• Sarawadee Kunlayanapak D.D.S.
• Vachara Phetcharakupt D.D.S., Dip. in Ortho. (Bergen), Dip.Th.B.O.
• Chintana Sirichompun D.D.S., M.D.Sc. (Orthodontics), Dip.Th.B.O.

Objectives To study the deactivation force of superelastic nickel-titanium alloy wires treated by the
direct electric resistance heat treatment method and to compare the deactivation forces of treated and
non-treated groups in the same brand.

Materials and methods The distal ends of 0.016x0.022 inches2
preformed rectangular archwires,
Sentalloy Heavy type (Tomy Co. Ltd.) and NiTi (Ormco Co. Ltd.) were cut into 21.5 millimeters and
tested by three-point bending method to study the deactivation force at 4 deactivation distances (2.0,
1.5, 1.0 and 0.5 millimeters). The optimum electric currents for wire bending in 3, 4 or 5 seconds were
used for treating the wires. Calculated by using the Law of Energy Conservation, the theoretical
temperatures were referred.

Results The means of the deactivation forces were analytically compared by a One-way ANOVA
at p = .05. In each brand and every deactivation distance, the deactivation forces between the treated
and non-treated groups were significantly different.

Conclusion The deactivation forces in the treated group were higher than those in the untreated group
of each brand. In addition, the increasing in the deactivation forces of the treated group varied in
accordance with the theoretical temperatures between 421.4 and 520.5oC.

(CU Dent J. 2005;28:19-28)