Finite Element Analysis of Stress and Displacement Patterns in the Maxillary Dentition During Miniscrew-Assisted en-Masse Retraction Using Variable Gable Bend Angles.

Introduction: Efficient anterior tooth retraction with simultaneous intrusion is critical for the orthodontic treatment of deep bites. Gable bends incorporated into archwires can influence the direction and magnitude of force application. This study aimed to evaluate the effect of different gable bend angles (0°, 10°, 15°, and 20°) on stress distribution and displacement patterns in the maxillary dentition using three-dimensional (3D) finite element analysis (FEA) in the context of miniscrew-assisted en-masse retraction.

Methodology: A 3D geometric model of the adult maxilla was constructed using high-resolution computed tomography (CT) scan data. The maxilla was segmented using MIMICS 8.11 (Materialise NV, Leuven, Belgium), and surface refinement was performed using RapidForm (INUS Technology Inc., 3D Systems, Rock Hill, SC). The model was meshed in HyperMesh 13.0 (Altair Engineering, Inc., Troy, MI), and analysis was performed using ANSYS 12.1 (ANSYS, Inc., Canonsburg, PA). The model included teeth from the central incisor to the second molar, with a 0.25-mm-thick periodontal ligament (PDL) and alveolar bone. Orthodontic appliances included 0.022" McLaughlin, Bennett, and Trevisi (MBT) brackets (3M Unitek, Monrovia, CA) from central incisor to second premolar, bands on molars, a 0.019" x 0.025" stainless steel archwire (Ortho Organizers, Carlsbad, CA), and a transpalatal arch using 0.9 mm wire (GAC Int., Bohemia, NY). A miniscrew (1.5 mm × 10 mm; S.K. Surgicals, Pune, Maharashtra, India) was placed between the second premolar and first molar at an angle of 30°from the occlusal plane. A 200 g retraction force was applied using elastomeric chains (American Orthodontics, Sheboygan, WI) from a 6-mm crimpable hook to the miniscrew. Four models were created with gable bend angles of 0°, 10°, 15°, and 20°, placed 2 mm away from the canine bracket. Each model contained 82,566 nodes and 392,108 elements.

Results: The von Mises stress increased with greater gable bend angles, especially around the implant site and canine PDL. Cortical bone stress ranged from 51.9 MPa (0°) to 64.9 MPa (20°). The anterior teeth showed enhanced retraction and intrusion with 15° and 20° gable bends. The posterior teeth exhibited minimal displacement and maintained their anchorage. Intrusion and controlled tipping of the anterior teeth were more prominent at higher gable bend angles.

Conclusions: Gable bend angles of 15° and 20° provided optimal biomechanical conditions for en-masse retraction with effective intrusion of the maxillary anterior teeth while preserving the posterior anchorage. These configurations may offer clinical advantages for managing deep-bite cases.