The Effects Of Different Attachment Geometries On Second Molar Uprighting In Clear Aligner Treatment: An In Vitro Study

Objective: Investigate the biomechanical impacts of various attachment designs on second molar uprighting, identify optimal geometry, and provide clinical guidelines for clear aligner treatment following first molar loss. Methods: This in vitro study was conducted by using 3D-printed dental models with mesially tilted second molars. Five groups were designed based on attachment geometry: one without attachment, horizontal, inclined attachment, twin alternative, and two vertical. Clear aligners were fabricated and applied to each model to deliver uprighting forces. Pre- and post-treatment tooth positions were measured to a fixed reference point by using CBCT, and changes in mesiodistal inclination, buccolingual inclination, vertical, and mesiodistal distances were recorded. Statistical analysis was performed using the Kruskal-Wallis test followed by pairwise comparisons to identify significant differences among groups. Results: The inclined attachment produced the greatest uprighting effect in mesiodistal inclination, indicating superior molar control compared to other geometries. Minimal buccolingual inclination change was observed in the single horizontal and inclined groups, while twin-type attachments showed greater deviation. Vertical positioning was largely maintained across groups, with no statistically significant differences. Mesiodistal distance varied between attachment types, with inclined and horizontal designs showing the greatest reduction. Overall, attachment geometry demonstrated measurable effects on molar movement across multiple dimensions. Conclusions: The inclined attachment showed better performance in second molar uprighting compared with single horizontal, twin, and two vertical attachments. Attachment geometry significantly influences molar control.