This study utilized a three-dimensional finite element method to investigate the biomechanical effects of various loading modalities on the intrusion of maxillary posterior teeth using orthodontic miniscrews in a patient with high-angle Class Ⅱ skeletal pattern, aiming to provide guidance for clinical orthodontic practice.

A three-dimensional finite element model was developed for a patient with a high-angle Class Ⅱ skeletal pattern, incorporating the maxillary dentition, alveolar bone, periodontal ligament, and clinical orthodontic appliances for the maxillary posterior teeth. The following loading conditions were configured: Condition 1: One miniscrew was placed on both the buccal and palatal sides between the first and second molars. Condition 2: One miniscrew was placed on the buccal side between the first and second molars, and the left and right first molars were connected via a transpalatal arch. Condition 3: One miniscrew was placed on the buccal side between the first and second molars, the left and right first molars were connected via a transpalatal arch, and a traction hook was designed extending from the palatal bar on the palatal sides of the second molars. Condition 4: One miniscrew was placed at the midpalatal suture region corresponding to the first molars, the left and right first molars were connected via a transpalatal arch, and midpoint traction hooks were designed on both sides of the palatal bar. Condition 5: One miniscrew was placed at the midpalatal suture region corresponding to the first molars, the left and right first molars were connected via a transpalatal arch, a traction hook was designed extending from the palatal bar on the palatal sides of the second molars, and midpoint traction hooks were added on both sides of the palatal bar. The stress distribution in the periodontal ligament and the displacement trends of the posterior teeth were investigated under these conditions.

In Condition 1, the stress gradients (defined as the ratio of mean stress in the cervical region to that in the apical region) for the second premolar, first molar, and second molar were 2.10, 2.09, and 2.26, respectively, the lowest among the five conditions. This setup exhibited the most uniform stress distribution and minimized the buccopalatal and mesiodistal inclination of the posterior teeth to the greatest extent, followed by Condition 4. In Condition 3, the hook designed on the palatal side of the second molar helped restrain its buccal inclinations, whereas in Condition 5, the palatally designed hook aggravated the degree of palatal inclination.

The most ideal method for intruding the maxillary posterior teeth is to place miniscrews on both the buccal and palatal sides between the maxillary first and second molars, followed by the use of a transpalatal arch combined with miniscrews placed in the midpalatal suture. When intruding the maxillary posterior teeth using buccal miniscrews with a transpalatal arch, a hook should be designed on the palatal side of the second molar to restrain buccal inclination. However, when using a midpalatal suture miniscrew with a transpalatal arch, it is unnecessary to design an additional hook on the palatal side of the second molar.