Abstract: BACKGROUND: Lingual movable wing is a new type of lingual orthodontic technique and the different stretching lengths of the wring affect the torque control effect of anterior teeth. However, there is yet no related biomechanical research. 
OBJECTIVE: To investigate the displacement trend of dentition during adduction of mandibular anterior teeth and the effect of different wing stretching lengths on the biomechanical effect of mandibular anterior teeth. 
METHODS: The data of the mandible and lower dentition were collected by cone-beam CT and reconstructed using Mimics software to establish a three-dimensional finite element model of mandibular anterior teeth adducted by the lingual movable wing. The ANSYS software was used to analyze the initial displacement of the mandibular anterior teeth under the following conditions: A, 2 mm stretching length; B, 2.5 mm stretching length; C, 3 mm stretching length; and D, 3.5 mm stretching length.
RESULTS AND CONCLUSION: The trend of initial displacement of lower dentition: The central incisors moved lingually with depression, the lateral incisors and canines moved mildly lingually with mesial lingual torsion, the second premolar was tilted distally with a marked lingual inclination and the first molar showed an overall mesial inclination with mesial crown eversion. Therefore, in the adduction cases of mandibular tooth extraction, attention should be paid to the lingual movement of the second premolar, which could be offset by corresponding techniques in clinic. The trend of anterior tooth displacement in all directions: from condition A to condition D, in the sagittal direction, the difference value in crown-root displacement of central incisors changed from -11.891 μm to -5.757 4 μm, indicating that the central incisor changes from oblique movement to overall movement. The difference value in crown-root displacement of lateral incisors changed from -11.828 1 μm to -6.711 45 μm, and that of canines changed from -7.572 3 μm to  -4.695 5 μm, indicating that the oblique movement of the lateral incisors and canines is also changing to an overall movement. In the vertical direction, from condition A to condition D, the reduction of incisors was gradually increased, while that of canines was gradually decreased. These findings indicate that the stretching length of the wing can affect the oblique movement trend of the anterior teeth. As the wing continues to stretch, the torque control of the lower anterior teeth will become better.

Key words: lingual movable wing correction technique, three-dimensional finite element, biomechanics, mandibular anterior tooth, torque, displacement trend, traditional lingual technique, adduction