Comparison of the effects of different attachment designs in maxillary molar expansion with clear aligners: A three dimensional finite element analysis method

In recent years, orthodontic treatment with clear aligners has become a preferred treatment method for patients due to the advantages it offers in terms of aesthetics and comfort. Limitations such as tipping movement and insufficient root control during dental expansion with clear aligners are among the significant biomechanical problems. Ensuring bodily movement, especially in upper molar teeth, is of great importance for long-term stability and periodontal health. Finite element analysis is frequently used in dentistry and orthodontics due to its advantages such as providing realistic results when data is submitted correctly and being non-invasive. The aim of this study is to determine the optimal method by evaluating the effects of different attachment designs and positions used during maxillary molar expansion with clear aligners using three-dimensional finite element analysis. In our study, the stress distribution and displacement amounts in the molar teeth and periodontal structures during expansion with clear aligners were analyzed in seven different groups consisting of different attachment positions and configurations, along with an attachment free control group, in a 20-year-old adult patient. These groups were: control group, (1) horizontal rectangular attachment applied to the buccal surface, (2) gingivally beveled horizontal rectangular attachment applied to the buccal surface, (3) application of an optimized expansion support attachment to the buccal surface, (4) application of an occlusally beveled horizontal rectangular attachment to the palatal surface of the first molar in addition to the optimized expansion support attachment, (5) application of a horizontal rectangular attachment to the palatal surface of the first molar in addition to the optimized expansion support attachment, (6) application of a horizontal rectangular attachment to the palatal surface of the first molar without adding an attachment to the buccal surface. Clear aligners with a thickness of 0.6 mm were applied in all groups. In the loading method, the deformation occurring in the clear aligner geometry when the teeth were moved 0.2 mm in the palatal direction was calculated, and the contact forces resulting from the deformation were applied in the opposite direction to the relevant tooth surfaces. In this way, it was aimed to accurately reflect the biomechanical effects of the transparent plate and obtain results compatible with the clinical environment. In all groups, expansion was observed to occur in the form of buccal movement of the crown and palatal movement of the root, and parallel movement could not be achieved. Optimized attachments showed higher expansion efficiency and root control compared to conventional attachments. In Group 4, where an occlusal beveled horizontal rectangular attachment was placed on the palatal surface along with a buccal optimized attachment, the highest expansion value and the lowest palatal movement of the root were identified. No difference in movement efficiency was found between Group 6, where attachments were placed only on the palatal surface, and the control group. Extrusion was observed in the palatal cusp in all groups. The findings demonstrate that attachment design, surface, and attachment angle have significant effects on the effectiveness of molar expansion and root control with clear aligners. In clinical practice, consideration of these variables is deemed beneficial for minimizing adverse effects and enhancing treatment success.