SCIENTIFIC SECTION Comparison of deactivation forces between thermally activated nickel– titanium archwires Manoela Moraes Figueire ˆ do, Rodrigo Hermont Canc ¸ado, Karina Maria Salvatore Freitas and Fabrı´cio Pinelli Valarelli Department of Orthodontics, Inga ´ Faculty, Maringa ´, PR, Brazil Objective: The aim of the present study was to investigate and compare load–deflection characteristics of commercially available thermally activated nickel–titanium archwires using a three-point bending test. Materials and methods: Sixty thermally activated 0.01960.025-inch nickel–titanium archwires from six different manufacturers were investigated. The superelastic properties of these archwires were evaluated by conducting a three-point bending test under identical testing conditions. Forces generated at deactivation for a deflection of 0.5, 1, 2 and 3 mm at a temperature of 37uC were selected for statistical comparison of the data. The results of forces of deactivation at all deflections applied were compared by two-way analysis of variance and the Tukey test. Results: Statistical differences ( P,0.05) were found at all force levels during deactivations. The results showed that the range of forces displayed great variation in quantitative behaviour. None of the archwires showed permanent deformation after the three-point bending test. Conclusions: This study revealed significant differences in deactivation forces among the six types of thermally activated nickel–titanium archwires tested. NiTinol Termoativado (Aditek) and NeoSentalloy F200 (GAC) produced the least amount of force in all four deactivation categories. Key words: Orthodontic wires, materials testing, nickel, titanium, elasticity Received 23 September 2011; accepted 20 February 2012 Introduction Orthodontic archwires are designed to move teeth with light, continuous force. 1 The application of such forces may reduce the potential for patient discomfort, tissue hyalinization and undermining resorption. When force is applied, the archwire should behave elastically over a period of weeks to months. 1–3 Thermally activated nickel–titanium archwires have been widely accepted as useful for initial alignment of malocclusions mainly because of their unique properties of superelasticity and shape memory. 3,4 An impressive characteristic of thermally activated nickel–titanium is its ability to produce light, continuous forces over long ranges of activation. 3,5,6 When this wire begins to recover its original shape, it provides a light, continuous force to the dentition and supporting periodontium, theoretically mini- mizing the potential for root resorption or necrosis. 3,7,8 Numerous studies have investigated the properties of superelastic nickel–titanium alloy 2,9–16 and these have shown that commercially available nickel–titanium alloys can behave in a variable manner, which often deviates from superelasticity. 17 The differences are often found in the shape of the force–displacement curve and the position of the superelastic plateau. The stress that occurs over the martensitic phase transformation is approximately constant and therefore a plateau is observed in the stress/strain curve. 18 However, variability has been found to exist in the delivery of these deactivation forces between some ther- mally activated Ni–Ti alloys. 19 The aim of the present study was to investigate and compare load–deflection characteristics between a group of commercially available thermally activated nickel– titanium archwires and provide data of clinical rele- vance. This study details the comparison of forces achieved during the deactivation of a deflection test that attempts to approximate clinical conditions. Materials and methods The samples consisted of 60 nickel–titanium alloy 0.01960.025-inch archwires commercially available Journal of Orthodontics, Vol. 39, 2012, 111–116 Address for correspondence: Professor R. H. Canc ¸ado, Department of Orthodontics, Bauru Dental School, University of Sa ˜o Paulo, Alameda Octavio Pinheiro Brisolla 9-75, Bauru, SP 17012-901, Brazil. Email: rohercan@uol.com.br # 2012 British Orthodontic Society DOI 10.1179/1465312512Z.00000000013