Journal Article

The load/deflection characteristics of thermally activated orthodontic archwires

Farnaz Parvizi and W. P. Rock

in The European Journal of Orthodontics

Published on behalf of European Orthodontics Society

Volume 25, issue 4, pages 417-421
Published in print August 2003 | ISSN: 0141-5387
Published online August 2003 | e-ISSN: 1460-2210 | DOI:
The load/deflection characteristics of thermally activated orthodontic archwires

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The objective of the study was to investigate the load/deflection characteristics of three commercially available thermally active nickel–titanium orthodontic archwires using a standard nickel–titanium archwire as a control. The thermally active wires were Regency Thermal, Orthoform, and Eurotherm and the control was Memory.

Round 0.4 mm and rectangular 0.4 × 0.56 mm wires were subjected to 2 and 4 mm of deflection in a water bath at temperatures of 20, 30, and 40°C and forces were measured in three‐point bend and phantom head situations.

Analysis of variance revealed that, irrespective of the test set up and wire type, wire size had a significant effect (P < 0.001) on the forces produced. An increase in size from 0.4 mm round to 0.4 × 0.56 mm rectangular wire approximately doubled the force values for a given deflection. The effect of wire deflection on the force values varied according to the test system, forces being much higher in the phantom head tests than in the beam tests. In the beam tests, an increase in wire deflection from 2 to 4 mm had no significant effect on the forces exerted, but in the phantom head tests the forces produced by each wire at 4 mm deflection were four to five times greater than those at 2 mm deflection.

Each of the thermally active wires produced less force that the non‐thermally active wire. However, there was a large variation between the three types of thermally active wire. In the beam tests each 10°C rise in temperature from 20 to 40°C had a highly significant effect on the force produced by each thermoelastic wire (P < 0.001). In the phantom head tests there were significant force increases between 20 and 30°C (P < 0.001), but between 30 and 40°C the forces did not change significantly.

Journal Article.  0 words. 

Subjects: Restorative Dentistry and Orthodontics

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