[Finite element simulation of distally moving mandibular molars by sequence with clear aligner]

To construct a finite element model of the mandibular molars distalization with clear aligner, and to explore the characteristics of dentition movement and aligner deformation.

The models of mandible, teeth, periodontal membrane and clear aligne were constructed using CBCT and oral scan data, and were divided into 8 groups according to the starting position of the second and first molar teeth. Working condition 1-4: the distance between the second molar and the first molar was 0, 1, 2, 3 mm, respectively. Working condition 5-8: the second molar had moved far to the target position of 3.2 mm, and the distance between the first molar and the second premolar was 0, 1, 2 and 3 mm, respectively. "Two-step method" was used to simulate the loading of the clear aligner and set the distance of the step to 0.2 mm, the characteristics of dental displacement and appliance shape change in each working condition were analyzed.

Under each working condition, the molar with pseudo-remote displacement showed tilt movement of the crown to the far, and the other teeth showed reverse tilt movement. As the initial position of the pseudo-distant molar changed to the distal, the distal movement of the pseudo-distant molar increased. In working condition 4, the maximum displacement of the second molar was 0.11 mm, and in working condition 8, the maximum displacement of the first molar was 0.10 mm. The change trend of the Von Mises equivalent stress value of the periodontal membrane of the pretended distalization teeth was similar to that of the displacement.

Clear aligner can complete distal movement of molar teeth, but the amount of movement cannot reach the expected value. As the initial position of the molars changed to the distal, the distance displacement will increase.