Evaluation of the effect of different length and structure of force arms in miniscrew assisted canine distalization applications on clear aligner by finite element analysis

Our aim was to evaluate the effects of using different structures and variable lengths of force arms in treatment of canine distalization with clear aligners via 3D finite element analysis (SEA) on tooth movements, periodontal tissue, clear aligner, force arm, miniscrew. A 3-dimensional (3D) model was created using tomography data (CT) of an adult patient with well-aligned teeth, the first premolar tooth extracted, the canine angled 90 degrees with the maxillary plane. The 3D maxillary model was obtained from the CT data via 3D Slicer (BWH, MA, USA) software. Reverse engineering and three-dimensional CAD activities via ALTAIR Evolve software (ALTAIR, Troy, MI, USA) were used to adapt solid models to the analysis environment. ALTAIR Hypermesh (ALTAIR, Troy, MI, USA was used to realize optimized mesh. Nastran-based ALTAIR Optistruct (ALTAIR, Troy, MI, USA) was used to solve implicit finite element models. 14 models were created in our study. In two models, only 0.1 or 0.2mm aligner activation was applied, power arm was not used. Another 12 models were created based on two different aligner activations (0.1 or 0.2 mm), three different power arm lengths (12, 13 or 14 mm) and two power arm materials (stainless steel or carbon fiber reincluded composite). The maximum periodontal stres was observed around the canine in all models. The highest tensile stress was observed in the mesio-buccal of the canine in models 13 and 14. Distal tipping of the canine crown decreased and palatal tipping increased in models with clear aligner activation and distally applied force with the power arm. In the model 13 and model 14 from the 2nd group, in the model 6 and model 7 from the 1st group, the most distal tipping and the most palatal tipping were observed. The least palatal tipping of anterior incisors in the palatal direction was observed in model 6 and model 7It has been observed that the deformation is high in the aligner regions corresponding to the regions where the displacement is high in the teeth. These regions were in the regions covering canine tooth, the extraction site and the lateral tooth. Different power arms of equal length showed similar results in tooth movements. However, less stress occurred in the carbon fiber reinforced composite power arm compared to the stainless steel power arm, and the stress was closer to the gingiva. The highest Von Mises stress in the power arm was seen in model 13. The highest Von Mises stress on the miniscrew in all models was in the neck region. In the alveolar bone where the screw was located the region with the highest tensile stress was located both closer to the occlusion and more mesially in 2nd group compared to 1st group. The highest tensile stress was observed in model 13 and model 14. The highest tensile stres of the screw region was observed in the model 13 and model 14. According to the results of our study, the power arm application in addition to the activation of the clear aligner helps to provide parallel movement of the teeth in the sagittal axis, but causes an increase in the amount of tipping in the transverse plane. Increasing the length of the power arm increases both aligner deformation and periodontal tissue stress. KFGK showed similar results in tooth movements when compared to PÇ, and had less stress in its internal structure. In addition, the fact that the stress region was located further away from the attachment may cause less deformation of the attachment, thus promising that it can be used as an alternative to PÇ. However, since it is the only study in this field, it should be evaluated in a wider perspective together with other studies. Keywords: Clear aligner, force arm, canine distalization, carbon fiber reincluded composite, finite element analysis