Three-Dimensional Change of Molar Position During Alignment and Leveling With PASS and MBT: A Randomized Controlled Trial.

Backgrounds: With the development of straight wire appliance (SWA), especially the rountine use of nickel-titanium (NiTi) archwires in the initial stage has largely eliminated the need for bending up. However, engaging fine NiTi wire into the molar buccal tube with built-in forward tipping prescription can induce unintended mesial tipping and mesialization of maxillary molars, leading to early anchorage loss. This single-center, two-arm parallel randomized clinical trial aimed to compare the physiologic anchorage spee-wire system (PASS) with the Mclaughlin-Bennet-Trevici straight-wire system (MBT) in terms of their ability to preserve maxillary anchorage control during the alignment and leveling. Methods: Sixty-four patients with Angle Class I or II malocclusion undergoing maxillary first premolar extraction were recruited. Minimal randomization was used to select the sample. Two bracket systems were used-PASS and MBT. Digital dental models were acquired at pre-treatment(T0), the first 3 months during treatment(T1), and the first 6 months during treatment(T2). Study models of different time point were superimposed to evaluate movements of maxillary first molars, canines, and central incisors. Results: During the first 6 months of the treatment, maxillary first molars in the PASS group exhibited distal tipping (2.67° ± 4.59°) and distal movement (0.03 ± 1.02 mm). In contrast, the MBT group showed mesial tipping (1.95° ± 3.04°) and mesial movement (0.67 ± 0.79 mm). Additionally, the maxillary canines also exhibited treatment difference. The increase of inter-canine width was significantly smaller increased in the PASS group (1.31 ± 2.00 mm) compared to the MBT group (2.37 ± 1.72 mm). No other difference was found. Conclusion: Compared with the MBT system, PASS was better at preserving maxillary anchorage during the alignment and leveling stage. These findings suggest that PASS offers superior physiological anchorage control in the early stages of treatment without the need for auxiliary appliances.