Effects of nickel-titanium and stainless steel leveling wires on the position of mandibular incisors

Objective: Investigate the effects of heat-activated NiTi and stainless steel wires to evaluate potential changes in the position of mandibular incisors in extraction cases as correlated with treatment length. Method: The sample consisted of 36 individuals of both genders, Brazilian Caucasians with mean initial age of 15 years and 5 months with Class I and Class II malocclusions, divided into two groups. In Group 1 (n=17) leveling was performed with Sequence 1, comprised of three different wire cross-sections: 0.016-in and 0.019 x 0.025-in heat-activated NiTi wires and 0.019 x 0.025-in stainless steel wires. In Group 2 (n=19) Sequence 2 was tested using only stainless steel wires (0.014-in, 0.016-in, 0.018-in, 0.020-in and 0.019 x 0,025-in) with passive torque in the mandibular incisors. Data were collected using computerized cephalometry and compared using Student’s t-test with 5% significance level. Results: In Group 1, mandibular incisors were inclined lingually although only the crowns showed significant movement (1.6 mm). In Group 2, mandibular incisors remained stable. No vertical changes were noted in either group. Conclusions: Sequence 2 yielded better mandibular incisor control with no changes in their initial positions, while Sequence 1 allowed torques in the bracket prescription to be expressed, leading to the lingual inclination of these teeth. Treatment length was shorter when Sequence 1 was used. The evaluated biomechanic variations presented advantages and disadvantages that should be known and considered by the orthodontist during treatment planning. Abstract