Short-term temperature changes influence the force exerted by superelastic nickel-titanium archwires activated in orthodontic bending

Abstract

Background : Alterations in mouth temperature may lead to changes in the force exerted by an activated superelastic wire. It has been assumed that variations in archwire stiffness associated with short-term cooling or heating are transient. This investigation studied the effect of short-term cooling or heating on the bending force exerted by nickel-titanium archwire. Material and methods : Six rectangular superelastic wires and one conventional nickel-titanium wire were tested in bending at 37 o C. The test specimens were deflected 0.5 mm, and the bending force was measured continually. The activated specimens were subjected to cold (10 o C) or hot (80 o C) water under constant deflection, simulating an inserted archwire that is subjected to cold or hot drinks or food during a meal. Results : The conventional nickel-titanium wire was marginally affected by brief cooling or heating. In contrast, some of the superelastic wires were strongly affected by short-time application of cold or hot water. Whereas the effect of brief heating disappeared quickly, some wires continued to exert sub-baseline bending forces (up to 32% less) after short-time application of cold water and showed little or no tendencies toward increase even after 30 minutes of postexposure restitution (up to 43% less). Conclusions : Short-term exposures to hot liquid increased the bending force exerted for a given deflection transiently. The effect of short-term exposures to cold liquid was not always transient; the bending force remained sub-baseline for a number of the thermosensitive wires tested for a prolonged time.(Am J Orthod Dentofacial Orthop 1998;114:503-9)