## 4 Discussion
To the best of our knowledge, this is the first study in the literature that proposes 3D-printed custom attachments and evaluates their reproduction accuracy of the planned shape and the presence of blowouts after bonding compared with traditional attachments created from composite flow. The accuracy of attachment replication can be affected by various factors, including the material of the transfer template, the material composition of the attachment, and the intraoperative skill of the operator. A recent study [19] assessed the accuracy and reproducibility of the attachment shape by comparing the attachment transfer with two different types of templates: Pet-G (glycol-modified polyethylene terephthalate template) and PE (polyethylene template); the study concluded that Pet-G allows more accurate reproduction of the attachment shape than PE. In addition, these authors also evaluated the influence of composite resin materials with different viscosities in reproducing the shape of the attachments, revealing that the accuracy of high-viscosity and low-viscosity composites is equivalent. Other authors carried out a comparative analysis of flowable and packable composite materials [22], concluding that flowable composite materials necessitated less time for preparation and showing no statistically significant differences in terms of damage when compared to packable composites at the one-year evaluation. More authors have shown that 3D-printed materials offer good accuracy and reproducibility of details, including composite attachments; however, they may show lower strength than traditional materials, especially in terms of the resistance to forces applied during orthodontic treatment [23]. Based on data from the previous literature [19; 22], a PET-G template was used in the present study to transfer both the traditional and 3D-printed attachments; in addition, the use of a flow composite was chosen to create the traditional attachments. The results of this study show statistically significant differences (\(p<0.05\)) in the accuracy between the 3D-printed custom attachments and the traditional flow-made attachments. On average, the 3D-printed custom attachments exhibited over 50% higher accuracy, with the most significant discrepancies observed on the gingival side. The greater inaccuracy in transferring the attachments at the gingival level (0.78 mm) can be due to the \"tenting effect\" that occurs during the thermoforming process. The tenting effect is when the thermoformed material tends to pull upward along the gingival as it cools [24]. This phenomenon can lead to challenges in achieving the optimal adherence of the thermoformed try to the teeth, especially in the gingival area, resulting in a greater inaccuracy in the shape reproduced in the template and, consequently, in the final attachment shape. These results are consistent with the study conducted by [PERSON] and colleagues, in which the median gap of thermoformed transparent aligners was evaluated using micro CT and a spectrophotometer, showing that the median gap at the gingival level consistently exceeded that at the occlusal surface [25]. Another factor contributing to the greater inaccuracy of traditional bindings made from flow composite is the difficulty of standardizing the amount of composite material used during the creation of the binding, which can lead to an inconsistency between the programmed shape and the actual shape. On the contrary, the use of custom 3D-printed attachments allows for better standardization of the composite amount flow during the bonding procedure by using a standardized amount of composite. The findings of this research indicate the potential benefits of customized 3D-printed attachments in the clear aligner therapy. However, additional investigations are necessary to assess the clinical impact of different amounts of attachment accuracy reproduction on the efficacy of clear aligners when it comes to achieving different types of dental movement.