To establish the three-dimensional finite element simulation model of periodontal membrane by micro-CT scanning data.

A human maxillary jaw segment containing central incisor was scanned with microCT for section images, which were managed with Mimics software to form a geometric model. The model was imported to remesh module for optimization and then the three-dimentional finite element model was constructed by Ansys.

The three-dimensional finite element models encompassing 12936 nodes and 6400 tetrahedral element, which highly resemble the structure of periodontal ligament. Tooth (60872 nodes and 42144 tetrahedral element) and alveolar bone models (41472 nodes and 32339 tetrahedral element) were constructed successfully.

The three-dimensional finite element simulation model of periodontal membrane can be established by micro-CT combined with Mimics and Ansys software. After adding the corresponding tooth alveolar bone, it can be further used in orthodontic biomechanics analysis.

This study investigated the effect of applying different torque values on the sagittal displacement tendency of mandibular incisors during intrusion using clear aligners, with the aim of providing a reference for achieving true vertical intrusion (intrusion without labiolingual movement) of mandibular incisors in clear aligner therapy.

This study was approved by the institutional ethics committee. A volunteer with an incisor mandibular plane angle of 94° was selected. Using cone-beam computed tomography and intraoral scan data, a high-precision three-dimensional finite element model was established. An intrusion amount of 0.2 mm was set for the mandibular incisors, and four simulation groups were defined by applying 0°, 1°, 2°, and 3° of root labial torque. The displacement tendency of the incisors and the stress distribution within the periodontal ligament were analyzed.

When 0° of root labial torque was applied, the mandibular incisors exhibited intrusion accompanied by crown-labial, root-lingual inclination. When 1°–3° of root labial torque was applied, the mandibular incisors exhibited intrusion accompanied by the inclination gradually shifted from crown-labial, root-lingual towards crown-lingual, root-labial. Based on the line graph of sagittal displacement, the central incisors and lateral incisors approximated true vertical intrusion when 1.8° and 2.5° of root labial torque was applied, respectively. The mandibular canines consistently exhibited extrusion accompanied by labial crown inclination. Stress within the periodontal ligament of the incisors and canines was primarily concentrated at the root apex and cervical region. After applying root labial torque, the area of stress concentration in the incisors cervical periodontal ligament shifted from the labial side to the lingual side. The stress in the periodontal ligament at the cervical region of the canines is predominantly concentrated on the labial side.

Applying appropriate torque control during mandibular incisor intrusion with clear aligners facilitates true vertical intrusion, thereby enhancing the efficiency of the intrusion.