ORIGINAL ARTICLE Comparison of mandibular arch changes during alignment and leveling with 2 preadjusted edgewise appliances Padhraig S. Fleming, a Andrew T. DiBiase, b Grammati Sarri, c and Robert T. Lee d London and Canterbury, United Kingdom Introduction: Our objective was to compare the effects of 2 preadjusted appliances on angular and linear changes of the mandibular incisors, and transverse mandibular arch dimensional changes over a minimum of 30 weeks. This was a prospective, randomized, controlled, clinical trial a the Royal London Hospital, School of Dentistry, in London and the Kent and Canterbury Hospital in Canterbury, United Kingdom. Methods: Sixty- six consecutive patients satisfying the inclusion criteria were enrolled and randomly allocated to treatment with a self-ligating bracket system (SmartClip, 3M Unitek, Monrovia, Calif) and conventional preadjusted edgewise brackets (Victory, 3M Unitek). Initial study models and cephalograms were obtained within a month of starting the trial. All subjects received treatment with the following archwire sequence: 0.016-in round, 0.017 3 0.025-in rectangular, 0.019 3 0.025-in rectangular martensitic active nickel-titanium archwires, and 0.019 3 0.025-in stainless steel archwires. Final records, including study models and a lateral cephalo- gram, were collected a minimum of 30 weeks after initial appliance placement. Lateral cephalograms were assessed for treatment-related changes in mandibular incisor inclination and position. Transverse dimensional changes in intercanine, interpremolar, and intermolar dimensions, and the amount of crowding alleviated dur- ing the study period were assessed by comparison of pretreatment and posttreatment models. All measure- ments were made with a digital caliper (150 mm ISO 9001 electronic caliper, Tesa Technology, Renens, Switzerland). Results: Sixty patients completed the study. After adjustment for pretreatment values, duration of treatment, and amount of crowding alleviated during the study period, bracket type had little effect on in- cisor inclination (P 5 0.437) and positional changes (P 5 0.35), and intercanine (P 5 0.967), inter-first premolar (P 5 0.495), and inter-second premolar (P 5 0.905) dimensions. However, the self-ligating appliance produced slightly more expansion in the molar region, a difference that was statistically significant (P 5 0.009). Pretreat- ment values for incisor inclination (P 5 0.044) and transverse dimensions (P 5 0.000) affected inclination and transverse changes, respectively, with proclination less likely when the labial segment was proclined at the outset and expansion unlikely during leveling and alignment in wider arches. Greater alleviation of crowding during the study period resulted in more incisor proclination (P 5 0.000) and advancement (P 5 0.000). Conclusions: There was little difference overall in the pattern of arch alignment and leveling related to the 2 preadjusted appliances. However, there was a statistically greater increase in intermolar width in the group treated with the self-ligating appliance, although the difference was only 0.91 mm. (Am J Orthod Dentofacial Orthop 2009;136:340-7) T reatment of a crowded dental arch on a nonex- traction basis, without tooth size reduction, requires an increase in arch perimeter to allow resolution of crowding and achievement of optimum arch alignment and leveling. 1 Without active distal movement, changes typically involve both transverse expansion and proclination. The nature and magnitude of these arch dimensional changes have implications for long-term stability. Expansion of the intercanine dimension and excessive proclination of the mandibular incisors are considered to be particularly unstable. 2,3 Relapse in such cases may develop due to constriction of the expanded inter- canine dimension and uprighting of the mandibular incisors during the posttreatment phase, and is likely to manifest as mandibular incisor irregularity. 4 Self-ligating brackets have enjoyed renewed popu- larity over the past decade. The chief advantages of a Specialist registrar, Orthodontics, Royal London Hospital, London, United Kingdom. b Consultant orthodontist, Kent and Canterbury NHS Trust, Canterbury, United Kingdom. c Postgraduate student, Royal London Hospital, London, United Kingdom. d Head, Orthodontics, Royal London Hospital, London, United Kingdom. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Reprint requests to: Padhraig S. Fleming, Maxillofacial Unit, Kent and Canter- bury Hospital, Ethelbert Road, Canterbury, CT1 3NG, United Kingdom; e-mail, padhraigfleming@hotmail.com. Submitted, May 2007; revised and accepted, August 2007. 0889-5406/$36.00 Copyright Ó 2009 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2007.08.030 340