The purposes of this study were to systematically review the evidence on the clinical use of self-ligating brackets (SLBs) and the validity of digital models, and to compare maxillary arch dimensional change during alignment with conventional brackets (CBs) and active or passive self-ligation in a clinical study. In the systematic reviews, multiple databases were searched, study selection, quality assessment and data extraction were performed, and meta-analyses conducted, where appropriate. In a laboratory study a technique to measure molar inclination change incorporating digital models was developed and validated. A multicentre, 3- arm parallel-group trial was conducted with 96 patients aged 16 and above randomly allocated into 3 equal groups (OvationTM, InOvationCTM or Damon QTM) and undergoing alignment with a DamonTM wire sequence for at least 34 weeks. Meta-analyses demonstrated no difference in arch dimensional changes between SLBs and CBs; however, a greater treatment time was found with self-ligation (2.2 months, 95% CI: 0.4, 3.98). The validity of direct measurement on digital models was confirmed in the other review, although meta-analysis was not possible. Complete data were obtained from 87 subjects in the trial. Bracket type had no significant effect on transverse dimensional changes with no difference in inter-molar width between passive self-ligation and CBs (0.32mm, 95% CI: -0.41, 1.05, p= 0.38) or active selfligation (0.4mm, 95% CI: -0.31, 1.11, p= 0.27). Incisor inclination changes with Damon QTM could not be differentiated from the conventional system (0.44 degrees, 95% CI: - 1.93, 2.8, p=0.71) or InOvationCTM (-0.22 degrees, 95% CI: -2.58, 2.14, p=0.85). Based on the systematic reviews, measurement of digital models is a valid alternative to plaster models, while little evidence to support the use of self-ligation was found. In the clinical trial no differences in arch dimensional changes during alignment between CBs and either active or passive self-ligation was found.