Abstract: Objective: To study the biomechanical mechanism of different hardness and displacement Clear Aligner during incisor intrusion in patients with periodontitis. Methods: A three-dimensional finite element model with mild and moderate periodontitis was established. The tooth displacement trend and periodontal ligament stress distribution were analyzed. Results: The incisors of 8 groups all showed intrusion with labial inclination. With the increase of hardness of Clear Aligner, the vertical displacement trend increased, and the labial inclination trend decreased. With the increase of displacement, the labial inclination trend increased. The maximum stress was concentrated in the tooth neck and apical area, and the minimum stress was distributed in the middle of the root. With the increase of hardness, the overall stress value of periodontal ligament increased, and the stress distribution of tooth neck became more uniform, but the stress of tooth neck was more concentrated with the increase of displacement. Conclusion: With the increase of the hardness of invisible appliance, the efficacy and three-dimensional control of the appliance are enhanced, while the increase in the displacement is not conducive to the three-dimensional control. Clinically, it is recommended to use a medium hardness appliance, which can achieve both tooth intrusion and maintain the health of periodontal tissue in patients with periodontitis.

Key words: clear aligner, intrusion, finite element, periodontitis