## 4 Discussion  
Satisfactory esthetics following orthognathic surgery are the result of using reliable and accurate prediction software [13; 14]. Therefore, there have been several attempts to clarify the accuracy of such programs. As the popularity of 3D orthognathic treatment planning using virtual models has increased, many commercial 3D planning programs with varying algorithms and models have been released on the market. Dolphin imaging software (Chatsworth, CA, USA) was one of the most widely used programs in the previous study, with plenty of evidence supporting its accuracy. However, Dolphin cannot superimpose or compare STL files. A majority of studies employed another program to address this issue [7; 15]. Simplant O&O, on the other hand, can both create and superimpose STL files, removing the need for additional software and reducing the error introduced by the imaging registration process. As a result, the goal of this study was to assess the soft tissue prediction accuracy of Simplant O&O software. Previously, many articles investigated the precision of this program in predicting osseous structures and its ability to transfer virtual planning to an actual surgical outcome, and they discovered that this program provided satisfactory results [16; 17]. However, there is a scarcity of literature on soft tissue prediction. To the best of our knowledge, this is the first study to assess Simplant O&O's soft tissue prediction accuracy in patients with type III skeletal malocclusion. According to our findings, the Simplant prediction images had an overall linear mean errors of 1.73 and 1.03 mm for the one-jaw and two-jaw groups, respectively. Pronasele had the highest accuracy of both groups while pogonion and soft tissue point B had the lowest. The simulation errors in the mandible area were higher for two reasons. First, the mandible has more bony movements than the maxilla. The average sagittal advancement of the maxilla was 1.8 \(\pm\) 1.3 mm, while the average mandibular setback distances were 4.5 and 6.5 mm for the one-jaw and two-jaw groups, respectively. This discrepancy corresponded to the surgical movement distance. Second, for the two-jaw group, the greater complexities in two-jaw surgeries may have resulted in small errors in the maxilla and larger errors in the mandible [18]. Even though five patients of the one-jaw group had only mandibular setbacks, all landmarks showed some discrepancies, indicating that there were also soft tissue changes in the upper jaws, even when no interventions on the maxilla were performed. According to the findings of [PERSON] et al. [19] and [PERSON] et al. [20], the thickness of the upper lip decreases after BSSRO because the surgery eliminates the pseudo-position of the lip that occurs as a result of compensation in class III cases. In both groups, all of the landmarks showed significant differences when compared to the actual postoperative CBCTs. Simplant O&O's soft-tissue prediction errors were expected to be less than 2 mm. Differences in the human face less than 2 mm are not visible to the human eye, according to [PERSON] et al. [12]. Furthermore, many researchers in the literature have stated that prediction errors of less than 3 mm are not clinically significant [21; 22; 23; 24]. Therefore, despite the fact that all of the landmarks showed significant differences, the mean values did not exceed the 2 mm accuracy threshold except for those of the stomian inferius and pogonion in the one-jaw group, as this is generally considered to be a visually perceptible facial difference, indicating that this error was not clinically significant. There was also a correlation between the surgical distances and the landmark discrepancies. The sagittal mandibular movements in the one-jaw group were significantly correlated with stomian inferius whereas the sagittal maxilla and mandibular movements in the two-jaw group were significantly correlated with pronasele and pogonion, respectively.