The purpose of this randomized controlled clinical trial was to compare the transverse development of the arches and the incisor inclination comparing two different ligating systems (SL vs CL) with the same arch form protocol (Damon arch form) and the same disarticulation protocols after the alignment and leveling period of non-extraction patients.

Materials and Methods: Fifty-four subjects were randomly with an electronic randomization program allocated to treatment with either a self-ligating bracket system (Damon Q-slot 0.022", Ormco Corp,) or a conventional bracket system (Orthos-slot 0.022", Ormco Corp). All patients were treated following the same protocol and arch wire sequence: 0.014-inch, 0.018-inch and 0.014x0.025-inch Damon copper nickel-titanium arch wires (Cu-NiTi; Ormco). Lateral cephalograms and study models, taken at prior to treatment (T0) and after alignment and levelling (T1), were used to compare the amount of arch expansion and incisor angulation changes that took place. In the analysis of results in a single observer analyzes the data blindly without knowing which group the patients belonged. Results: Models and cephalograms of the patients and both stages(T0-T1) were measured at the data were analyzed in STATA S.E. Treatment produce statistically significant increases in transverse arch dimensions especially in premolars maxillary (2.8-4.3mm) and mandibullary (2.0-4.2mm) of both group. The expansion in the maxillary arch was similar for both groups, but in the mandibular arch was greater in the self ligation group in about 2 mm more. Conclusions: The treatment with self ligation brackets produced more expansion in the mandibular arch than the conventional ligation brackets when used the same arch Damon protocols.

Inclusion Criteria:

1. ANB angle between 0º- 5º
2. Systemically and periodontally healthy subjects not taking any medications.
3. Maxillary and/or mandibular irregularity index (canine-to-canine) between mild to moderate
4. A non-extraction treatment approach.
5. Permanent dentition with second molars erupted or in a functional eruptive phase.

Exclusion Criteria:

1. Systemically and periodontally compromise subjects and taking any medications. (2 ) subjects who did not want participate in the investigation