Objective: To analyze and compare the efficiency of the correction of mandibular crowding between two types of bracket systems. Material and method:According to the results of the power analysis for sample size calculation, 19 Angle Class I patients were included in the study and randomly divided into two groups: GI (n=10, mean age 19.68years, min 13.86, max 28.78, self-ligating brackets), and GII (n= 9, mean age 20.98years, min11.13, max 29.85, conventional preadjusted brackets). To carry out this study, the sequence of wires used was similar for both groups. Dental casts were made available at the start of the treatment (T1), after 180 days of leveling and alignment (T2), and at the completion of leveling (mean, 600 days, T3). The degree of crowding was measured by means of Little's and Fleming's irregularity indexes, by using a Mitutoyo digital caliper. Student's t test and ANOVA were used to compare the efficiency of mandibular alignment between the two groups. Results:The results showed that in the initial alignment phase (after 180 days), no statistically significant difference was found between the groups. On the other hand, from phase T1 to T3, it was observed a statistically significant difference between the groups regarding the correction of mandibular crowding.