Biomechanical Evaluation of Attachment and Trimline Modifications in Maxillary Molar Distalization Using Clear Aligners

Upper molar distalization using clear aligners requires optimal force direction and control to ensure effective and predictable tooth movement. This study aimed to evaluate the biomechanical effects of different aligner trimline lengths (trimline ending at the gingival margin vs. 2 mm extended) and attachment designs (no attachment, vertical rectangular, 25-degree beveled vertical, and double horizontal) on maxillary first molar distalization using finite element analysis. A three-dimensional maxillary model was constructed from CBCT data, and eight different aligner configurations were simulated under identical distalizing force. The stress distribution within the periodontal ligament of the maxillary first molar and displacement of crown and root landmarks in three axes were analyzed. The models with no attachments and trimlines ending at the gingival margin exhibited the highest degree of uncontrolled tipping and uneven stress distribution. In contrast, models combining extended trimlines with either beveled vertical or double horizontal attachments demonstrated more controlled bodily movement, reduced palatal root mesial displacement, and more uniform vertical movement. Overall, extended trimlines were associated with increased total distalization and improved force transmission. These findings provide biomechanical insight into optimizing aligner configuration for upper molar distalization and may guide clinicians and manufacturers in improving treatment precision and predictability.