4. Loop configuration and loop length were the most effective factors on the elastic properties of looped wires, and gabling was the least effective.