## 4 Discussion
GT: Geniova; CA: clear aligner; SD: Standard deviation; Diff: difference; CI: confidence interval; sig: significance; 13_23: upper amines; 14_24: upper first premolars; 15_25: upper second premolars; 33_43: lower amines; 34_44: lower first premolars; 35_55: lower second premolars; cusp: cuspid level; cerv: cervical level. to the CA group. Expansion was similar in both groups, except for the lower first and second premolars, which showed larger expansion in the CA group. The percentage of achieved expansion was similar for GT and CA groups at the cusps and cervical levels. Although the GT group showed non-significant greater prediction accuracy of expansion compared to the CA group in the upper arch, it was lower for the lower arch. In general terms, the predictability of virtual set-up measurements was similar for both the GT and CA groups. The treatment modality in this study was not randomly assigned. However, the treatment planning for all patients was completed before the treatment modality was selected. This ensured that the initial malocclusion and treatment planning were not influenced by the specific system of aligners used, which was chosen based on the patient's preferences after the study was explained. Additionally, the treatment modality was not selected by the orthodontist after considering the patient's malocclusion, further supporting the independence of the treatment modality from the initial malocclusion. It might be hypothesized that the results observed in the GT group (less treatment time and fewer aligners) could be due to the biomechanical properties of this novel system, which is based on principles of conventional multi-bracket appliances. Round nickel-titanium arches, ligated to the virtual brackets, generate continuous light forces for tooth movements. The difference in size and position between the virtual brackets generates movement in the three planes of space, as the brackets can change in size (height, width, and length) and position according to the desired design. Customization of the virtual bracket size in the GT appliance allows for greater or lesser deflection in the nickel-titanium arch during transverse movements, even in the absence of dental crowding. As an example, in cases of crossbites involving premolars without crowding, increased force can be generated due to the deflection caused by the virtual bracket size. This differentiates it from metallic brackets, which have a standard dimension and produce a 'constant' deflection force only when dental crowding is present. This could indicate that in cases of single-tooth crossbites, or a small group of teeth, the GT hybrid aligners may be more effective than conventional aligners and even traditional brackets due to the greater force generated by the deflection of the nickel-titanium arch. This biomechanics allows for faster achievement of transverse dental movement than aligners alone. Fewer aligners may lead to a shorter treatment duration and fewer adjustments, which can be more convenient for patients. Moreover, it can result in lower treatment costs, making orthodontic treatment more accessible. Aligners are typically made of plastic, and using fewer aligners can reduce the amount of plastic waste generated during treatment and help reduce the carbon footprint associated with orthodontic treatment. This is particularly important from an environmental perspective, as plastic waste can have significant negative impacts on ecosystems and wildlife. Transverse expansion has been achieved through various orthodontic techniques, each exhibiting distinct dentoalveolar and skeletal effects. Aligners, particularly the Invisalign(r) system, have gained prominence due to their aesthetic and patient-comfort advantages [29; 30; 31; 32].