PASS versus MBT™ for evaluation of anchorage control in three-dimensional measurements: a randomized controlled trial

Background: Growth and development might lead to anchorage loss during orthodontic treatment, such as the mesial drift of molars, the compensation characteristics of upper molars following mandibular growth, or the angulation of molars before treatment. Different anchorage reinforcement devices have been developed to prevent mechanical anchorage loss, but the anchorage loss resulting from physiological factors should also be taken into account. Objective: To explore the efficacy of a new strategy to control physiologic anchorage compared with that of the conventional straight-wire appliance. Trial design: Randomized controlled trial (RCT). Methods: Participants of Han ethnicity were randomized into the physiologic anchorage spee-wire system (PASS) group or McLaughlin-Bennett-Trevisi (MBT (TM)) straight-wire group by minimization random allocation. The eligibility criteria were patients with a Class I or II molar relationship, permanent dentition (11-35 years old), fixed appliances involving the extraction of at least two upper first premolars, and medium or maximum anchorage requirements. Pre-treatment and posttreatment dental casts were scanned into digital casts and measured using a blinded method. Mesial displacements of the upper first molars were considered as the primary outcome for evaluating anchorage control. Measurements were taken for subgroups based on age. Results: Data from 60 participants were analysed.The baseline characteristics were not significantly different between groups. Mesial displacement of the upper first molar (in mm) was 2.96 +/- 1.52 in the PASS group and 2.70 +/- 1.66 in the MBT group (P = 0.521). The variation in incisor torque was -6.94 +/- 6.35 degree in the PASS group and -11.76 +/- 7.65 degree in the MBT group (P= 0. 010). The incisor retraction (in mm) was 4.24 +/- 1.99 and 5.67 +/- 2.27 in the PASS and MBT groups, respectively (P= 0.012). Adverse effects were not documented in any patient. Limitation: The study was a single-centre study. Conclusions: Compared with the MBT group, the PASS group without additional anchorage devices could attain well anchorage control by considering the dentoalveolar compensation of anchor teeth.