OBJECTIVE: To study the effects of the leveling phase performed with heat activated NiTi and stainless steel archwires evaluating the possible changes in lower incisors position in extraction cases, as well as its correlation with treatment time. METHODS: The sample comprised 36 white Brazilians subjects, male and female, mean age of 15 years and 5 months, with Angle Class I and II malocclusion, arranged in two groups. In Group 1 (n=17), the leveling phase was performed with sequence 1, using three archwires (NiTi heat activated 0.016" and 0.019"x0.025" and stainless steel 0.019"x0.025"). In Group 2 (n=19), sequence 2 was tested, in which only stainless steel archwires were used (0.014", 0.016", 0.018", 0.020" and 0.019"x0.025" with passive torque in lower incisors). The data were collected using the computerized cephalometry and were compared by Student's t test at significance level of 5%. RESULTS: In Group 1, lower incisors tipped lingually and only the crown presented a lingual movement that was statistically significant (1.6mm). In Group 2, the lower incisors remained unchanged. There was no vertical change in either groups. CONCLUSIONS: Sequence 2 showed better control of the lower incisors and no changes in their position were observed whereas sequence 1 allowed torque expression of brackets prescription with lingual tip of these teeth. Treatment time was shorter using sequence 1. Both biomechanical variations studied showed advantages and disadvantages that should be known and evaluated by the orthodontist during case planning.
Leveling; Archwires; Biomechanics
