The Effect of Heat Treatment on the Bending Properties of a Cobalt-Chromium Orthodontic Wire

Introduction: Elgiloy, a brand name of the original cobalt-chromium orthodontic wire, has been around for more than 50 years; yet despite this, little literature is available. Most of the literature on Elgiloy wires tends to evaluate the wires in tension. For these reasons, this study aimed to determine the bending properties of the four available tempers of Elgiloy wires and how heat treatment affects the wires’ bending properties. Materials and Methods: All four tempers of Elgiloy (red, yellow, green, and blue) were ordered in straight lengths containing 20 wires per pack that are each 0.018 inches in diameter and 14 inches in length. Two consecutive 20 mm segments were cut from each wire in all four tempers creating 40 specimens in each temper. Half of the wire segments were heat treated at 500oC for five hours and the other half remained as-received for the testing process (n=20/temper/condition). All 160 segments of Elgiloy wire were tested by a three-point bend test at 23oC (room temperature). Stiffness, flexural modulus, percent recovery, and force values were statistically compared using ANOVA (p\u3c0.05). Results: The heat treated wires showed significantly increased force values at the various deflections when compared to their as-received counterpart. Some of the different tempers for heat treated and as-received groups did have similar force values at a given deflection, but differences were observed between the tempers. The stiffness, flexural modulus, and percent recovery were also calculated for all eight groups. Heat treatment significantly increased stiffness, flexural modulus, and percent recovery for all four tempers of Elgiloy. Conclusion: Heat treatment of Elgiloy wires led to a significant increase in stiffness, modulus, percent recovery, and force values required to deflect the wire at various deflection measurements. Despite Elgiloy wire being around for a long period of time, not a lot of literature is available. Therefore, further research and investigation is needed to determine how heat treatment of Elgiloy wires can influence their clinical use