2025, Vol. 29 ›› Issue (28): 6012-6019

Finite element analysis on miniscrews and hooks with different locations assisted clear aligners in maxillary molar distalization

Ye Panpan1, Xu Changxi1, Li Hui2, Zhang Yang3, Xu Xiaolin2, Wang Hongning2   

Abstract: BACKGROUND: The utilization of miniscrews for assisting in molar distalization with clear aligners is a commonly adopted clinical approach. However, treatment outcomes may be influenced by the implantation position of miniscrew and the hooks in various tooth location.
OBJECTIVE: To analyze the biomechanical effects of hooks at different tooth positions and the assistance of buccal and palatal miniscrews in distalizing molars with clear aligners by using the finite element method.
METHODS: By integrating volunteer cone beam CT and Itero intraoral scan data, high-precision finite element models were constructed to simulate the combined use of miniscrews and hooks to assist in the distalization of the maxillary first and second molars with clear aligners, aiming for a designed distalization magnitude of 0.2 mm. Four conditions were established based on the placement of buccal or palatal miniscrews, as well as the located of hooks at the canine or first premolar. The buccal anchorage screw was used in combination with hooks on the buccal side of the canine; the buccal anchorage screw was used in combination with hooks on the buccal side of the first premolar; the palatal anchorage screw was used in combination with hooks on the lingual side of the canine, and the palatal anchorage screw was used in combination with hooks on the lingual side of the first premolar. Analysis using ANSYS software was conducted to evaluate the three-dimensional displacement trends of maxillary teeth and the maximum equivalent stress on the periodontal ligament under each condition.
RESULTS AND CONCLUSION: (1) Regardless of whether hooks were placed on canines or first premolars, palatal miniscrews had been shown to enhance the distal movement of maxillary molars and reduce the mesial movement of premolars as well as the labial tipping tendency of anterior teeth, compared to buccal miniscrews. The maximum equivalent stress in the periodontal ligament of molars was increased, while that of anterior teeth was decreased. (2) Regardless of whether the miniscrews were located on the buccal or palatal side, compared with hooks at the first premolar, when hooks were done at the canine, the labial inclination trend of the anterior teeth was reduced, the distal movement of the molars was reduced, the mesial movement of the premolars was increased, and the maximum equivalent stress of the molar and the periodontal membrane of the anterior teeth was reduced. (3) Regardless of whether miniscrews were located on the buccal or palatal side, and the hooks were located on the canine or the first premolar, the molar could not achieve overall movement. (4) The results show that clear aligner combined with palatal miniscrews and hooks at the first premolar are more conducive to improving the efficiency of maxillary molar distalization, but attention should be paid to protecting the anterior tooth miniscrews and molar torque control; clear aligner combined with palatal miniscrews and hooks at the canine is more conducive to reducing the labial tipping tendency of anterior teeth, but the efficiency of molar distalization will be relatively reduced.

Key words: finite element analysis, clear aligner, molar distalization, miniscrew, hook, elastic traction