Finite element analysis of different methods for uprighting partially impacted mandibular second molars

This study used finite element analysis (FEA) to compare four skeletal anchorage-assisted approaches for uprighting mesioangularly impacted mandibular second molars by evaluating screw and root stresses, as well as tooth displacement in multiple directions. The mandibular complex, including the teeth, periodontal ligament, alveolar bone, and planned orthodontic mechanics, was modeled for FEA. Twelve scenarios were analyzed by combining four skeletal anchorage-assisted uprighting methods -open coil spring, Nienkemper, cantilever spring, and ramus screw- with three impaction angulations (45°, 60°, and 75°). Screw and root stresses, together with tooth displacement along the X-, Y-, and Z-axes, were evaluated. Maximum transverse (X-axis) displacement occurred in the ramus screw group, whereas peak sagittal (Y-axis) displacement was observed in the Nienkemper group. The highest vertical (Z-axis) displacement was also recorded in the ramus screw group. Under the simulated conditions, the Nienkemper method demonstrated greater distal crown displacement with relatively improved vertical control, whereas the cantilever spring showed less distal crown movement and more favorable mesial root control. The ramus screw method produced greater coronal displacement, particularly in severe impaction scenarios. These findings should be interpreted as preliminary biomechanical tendencies rather than direct clinical recommendations. Clinical application requires consideration of patient-specific anatomical factors and adjunctive orthodontic mechanics.