###### Abstract  
Background: The aim of this study was to examine whether the thickness of the preoperative soft tissue affects the degree of soft tissue movement relative to the hard tissue movement after orthognathic surgery. Methods: This is a retrospective examination of lateral cephalometric X-rays of patients who underwent orthognathic surgery in single medical center, during a 5-year period. Demographic and operative data were collected. Soft tissue thickness was measured in preoperative cephalometric X-ray, followed by superimposition of postoperative (>6 months) cephalometric X-rays by overlapping fixed bony points. Results: In the upper jaw, there was a decrease in the relative movement of soft tissue with an increase in the initial thickness in surgeries performing advancements up to 5 mm (r = \(-\)0.288). In mandibular advancements, there was a clear decrease in soft tissue movement ratio with an increase in the initial soft tissue thickness (r = \(-\)0.418), while there was no correlation in mandibular setback cases (r = 0.062). The same correlation between the decrease in relative soft tissue movement and the increase in initial soft tissue thickness was found in advancement genioplasty (r = \(-\)0.411). Conclusion: This research shows a general pattern of decrease in relative movement of soft tissue in orthognathic surgery correlated to an increase in its initial thickness.  
orthognathic surgery; soft tissue movement; surgery prediction; surgery tracing +
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influence of the pre-surgical ST thickness on its relative movement and it affects pre-surgical planning and outcome prediction [11; 12].  
Prediction of ST changes is completed by two-dimensional cephalometric evaluation, performed pre- and post-surgery [13]. This evaluation may be performed manually or digitally, using various digital software options, sometimes combined with video shots. Additionally, there are three-dimensional prediction methods [13].  
Manual prediction is based on expected changes [14], while digital software programs are based on average values from databases, reported in previous studies that measured the relationship between soft and hard tissue movement, both giving limited and inaccurate estimates of predicted ST movement [15; 16]. As a consequence, the accuracy of the simulations is based on the reliability and accuracy of the database used [1].  
All manual and most digital methods assume that ST response is linear to HT movement, regardless the preoperative amount and movement direction of the skeletal tissue [1; 14]. The validity of this assumption is not only debatable, but also inconsistent in different reports from various studies [10].  
Additionally, previous reviews showed that differences in measuring and prediction methods, it was impossible to achieve significant conclusions regarding ST movement in this surgery [17].  
The great variability and lack of agreed measuring standard complicate accurate assessment of post-surgical ST outcome, as well as the influence of pre-surgical ST thickness on its movement ratio.  
The aim of this study was to examine whether the thickness of the preoperative ST affects the degree of ST movement relative to the HT movement after orthognathic surgery. Null hypothesis was that there is an influence of initial ST thickness on its relative movement after orthognathic surgery.