Efficiency of mandibular arch alignment with 2 preadjusted edgewise appliances

Introduction: The aim of this study was to compare the efficiency of mandibular arch alignment in 3 dimensions with a self-ligating bracket system (SmartClip, 3M Unitek, Monrovia, Calif) and a conventional preadjusted edgewise twin bracket (Victory, 3M Unitek) in nonextraction patients. This was a prospective, randomized, controlled clinical trial at the Royal London Hospital, School of Dentistry, and Kent and Canterbury Hospital, United Kingdom. Sixty-six consecutive patients satisfying the inclusion criteria were enrolled in the study. They were randomly allocated with a computer-generated system to 1 of the 2 bracket systems. Methods: Pretreatment mandibular arch irregularity was measured by using a coordinate measuring machine (Merlin II, International Metrology Systems, Gloucester, United Kingdom). A 0.016-in round martensitic active nickel-titanium aligning archwire (M Unitek) was placed in all subjects. Mandibular arch irregularity was re-measured 8 weeks later. Results: Sixty-five subjects completed the study. Bracket type had little influence on alignment efficiency overall (P = 0.08), or in the buccal (P = 0.173) or labial segments (P = 0.528) after adjustment for pretreatment differences by analysis of covariance (ANCOVA). Alignment efficiency was highly correlated to pretreatment irregularity overall (P <0.001), both in the buccal (P = 0.001) and labial (P <0.001) segments. Increasing age appeared to have a negative effect on alleviation of irregularity, although this effect did not reach statistical significance (P = 0.053). Conclusions: The null hypothesis that efficiency of alignment in the mandibular arch in nonextraction patients is independent of bracket type was accepted. Alignment efficiency is largely influenced by initial irregularity. (Am J Orthod Dentofacial Orthop 2009; 135: 597-602)