Effect of thermocycling on surface roughness and springback properties of different orthodontic arch wires: An in vitro comparative study

Objective: Comparative evaluation of surface roughness and springback properties of stainless steel (SS), nickel-titanium (NiTi), copper nickel-titanium (CuNiTi) and Teflon-coated NiTi orthodontic archwires before and after thermocycling.
Materials and Methods: A total number of 360 specimens were utilized in this study. For each type of wire, specimens were divided into three groups as follow; Group 1 (control): as-received archwires, Groups 2 and 3: specimens were subjected to thermocycling (500 cycles and 1000 cycles, respectively). Surface roughness (Ra) was determined by using a profilometer. Flexural modulus of elasticity (E) and yield strength (YS) of the wires were measured using a three-point bending test in a universal testing machine. The springback ratio (YS/E) was calculated for each wire. Data were statistically analyzed using ANOVA and Bonferroni post hoc tests (α=.05).
Results: For all types of wire, the highest surface roughness was noted with 1000 cycles, followed by 500 cycles and the lowest surface roughness was detected in control group. No significant difference in surface roughness between control and 500 TC group was detected for all types of wire. After thermocycling, the highest surface roughness was noted in Teflon coated NiTi, followed by CuNiTi and NiTi and the lowest values was detected in SS. There was a significant difference in the springback ratio after thermocycling regimens for SS, NiTi and Teflon coated NiTi only (P < 0.001).
Conclusion: The thermocycling process can induce changes in surface roughness and springback properties of orthodontic archwires. Stainless steel archwire displayed the least amount of surface roughness after thermocycling and we recommend its utilization in sliding mechanics to reduce friction during orthodontic tooth movement. In spite of higher surface roughness of NiTi-based archwires, the properties of higher springback and wide range of action make them appropriate choices for the clinicians during various stages of orthodontic treatment.