Mechanical and Thermal Properties of Copper-Nickel-Titanium Orthodontic Archwires

Objectives: Copper-Nickel-Titanium (CuNiTi) was introduced as an orthodontic archwire in the early 1990s by the Ormco Corporation and was offered in three temperature variants (27/35/40^oC) corresponding to its austenite-finish temperature (Af). With the expiration of the patent, several other manufacturers are now offering CuNiTi archwires. The ojective was to examine the bending and thermal properties of CuNiTi wires currently on the market.
Methods: Round (0.018”) and rectangular (0.016x0.022”) archwires in two temperature variants (27^oC/35^oC) from six companies (Ormco, Rocky Mountain Orthodontics (RMO), GAC, Ortho Organizers, Ortho Technology, American Orthodontics (AO)) were tested. Segments were investigated by differential scanning calorimetry over the temperature range from -100^oC to 100^oC at 10^oC per minute (n=10/brand/size/variant) and by three-point bending (n=20/brand/size/variant) to determine the activation and deactivation forces. Data were compared using one-way analysis of variance at a 0.05 significance level with a Tukey's HSD test post hoc analysis.
Results: Different letters for a measure indicate significantly different values (p<0.05). A wide variation in force and Af were observed for both the round and rectangular wires (not shown). Some brands showed little difference between temperature variants.
Conclusions: Despite similar labeling/claims, CuNiTi wires from different companies possess different properties and an orthodontist should not assume equivalence between brands.