This study evaluated the biomechanical effects of different attachment configurations on buccal uprighting of lingually inclined mandibular second molars using clear aligners (CAs). Finite element analysis was performed to simulate a 2° uprighting movement, with boundary conditions applied to the basal bone and loading generated through geometric mismatch between the aligner and dentition. Six experimental groups were established according to attachment placement on the first and second molars. Three-dimensional tooth displacement, crown-to-root displacement ratio (C/R ratio), moment-to-force ratio (M/F ratio), and anchorage loss were analyzed. Group 5, combining a buccal attachment on the first molar and a lingual attachment on the second molar, demonstrated the most favorable biomechanical performance, with controlled tipping (C/R ratio −1.67), minimal anchorage loss (3.2%), and an optimal M/F ratio (5.5). In contrast, Group 3 exhibited excessive anchorage loss (44.8%) and inefficient force transmission, while Group 6 showed reduced efficiency despite a high M/F ratio, indicating mechanical overconstraint. These findings suggest that attachment configuration plays a critical role in determining force–moment systems in CA therapy, and increasing attachment number does not necessarily improve treatment efficiency. Strategic placement of attachments can enhance biomechanical control and optimize clinical outcomes in mandibular second molar uprighting.
Soung et al. (Fri,) studied this question.