Objectives: To assess and compare treatment effects and treatment time in adolescents with crowded and displaced teeth during and after non‐extraction treatments using a passive self‐ligating bracket system (PSLB) and a conventional bracket system (CB).

Materials and Methods: Consecutive adolescents (12–17 years old) with crowded and displaced teeth were randomised through computer generated block randomisation in a two‐arm parallel‐group design, to non‐extraction fixed appliance treatment with either PSLB (Damon Q, n  = 62) or CB (Victory, n  = 70) at four orthodontic clinics. Study models and cephalograms were collected at baseline, post‐alignment and post‐treatment. Primary outcome was assessed with weighted Peer Assessment Rating index (wPAR) and secondary outcomes with Little's Irregularity Index (LII), and as transversal width (mm), incisor inclination (°), position (mm) and treatment time (months).

Results: Intergroup differences in wPAR with mean score reductions of −24.07 (CB) and −22.11 (PSLB), LII upper/lower arch reductions of −9.02/−5.96 (CB) and −8.44/−5.29 (PSLB), and mean treatment times of 21.74 (CB) and 24.35 (PSLB) months were non‐significant (NS). Lateral expansion was greater in the PSLB group during alignment; mean intergroup maxillary differences (MD) were 1.35 at inter‐canines, 1.21 mm at first inter‐premolars, and mandibular MD were 0.75 at first, 0.76 mm at second inter‐premolars ( p  ≤ 0.019). Greater incisor proclination was observed in the CB group (L1NB, MD = 2.28°; ILiML, MD = 2.23°) ( p  ≤ 0.016). Intergroup differences post‐treatment were NS.

Conclusion: Great occlusal treatment outcomes were observed in both groups with no significant difference in treatment time. Although the expansion patterns differed during alignment, no significant intergroup difference remained after treatment.

Trial Registration: The protocol is registered on ClinicalTrials.gov (NCT05664282)