# 3D Soft-Tissue Prediction Methodologies for Orthognathic Surgery--A Literature Review
## 3 Results
### Prediction Methodologies
#### 3.2.1 Works Based on Traditional (2D) Methodologies
Some angles were also compared between the following lines: line 1, the line connecting the bilateral mandibular angles; line 3, the line connecting the bilateral eyespots; line 2, the line connecting the bilateral oral angles. In the asymmetry group, they measured angle 1, identified by line 1 and line 3 and angle 2, identified by line 2 and line 3 on the frontal facial photograph to assess the asymmetry of the face. In the class II and class III groups, the value of angle 3, identified by the angle formed by lines connecting eyespot, upper lip, and soft tissue B-point on the lateral facial photograph was measured. Angle 3 was the reference for evaluating the convexity of the face, which was originally defined as soft-tissue convexity (Figure 3). The distances measured between landmarks on the actual and on the predicted images were analyzed, and the similarity between real and software-generated images was assessed by 39 evaluators. The mean difference measured between the positions of landmarks is less than 3.4 mm and less than 1.0\({}^{\circ}\) in the evaluated angles. Moreover, more than half of the evaluators stated that, in all groups, the predicted images were very'similar' or'similar' to the actual situation of the patients in the post-operative condition. Less than 6% of the evaluators ranked the predicted images as 'different' from the actual outcome. In conclusion, OrthoForecast is considered by the authors to be a software with high levels of accuracy, reliability and usefulness [15]. [PERSON] et al. evaluated another prediction software, TIOPS. This is a computerized, cephalometric, orthognathic surgical planning system previously used in studies on hard tissue stability and accuracy. As other soft tissue prediction systems, TIOPS is based on predefined ratios of hard to soft tissue movements; its present algorithms partly rely on cephalometric observation of the post-operative situation. The study included 52 patients. Clinical photographs, study models mounted on an articulator (SAM) and standardized lateral cephalometric radiographs of the pre-operative situation were performed. Standardized lateral cephalometric radiographs were performed 5-6 weeks after surgery. The mean accuracy of the planned and predicted results of both hard and soft tissue varied from 0.0 mm to 0.5 mm from one cephalometric reference point to another. In the locus of cephalometric reference points, where it was shown that there were significant differences between planned/predicted hard and soft tissue changing in terms of position, these significant inaccuracies were moderately small and varied from 0.2 mm to 1.1 mm, with the exception of the horizontal position of the lower lip. However, the variability of the previewed hard and soft tissue individual result was evaluated to be relatively high. The study demonstrated moderately high predictability of the immediate post-surgical hard and soft tissue outcome. However, due to the significant variability of  
Figure 3: Construction of feature points and lines (**A**) 1, Angle between line 1 (connecting the bilateral mandibular angles) and line 3 (connecting the bilateral eyespots); 2, angle between line 2 (connecting the bilateral oral angles) and line 3; (**B**) 3, angle formed with lines connecting the eyespot point, upper lip point, and soft tissue B-point [15]. simulated individual results, it would be better to be cautious in presenting the planned and predicted hard and soft-tissue results to the individual patient in the pre-operative [16]. Finally, [PERSON] et al. evaluated the accuracy of soft tissue predictions generated by the CASSOS (Computer-Assisted Simulation System for Orthongathic Surgery) software in Chinese skeletal class III patients underwent bimaxillary surgery. The digitization of pre-surgical and post-surgical lateral cephalograms of 35 patients was performed with the CASSOS program. A simulation of the surgery was performed on the pre-surgical tracing.