Introduction: The evaluation of flapless corticision in conjunction with the conventional treatment in the non-extraction decrowding of lower anterior teeth has not been performed yet in any randomised clinical trial, particularly in terms of treatment time and periodontal indices. Aim: The aim of the study was to compare the duration of leveling and alignment of mild and moderate crowding cases in the lower dental arch between the corticision-assisted fixed orthodontic treatment and the traditional method; and to compare the periodontal indexes between the two groups. Materials and Methods: A parallel-group Randomised Controlled Clinical Trial (RCT) was conducted on 60 patients (mean age 2 1.40±1.63 years). Patients were randomly assigned to either the corticision group or the control group (30 each). Immediately after fixed appliance bonding, three radiographic-guided incisions were performed on the labial surfaces of the alveolar bone between lower anterior teeth by reinforced scalpels and mallets in order to accelerate alignment for patients in the corticision group. Patients in the control group were treated with conventional orthodontics. The outcome measures were the overall time needed for leveling and alignment, periodontal parameters such as Plaque Index (PI), Probing Depth (PD), Gingival Index (GI), and the width of the attached gingiva. Results: The overall treatment time was significantly shorter in the corticision group than the control group. The average leveling and alignment period for the corticision group was 116.46±15.97 days, while it was 159.69±13.76 days in the control group. Comparing the groups, a significant reduction of about 27% was found in the leveling and alignment duration of the corticision group. There were no significant differences in the periodontal parameters (PI, PD, GI, the width of attached gingiva) at the end of leveling and alignment phase in both the groups. Conclusion: Corticision seems to be an effective method to accelerate leveling and alignment in cases of mild and moderate crowding. It did not cause negative effect on the periodontal tissues.