Analysis of the Forces and Moments in Canine Bodily Movement with Different Clear Aligners' Extraction Space Designs  
[PERSON]  
1 Department of Orthodontics, Dental Research Institute, School of Dentistry, Pusan National University,  
Yangan 50612, Republic of Korea; [EMAIL_ADDRESS] (Y.-K.C.)  
[PERSON]  
1 Department of Orthodontics, Dental Research Institute, School of Dentistry, Pusan National University,  
Yangan 50612, Republic of Korea; [EMAIL_ADDRESS] (Y.-K.C.)  
[PERSON]  
2 Department of Oral Pathology, School of Dentistry, Pusan National University,  
Yangan 50612, Republic of Korea; [EMAIL_ADDRESS]  
[PERSON]  
1 Department of Orthodontics, Dental Research Institute, School of Dentistry, Pusan National University,
which can lead to torque loss and the extrusion of the anterior teeth [13; 14]. This often results in a \"roller coaster\" effect, i.e., distal tilting of the anterior teeth and mesial tilting of the molars associated with anchorage loss, thus exhibiting undesirable results such as insufficient retraction of the anterior teeth and excessive mesial displacement of the maxillary first molars [15]. Therefore, in many CA cases with extractions, the final occlusion presents an undesirable Class II molar relationship. This poses significant challenges for orthodontists during CA treatment. Flexible CA materials are prone to change, especially for space closure, and may not be suitable for bodily movements [15; 16].  
Various methods have been used to solve the problem of space closure during orthodontic treatment with CA. For instance, a certain amount of intrusion is intentionally added to the incisors when they move posteriorly to control their movement. Unfortunately, the effectiveness of additional intrusion has not been proven, and the most efficient ratio between the amount of posterior movement and intrusion remains unclear [13; 14]. Additionally, to solve the problem of anchorage loss in the molars, the use of Class II elastics with CAs has been proposed [17], and attempts have been made to modify the design of CAs for better utilization of the forces and moments applied to the teeth. For instance, modifications in the CA design include adding a power ridge to control the maxillary anterior torque effectively or thickening the buccal side of the CA to increase its stiffness [18]. However, despite these attempts, achieving effective space closure using CAs remains challenging and under-researched.  
This study focused on manipulating the design of CAs to efficiently apply forces and moments. In premolar extraction cases, the design of the edentulous area may affect the amount of tooth coverage by the CA adjacent to the edentulous area. For most CAs, the edentulous space acts as a hollow space with the shape of the extracted tooth, which does not provide a sufficiently strong grasp on the tooth adjacent to the extraction space and can affect the stiffness of the CA. Therefore, to grasp the adjacent teeth more firmly and ensure a larger contact area, the following alternatives can be considered: the vertical height of the CA in the edentulous area could be reduced to the alveolar bone level; the width could be reduced to a half-pontic size; or a beam design could be used to increase the stiffness of the CA.  
This study aimed to measure and compare the forces and moments generated by different CA designs during the distal bodily movement of maxillary canines into the maxillary premolar extraction space, and to propose a design for more efficient space closure using a miniature six-axis force/moment sensor and a 3D printed customized apparatus.