The Mechanical Effects of Flaming Nickel-Titanium Orthodontic Archwires

Objective: To assess the mechanical effects of nickel-titanium orthodontic archwire flaming and their distribution along the wire. Methodology: Two sizes of pre-formed austenitic nickel-titanium archwires were tested (n=10). The terminal 5mm of each wire was heated for five seconds using a butane lighter. Micro-hardness testing was used to determine the heat-affected zone for all wires. Cantilever bending was performed to assess the mechanical properties of heated wires. Results: The heat-affected zone was found to extend less than 2 mm past the flame boundary for all wires. For each wire gauge, the flamed zone was characterized by a lower and flatter super-elastic plateau and an increased tendency for plastic deformation when compared to controls. Conclusions: The limited ability of austenitic nickel-titanium orthodontic archwires to conduct heat past the boundary of the flamed region suggests no need to alter current clinical practice.