SHORT-TERM TEMPERATURE-CHANGES INFLUENCE THE FORCE EXERTED BY SUPERELASTIC NICKEL-TITANIUM ARCHWIRES ACTIVATED IN ORTHODONTIC BENDING

Background: Alterations in mouth temperature may lead to changes in th e force exerted by an activated superelastic wire. It has been assumed that variations in archwire stiffness associated with short-term cool ing 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 degrees C. The test specimens were deflected 0.5 mm, and the be nding force was measured continually The activated specimens were subj ected to cold (10 degrees C) or hot (80 degrees C) water under constan t deflection, simulating an inserted archwire that is subjected to col d or hot drinks or food during a meat. Results: The conventional nicke l-titanium wire was marginally affected by brief cooling or heating. I n contrast, some of the superelastic wires were strongly affected by s hort-time application of cold or hot water. Whereas the effect of brie f heating disappeared quickly, some wires continued to exert sub-basel ine bending forces (up to 32% less) after short-time application of co ld 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 exerte d for a given deflection transiently. The effect of short-term exposur es to cold liquid was not always transient; the bending force remained sub-baseline for a number of the thermosensitive wires tested for a p rolonged time.