## 4 Discussion
[14], who compared the 3D models of patients affected by FPCB to a control group of patients without FPCB by analysing differences between mirrored casts of the palatal vault. Their study demonstrated a lower percentage of the models in the study group (83.36%) compared to the control group (92.82%), with the most pronounced asymmetries located at the alveolar bone level. The higher matching percentages found by [PERSON] et al. [14] compared to the present study may be attributed to the fact that their analysis did not include the teeth in the maxillary section. Conversely, the maxillary arch asymmetry observed in patients with FPCB found in the present study is not supported by the findings of [PERSON] et al. [17], who reported a palatal vault correspondence of 91.84% in untreated patients with functional posterior crossbite and children without crossbite. However, they used a tolerance range of \(-0.5\) mm to \(+\) 0.5 mm for matching, whereas the present study employed a stricter tolerance range of \(-0.25\) mm to \(+\) 0.25 mm. Furthermore, it is important to emphasise that the maxillary asymmetry highlighted by the 3D analysis is not only due to the difference in transverse linear distances between the two halves of the maxillary arch but also due to the difference in sagittal linear distances between the two halves of the maxillary arch. This was previously found by a study using scanned dental casts, which showed patients with FPCB exhibiting asymmetric rotation and mesial displacement of the upper first molars compared to a control group of Class I non-crossbite subjects [25]. The routine approach of symmetrically expanding the upper arch for patients affected by FPCB is challenged by these results. If an asymmetric arch is clinically verified, this may indicate the need for orthodontic treatment that not only corrects the maxillary palatal vault constriction but simultaneously addresses the dento-alveolar asymmetry. These transverse and sagittal dental-alveolar asymmetries should be assessed at an early age to ensure proper management during the different phases of the orthodontic treatment. Previously, some authors [13; 26] have emphasised the importance of correcting maxillary arch asymmetry, when it occurs in the transverse plane, with asymmetrical maxillary expansion [26]. If the maxillary arch asymmetry is present in the sagittal plane, it may worsen the asymmetric Class I molar relationship and the midline discrepancy, which are both caused by the mandibular shift. In this case, correction of the mandibular shift in a Class I FPCB patient should be performed alongside correction of the asymmetric sagittal position of the canines and molars, ensuring a correct molar relationship and aligning the upper midline with the palatal raphe. [PERSON] [27] and [PERSON] [28] emphasised that during the intertransitional mixed dentition, the positioning and rotation of the first molars, along with the transition from deciduous to permanent anterior teeth, significantly influence mandibular movement patterns and temporomandibular joint (TMJ) adaptations. Thus, establishing a Class I molar relationship during this critical period is essential for guiding proper TMJ and mandibular structural development. Molar asymmetrical de-rotation and distalisation [25], combined with asymmetric slicing or extraction of deciduous teeth [29; 30], may aid in achieving a symmetric molar Class I relationship and correcting upper arch midline deviation. Failure to correct these dento-alveolar asymmetries can affect permanent occlusion, mandibular growth, and TMJ adaptation [31], potentially leading to more complex orthodontic mechanics or the need for asymmetric extractions at later stages. Early diagnosis and management of maxillary arch asymmetries could reduce the need for more complicated orthodontic mechanics or asymmetric extractions in later stages.