## 4 Discussion
The analysis performed by the authors points out significant differences in the distribution of stresses reduced according to [PERSON] as well as displacement patterns for the modelled variants of osteotomies. No osteotomy performed (model 1) generates stresses \(>\)10 MPa in the palatal suture, anterior maxillary sinus wall, zygomaticoalveolar crest and the teeth, to which the appliance is fixed. The displacements in the buccolingual direction (X axis) for all measuring points were 0.04 mm. According to our analysis no increase occurred in the transverse dimensions of the midface. The results of the study correlate with work of numerous authors in the field of maxillary expansion [1; 6; 13; 32]. The absence of osteotomy generates stresses with no maxillary expansion, which may lead to uncontrolled fractures and pain in the patient. [33]. [PERSON] et al. present a different opinion. The authors report on an effective maxillary expansion therapy received by 47 adult patients, with no use of surgical procedures [34]. Osteotomy of the palatal suture (model 2) decreases stresses, according to [PERSON], down to 1.1 MPa in the hard palate and the alveolar process of the maxilla in the incisal region. An increase in stress also occurs in the arcus supercilliaris region up to a maximum of 10 MPa. An increase in transverse dimensions (displacements along the X axis) in the variants with palatal osteotomy ranges from 0.22 to 0.4 mm. It seems that, in order to increase lateral dimensions of the maxilla, osteotomy of the palatal suture produces a satisfactory effect with a moderate increase in stress in the facial skeleton. Maxillary incision only along the Le Fort I line (models 3 and 4) results in unfavorable redistribution of stress reduced according to [PERSON] to the region below the osteotomy line. The analysis showed stresses \(>\)10 MPa around the entire region of the maxillary alveolar process, on lowest point of the aperture piriformis and the anterior and posterior region of the hard palate. Increases in transverse dimensions (displacement along the X axis) are minimal and range from 0.04 to 0.13 mm. This gives no grounds for performing an independent Le Fort I osteotomy and Le Fort I osteotomy with separation in PMJ. Practically, no displacement along the X axis occurs when stresses exceed 10 MPa. Furthermore, the incisors are displaced in the posterior direction at a level of 0.5 mm, which is undesirable. The combination of Le Fort I osteotomy with an incision in the palatal suture without separation in PMJ (model 5) results in a favorable decrease in stress, according to [PERSON], below the osteotomy line according to the Le Fort I line to maximum values of 7.7 MPa. In addition, a significant reduction in stress occurs on the teeth to which the appliance is fixed to a level of 4.4 MPa. This is of great significance for possible periodontal effects of the teeth to which the appliance is fixed [1; 13; 17]. Increases in transverse dimensions (displacement along the X axis) range from 0.22 to 0.31 mm for selected structures specified in Table 4. The expansion in relation to the anterior and lateral teeth is the same and is 0.31 mm. What occurs is parallel expansion. The combination of Le Fort I osteotomy with an incision in the palatal suture and separation in PMJ (model 6) gives a significant reduction in stress in the orbital regions and the entire midface to values of 4.4 MPa maximally. According to our analysis, separation in PMJ decreases stresses reduced according to [PERSON] from \(>\)10 MPa to 7.7 MPa of the maximum values in the entire facial skeleton. In the literature, there is no unambiguous position of the authors regarding separation of the maxilla from the pterygoid process of the spinenoid bone [17]. The proponents of full maxillary separation argue that it positively affects the extent of expansion of the maxilla and ensures adequate rotation of its fragments [35; 36; 37; 38; 39].