## 4 Discussion  
In the current research, we retrospectively analyzed cephalometric X-rays of orthographic surgery patients in order to check the preoperative thickness of their ST and the  
Figure 4: Correlation between initial soft tissue thickness in the maxilla (x axis) and the relation between postoperative soft and hard tissue movement (y axis)—cases of maxillary advancement of 5 mm or less (N = 16, \(p\) = 0.28). Correlation between initial soft tissue thickness in the mandible (x axis) and the relation between postoperative soft and hard tissue movement (y axis)—mandibular setback cases (N = 21, \(p\) = 0.79). Figure 5: Correlation between initial soft tissue thickness in the mandible (x axis) and the relation between postoperative soft and hard tissue movement (y axis)—mandibular advancement cases (N = 14, \(p\) = 0.12). amount of its movement in different types of surgeries involving the maxilla, mandible, and the chin. The research was performed to check whether preoperative ST thickness affects the relative degree of ST movement in orthognathic surgery. The analysis was divided into three categories: surgeries involving the maxilla, surgeries involving the mandible, and surgeries involving the chin. In the maxilla (33 cases), in was revealed that overall trend pointed on decrease in relative ST movement with the increase in its initial thickness (r = \(-0.101\)). Though, dividing the cases to those involving 5 mm or less advancement (16 cases) and more than 5 mm advancement (17 cases), revealed that in \(\leq\)5 mm there was clear trend of decrease in relative ST movement with the increase in its initial thickness (r = \(-0.2882\)), while in \(>\)5 mm cases the trend was quite the opposite (r = 0.3082). Same stratification was performed in previous report, showing that in \(>\)5 mm maxillary advancement, it is more difficult to predict ST relative movement [18]. A possible explanation for the decrease in relative ST movement with the increase in its initial thickness may be related to the fact that thick ST absorbs part of the operative changes to the HT [18]. Moreover, several previous reports showed that higher initial ST thickness causes its relatively smaller movement in correlation to HT movement [7, 18, 19]. The unusual finding was in \(>\)5 mm maxillary advancements, with a clear trend of increase in relative ST movement with the increase in its initial thickness and the explanation for this may be that the ST, even a thick one, cannot absorb relatively large movement (\(>\)5 mm). Previous reports in similar movements showed great difficulty in relative ST movement prediction and difficulty to achieve good correlation [7]. In surgeries involving the mandible (35 cases), there was no possibility to point a clear general trend because of the great difference between the characteristics of advancement and setback surgeries. Checking up separately setback (21 cases) and advancement (14 cases) surgeries, revealed that in advancement cases there is a clear trend of decrease in relative ST movement with the increase in its initial thickness (r = \(-0.4178\)), while setback cases did not show any clear trend (r = \(-0.0625\)). Regarding preoperative condition, setback cases have significantly thicker ST. The trend of decrease in relative ST movement with the increase in its initial thickness may be explained identically as it was in small advancements of the maxilla with the absorption of HT movement by thick ST [18]. However, in setback cases it is not possible to point out any trend, in line with previous reports, showing very low regression coefficient of hard and ST movement in mandibular setback cases [15, 20, 21]. Same findings were presented in a systematic review on this subject [22]. The explanation primary relates to the surgical movement itself, as in advancement there is an anterior pulling of the tissue causing its stretching and the amount of the stretch depends on its ability to absorb the subsequent tension--an ability very much dictated by its initial thickness.