Korean J Orthod.  2006 Oct;36(5):349-359.

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

Affiliations
  • 1Department of Orthodontics, School of Dentistry, Chosun University, Korea. shlim@chosun.ac.kr

Abstract


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.

Keyword

Load-deflection curve; Three point bending; Nickel-titanium; Heat treatment
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