###### Abstract  
This study evaluated the effects of different clear aligner (CA) designs on forces and moments during maxillary second molar distalization. Four designs were tested: attachment only (group 1), neither attachment nor enhanced structure (group 2), a combination of attachment and enhanced structure (group 3), and enhanced structure only (group 4). CAs were fabricated from thermoformed polyethylene terephthalate glycol with 30 CAs per group. Forces and moments were measured using a multi-axis transducer as the molars were distally displaced by 0.25 mm. All groups experienced buccalostal and intrusive forces. Group 3 showed the highest distalizing force (Fy = 2.51 \(\pm\) 0.37 N) and intrusive force (Fz = \(-\)2.04 \(\pm\) 0.48 N) and also the largest rotational moment (Mz = 3.89 \(\pm\) 0.71 Nmm). Groups 3 and 4 (with enhanced structures) demonstrated significant intrusive forces (_p_ < 0.05). Most groups exhibited mesiodistal angulation, lingual inclination, and distal rotational moments. Group 2 had the lowest moment-to-force ratio (Mx/Fy = 3.27 \(\pm\) 0.44 mm), indicating inefficient bodily movement. Group 3 demonstrated significantly greater moments across all axes compared to other groups. The results indicate that designs incorporating enhanced structures with attachments increase CA stiffness and applied forces/moments, enhancing distalization efficiency while minimizing vertical side effects. This suggests that, clinically, reinforced CAs can serve as a simple yet effective modification to existing protocols in Class II orthodontic cases, enabling more efficient molar distalization without requiring complete appliance redesign or additional fabrication and allowing easy adaptation to individual treatment needs. c 202515665 10 May 202516 May 20257 June 202511 June 202513 June 202513 June 202513 June 202513 June 202513 June 202513 June 202513 June 202513 June 202513 June 2025144444444444444444444444444444444444444444444444444444444444  
reinforcements have been introduced to address these limitations. However, their clinical applicability and efficiency, especially in inducing the bodily movement of maxillary molars, remain underexplored. Maxillary molar distalization is a crucial biomechanical strategy for the non-extraction treatment of Class II malocclusions [7]. Among all types of tooth movement, the predictability and efficiency of molar distalization are significant with CAs [8]. This is attributed to the unique biomechanical properties of CAs, where the CAs completely cover the tooth crown, enabling 3D tooth movement. However, molar distalization presents several challenges, possibly having unintended consequences, including incisor proclination, intrusion, distal tilting of the molar, an increase in lower facial height, and clockwise rotation of the mandible due to the loss of anterior anchorage [9; 10]. The main challenge in maxillary molar distalization with CAs is achieving bodily movement, as distal tipping is more commonly observed than true bodily movement [11]. This limitation is primarily attributed to insufficient appliance stiffness, crown-level force application, and inadequate anchorage control. These problems are mainly attributed to the weak stiffness of the aligner material and an incomplete understanding of CA biomechanics [12; 13]. However, regarding vertical skeletal control, recent studies have demonstrated that maxillary molar distalization with CAs does not significantly affect the vertical skeletal dimension. Unlike traditional appliances that may induce clockwise mandibular rotation or increase lower facial height, CAs have been shown to maintain vertical stability during distalization [10; 14]. This finding suggests that CA-based molar distalization may offer a biomechanically favorable treatment option, particularly in patients where vertical dimensional control is critical. The stiffness of CA materials is equal to or less than that of nickel-titanium archives in fixed appliances [15].