Abstract: Objective: To analyze the effects of attachments and rotation values on the stress distribution of periodontal ligament and displacement distribution of mandibular left second premolar with three-dimensional finite element method. Methods: The DICOM files of mandibular dentition were obtained with CT. Nine three-dimensional finite element models, i.e. mandibular left second premolar rotated 1.2°, 2.5°, and 3.3° without attachment, rectangular attachment, and torsion attachment, were established with Mimics and Geomagic Hypermesh software, respectively. The displacement tendency and the stress distribution were analyzed. Results: The stress distribution of periodontal ligament of all models were similar, however, the attachment group > without attachment group, the torsion group > the rectangular attachment group, 3.3°>2.5°>1.2°, the maximum stress value in all models was 10.15 MPa, and the minimum stress value was 6.106 MPa. When the mandibular left second premolar was rotated with attachment, the displacements were as follows: the torsion group > the rectangular attachment group >without attachment group, 2.5°>3.3°>1.2°, the maximum activation value for left second premolar in all models was 1.439×10^-2 mm, the minimum value was 9.15×10^-3 mm, and there were intrusion and inclination tendency in all models. Conclusion: When rotating the mandibular second premolar with clear aligner, rotated the torsion attachment for 2.5°favors the tooth rotation.

Key words: Clear aligner, three-dimensional finite element analysis, the second premolar rotation, torsion attachment, periodontal ligament