Objective: This clinical study investigated mandibular arch dimensional changes of three different aligning arch wires during initial orthodontic leveling and alignment. Materials and methods: Thirty patients, 15 females and 15 males with a mean age of 17.81±1.96 years were randomly allocated into three equal groups: A, single strand nickel titanium (NiTi) arch wires; B, Niobium-titanium-tantalum-Zirconium (nickel-free Gummetal) arch wires; and C, multi-strand NiTi arch wires. All had moderate anterior crowding treated via non-extraction approach. 3D digital models were taken before and after 3 months. Mandibular arch dimensional changes determined by calculating the amount of changes. Results: The inter-canine width was significantly increased after 12 weeks observation period with both single strand and multi-strand NiTi arch wires by an average 0.98 mm and 1.12 mm. While, the inter-1^stpremolar width was significantly increased in patients treated with single strand NiTi arch wire by an average 1.86 mm. However, the inter-molar width was insignificantly changed with the three investigated arch wires.
Conclusion: Both single strand and multi-strand NiTi arch wires resulted in greater mandibular arch expansion especially in the inter-canine region during leveling and alignment stage. While, the Gummetal arch wire revealed insignificant changes in transverse mandibular arch dimensions